Steel, the Resurrection of a Forgotten Water ... - ACS Publications

Subscriber access provided by READING UNIV

Review

Steel, the Resurrection of a Forgotten Water-Splitting Catalyst Helmut Schäfer, and Marian Chatenet ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.8b00024 • Publication Date (Web): 02 Feb 2018 Downloaded from http://pubs.acs.org on February 2, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Energy Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Steel, the Resurrection of a Forgotten Water-Splitting Catalyst

Helmut Schäfera* and Marian Chatenetb, c *

a

University of Osnabrück, Institute of Chemistry of New Materials, Barbarastrasse 7, 49076 Osnabrück, Germany

b

Univ. Grenoble Alpes, CNRS, Grenoble-INP#, LEPMI, 38000 -Grenoble, France

c

French University Institute, Paris, France

#

Institute of Engineering, Univ. Grenoble Alpes

* [email protected], [email protected]

Abstract: Due to the limited availability of fossil fuels, the splitting of water into oxygen and hydrogen upon exploitation of solar energy becomes an increasingly-important clean energy production/storage technique. Despite its early use as hydrogen-evolution catalyst in alkaline electrolysis, until very recently, steel was neither supposed to be an active and stable watersplitting catalyst nor an interesting scientific object at all. The authors of this contribution have shown in recent papers the potential of steel not only in terms of pure material properties, but moreover placed the qualities of steel as a striking scientific item. They herewith review what is known about the water-splitting properties of untreated- and surface-modified steel and try to figure out a potential transfer to a broader application of modified steels in heterogeneous catalysis. The synopsis is basically limited to the usage of steel as a real electrocatalyst, thus presenting the catalytic active species itself.

1 ACS Paragon Plus Environment

ACS Energy Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Content (TOC)


Page 2 of 53

Page 3 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

CONTENTS

(1) THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS AS HYDROGEN-EVOLVING ELECTRODE (2) THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS AS OXYGEN-EVOLVING ELECTRODE (2.1) The exploitation of steel as conductive substrate in oxygen evolving electrodes (2.2) Oxygen evolution on Ni-Cr based stainless steels (2.2.1) Oxygen evolution on untreated- or in situ-treated Cr-Ni based stainless steel (2.2.2) Oxygen evolution on ex situ-treated Cr-Ni based stainless steel (2.2.3) Oxygen evolution on three-dimensional Cr-Ni based stainless steel (2.3) Oxygen evolution on ex situ-treated Co based tool steels at low pH values (2.4) Oxygen evolution on standard carbon steels (3) THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS FOR FULL WATER-SPLITTING (4) SUMMARY AND FUTURE OUTLOOK

Fossil fuels being promised to complete depletion in a more-or-less close future, mankind needs to find other means to harvest energy in a more durable manner

1, 2

. Electricity of

renewable origin (solar, wind or water-based) is an obvious and very actual solution, but its proper use at a large scale is subjected to our propensity to efficiently store it upon production peaks, in order to feed the grid (without destabilizing it) upon demand. To this goal, pumped hydro/turbines is the most efficient electrical storage/production solution, but it is not implementable everywhere and most relevant sites are already saturated. Electrochemical



storage is another obvious option, but Li-ion batteries (the present state-of-art) are too expensive and subjected to economic stress on their core material (lithium), while the other types of batteries either suffer insufficient performances (alkaline, lead-acid, etc.) or are still at their infancy in terms of technological developments (Li-air, Li-S, redox flow batteries) 3, 4. Hydrogen can be seen as a clean energy carrier and moreover shows among the known fuels the highest specific energy density. However, at present, hydrogen is essentially produced from oil, coal and natural gas (96% from fossil fuels in 2004 5), byproducts of these procedures being greenhouse gases. As such and considering, again, the limited availability of fossil fuels, watersplitting emerged as a technique that will help to implement the urgently-required hydrogen economy. More specifically, electrochemically-initiated splitting of water into H2 and O2 upon exploitation of renewable electricity is the most promising energy conversion route, 6, 7, 8, 9, 10, 11 being admitted that it converts water into an (in-principle) inexhaustible energy source. The H2 and O2 generation from water and subsequent usage in fuel cells can be done in a chemical loop that does not generate any pollution by greenhouse gases. However, the round-trip efficiency of water electrolysis into H2 and O2 (efficiency of ca. 60% or less) followed by H2 and O2 usage in fuel cells (efficiency of ca. 60% or less) has yet to be improved. In particular, scientists and engineers started to pay significant attention to the efficiency of the electrocatalytically-initiated water-splitting reaction and started to develop electrode materials that showed low overpotential values for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). The overall efficiency of the water-splitting reaction critically depends on the overpotential values of OER and HER: the standard equilibrium potential E0 at 25°C and 1 atm are 0 V (HER), 1.228 V (OER) respectively. According to W = UQ


Page 4 of 53

Page 5 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

with W = energy consumption, U = cell voltage and Q = electric quantity, the theoretical energy consumption amounts to 2.94 kWh/m3H2. However, in an industrial cell the practical decomposition voltage is ca. Upr = 2.1 V, which means that the objectively energy consumption is 5.02 kWh/m3 H2 and the energy efficiency of the water electrolysis for hydrogen production is reduced to 59% (2.94/5.02)

11, 12

. Thus, it is not surprising that a huge amount of scientific

papers is dedicated to studies that aim to reduce the overpotential values of the anode and cathode reactions whilst electrocatalytically-initiated water electrolysis (Figure 1, Table 1-Table 3).

Figure 1. The scientific output of research (Years 2000-2017) related to electrocatalytically initiated water-splitting covering oxygen evolution and/or hydrogen evolution. Source: ISI Web of Knowledge.



Page 6 of 53

Although the main-stream studies concern the use of Pt-group metal electrocatalysts (PGM) 13, 14, 15, 16, 17, 18, 19

29, 30

(which are of very limited availability), or of non-PGM ones 20, 21, 22, 23, 24, 25, 26, 27, 28,

, which are generally not durable and less active (for details, see section 2 and section 3,

plus Table 2, and Table 3), the present paper will focus on the simple usage of steel in this regards, being admitted that many of the non-PGM active compounds presented above contain materials that are “naturally” present in stainless steels (Fe, Ni, Co, Mo, etc.).

Alkaline electrolysis is considered the standard for large-scale industrial electrolysis 6, 31. As a matter of fact, the industrial realization of water electrolysis is inconceivable without the use of steel. According to standard EN 10020 set up by the European Committee for Standardization, steel is a material for which the mass fraction of iron is greater than that of any other element, and the carbon content is generally below 2%. Mild steel is the (cost-efficient) material of choice when it is going to the construction of tanks, frames, gaskets etc. for usage up to 80°C 31 and in conditions where corrosion is not a detrimental issue, e.g. when the mild steel is protected by a proper coating

32, 33

. Discovered in 1913, stainless steels are another class of

steels that display corrosion-resistance properties

34

. They can be divided and classified

according to their chemical composition, metallurgical structure and mechanical properties, which can be varied almost without limits, depending on the nature and proportion of coelements added to iron

35

. The first investigation of four different crystalline phases in the

Chromium-Nickel-Iron system has been carried out by Benno Maurer and Eduard Strauss; it resulted in the new stainless steel called “Versuchsschmelze 2A” (V2A; AISI 304) and the Strauss-Maurer Chromium-Nickel phase diagram, which had been continuously modified by


Page 7 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

various researchers like e.g. Schaeffler and Speidel 36, 37, 38 to expand its applicability and ensure high reliability (Figure 2). In this phase diagram, three main families of steels can be isolated: Martensitic, Austenitic and Ferritic steels Martensitic stainless steel (with low nickel and low chromium content) is suitable for manufacturing compounds used either at high or low temperature, for industrial purposes and serves also as a reliable construction material for use at temperatures above 80°C properties of stainless steels can be changed by heat-treatment

40

12, 39

. The

. Upon increase of the Ni

content, the toughness and high-temperature strength both increase, which is related to the occurrence of a transition to Austenitic steels (via Martensitic-Austenitic steels).



Page 8 of 53

Figure 2. Modified Schaeffler diagram with experimental results of high nitrogen stainless steel (HNS) 1, 2, 3, and 4. Solid symbols representing full austenite; open symbols representing dferrite+austenite. Reprinted from Ref. 38 copyright Springer. Stainless steels are popular for use as current collector or conductive substrate in numerous applications, among others, redox-flow, sodium or Li-ion batteries

41, 42, 43

, supercapacitors

44

microbial or proton-exchange membrane fuel cells 45, 46, 47, 48 and photoelectric devices 49, 50. In all these cases, their conductivity and corrosion-resistance (chemical and/or electrochemical inertness) are key parameters. Nevertheless, stainless steels were also demonstrated as active materials (and not only as conductive materials), and therefore used for their “intrinsic” electrocatalytic activities in the field of sensors 51, 52 (in that case, the reaction current density is usually small) or waste-water treatment

53

; in that latter case however, the steel electrode

was sacrificial. Concerning H2 production, even though the H2 production from spontaneous corrosion of steels is usually suffered/not desired been used intentionally

56

54, 55, 62

, sacrificial steel electrodes have also

, but this means of H2 production is obviously not durable. More

interesting, stainless steel has been employed as hydrogen evolution reaction (HER) electrode material in earlier developments of alkaline electrolyzers 6, owing to their appreciable performances and relative stability for this reaction was, besides nickel and nickel alloys

57, 58, 59, 64

. In recent time, stainless steel

60, 116

, found to be particularly suited for cathode/anode

pairs in alkaline-based water electrolysis systems, as will be more thoroughly described below. Table 1 gives an overview of steel types/compositions that are discussed in this review. It is by no means comprehensive, as for instance only one representative for mild steel (S235) is listed.


Page 9 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Type of steel

Classificatio

Composition in

n according

Weight %

to (AISI)*

[rest is Fe]

Mechanical properties

Reference

Table 1. Overview of the mechanical properties/Chemical compositions of steel types that are discussed in this review. *AISI=American Iron and Steel Institute



Steel

High Steel

Stainless Steel

Tensile

4140

Mild Steel

S 235

Martensitic Stainless Steel

410

Ferritic Stainless Steel

430

Ferritic Stainless Steel Austenitic Stainless Steel

434 304

0.40 (C)/0.25 (Si) 0.85 (Mn)/1.00 (Cr) 0.25 (Mo) 0.17(C)/1.40(Mn) 0.55(Cu)/0.035 (P) 0.035(S)/0.012(N) 0.10 (C)/0.22(Si) 0.49 (Mn)/12.20 (Cr) 0.20 (Ni)/0.021 (P) 0.015 (S) 0.08(C)/16-18(Cr) ≤1(Mn)/≤0.04 (P) ≤0.015 (S)/≤1(Si) 0.07(C)/17.7(Cr) ≤0.07(C)/≤1.0(Si) ≤2.0 (Mn)/≤19.50(Cr) ≤10.50(Ni)/≤0.045 (P) ≤0.015 (S)

Page 10 of 53

Tensile

Brinell

Strength

Hardness

(MPa)

(HB)

850-1000

248-302

61

340-470

102-140

33,53,59,6 3, 161

650-850

220

57

400-630

200

58

400-630

200

139

500-700

215

42,51,64,8 7,

109

110,113, 118,127,12 3, 124,

Austenitic Stainless Steel

302


316L

0.15(C)/0.75(Si) 2.0 (Mn)/≤19.0(Cr) ≤10.0(Ni)/≤0.045 (P) ≤0.03 (S) ≤0.03 (C)/≤1.0(Si) ≤2.0(Mn)/≤18.50(Cr) ≤2.5(Mo)/≤13.0(Ni) ≤0.045(P)/≤0.03(S)

515-620

201

113, 135

500-700

215

47, 68, 107 114,115, 117,136,13 6,

138,

140, 141 Austenitic Stainless Steel

316


321

Alloy Ni42

Hot work tool steel According to German standard:1.2888 EN ISO 4957: X20CoCrWMo10-9

Ni42

_

≤0.07(C)/≤1.0(Si) ≤2.0(Mn)/≤18.50(Cr) ≤2.5(Mo)/≤13.0(Ni) ≤0.045(P)/≤0.015(S) ≤0.08(C)/≤1.0(Si) ≤2.0(Mn)/≤17.0(Cr) ≤9.0(Ni)/ ≤0.4(Ti) ≤0.045(P)/≤0.015(S) ≤0.12(C)/≤0.3(Si) ≤1.0(Mn)/≤43.0(Ni) 0.2(C)/10(Co)/10(Cr) 0.5(Mn)/2(Mo)/ 0.3(Si)/5.5(W)


500-700

215

86,

134,

142 500-700

215

113

>500

≤130

83

1500-1600

500

96, 146

Page 11 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

2. THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS AS Until recently steel was neither

HYDROGEN-EVOLVING ELECTRODE

supposed to be an active/stable

The first reports dealing with electrocatalytically-

water-splitting catalyst nor an

initiated water-splitting upon steel surfaces were

interesting object in terms of

fundamental research studies particularly dedicated to

materials-chemistry at all.

the kinetic investigation of the hydrogen evolution

reaction (HER; Figure 3) upon untreated steel, usually as a result of its corrosion and related hydrogen embrittlement 55, 61, 62,. To be more precise, one generally believes that for pH ≥ 7 the H2O molecule itself is the reactant and in more acidic milieu protons (H3O+ ions) will interact with the cathode. In such application, mild steel was frequently used as it was seen as the cheapest and most common representative of iron 63.

Thus, for instance Leach and Saunders reported on the mechanism of hydrogen evolution upon mild steel in 1966

59

; they stated that in acidic medium the HER takes place on the surface,

whereas dissolution of the hydrogen formed in the metal plays a role when it comes to HER in alkaline regime 59. To the best of the authors’ knowledge, stainless steel has been exploited as a hydrogen-evolving electrode in sodium hydroxide solution in 1970 by O’Brien and Seto for the first time

64

. Obviously, upon discharging a water molecule, an adsorbed intermediate M-H is

formed, which then, in a fast-occurring step, releases molecular hydrogen. Later on, the investigation of the kinetics of the hydrogen evolution reaction on Austenitic-, Martensitic- and



Page 12 of 53

Figure 3. Schematic representation of water oxidation electrocatalysis (OER) in combination with a H2 evolution (HER). Reprinted from Ref. 65 copyright Royal Society of Chemistry (RSC).

Ferritic stainless steel was extended to acidic

57, 58

and neutral pH regimes

66

. Despite their

indubitable fundamental interest, all these early investigations have something in common: less attention was payed to current/voltage behavior, particularly under steady-state conditions. There is a complete lack of long-term chronopotentiometry- or Faradaic efficiencymeasurements, thus revealing that 40-50 years ago, water-splitting was rather assigned to 12 ACS Paragon Plus Environment

Page 13 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

fundamental research and not seriously taken into consideration as a promising route to alternative fuels. Whereas a variety of newly synthetic materials like metal-sulfides, -selenides, -carbides, -nitrides, and -phosphides listed above and reviewed in

67

have been recently

developed and intensively evaluated in terms of their HER electrode properties, reports dealing with H2 production via water-splitting on steel surfaces are still rare. Lavorante et al. reported in 2016 about 316L steel, a Cr, Ni, Mo-based austenitic stainless steel to be used as HER + OER electrodes in alkaline water electrolyzers

68

. Besides untreated steel samples, specimen with

increased active area elaborated upon chemical or mechanical treatment were evaluated through steady-state polarization experiments carried ..40-50 years ago water-splitting

out in 30% wt. KOH 68: mechanized electrodes exhibited

was not seriously taken into

the best activity for full water-splitting (∑η = 1270 mV at

consideration

technique

j = 175 mA/cm2). However, evaluating a non-platinum-

suitable for the production of

based working electrode for the HER upon exploitation

alternative fuels..

of a Pt counter electrode (as performed in their study) is

as

a

debatable 69; indeed, dissolution of Pt at positive potentials in aggressive media 70, 71, 72, 73, 74 is possible (if not likely) and further deposition at the working electrode over time, could bias the measurements of the working electrode activity. This was demonstrated a serious issue for long-term polarization experiments carried out in strong acids.



Page 14 of 53

Table 2. Electrochemical HER characteristics of recently developed electrocatalysts. The overpotential values are based on long term chronopotentiometry measurements * j= current density in mA/cm2. **Measurement performed at 343.15 k.

Faradaic Eff. (%) HER (pH)

Reference

101.8 (13)

83

380 (50;14)

-

139

136 (10;14)

147 (14)

100(14)

86

-

-

75

82(14)

-

75

Overpotential (η η) in mV HER (j*; pH)

Modified Ni42 steel

189 (10;0) 268.4(10;1) 333(10;13) 299(10;14) 275**(10;14.6)

Steel scrubber (AISI 434) Modified Stainless steel AISI 316 Commercial Pt/C NiO/Ni core shell NP on CNT NiO/Ni CNT on Ni foam

-1

Tafel slope (mV dec ) HER (pH) 198.2 (7) 71.6 (13) 117.9 (0) 80.5(1) 124.4 (13) 117,5(14) 121 (14)

HER Catalyst

40(20;14) 50(100;14) 100(15;9,5) 100(10;14) 100(2.5;9,5) 100(100;14)

Ni2P

100 (10;0)

Co2P

115 (10;0)

CoP

110 (10;0)

Fe

360 (10; 13)

CoSe

121 (10; 14)

NiCo2S4

305 (100; 14)

NiSe

185 (50; 14)

Pt-MoS2 nanosheets on carbon fibers

35 (10;0)

51(14) 81(0) 52 (14) 45(0) 64 (14) 41(0) 69 (14) 84 (14) 89(14) 141(14) 64 (14) 120 (14) 53.6 (0)


75 100 (0)

76

80 (14)

77 77

105.2 (13)

78

100 (14)

79

-

80

100 (14)

81

-

82

Page 15 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

In a recently-published study, were evaluated the OER and the HER properties of electrooxidized Ni42 steel at pH between 0 and 14.6 83. In comparison with untreated Ni42 steel, the electrooxidized specimen obtained upon hard anodization in 7.2 M NaOH (Ni42-300, Figure 4) showed superior HER characteristics (η = 333 mV at j = 10 mA/cm2; pH 13) performances reached still did not approach those of

83

, but the

state-of-the-art noble HER

electrocatalysts. Recently-developed catalysts based on phosphides of transition metals like Ni or Co show HER overpotentials of ≤ 100 mV at 10 mA/cm2 in alkaline or acidic regime. Table 2 gives some idea of the efficiency of steel based HER catalysts at various pH values relatively to established ones belonging to the PGM or non-PGM families.



Figure 4. Tafel plots of Ni42 specimen hard anodized in 7.2 M NaOH based on HER measurements carried out in electrolytes with pH 1, 13 (a) and 0, 14 (b). Reprinted from Ref. 83 copyright Wiley, VCH. Table 2 demonstrates that a satisfying HER electrode (an electrode that competes with state-ofthe-art HER catalysts) that solely consists of stainless …the low activity of steel to

steel has not been generated so far. All the further

promote the cathodic evolution of

attempts of the authors to substantially increase the HER

hydrogen likely has its origin in the

activity of steels failed and the literature does not report

absence of noble ingredients..

such studies so far. Due to the fact that particularly noble

metals have proven to be active HER electrocatalysts 84, it can reasonably be claimed that the low activity of steel to promote the cathodic evolution of hydrogen has its origin in the absence of sufficiently noble ingredients. As such, the authors think that steel may not be activated substantially in terms of HER efficiency without doping with more active elements (even though the next section will show that, upon appropriate (electro)chemical treatment, the surface of stainless steels can be strongly enriched in Ni, a material that shows appreciable HER activity, see Table 2). In contrary to steel, aluminum lightweight alloys like e.g. AA 2024 indeed contain (more) noble elements like e.g. Cu and should have the ability to exhibit higher HER activity upon appropriate surface treatment. Notably also, the high HER activity of metal carbides, nitrides, and –phosphides could render steels surfaces appropriately-treated with carbon, nitrogen or phosphorus more active towards the HER. Such surface-modification procedures applied to steel, like for instance nitriding, are highly-established in order to improve mechanical properties

85

, and these procedures could also be adapted to enhance the HER

activity of the base steel material. To the best of the authors’ knowledge, enhanced HER has


Page 16 of 53

Page 17 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

not been shown for steels modified by carbides in detail, but was nevertheless recently demonstrated for sulfurized 316 stainless steel (η = 136 mV at j = 10 mA/cm2 at pH 14) 86, and in depth investigated for nitride and phosphide-doped (N-P-doped) surface-etched stainless steel of the 304 family 87.

2 THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS AS OXYGEN-EVOLVING ELECTRODE Although H2 with a price of 8 €/kg, is the more valuable water-splitting product, the other half cell reaction leading to oxygen (OER, Figure 3) is even more in the focus of interest: the electrocatalytically-initiated water oxidation reaction contributes to most of the cell overvoltage, due to the sluggish kinetics

88

and the related large oxygen evolution reaction

(OER) overpotential. The OER is a complex process involving the transfer of 4 electrons, likely in numerous steps (Eq. 1; Figure 3): 4 OH- → 2 H2O + O2 + 4 e-

(Eq. 1)

One very common option to obtain an active and stable catalytic surface for the OER consists of depositing metal/oxides at a conductive substrate, e.g. steel. Taking into consideration the enormous popularity of approaches based on the exploitation of steel as the component which is solely responsible to ensure the transport of charges to the catalytic active species (in other words, steel is only a current collector, in principle inert) we will very briefly summarize recently reported approaches that are limited to the usage of steel as a support for the real active catalyst being added from outside. However, one must recall that this review is essentially focused on untreated-, in situ-treated stainless steels, or ex situ-treated stainless steels i.e. on catalytic surfaces only containing the very components/elements of the bare steel material. 17 ACS Paragon Plus Environment


Table 3. Overview of the OER key data of some recently developed electrocatalysts. Significant deviation means ≥ 30%.


Page 18 of 53

Page 19 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

OER Catalyst

Average Overpotential at 2 Current density (mA /cm ) based on projected area

Modified S235 steel Unmodified AISI 302 steel Modified AISI 304 steel Modified AISI 304 steel Modified AISI 304 steel Ni(Fe)OxHy on AISI 304 steel mesh FeNi-hydroxide on AISI 316 steel Modified AISI 316 steel Modified AISI 316 steel Unmodified AISI 316L steel Unmodified AISI 316L steel

347 mV (2) at pH 13 462 mV (1) at pH 7 400 mV (6.3) at pH 14 502 mV (0.65) at pH 7 265 mV (1.5) at pH 13 269.2 mV (10) at pH 13 212 mV (10) at pH 14 260 mV (10) at pH 14 288 mV (50) at pH 14 230 mV (20) at pH 14

Significant deviation* between projected area and real surface area No

Tafel slope (pH)

-1

58.5 mV dec (13) -1

67 %(2) at pH 13

161

33 mV dec (14)

-

113

No

-

-

118

No

49 mV dec (13)

-1

75.5%(10) at pH 13

124

Yes

41 mV dec (14)

-1

_

123

-1

_

110

-1

_

142

-1

100% (10)

134

-1

100% (10)

86

-1

96%(10) at pH 14

117

-1

_

114, 115

-1

_

107

99.4% (2) at pH 7

83

36 mV dec (14)

210 mV (10) at pH 14

Yes

56 mV dec (14)

280 mV (10) at pH 14

Yes

34 mV dec (14)

262 mV (10) at pH 14

No

42 mV dec (14)

No

30 mV dec (14)

No

42 mV dec (14)

Yes

42 mV dec (14)

491 mV (4) at pH 7 254 mV (10) at pH 13 215 mV (10) at pH 14 298 mV (10) at pH 7 230 mV (10) at pH 13

No

150.88 mV dec (7) -1 71.6 mV dec (13)

No

140.8 mV dec (7) -1 47.1 mV dec (13)

75.6% (10) at pH 7 83.2% (5) at pH 7

146

574 mV (10) at pH 1

No

-

95.2% (10) at pH 1

96

400 mV(2.3) at pH 13 360 mV(10) at pH 14 240 mV (10) at pH 14

No No Yes

55 mV dec (13) -1 40 mV dec (14) -1 159.3 mV dec (14)

-

IrO2-RuO2

351mV (10) at pH 13 572mV (5) at pH 7

No

-

20 wt. %Pt on Ni foam IrOx/SrIrO3 IrO2-RuO2 on Sb doped SnO2 NP RuO2 IrO2 Ru Ir

340 mV (3.5) at pH 14

Yes

89.81 mV dec (13) -1 225.8 mV dec (7) -1 502.7 mV dec (14)

125 89 90 83,146,161

-

90

280 (10) at pH 0 260 (1) at pH 0

No No

~39 mV dec (0) -1 60 mV dec (0)

-

91 92

220 (1) at pH 1 380(5) at pH 1 340 (10) at pH -0.3 340 (10) at pH -0.3

No No No No

62 mV dec (14) -

90% (5) at pH 1 99% (5) at pH 1 92% (10) at pH -0.3 93% (10) at pH -0.3

Pt

400 (10) at pH 0

No

-

-

93,110 93 94 94 95

Ni(OH)2/ 316L steel nanoparticles on Ni foam Modified Ni42 steel Modified X20CoCrWMo1 0-9 steel Modified X20CoCrWMo1 0-9 steel Ni deposited on Au Ni- metal electrode Ni3S2 on Ni foam

300 mV (10) at pH 14 (1 M KOH) 330 mV (100) at pH 14 (1 M KOH) 245 mV (10) at pH 14.6 (5 M KOH) 285 mV (100) at pH 14 .6 (5 M KOH) 405 mV (10) at pH 14.3 (5 M LiOH) 545 mV (100) at pH 14.3 (5 M LiOH) 220 mV (10) at pH 14 250 mV (125) at pH 14 450 mV (500) at pH 14

Reference

No

Yes

370 mV (10) at pH 14

Faradaic Efficiency at current density 2 (mA/cm )

-1

-1

-1

-1

-1

-1



Page 20 of 53

2.1 The exploitation of steel as conductive substrate in oxygen evolving electrodes Its good conductivity makes of steel an ideal candidate to act as a substrate for electrochemical processes like electrocatalytically-initiated OER 135. In addition, stainless steel (like for instance Cr, Ni-based AISI 316) was found to be highly stable towards positive potentials when applied in alkaline media

117

. Very recently a Co-based tool steel was found to be reasonably stable at

oxidative potentials in acids as well 96. In contrast, carbon, also a common conductive support for different kind of active OER catalysts, can be thermodynamically oxidised at a potential as low as 0.207 V vs. the reversible hydrogen electrode

97

, and numerous reports point towards

the critical instability of carbon substrates in fuel cell or electrolyzer conditions

98, 99, 100, 101

.

Therefore, a substantial corrosion of carbon is expected at typical operating potentials for the OER, because carbon is not prone to form a stable passivation layer, on the contrary to what stainless steels can do. A further big advantage of stainless steel as conductive substrate for catalytic active layers is, besides its cheapness, its availability in a variety of geometric shapes (See also chapter 3.2.3). However, as steel is non-transparent for X-Ray radiation, removing the catalytic active layer is a prerequisite for any kind of X-Ray based investigation of the species situated on the very surface of the electrode. Using indium tin oxide (ITO) or fluorine-doped tin oxide (FTO), materials that are highly transparent towards X-Ray radiation could enable studying such catalytic active layers. However, the scarcity of In

102

and the limited

electrochemical stability of tin based oxides are serious drawbacks 103, 104. In addition, ITO is a brittle, crystalline material and crystalline films may fracture upon mechanical stress

105

. This

short review enables to conclude that steel, despite some drawbacks, has serious assets to be used as substrate for catalytic active layers, which explains its popularity for such application.


Page 21 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Oxides, hydroxides or oxide-hydroxides of cobalt

106, 140

, nickel

41, 107, 108, 109

or Ni, Fe

110, 142

frequently represent the active periphery of a hybrid material using steel as the conductive support. Resulting in very good OER performance (overpotentials values of ca. η=220 mV at 10 mA/cm2 and pH 14; see e.g. ref. 107) combined with high electrocatalytic stability of the steel/active layer composite, recent published reports 107, 110, 136, 140, 142 clearly demonstrate the usefulness of steel when solely exploited as conductive support for OER electrocatalysts. This is true even when electrolysis conditions typically adopted in industry are chosen (10 M KOH, j= 500 mA/cm2) as was shown for Ni(OH)2 coated stainless steel nanoparticles deposited on Nifoam 107 (Figure 5).

Figure 5. (a–c) Scanning electron microscopy images of Stainless Steel/Ni(OH)2 hybrid nanoparticles deposited on Ni foam.; (d–f) HRTEM images of the co-deposited Stainless Steel/Ni(OH)2 hybrid nanoparticles. Reprinted from Ref. 107 copyright Royal Society of Chemistry (RSC).



Table 3 gives some idea of the position of current heterogeneous OER catalysts (including steelbased ones) in terms of their efficiency at various pH values. It should be noted at this point that in almost every report related to OER electrocatalysts the current density data have been calculated on the basis of the projected area of the catalyst which can substantially differ from the real surface area (third column in Table 3). Some electrocatalysts indeed show a significant roughness, which explains the high current density values listed in (Table 3). In particular, a 3D cross-linked nanosheet array consisting of Ni(Fe)hydroxide (Figure 6) has been designed starting from stainless steel mesh by a hydrothermal treatment of the stainless steel in aqueous solution of NH4HCO3/NiCl2 salts

110

. There has been a long-going discussion

about the possible positive interaction between the active layer and its substrate 111, and it is nowadays generally accepted that in situ growth of OER catalysts on conductive substrates combined with diffusion across the substrate/layer junction is preferable for achieving both high catalytic OER activity plus high stability towards electrocatalytically-initiated oxygen evolution 112, 135. Regarding the overall OER performance, Schäfer et al. showed the enormous superiority of Co3O4 grown intrinsically (‘‘from within itself’’) over Co3O4 when electrodeposited on the same steel 146.


Page 22 of 53

Page 23 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Figure 6. Schematic image of fabrication process of cross-linked Ni(Fe) hydroxide nanosheet arrays on stainless steel. Reprinted from Ref. 110 copyright Springer.

2.2 Oxygen evolution on Ni-Cr based stainless steels 2.2.1 Oxygen evolution on untreated- or in situ-treated Cr-Ni based stainless steel Rather less work has been done regarding the evaluation of untreated stainless steel for usage as oxygen-evolving electrode than for hydrogen-evolving electrodes. A literature review for studies earlier than 2000 brought only one paper to light: Tiwari et al. investigated unmodified AISI 302, 304 and 321 (austenitic) stainless steel as potential OER electrodes in 1 M KOH solutions

113

. The electrochemical characterization of the Cr-Ni-Mn based alloys covers cyclic

voltammetry studies, Mott-Schottky and Tafel analyses. To the best of the authors’ knowledge, the long-term (40 h) voltage vs. current behaviour of a stainless steel working electrode in alkaline regime was shown in this study for the first time: unmasked AISI 302 steel was demonstrated as an efficient and durable oxygen-evolving electrode in strong alkaline environment (η≈400 mV at j = 25 mA/cm2 at pH 14). Unfortunately, the charge to oxygen conversion rate has not been determined, and changes regarding the surface composition that certainly occurred within the measuring period have not been thoroughly investigated at that time. In consequence, the report gives little information about the catalytic active phase on the surface of the steel whilst water electrolysis; only was it postulated that the surface could be



Page 24 of 53

enriched not only in Cr-oxides (as is generally the case for stainless steels), but also in Ni-oxides as a result of the treatment in strong alkaline environment, this mixed (spinel-like) composition being prone to accelerate the OER more than for pure Ni surfaces. The first in-depth report of oxygen evolution electrocatalysis upon stainless steel (for application in aqueous lithium-air batteries) was shown in 2012 by Moureaux et al.

114

. Long-

time (> 3000 h) polarization was performed in 5 M LiOH at 0.8 V vs. Hg/HgO (i.e. η≈500 mV) and the changes of the catalyst regarding e.g. crack formation and composition of the surface in operation has been investigated in detail. The Ni content in the surface was found to be drastically increased upon operation (83 at% of cationic composition), which confirms the postulate of Tiwari et al. 113. It was shown that a partial dissolution (leaking of Fe and Cr out of the steel) of the working electrode is responsible for the changes of the composition and the observed surface-enrichment in nickel. As a result, the OER activity of the electrode substantially increased over time (a stable OER overvoltage of η ≈ 500 mV was measured at j = 25 mA/cm2 in 5 M LiOH after ca. 500 h of “activation” and for the rest 2500 h of operation within the 3000 h test, Figure 7). Besides, the OER overvoltage was found well inferior in KOH and LiOH electrolytes (Table 3), reaching values that outperform many non-PGM (and even noble) OER electrocatalysts in alkaline environments 115.


Page 25 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Figure 7. Increase of the OER catalytic activity of a 316L electrode in 5 M LiOH during the first 144 h of operation as seen by the substantial shift of the corresponding CV curve toward lower potential. The inset shows an enlarged view. (a). This in situ “activation” yields the substantial increase of the current density whilst long-time polarization at constant potential of 0.8 V vs. Hg/HgO in the same electrolyte (the (E) and (CE) symbolize the replacement of the electrolyte and counter-electrode, respectively, in the course of the aging test, which were necessary to maintain the measurement unbiased – in other words, the current density variations were provoked by the gradual failure of the reference and/or counter-electrode, not by that of the “activated” 316L electrode) (b). Reprinted from Ref. 114 copyright Elsevier B.V. The very high electrocatalytic activity of 316L stainless steel after such “alkaline activation procedure” was accounted for by a hypo/hyper d effect, taking its origin in the complex chemistry of the in situ-formed oxide layer, as postulated by Tiwari et al. and Chen et al. for complex Ni-containing surface layers 113, 116. More importantly, Moureaux et al. did emphasize that such in situ-prepared surfaces had a self-healing potential, explaining their ultra-long-term durability (Figure 7) 114. As their ”active layer” is formed in situ from the components of the bulk stainless steel, even if this layer detaches or degrades, it will re-form in situ using the same components of the bulk stainless steel according to the same mechanisms as for the first layer. Anyhow, one must recognize that this surface was extremely stable upon OER in these conditions, as Moureaux et al. did note that “the electrode consumption is only 315 nm after 1800 h of operation”, making of 316L stainless steel a super-stable OER catalyst in the environment of an aqueous LiOH battery. One very recently-published report evaluates the capability of untreated Cr, Ni based AISI 316 steel for water-oxidation-catalysis 117 in 1 M KOH. OER polarization experiments unmasked the electrode to be both highly efficient (η = 370 mV at j = 10 mA/cm2) and durable through 20 h of chronopotentiometry. The electrocatalytic OER activity is throughout the test comparable with 25 ACS Paragon Plus Environment


that of pure nickel

89, 125

(Table 3). At first time, the Faradaic efficiency for OER-based

electrocatalysis upon 316 steel has been shown. Astonishingly, an increase in OER activity whilst operation in strong alkaline milieu as described by Moureaux for the same steel type 114 is not mentioned in the report, which may be due to the shorter duration of the experiment. Notably also, the high charge to oxygen conversion rate of 96% achieved with a non-preoxidized steel is worth mentioning. Whatever the clear interest of in situ-treated or untreated stainless steel electrodes for OER, it must be stressed that the literature is more abundant regarding stainless steel electrodes ex situ -treated (i.e. electrodes treated in a different medium from their medium of usage), as detailed in the next section.

2.2.2 Oxygen evolution on ex situ-treated Cr-Ni based stainless steel In 2015, the group of Schäfer showed the first example of a series of studies in which steel was for the first time intentionally surface-modified (without bringing hetero-elements) prior to electrocatalysis in order to improve the electrocatalytic water-splitting properties 118. Generally, OER electrocatalysts efficiently and durably working in alkaline regime are clearly dominating (Table 3), whereas representatives that exhibit reasonable performance and stability under neutral conditions are still rare. To the best of the authors´ knowledge, this study is the first demonstration of usage of steel as an OER catalyst for water-splitting in the neutral regime.


Page 26 of 53

Page 27 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

More specifically, AISI 304 stainless steel was, upon a very straightforward surface oxidation in air/chlorine mixture at room temperature, converted into a durable OER electrocatalyst with acceptable OER activity at pH 13 (η≈260 mV at j=1.5 mA/cm2), pH 7 (η≈500 mV at j=0.65 mA/cm2) respectively (Table 3, Figure 8a). Untreated specimens were found to be rather inactive and the increase in OER activity has very likely its origin in an Cr enrichment/Fe suppression on the outer-sphere (surface) whilst the chemical oxidation process. The origin of the changes of the chemical composition on the very surface upon chlorination is not yet clear and the knowledge is limited to the exclusion of mechanism that can only take place under wet chemical conditions (dissolution/dissolutionprecipitation processes). An XPS investigation brought to light that Cr is enriched on the surface of the modified AISI 304 steel, relatively to untreated stainless steel. Positions and shapes of the XPS signals are in agreement with the assumption that a chromium doped Fe-oxidehydroxide is the active species located on the surface.



Page 28 of 53

Figure 8. Dynamic voltage/current behavior determined in 0.1 M KOH of AISI 304 steel, surface oxidized for 300 min. Surface oxidation of AISI 304 steel upon Cl/air in situ generated from reaction of aqueous HCl + KMnO4 (inset) (a). CVs of untreated steel AISI 304 (red curve), electrooxidized AISI 304 steel (black curve, sample Elox300) recorded in 0.1 M KOH. Electro oxidation of AISI 304 steel at j = 1700 mA/cm2 in 7.2 M KOH (inset). (a) Reprinted from Ref. 118 (b) Reprinted from Ref. 124.

Chromium-containing materials cannot be seen as problematic in general as the toxicity is basically restricted to hexavalent chromium (Cr(VI))

119

.

Thus, via easy and fast surface

modification applied to an in-principle everywhere-available material, a FeCr oxide-based thinlayer was formed on the top of the chlorine/air treated stainless steel. The exploitation of ironchromium oxide-based catalysts are not limited to water electrolysis but have received attention for catalysis in general. It was for instance used for the catalytically-initiated reforming of ethylene glycol in aqueous phase 120. Furthermore it was exploited for pyrolysis of diesel fuel

121

. Hydrogen gas was produced from biomass using a Fe-Cr-based catalysts

122

.

Therefore, this kind of surface modification that ends up in a Cr-rich iron oxide layer could pave the way for a broader application in catalysis. Another example of surface-oxidation based on non-electrochemical corrosion of the same material (AISI 304 steel) was recently shown by Anantharaj et al. 123.


Page 29 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

The second contribution of Schäfer’s group paper series Recent

papers

showed

the

dealing

with

modified

steels

as

water-splitting

potential of steel not only in terms

electrodes was published in the same year and reports

of pure material properties but

on AISI 304 stainless steel anodized under particular

moreover placed the qualities of

harsh conditions (j = 1.8 A/cm2, t = 300 min, 7.2 M

steel as a striking scientific item on

NaOH)

its own.

mimic the composition of recently-developed advanced

124

(Figure 8b). The aim of this study was to

and highly active Fe-Ni based OER electrocatalysts prepared by the groups of Bell and Boettcher 125, 126

. These groups unmasked for electrodeposited iron- nickel oxide hydroxide slim films a

stoichiometry of around Ni(2/3)Fe(1/3) as the optimal Ni:Fe ratio with respect to electrocatalytic OER performance. In fact, surface- modification of stainless steel led to the same outcome, i.e. upon this straightforward approach unrivalled cheap starting material (AISI 304) was rendered in a highly active (η=212 mV) and durable OER electrocatalyst at j=12 mA/cm2 current density in 1 M KOH with the same composition (67at% Ni, 33 at% Fe). These key figures achieved with an unrivalled-inexpensive material are among the best-presented activity characteristics for the anodic water-splitting reaction in alkaline media (Table 3); the catalyst outperforms state-ofthe-art electrocatalysts like IrO2-RuO2 and Ni3S2 on Ni foam (Table 3), well-known for their spectacular OER properties. No evidence for a classical matrix-layer architecture of the outersphere was found and the changes of the composition very likely occurs upon a dissolutionbased mechanism that basically covers dissolution of Fe and Cr out of the steel upon of strong positive potentials whilst electro-oxidation. A substantial Ni-enrichment up to 83% Ni on the surface of a similar Ni, Cr- based stainless steel (AISI 316) upon long exploitation as oxygen-



evolving electrode in saturated LiOH has also been reported by Moureaux in the group of Chatenet 114 (see Figure 7).

Figure 9. SEM top view images of samples (a) blank, untreated 316 steel; (b-d) steel 316 immersed into NaOH and (NH4)2S2O8 mixture for 6 h (b), 12 h (c) and 18 h (d) respectively. Scale bar, 500 nm. Reprinted from Ref. 135 copyright Wiley VCH. Very recently AISI 304 steel has been transformed into a surprisingly-active OER catalyst for the anodic water splitting under neutral condition (pH 6.7-7.3) upon a similar approach. A dissolution-precipitation was unmasked as the basically responsible origin for the formation of the active layer 127. A remarkable OER performance (η= 504 mV at j=10 mA/cm2 at pH 7) even superior to the OER activity of IrO2-RuO2 (Table 3) was determined.


Page 30 of 53

Page 31 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

AISI 304-based OER electrocatalysts achieved upon both approaches 124, 127 exhibited cracks on the periphery after long-term usage as oxygen-evolving electrode in strong alkaline media. Crack formation can be interpreted as a sign for a limited long-term durability. However, it turned out that activated AISI 304 steel is resistant towards intensive long-term usage in KOH. The same crack formation in combination with self-healing capabilities was found for AISI 316 L steel (See 3.2.1, page 24) the composition of which does not substantially differ from that of 304 steel (Table 1). A Fe-Ni-based material cannot only serve as a water-splitting catalyst, it is interesting on its own. It does not take much imagination to give Fe-Ni- covered stainless steel like the one reported in 2015 124 a wide range of applications because iron-nickel bimetallic systems have already been discussed for tremendous kinds of applications. Just to name a few, some are reported below. Selective conversion of furfural to methylfuran was very well supported at 1 bar in the 210250°C temperature range 128. The Selective conversion of m-cresol to toluene was found to be supported in a similar way Tropsch catalysts

130

129

. These systems are since decades known as promising Fischer-

. Moreover its activity towards the catalysis of the steam reforming

reaction of tar to synthetic gas (syngas) 131 or the partial oxidation of methane to syngas 132 was proven. Besides the proven suitability for usage in industrial applications it can function as a smart catalyst in supporting reactions leading to nanosized materials 133. A combination of chemical oxidation implemented by a hydrothermal method and electrochemical oxidation implemented by polarization cycles have been used by Zhong et al. to activate a stainless steel plate

134

. The stainless steel was corroded in ammonium solution at



Page 32 of 53

200°C under pressure obviously leading to a metal-hydroxide surface which was then converted into a metal-oxide-hydroxide enriched surface upon applying electrochemical oxidationreduction cycles. A reasonable OER activity was proven upon long-term chronopotentiometry (η = 290 mV at j = 10 mA/cm2 in 1 M KOH). Very recently the group of Buddie Mullins reported that surface-activated 302 stainless steel could be an efficient OER electrode in strong alkaline solution (135). A uniform brown film with rippled sheet structure (Figure 9) was created on AISI 302 steel by immersing it into an alkaline oxidant solution containing NaOH and (NH4)2S2O8. Peroxydisulfates are known to be strong oxidants and in this case oxidized the Fe, Ni-based alloy to result in the formation of a Fe(Ni)OOH layer

135

. The obtained electrode showed good

electrocatalytic performance, confirmed by a low overpotential (η=300 mV at j = 10 mA/cm2) and a relatively low Tafel slope of 34 mV/decade. Regarding both-, the overpotential and Tafel slope, this catalyst outperforms e.g. a pure nickel electrode and Pt loaded on Ni foam (Table 3).

2.2.3 Oxygen evolution on three-dimensional Cr-Ni based stainless steel To increase the specific surface area i.e. to increase the catalytic active surface per projected area 3D stainless steel electrodes have been introduced in 2017 as prospective water-splitting electrodes. Huang et al.

136

exploited selective laser melting (SLM) to achieve a controlled

cellular stainless steel structure. In a first step a 3D cellular model fulfilling the design criteria was created upon a computer-aided-design (CAD), which was then transferred into the real 3D stainless steel electrode by the exploitation of the SLM technique. High OER-based current density is an advantage; however the method seems to be time-consuming and costly. In addition, high current densities like shown by this 3D catalyst (η =332 mV at j=40 mA/cm2 at pH 32 ACS Paragon Plus Environment

Page 33 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

14) are basically due to the geometry of the electrode and are not solely based on the electrode material itself. As a matter of fact, real surface area-corrected current densities achieved upon these structures are certainly substantially lower and, in addition, the authors are wondering if it is really required to synthesize 3D stainless steel structures upon an elaborate process. Threedimensional structures based on stainless steel are more or less omnipresent like e.g. stainless steel sponges 137, felts 138-tangles, scrubbers 139 (see Figure 14) and different sorts of meshes 110, 140

. The latter are widely-used in screening and filtering under acidic or alkaline conditions, and

these structures could be used “as is” for water-splitting. Thus, for instance Zhu et al. reported on the transformation of rusty stainless steel mesh into stable cathodes for battery applications. Stainless steel was “artificially corroded and via a dip coating process and converted into a Prussian blue-based electrode material

141

. Zhang et al.

reported in 2017 on a 3D OER electrocatalyst consisting of interconnected Ni(Fe)OxHy covered on stainless steel mesh (SSNNi); the catalyst, supported by the 3D architecture, showed low overpotential at high current densities (η=230 mV at j=20 mA/cm2; Table 3)

110

. This catalyst

outperforms e.g. Pt on Ni foam and Ni metal-based catalyst (Table 3). Stainless steel fabrics have been successfully used as an approach to facilitate gas bubble escape whilst electrocatalytically- realized water-splitting 142, and the authors think these strategies of using “expended” steel surfaces shall be in the highlight in a close future.

2.3 Oxygen evolution on ex situ-treated Co based tool steels Since the report of Nocera et al. on Co-based OER electrocatalysts

147

, highly active for anodic

water-splitting in neutral regime, many groups spent tremendous effort in developing newly-



Page 34 of 53

developed OER electrocatalysts suitable for water-splitting at pH 7. Many of the suggested systems were also based on cobalt, like e.g. Co-based cobalt borate/graphene 143, nano-scaled cobalt oxide-based catalysts like Co3O4 nanowire arrays nanocomposites

145

144

and graphene Co3O4

. Some tool steels contain significant amounts of Co, so one could imagine

ways to enrich the surface of such steels to obtain catalytically-active (Co-enriched) surfaces. Motivated by the superlative, sheer unrivalled properties of Co3O4, which are limited in any case to OER electrocatalysis, the group of Schäfer intended to gain an intrinsically-grown, Co3O4-based ceramic–alloy composite with high OER activity at pH 7 starting from simple steel. As a matter of fact, upon electrooxidation of X20CoCrWMo10-9, a hot work tool steel, the Co content on the surface was increased from 17.1 at. % to 71.6 at.%. 146 . An ICP-OES investigation of the electrolyte unmasked dissolution of Fe, Cr and Mo out of the steel during anodization as the “driving force” for the changes of the composition. More specifically, XPS and FTIR studies on this new material demonstrated the formation of a pure Co3O4 containing ‘‘outer zone’’ on top of the steel, that positively-enhanced the OER activity of such treated stainless steel. However, the existence of Co3O4 solely did not explain the outstanding OER properties of the new composite: X20CoCrWMo10-9//Co3O4 derived from steady-state or non-steady-state OER measurements (η = 298 mV at j = 10 mA/cm2 and pH 7; Figure 10) substantially outperformed the OER activity of all known OER electrocatalysts that have been tested in neutral milieu like IrO2-RuO2, cobalt phosphate compounds 147 or graphene Co3O4 nanocomposites 145 just to name a few (Table 3).


Page 35 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Figure 10. Comparison of the non-steady state (a) and steady state (b) OER properties of untreated (sample Co) and surface oxidized (sample Co-300) steel X20CoCrWMo10-9. Reprinted from Ref. 146.

The current density achieved with this new anode in pH 7 corrected 0.1 M phosphate buffer is over a wide range of η around 10 times higher compared to recently-developed, up-to-date electrocatalysts. A classical substrate-layer structure exhibiting a substantial demarcation between the periphery and the substrate, typically characteristic of the specimen achieved from electrodepositionbased approaches was not proven (Figure 11). A metal–ceramic transition can hardly be defined and an abrupt change in the composition is completely suppressed by this intrinsic ‘‘from within itself’’ formation of the X20CoCrWMo10-9 steel//Co3O4 composite.



Page 36 of 53

Figure 11. SEM micrograph of a FIB machined cross section of the X20CoCrWMo10-9 steel//Co3O4 composite. The rear wall of the trapezoidal trough is shown. This wall is orientated perpendicular to the surface of the specimen thus presenting a cross section of X20CoCrWMo10-9 steel//Co3O4 composite. the SEM images were acquired using an energy selective backscattered detector ESB (a), a secondary electron detector SESI (b), respectively. Reprinted from Ref. 146. Co3O4 can be considered as a “dreamlike” material and has many other applications apart from supporting OER. For instance the oxidation of CO, one of the most extensively-investigated examples for heterogeneous catalysis, plays a major role when it comes to cleaning air and automotive emissions148.

In this regard, high-activity at low temperature is a desired

characteristic. Xie et al. showed that Co3O4 can, under optimized conditions, catalyze the oxidation of CO at temperatures as low as -77 °C

149

. In addition, Co3O4 catalyzes methane

combustion 150 and has proven capabilities for sensor applications. It was successfully exploited as an alcohol sensor material 151, 153 and as a gas sensor 152, 153, and showed significant activity toward photocatalytically-initiated degradation of organic compounds like e.g. Phenol


154

.

Page 37 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

Moreover the lithium storage/insertion properties of Co3O4 have been studied intensively and it turned out to be a promising positive electrode material in lithium-ion batteries

155, 156

. OER

electrocatalysis is scientifically in close neighborhood to ORR (oxygen reduction reaction) on which the half-cell reaction of the fuel cell is based on, and as a matter of fact, spinel Co3O4 is a promising and well-known candidate for ORR electrodes

157, 158, 159

. Furthermore mesoporous

Co3O4 exhibited superior properties relevant to application in supercapacitors 160.

2.3. Oxygen evolution on ex situ-treated Co based tool steels at low pH values To the best of the authors´ knowledge, only one work among the published ones reports on electrocatalytically-driven oxygen evolution upon surface modified steel in acidic regime

96

.

Very recently, a reasonable stable OER electrode was designed via electro-oxidation of a cobaltbased steel carried out in aqueous LiOH solution. The electrode that solely consists of earthabundant elements exhibited a reasonable durability (weight loss: 39 µg/mm2 after 50000 s of chronopotentiometry at pH 1) together with an acceptable OER performance: overpotential values down to η= 574 mV for j=10 mA cm-2 OER based current density were measured at pH 1. However, the OER performance in 0.05 M sulfuric acid (pH 1) is still not on benchmark level and noble metal (Ir, Ru, Pt) based catalysts exhibit lower overpotential values for the OER in acids (Table 3). In addition, the mass loss of the steel-based oxygen evolving electrode that occurs whilst long-term operation in acids (although present also for noble metal based systems!) was substantially higher compared to operation of similar electrodes at higher pH values.



2.4. Oxygen evolution on standard carbon steels Mild steel S235 (standard Manganese-Carbon steel) consists of 99 at% Fe and can therefore be seen as a cheap iron source. As mentioned in the previous sections, untreated S235 steel was used as a H2-evolving electrode. Applying a Cl2/air pre-oxidation to steel S235 prior to OER electrocatalysis at pH 13 and pH 7 can modulate its electrocatalytic activity; the OER kinetics at pH 13 was moderate (η = 347 mV at j = 2 mA/cm2) but however the one determined at pH 7 (η=462 mV at j = 1 mA/cm2) is comparable to the CoPi catalyst introduced by Nocera in 2008 147 and throughout satisfying taking into consideration the cheapness of the material as well as the straightforwardness of the activation procedure 161. Besides acceptable efficiency the specimen exhibited excellent long-term durability whilst OER water electrolysis. The surface composition of the oxidized sample (cationic distribution: 99.1 at% Fe, 0.84 at% Mn) differed slightly from the one of untreated steel (cationic distribution: 99.1 at% Fe, 0.53 at% Mn). A dissolution-based mechanism as the origin for this kind of layer formation is difficult to imagine, taking into account that the enrichment occurs in gas atmosphere. Iron-manganese-oxide-based materials are interesting, not only in terms of electrocatalysis, making Fe-Mn-containing steel potentially suitable materials for a number of reactions to be catalyzed. Thus, for instance Fe-Mn oxide exhibited an acceptable degradation efficiency for reactive brilliant blue which was used as a model compound for textile wastewater supported on Fe-Mn

163

162

. Similarly, decomposition of diethylether was

. Also for the catalysis of gas reactions like e.g. degradation of ozone

this material showed interesting properties

164

. Furthermore, Fe/Mn systems have proven

activity for the catalysis of the Fischer Tropsch process 165, 166.


Page 38 of 53

Page 39 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

3. THE EXPLOITATION OF STEEL IN ELECTROCATALYSIS FOR FULL WATER-SPLITTING Three recently-published reports deal with the exploitation of surface modified steels for usage as both OER and HER electrodes

83, 86, 139

. It has been found that steel Ni42, when surface

oxidized in an optimized way, can act as sufficiently-active and outstandingly stable OER electrocatalyst at pH 7, 13, 14 and 14.6; it was also reasonably active and stable for the HER at pH 0, 1, 13, 14 and 14.6

83

. No degradation of the catalyst was detected when used as an

oxygen evolving-electrode, when conditions close to standard industrial operations are applied. Thus, besides OER-based polarization experiments carried out at room temperature, OER was performed in 7 M KOH at T=70 °C 83. Moreover, even at extremely positive potentials of more than E=6 V vs. RHE (j=2000 mA/cm2), conditions that had been applied whilst electro-activation, the Ni42 steel anode did not show any detectable weight loss. The overlap between the pH range allowing both-, HER and OER-, (e.g. at pH 13, 14, 14.6) makes the electrocatalyst suitable as oxygen-and hydrogen-evolving electrodes in one single electrolyte. In other words, Ni42 steel surface oxidized under optimized conditions (sample Ni42-300) can be used in electrolysis cells with the so-called bipolar cell configuration (Figure 12) 11, 108. Conductive plates which are placed in an electrolyte between two “outer” electrodes connected to the positive and the negative pole of a power source will carry opposite charges on their periphery transforming the electrodes to the so-called bipolar electrodes. A bipolar cell configuration substantially simplifies the design of a water-splitting device as both, OER and



HER, are catalyzed upon each of these bipolar electrodes and only both “outer” electrodes but not the central electrodes require a direct power feed.

Figure 12. A comparison of possible cell configurations for electrolyzer modules. Unipolar arrangement (a), bipolar arrangement (b) of the electrodes. Reprinted from Ref. 11, by permission of ©Sociedade Brasileira de Química. The origin of the bifunctionality of electro-activated Ni42 steel-, and the mechanism of the layer formation are still not absolutely clear. The absence of any mass-loss whilst electro-activation is unique among the stainless steel investigated so far. In addition to the determination of a weight loss, an ICP-OES investigation of the electrolyte exhibited no clear hints that dissolution of ingredients out of the steel took place. Therefore, electromigration cannot be excluded with


Page 40 of 53

Page 41 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

absolute certainty as the driving force for changes of the composition of the outer-sphere as shown by XPS spectroscopy.

In a recently-published paper, Liu et al. reports on a sulfurization, phosphorization and nitridation treatment of stainless steel 316 foil

86

. Sulfurization resulted in the formation of a

surface layer of sulfides upon steel making of it a competent electrocatalyst for overall watersplitting (Figure 13). A current density of j = 10 mA/cm2 was reached in 1 M KOH electrolyte at overpotential values of η = 136 mV (HER) and η =262 mV (OER), respectively. A cell voltage of U = 1.64 V was required for j = 10 mA/cm2 of overall water-splitting when the sulfurized stainless steel was used simultaneously for both half-cell reactions. The question that remains though is: are these surface layers ex situ-formed upon sulfurization, phosphorization and nitridation sufficiently stable for long-term operation? One can speculate that these will have less chance to be stable than layers in situ-formed, as proposed in the previous section. Metal sulphides,phosphides nitrides and carbides are supposed to be oxidized upon highly positive potentials experienced at the anode in a water electrolysis cell. Moreover, phosphides for instance were found to be instable in alkaline media even upon negative potentials as reported by Schaak et al. 76 . Household scrubbers are typically based on ferritic steel of the type AISI 430 or 434 and turned out to be very economical electrodes for electrocatalytically-initiated water splitting. Moreover they allow the combination of three-dimensionality of the electrode plus full water splitting capability (Figure 14) as shown by Anantharaj et al. 139



Process

Catalytic

Loading

Relative cost of

Page 42 of 53

Overpotential (iR

Tafel

Figure 13. Sulfurization, phosphorization and nitridation of stainless steel foil renders the steel into a competent electrocatalyst suitable to support both half-cell reactions. Reprinted from Ref. 86.


Page 43 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

HER

OER

-2

material

(mg cm )

the electrode material (US$)

free) at area normalized activity ( mV)

Slope -1 (mV dec )

SS Scrubber Pt/C

10 ± 0.1

0.00012

380 @ 50 mA cm

-2

121

0.205

32.52

120 @ 50 mA cm

-2

59

SS Scrubber Ni(OH)2 RuO2

10 ± 0.1

0.00012

418 @ 10 mA cm

-2

63

0.205 0.205

0.58 12.35

385 @ 10 mA cm -2 320 @ 10 mA cm

-2

61 80

Figure 14. The exploitation of metal household scrubbers as potential electrodes in water electrolysis. Reprinted from Ref. 139.

4. SUMMARY AND FUTURE OUTLOOK Much work has been done that aimed to improve steel materials to be used as anodes in water electrolysis. Several authors including the ones of this paper showed that surface-modified steel has enormous potential as outstandingly-efficient and outstandingly-stable oxygen-evolving electrode in the electrocatalytically initiated splitting of water carried out in neutral and alkaline regime. Alkaline water electrolysis can be seen as the most widespread and mature technology of “clean” hydrogen production. At high pH, the present survey demonstrated that stainless steel 43 ACS Paragon Plus Environment


Page 44 of 53

electrodes present number of assets to be used as both OER and HER electrodes, because stainless steels contain non-negligible proportion of transition metals (Ni, Mn, Co, Fe) that can be active for these reactions when in the “adequate” phase(s), these elements being prone to concentrate at the stainless steel surface upon a proper treatment of the steel (without adding hetero-elements). However alkaline electrolyzers are not the method of choice for the storage of renewable energy due to their high dynamics. Proton exchange membrane (PEM) electrolyzers benefit from higher gas purity, higher efficiency and are more resistant against frequently occurring changes of the current load 6, but the operation of these electrolyzers requires a low pH condition. It is easy to imagine that the development of anodes solely consisting of earth-abundant elements suitable for usage in acids is a challenging task especially taking into consideration the strong oxidative potentials encountered in water electrolyzers. The development of steel-based electrodes for this purpose presents ongoing research

96

and

some work remains to be done to further improve both activity and stability of the steel specimen. Although surface-modified steel has been widely investigated as electrode materials in water-splitting applications, relatively less effort was spent in transferring the materials to catalysis in general. The materials are promising to be used for catalysis of tremendous reactions as the catalytic active species on the surface of the modified steels (e.g. NiO(OH), Co3O4) have proven their activity for a variety of industrial relevant reactions.

AUTHOR INFORMATION Corresponding Authors


Page 45 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

*Email:[email protected] *Email: [email protected] ORCID Helmut Schäfer: 0000-0001-5906-3354 Marian Chatenet: 0000-0002-9673-4775 Notes The authors declare no competing financial interest

Biographies

Helmut Schäfer (Senior Scientist) received his PhD in 2001 at the University of Oldenburg, Germany. After postdoc stays at IWT Bremen, German Aerospace Center in Cologne and Freie Universität Berlin he became faculty member at the University of Osnabrueck in 2017. His research interests cover renewable energy sources, energy conversion, luminescent materials, electrocatalysis and nanoscience.

Marian Chatenet (Professor at Grenoble-INP in electrochemistry) makes his research on electrocatalysis of complex reactions and activity/durability of electrocatalysts for fuel cell/electrolyzers. He published 8 book chapters, 130+ publications, 5 patents, 21 extended abstracts, gave 170+ communications in (inter)national conference (30+ invited) and 37 invited seminars (h-index: 37, 3800+ citations). http://lepmi.grenoble-inp.fr/personnels/m-chatenet-marian--429692.kjsp?RH=EPMI_MEMBRES

References



1

Ghoniem, A. F. Needs, resources and climate change: Clean and efficient conversion technologies. Prog. Energ. Comb. Sci. 2011, 37, 15-51. 2 Kamat, P. V. Meeting the Clean Energy Demand: Nanostructure Architectures for Solar Energy Conversion. J. Phys. Chem. C, 2007, 111, 2834-2860. 3 Tarascon, J. M.; Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 2001, 414, 359367. 4 Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. LigO2 and LigS batteries with high energy storage. Nat. Mater. 2012, 11, 19-29. 5 Balat, M. Potential important of hydrogen as a future solution to environmental and transportation problems. Int. J. Hydrogen Energ. 2008, 33, 4013-4029. 6 Le Formal, F.; Bouree, W. S.; Prevot, M. S.; Sivula, K. Challenges towards Economic Fuel Generation from Renewable Electricity: The Need for Efficient Electro-Catalysis. Chimia 2015, 69, 12, 789-798. 7 Götz, M.; Lefebvre, J.; Mörs, F.; McDaniel Koch, A.; Graf, F.; Bajohr, S.; Reimert, R.; Kolb, T. Renewable Power-toGas: A technological and economic review. Renew. Energy 2016, 85, 1371-1390. 8 Lu, Q.; Yu, Y.; Ma, Q.; Chen, B.; Zhang, H. 2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions. Adv. Mater. 2016, 28, 1917-1933. 9 Wang, J.; Zhang, H.; Wang, X. Recent Methods for the Synthesis of Noble-Metal-Free Hydrogen-Evolution Electrocatalysts: From Nanoscale to Sub-nanoscale. Small Methods 2017, 1, 1700118, 1-15. 10 Zhang, X.; Lai, Z.; Tan, C.; Zhang, H. solution-Processed Two-Dimensional MoS2 Nanosheets: Preparation, Hybridization, and Applications. Angew. Chem. Int. Ed. 2016, 55, 8816-8838. 11 Santos, D. M. F.; César, A. C.; Sequeira, J. L.; Figueiredo, J.L. HYDROGEN PRODUCTION BY ALKALINE WATER ELECTROLYSIS. Quim. Nova 2013, 8, 1176-1193. 12 Mittelsteadt, C.; Norman, T.; Rich, M.; Giner, J. W. Electrochemical Energy Storage for Renewable Sources and Grid Balancing, Chapter 11: PEM Electrolyzers and PEM Regenerative Fuel Cells Industrial View, Inc. Newton, MA, USA, 2015, 159-181. 13 Grigoriev, S. A.; Millet, P.; Fateev, V. N. Evaluation of carbon-supported Pt and Pd nanoparticles for the hydrogen evolution reaction in PEM water electrolysers. J. Power Sources 2008, 177, 281-285. 14 Lervik, I. A.; Tsypkin, M.; Owe, L. E.; Sunde, S. Electronic structure vs. electrocatalytic activity of iridium oxide. J. Electroanal. Chem. 2010, 645, 135-142. 15 Sunde, S.; Lervik, I. A.; Tsypkin, M.; Owe, L. E. Impedance analysis of nanostructured iridium oxide electrocatalysts. Electrochim. Acta 2010, 55, 7751-7760. 16 Ye, F.; Li, J.; Wang, X.; Wang, T.; Li, S.; Wei, H.; Li, Q; Christensen, E. Electrocatalytic properties of Ti/Pt-IrO2 anode for oxygen evolution in PEM water electrolysis. Int. J. Hydrogen Energ. 2010, 35, 8049-8055. 17 Owe, L. E.; Tsypkin, M.; Wallwork, K. S.; Haverkamp, R. G.; Sunde, S. Iridium-ruthenium single phase mixed oxides for oxygen evolution: Composition dependence of electrocatalytic activity. Electrochim. Acta 2012, 70, 158164. 18 Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energ. 2013, 38, 4901-4934. 19 Wang, L.; Zhu, Y.; Zeng, Z.; Lin, C.; Giroux, M.; Jiang, L.; Han, Y.; Greeley, J.; Wang, C.; Jin, J. Platinum-nickel hydroxide nanocomposites for electrocatalytic reduction of water, Nano Energy 2017, 31, 456-461. 20 Hall, D. E. Alkaline Water Electrolysis Anode Materials. J. Electrochem. Soc. 1985, 132, 41C-48C. 21 Singh, R. N.; Mishra, D.; Anindita, S.; Sinha, A. S. K.; Singh, A. Novel electrocatalysts for generating oxygen from alkaline water electrolysis. Electrochem. Commun. 2007, 9, 1369-1373. 22 Chen, W. F.; Wang, C. H.; Sasaki, K.; Marinkovic, N.; Xu, W.; Muckerman, J. T.; Zhu, Y.; Adzic, R. R. Highly active and durable nanostructured molybdenum carbide electrocatalysts for hydrogen production. Energy Environ. Sci. 2013, 6, 943-951. 23 Wang, X.; Kolen'Ko, Y. V.; Bao, X. Q.; Kovnir, K.; Liu, L. One-Step Synthesis of Self-Supported Nickel Phosphide Nanosheet Array Cathodes for Efficient Electrocatalytic Hydrogen Generation, Angew. Chem. Int. Ed. 2015, 54, 8188-8192.


Page 46 of 53

Page 47 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

24

Yang, Y.; Xu, D.; Wu, Q.; Xiang, M.; Diao, P. Preparation of layered MoS2/Graphene films and their electrocatalytic performance of hydrogen generation, Beijing Hangkong Hangtian Daxue Xuebao/Journal of Beijing University of Aeronautics and Astronautics, 2015, 41, 2158-2165. 25 Bates, M. K.; Jia, Q.; Doan, H.; Liang, W.; Mukerjee, S. Charge-Transfer Effects in Ni-Fe and Ni-Fe-Co Mixed-Metal Oxides for the Alkaline Oxygen Evolution Reaction. ACS Catal. 2016, 6, 155-161. 26 Chung, Y. H.; Gupta, K.; Jang, J. H.; Park, H. S.; Jang, I.; Lee, Y. K.; Lee, S. C.; Yoo, S. J. Rationalization of electrocatalysis of nickel phosphide nanowires for efficient hydrogen production. Nano Energy 2016, 26, 496-503. 27 Li, J.; Zhou, X.; Xia, Z.; Gao, W.; Ma, Y.; Qu, Y. Highly Efficient and Robust Nickel Phosphides as Bifunctional Electrocatalysts for Overall Water-Splitting. ACS Appl. Mater. Inter. 2016, 8, 10826-10834. 28 Liu, K.; Zhang, W.; Lei, F.; Liang, L.; Gu, B.; Sun, Y.; Ye, B.; Ni, W.; Xie, Y. Nitrogen-doping induced oxygen divacancies in freestanding molybdenum trioxide single-layers boosting electrocatalytic hydrogen evolution. Nano Energy 2016, 30, 810-817. 29 Ma, Y. Y.; Wu, C. X.; Feng, X. J.; Tan, H. Q.; Yan, L. K.; Liu, Y.; Kang, Z. H.; Wang, E. B.; Li, Y. G. Highly efficient hydrogen evolution from seawater by a low-cost and stable CoMoP@C electrocatalyst superior to Pt/C. Energy Environ. Sci. 2017, 10, 788-798. 30 Wang, T.; Wang, X.; Liu, Y.; Zheng, J.; Li, X. A highly efficient and stable biphasic nanocrystalline Ni-Mo-N catalyst for hydrogen evolution in both acidic and alkaline electrolytes. Nano Energy 2016, 22, 111-119. 31 LeRoy, R. L. Industrial Water Electrolysis: Present and Future. Int. J. Hydrogen Energ. 1983, 8, 6, 401-417. 32 Shen, G. X.; Chen, Y. C.; Lin, C. J. Corrosion protection of 316 L stainless steel by a TiO2 nanoparticle coating prepared by sol–gel method. Thin Solid Films 2005, 1-2, 130-136. 33 Lu, W. K.; Elsenbaumer, R. L.; Wessling, B. Corrosion protection of mild steel by coatings containing polyaniline. Synthetic Metals 1995, 1-3, 2163-2166. 34 Lo, K. H. ; Shek, C. H.; Lai, J. K. L. Recent developments in stainless steels. Mater. Sci. Eng. R 2009, 65, 39–104. 35 Lo, K. H.; Shek, C. H.; Lai, J. K. L. Recent developments in stainless steels. Mater. Sci. Eng. R 2010, 65, 39-104. 36 Schaeffler, A. L. CONSTITUTION DIAGRAM FOR STAINLESS-STEEL WELD METAL .2. SCHAEFFLER DIAGRAM. Metal Progress 1974, 1, 227-227. 37 Speidel, M. O. and Speidel, H. J.: High Nitrogen Steel 06, H. Dong, H.; Su, J.; Speidel, M. O. eds., Metallurgical Industry Press,Beijing, 2006, pp. 21–29. 38 Wang, Q.; Ren, Y.; Yao, C.; Yang, K.; Misra, R. D. K. Residual Ferrite and Relationship Between Composition and Microstructure in High-Nitrogen Austenitic Stainless Steels. Metallurg. Mater. Trans. A 2015, 5537-5545. 39 Wang, M.; Wang, Z.; Gong, X.; Guo, Z. The intensification technologies to water electrolysis for hydrogen production-A review. Renew. Sust. Energ. Rev. 2014, 29, 573-588. 40 Gooch, T. G. Heat treatment of welding 13%Cr-4%Ni Martensitic Stainless Steel for Sour Service. Weld. Res. Suppl. 1995, 213-222. 41 Arenas, L. F.; Ponce de León, C.; Walsh, F. C. 3D-printed porous electrodes for advanced electrochemical flow reactors: A Ni/stainless steel electrode and its mass transport characteristics. Electrochem. Commun. 2017, 77, 133-137. 42 Li, X.; Qiao, L.; Li, D.; Wang, X.; Xie, W.; He, D. Three-dimensional network structured a-Fe2O3 made from a stainless steel plate as a high-performance electrode for lithium ion batteries. J. Mater. Chem. A 2013, 1, 64006406. 43 Lee, J.; Hun Shin; S.; Lee, J. K.; Choi, S.; Kim, J. H. Corrosion behavior of surface treated steel in liquid sodium negative electrode of liquid metal battery. J. Power Sources 2016, 307, 526-537. 44 Sagu, J. S.; Wijayantha, K. G. U.; Bohm, M.; Bohm, S.; Rout, T. K. Anodized Steel Electrodes for Supercapacitors. ACS Appl. Mater. Inter. 2016, 8, 6277−6285. 45 Wind, J.; LaCroix, A.; Braeuninger, S.; Hedrich, P.; Heller, C.; Schudy, M. Metal bipolar plates and coatings, in: W. Vielstich, H.A. Gasteiger, A. Lamm (Eds.) Handbook of Fuel Cells Fundamentals, Technology and Applications, vol. 3, Wiley, Chichester, 2003, 294-307. 46 Dumas, C.; Mollica, A.; Feron, D.; Basseguy, R.; Etcheverry ,L.; Bergel, A. Marine microbial fuel cell: Use of stainless steel electrodes as anode and cathode materials. Electrochim. Acta 2007, 53, 468–473. 47 Ledezma, P.; Donose, B. C.; Freguia, F.; Keller, J. Oxidized stainless steel: a very effective electrode material for microbial fuel cell bioanodes but at high risk of corrosion. Electrochim. Acta 2015, 158, 356–360.



48

Pocaznoi, D.; Calmet, D.; Etcheverry, L.; Erable, B.; Bergel, A. Stainless steel is a promising electrode material for anodes of microbial fuel cells. Energy Environ. Sci. 2012, 5, 9645-9652. 49 Suh, Y. D.; Jung, J.; Lee, H.; Yeo, J.; Hong, S.; Lee, P.; Lee, D.; Ko, S. H. Nanowire reinforced nanoparticle nanocomposite for highly flexible transparent electrodes: borrowing ideas from macrocomposites in steel-wire reinforced concrete J. Mater. Chem. C 2017, 5, 791—798. 50 Vesel, A.; Balat-Pichelin, M. Synthesis of iron-oxide nanowires using industrial-grade iron Substrates. Vacuum 2014, 100, 71-73. 51 Ayoub, H.; Lair, V.; Griveau, S.; Brunswick, P.; Bedioui, F.; Cassir, M. Electrochemical Characterization of Stainless Steel as a New Electrode Material in a Medical Device for the Diagnosis of Sudomotor Dysfunction. Electroanal. 2012, 6, 1324–1333. 52 Shashanka, R.; Chaira, D.; Kumara Swamy, B. E.; Electrocatalytic Response of Duplex and Yittria Dispersed Duplex Stainless Steel Modified Carbon Paste Electrode in Detecting Folic Acid Using Cyclic Voltammetry. Int. J. Electrochem. Sci. 2015, 10, 5586 – 5598. 53 Sengil, I. A.; M. Özacar, M. Treatment of dairy wastewaters by electrocoagulation using mild steel electrodes. J. Hazard. Mater. 2006, B 137, 1197-1205. 54 Sadawy, M. M. ELECTROCHEMICAL EVALUATION OF MARTENSITICAUSTENITIC STAINLESS STEEL IN SULFURIC ACID SOLUTIONS. Supplemental Proceedings: Volume 2: Materials Fabrication, Properties, Characterization, and Modeling TMS (The Minerals, Metals & Materials Society) 2011, 691-698. 55 Benedetti, A.; Zanotti, C.; Giuliani, P.; Faimali, M. Non-isothermal effects induced by natural illumination and infrared irradiation on cathodically polarized carbon steel electrodes. Corros. Sci. 2014, 84, 125–134. 56 El-Meligi, A. A.; Ismail, N. Hydrogen evolution reaction of low carbon steel electrode in hydrochloric acid as a source for hydrogen production. International J. Hydrogen Energ. 2009, 34, 91–97. 57 Bicelli, L. P.; Romagnani, C.; Rosania, M. T. HYDROGENEVOLUTION REACTION ON MARTENSITIC STAINLESS STEEL, J CHIM PHYS, 1976, 7-8, 783-786. 58 Bicelli, L. P.; Romagnani, C.; Rosania, M. T. Hydrogen Evolution reaction on Ferritic Stainless Steel. J CHIM PHYS 1977, 5, 529-532. 59 Leach, J. S. L.; Saunders, S. R. J. Some aspects of the Mechanism of the Hydrogen Evolution at a Mild Steel Electrode. J. Electrochem. Soc. 1966, 113, 7, 681-687. 60 BOCKRIS, J. O'M.; POTTER, E. C. The Mechanism of Hydrogen Evolution at Nickel Cathodes in Aqueous Solutions. J. Chem. Phys. 1952, 20, 4, 614-628. 61 Benzad, A.; Huet, F.; Jérome, M.; Wenger, F.; Gabrielli, C.; Galland, J. Electrochemical noise analysis of cathodically polarised AISI 4140 steel. I. Characterisation of hydrogen evolution on vertical unstressed electrodes. Electrochim. Acta 2002, 47, 4315-4323. 62 Remita, E.; Tribollet, B.; Sutter, E.; Vivier, V.; Ropital, F.; Kittel, J. Hydrogen evolution in aqueous solutions containing dissolved. CO2: Quantitative contribution of the buffering effect. Corros. Sci. 2008, 50, 1433–1440. 63 Ateya, B. G; Elnizamy, F. M. A. Kinetics of the hydrogen evolution reaction on mild steel electrodes in sulfuric acid. Corros. Sci. 1980, 20, 461-464. 64 O´Brien, R. N.; Seto, P. The mechanism of hydrogen evolution at a stainless steel electrode in basic solution. J. Electrochem. Soc: Electrochem. Sci. 1970, 117, 32-34. 65 Joya, K. S.; Ahmad, Z.; Joya Y. F.; Garcia-Esparza, A. T.; de Groot, H. J. M. Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst. Nanoscale 2016, 8, 1503315040. 66 Radhakrishnamurthy, P.; Sathyanarayana, S.; Reddy, K. N. Kinetics of hydrogen evolution reaction on a stainless steel electrode. J. Appl. Electrochem. 1977, 7, 51-55. 67 Zou, X. X.; Zhang, Y. Noble metal-free hydrogen evolution catalysts for water-splitting. Chem. Soc. Rev. 2015, 15, 5148-5180. 68 Lavorante, M. J.; Franco, J. I. Performance of stainless steel 316L electrodes with modified surface to be use in alkaline water electrolyzers. Int. J. Hydrogen Energ. 2016, 23, 9731-9737. 69 Chen, J. G.; Jones, C. W.; Vojislav, S. L.; Stamenkovic, R. Best Practices in Pursuit of Topics in Heterogeneous Electrocatalysis ACS Catal. 2017, 7, 6392−6393.


Page 48 of 53

Page 49 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

70

Cherevko, S.; Topalov, A.; Zeradjanin, A.; Keeley, G.; Mayrhofer, K. J. Temperature-Dependent Dissolution of Polycrystalline Platinum in Sulfuric Acid Electrolyte. Electrocatal. 2014, 5, 235-240. 71 S. Cherevko, s.; Zeradjanin, A. R.; Keeley, G. P.; Mayrhofer, K. J. J. A comparative study on gold and platinum dissolution in acidic and alkaline media. J. Electrochem. Soc. 2014, 161, H822-H830. 72 A.A. Topalov, A. A.; S. Cherevko, S.; A.R. Zeradjanin, A. R.; J.C. Meier, J. C.; Katsounaros, I.; Mayrhofer, K. J. J. Towards a comprehensive understanding of platinum dissolution in acidic media. Chem. Sci. 2014, 5, 631-638. 73 Topalov, A. A.; Zeradjanin, A. R.; Cherevko, S.; Mayrhofer, K. J. J. The impact of dissolved reactive gases on platinum dissolution in acidic media. Electrochem. Commun. 2014, 40, 49-53. 74 Cherevko, S.; Keeley, G. P.; Geiger, S.; Zeradjanin, A. R.; Hodnik, N.; Kulyk, N.; Mayrhofer, K. J. J. Dissolution of Platinum in the Operational Range of Fuel Cells. ChemElectroChem 2015, 2, 1471-1478. 75 Gong, M.; Zhou, W.; Tsai, M.-C.; Zhou, J.; Guan, M.; Lin, M.-C.; Zhang, B.; Hu, Y.; Wang, D.-Y.; Yang et al. Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis. Nat. Commun. 2014, 5: 4695, 1-6, DOI: 10.1038/ncomms5695. 76 E. J. Popczun, E. J.; McKone, J. R.; Read, C. G.; Biacchi, A. J.; Wiltrout, A. M.; Lewis, N. S.; Schaak, R. E. Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 9267. 77 Jin, Z.; Li, P.; Xiao, D. Metallic Co2P ultrathin nanowires distinguished from CoP as robust electrocatalysts for overall water-splitting. Green Chemistry 2016, 18, 1459-1464. 78 Martindale, B. C. M.; Reisner, E. Bi-Functional Iron-Only Electrodes for Efficient Water Splitting with Enhanced Stability through In Situ Electrochemical Regeneration. Adv. Energy Mater. 2016, 6, 6, 1-9. 79 Liu, T.; Q. Liu, Q.; Asiri, A. M.; Luo, Y.; Su, X. An amorphous CoSe film behaves as an active and stable full watersplitting electrocatalyst under strongly alkaline conditions. Chem. Commun. 2015, 51, 16683. 80 Liu, D.; Lu, Q.; Sun, X.; Asiri, A. M. NiCo2S4 nanowires array as an efficient bifunctional electrocatalyst for full water splitting with superior activity. Nanoscale 2015, 7, 15122-15126. 81 Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X. NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54, 9351-9355. 82 Hou, D; Zhou, W.; Liu, X.; Zhou, K.; Xie, J.; Li, G. Pt nanoparticles/MoS2 nanosheets/carbon fibers as efficient catalyst for the hydrogen evolution reaction. Electrochim Acta 2015, 166, 26–31. 83 Schäfer, H.; Chevrier, D. M.; Zhang, P.; Stangl J.; Müller-Buschbaum, K.; Hardege, J. D.; Kuepper, K.; Wollschläger, J.; Krupp, U.; Dühnen, S. et al. Electro-Oxidation of Ni42 Steel: A Highly Active Bifunctional Electrocatalyst. Adv. Funct. Mater. 2016, 26, 6402-6417. 84 Zhang, C.; Hong, Y.; Dai, R.; Lin, X.; Long, L.-S.; Wang, C.; Lin, W. Highly Active Hydrogen Evolution Electrodes via Co-Deposition of Platinum and Polyoxometalates. ACS Appl. Mater. Inter. 2015, 7, 11648-11653. 85 Menthe, E.; Bulak, A.; Olfe, J.; Zimmermann, A.; Rie, K.-T. Improvement of the mechanical properties of austenitic stainless steel after plasma nitriding. Surf. Coat. Technol. 2000, 133-134, 259-263. 86 Liu, X.; You, B.; Sun, Y. Facile Surface Modification of Ubiquitous Stainless Steel Led to Competent Electrocatalysts for Overall Water-splitting. ACS Sustain. Chem. Eng. 2017, 5, 4778-4784. 87 Balogun, M.-S.; Qiu, W.; Huang, Y.; Yang, H.; Xu, R.; Zhao, W.; Li, G.-R.; Ji, H.; Tong, Y. Cost-Effective Alkaline Water Electrolysis Based on Nitrogen- and Phosphorus-Doped Self-Supportive Electrocatalysts. Adv. Mater. 2017, 34, 1702095, 1-11. 88 Koper, M. Thermodynamic theory of multi-electron transfer reactions: Implications for electrocatalysis. J. Electroanal. Chem. 2011, 660, 254-260. 89 Lyons, M. E. G., Brandon M. P. A comparative study of the oxygen evolution reaction on oxidized nickel, cobalt and iron electrodes in base. J. Electroanal. Chem. 2010, 641, 119-130. 90 Zhou, W.; Wu, X.-J.; Cao, X.; Huang, X., Tan, C.; Tian, j.; Liu, H.; Wang, J.; Zhang, H. Ni3S2 nanorods/Ni foam composite electrode with low overpotential for electrocatalytic oxygen evolution. Energy Environ. Sci. 2013, 6, 2921-2924. 91 Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K. et al. A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction. Science 2016, 353, 6303, 1011-1014. 92 Marshall, A. T.; Haverkamp, R. G. Electrochimica Acta 2010, 55, 1978-1984.



93

Danilovicet, N.; Subbaraman, R.; Chang, K.-C; Chang, S. H.; Kang, Y. I.; Snyder, J.; Paulikas, A. P.; Strmcnik, D.; Kim, Y.-T.; Myers, D. et al. Activity–Stability Trends for the Oxygen Evolution Reaction on Monometallic Oxides in Acidic Environments. J. Phys. Chem. Lett. 2014, 5, 2474-2478. 94 McCrory, C. C. L.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, I. C. Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. J. Am. Chem. Soc. 2015, 137, 43474357. 95 Mamaca, N.; Mayousse, E.; Arrii-Clacens, S.; Napporn, T. W.; Servat, K.; Guillet, N. Electrochemical activity of ruthenium and iridium based catalysts for oxygenevolution reaction. Appl Catal B 2012, 111–112, 376–80. 96 Schäfer, H.; Küpper, K., Müller-Buschbaum, K. M.; Daum, D.; Steinhart, M.; Wollschläger, J.; Krupp, U.; Schmidt, M.; Han, W., Stangl, J. Electro-oxidation of a cobalt based steel in LiOH: a non-noble metal based electro-catalyst suitable for durable water-splitting in an acidic milieu. Nanoscale 2017, 9, 17829-17838. 97 Polymer Electrolyte Fuel Cell Durability, ed. F. N. Büchi, M. Inaba and T. J. Schmidt, Springer Science and Business Media LLC, New York, 2009, pp. 199–221. 98 Dubau, L.; Castanheira, L.; Chatenet, M.; Maillard, F.; Dillet, J.; Maranzana, G.; Abbou, S.; Lottin, O.; De Moor, G.; El Kaddouri, A. et al. Carbon corrosion induced by membrane failure: The weak link of PEMFC long-term performance, Int. J. Hydrogen Energy 2014, 39, 21902-21914. 99 Castanheira, L.; Dubau, L.; Mermoux, M.; Berthomé, G.; Caqué, N.; Rossinot, E.; Chatenet, M.; Maillard, F. Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: From Model Experiments to Real-Life Operation in Membrane Electrode Assemblies, ACS Catal. 2014 ,4, 2258-2267. 100 Castanheira, L.; Silva, W. O.; Lima, F. H. B.; Crisci, A.; Dubau, L.; Maillard, F. Carbon corrosion in proton-exchange membrane fuel cells: Effect of the carbon structure, the degradation protocol, and the gas atmosphere. ACS Catal. 2015, 5, 2184-2194. 101 Yi, Y.; Weinberg, G.; Prenzel, M.; Greiner, M.; Heumann, S.; Becker, S.; Schlögl, R. Electrochemical corrosion of a glassy carbon electrode, Catal. Today 2017, 295, 32-40. 102 Candelise, C.; Speirs, J.F.; Gross, R.J.K. Materials availability for thin film (TF) PV technologies development: a real concern? Renew. Sustain. Energy Rev. 2011, 9, 4972-4981. 103 Kraft, A; Hennig, H.; Herbst, A; Heckner, K.-H. Changes in electrochemical and photoelectrochemical properties of tin-doped indium oxide layers after strong anodic polarization. J. Electroanal. Chem. 1994, 365, 191-196. 104 Geiger, S.; Kasian, O.; Mingers A. M.; Mayrhofer, K. J. J; Cherevko, S. Stability limits of tin-based electrocatalysts supports. Scientific Reports 2017, 7, 1-7, DOI:10.1038/s41598-017-04079-9. 105 Wassei, J. K.; Kaner, R. B. Graphene, a promising transparent conductor. Mater. Today 2010, 3, 52-59. 106 Dinamani, M.; Kamath, P. V. Electrocatalysis of oxygen evolution at stainless steel anodes by electrosynthesized cobalt hydroxide coatings. J. Appl. Electrochem. 2000, 30, 1157-1161. 107 Balram, A.; Zhang, H.; Santhanagopalan, S. In Situ Decoration of Stainless Steel Nanoparticles for Synergistic Enhancement of α-Ni(OH)2 Oxygen Evolution Reaction Catalysis. Mater. Chem. Front. 2017, 1, 2376-2382. 108 Hu, C.-C.; Wu, Y.-R. Bipolar performance of the electroplated iron–nickel deposits for water electrolysis. Mat. Chem. Phys. 2003, 82, 588–596. 109 Qian, L.; Chen, W.; Huang, R.; Xiao, D. Direct growth of NiCo2Sx nanostructures on stainless steel with enhanced electrocatalytic activity for methanol oxidation. RSC Adv. 2015, 5, 4092-4098. 110 Zhang, Q.; Zhong, H.; Meng, F.; Bao, D.; Zhang, X.; Wei, X. Three-dimensional interconnected Ni(Fe)OxHy nanosheets on stainless steel mesh as a robust integrated oxygen evolution electrode. Nano Res. 2017, DOI 10.1007/s12274-017-1743-8, 1-7. 111 Iwakura, C.; Honji, A.; Tamura, H. The anodic evolution of oxygen on Co3O4 film electrodes in alkaline solutions. Electrochim. Acta 1981, 25, 1319–1326. 112 Fan, J. Q.; Chen, Z. F.; Shi, H. J.; Zhao, G. H. In situ grown, self-supported iron–cobalt–nickel alloy amorphous oxide nanosheets with low overpotential toward water oxidation. Chem. Commun. 2016, 52, 4290-4293. 113 Tiwari, S. K.; Singh, A. K. L.; Singh, R. N. Studies on the electrocatalytic properties of some austenitic stainless steels for oxygen evolution in an alkaline medium. J. Electroanal. Chem. 1991, 319, 263-274. 114 Moureaux, F.; Stevens, P.; Toussaint, G.; Chatenet, M. Development of an oxygen-evolution electrode from 316L stainless steel: Application to the oxygen evolution reaction in aqueous lithium air batteries. J. Power Sources 2013, 229, 123-132.


Page 50 of 53

Page 51 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

115

Moureaux, F., PhD thesis, Grenoble-INP, 2011. Chen, Q.; Wang, R.; Yu, M.; Zeng, Y.; Lu, F.; Kuang, X.; Lu, X. Bifunctional Iron–Nickel Nitride Nanoparticles as Flexible and Robust Electrode for Overall Water Splitting. Electrochim. Acta 2017, 247, 666-673. 117 Yu, F.; Li, F.; Sun, L. Stainless steel as an efficient electrocatalyst for water oxidation in alkaline solution. Int. J. Hydrogen Energ. 2016, 41, 5230-5233. 118 Schäfer, H.; Beladi-Mousavi, S. M.; Walder, L.; Wollschläger, J.; Kuschel, O.; Ichilmann, S.; Sadaf, S.; Steinhart, M.; Küpper, K.; Schneider, l. Surface Oxidation of Stainless Steel: Oxygen Evolution Electrocatalysts with High Catalytic Activity. ACS Catal. 2015, 5, 2671-2680. 119 Reisch, M. S. Confronting the looming hexavalent chromium ban. Chem. Eng. News 2017, 95, 28-29. 120 Liu, X.; Shen, K.; Wang, Y.; Wang, Y.; Guo, Y.; Guo, Y.; Yong, Z.; Lu, G. Preparation and catalytic properties of Pt supported Fe-Cr mixed oxide catalysts in the aqueous-phase reforming of ethylene glycol. Catal. Commun. 2008, 9, 2316-2318. 121 Xanthopoulou, G. Oxide catalysts for pyrolysis of diesel fuel made by self-propagating high-temperature synthesis (SHS) Part II: Fe-Cr oxide catalysts based on chromite concentrates. Appl. Catal. A-General. 1999, 187, 7988. 122 Marono, M.; Sanchez, J. M.; Ruiz, E. Hydrogen-rich gas production from oxygen pressurized gasification of biomass using a Fe-Cr Water Gas Shift catalyst. Int. J. Hydrogen Energ. 2010, 35, 37-45. 123 Anantharaj, S.; Venkatesh, M.; Salunke, A. S.; Simha, T. V. S. V.; Prabu, V.; Kundu, S. High-Performance Oxygen Evolution Anode from Stainless Steel via Controlled Surface Oxidation and Cr Removal. ACS Sustainable Chem. Eng. 2017, 5, 10072-10083. 124 Schäfer, H.; Sadaf, S.; Walder, L.; Kuepper, K.; Dinklage, S.; Wollschläger, J.; Schneider, L.; Steinhart, M.; Hardege, J.; Daum, D. Stainless steel made to rust: a robust water-splitting catalyst with benchmark characteristics. Energy Environ. Sci. 2015, 8, 2685-2697. 125 Louie, M. W.; Bell, A. T. An Investigation of Thin-Film Ni–Fe Oxide Catalysts for the Electrochemical Evolution of Oxygen. J. Am. Chem. Soc. 2013, 135, 12329-12337. 126 Trotochaud, L.; Young, S. L.; Rannes, J. K.; Boettcher, S. W. Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation. J. Am. Chem. Soc. 2014, 136, 6744-6753. 127 Lee, M.; Jeon, H. S.; Lee, S. Y.; Kim, H.; Sim, S. J.; Hwang, Y. J.; Min, B. K. A self-generated and degradationresistive cratered stainless steel electrocatalyst for efficient water oxidation in a neutral electrolyte. J. Mater. Chem. A. 2017, 5, 19210-19218. 128 Sitthisa, S.; An, W.; Resasco, D. E. Selective conversion of furfural to methylfuran over silica-supported Ni-Fe bimetallic catalysts. J. Catal. 2011, 284, 90-101. 129 Nie, L.; De Souza, P. M.; Noronha, F. B., An, W., Sooknoi, T., Resasco, D. E. Selective conversion of m-cresol to toluene over bimetallic Ni-Fe catalysts. J. Mol. Catal. A: Chem. 2014, 388, 47-55. 130 Unmuth, E. E.; Schwartz, L. H. Butt, J. B. IRON ALLOY FISCHER-TROPSCH CATALYSTS .1. OXIDATION-REDUCTION STUDIES OF THE FE-NI SYSTEM. J. Catal. 1980, 61, 242-255. 131 Wang, L.; Li, D. L.; Koike, M., Koso, S., Nakagawa, Y.; Xu, Y.; Tomishige, K. Catalytic performance and characterization of Ni-Fe catalysts for the steam reforming of tar from biomass pyrolysis to synthesis gas. Appl. Catal. A: Gen. 2011, 392, 248-255. 132 Wang, J. G.; Liu, C. J.; Zhang, Y. P.; Yu, K. L.; Zhu, X. L.; He, F. Partial oxidation of methane to syngas over glow discharge plasma treated Ni-Fe/Al2O3 catalyst. Catal. Today 2004, 89, 183-191. 133 Tsoufis, T.; Xidas, P.; Jankovic, L; Gournis, D; Saranti, A; Bakas, T; Karakassides, M. A. Catalytic production of carbon nanotubes over Fe-Ni bimetallic catalysts supported on MgO. Diam. Relat. Mater. 2007, 16, 155-160. 134 Zhong, H.; Wang, J.; Meng, F.; Zhang, X. In situ Activating Ubiquitous Rust towards Low-Cost, Efficient, FreeStanding, and Recoverable Oxygen Evolution Electrodes. Angew. Chem. Int. Ed. 2016, 55, 9937-9941. 135 Tang, D.; Mabayoje, O.; Lai, Y.; Liu, Y.; Buddie Mullins, C. In Situ Growth of Fe(Ni)OOH Catalyst on Stainless Steel for Water Oxidation. ChemistrySelect 2017, 2, 2230-2234. 136 Huang, X.; Chang, S.; Lee, W. S. V.; Ding, J.; Xue, J. M. Three-dimensional printed cellular stainless steel as a high-activity catalytic electrode for oxygen evolution. J. Mater. Chem. A 2017, 5, 18176-18182. 116



137

Couto, S. R.; Sanroman, M. A.; Hofer, D.; Gubitz, G. M. Stainless steel sponge: a novel carrier for the immobilisation of the white-rot fungus Trametes hirsuta for decolourization of textile dyes. Bioresour Technol 2004, 95, 67-72. 138 Liu, D.; Zheng, T.; Buisman, C.; Ter Heijne, A. Heat-Treated Stainless Steel Felt as a new Cathode Material in a Methane-Producing Bioelectrochemical System. ACS Sustainable Chem. Eng. 2017, 5, 11346-11353. 139 Anantharaj, S.; Chatterjee, S.; Swaathini, K. C.; AmarnathT. S.; Subhashini, E.; Pattanayakm D. K.; Kundu, S. Stainless Steel Scrubber: A Cost Efficient Catalytic Electrode for Full Water Splitting in Alkaline Medium. ACS Sustain. Chem. Eng. 2017, DOI:10.1021/acssuschemeng.7b03964 140 Jadhav, A. R.; Puguan, J. M. C.; Kim, H. Microwave-Assisted Synthesis of a Stainless Steel Mesh-Supported Co3O4 Microrod Array As a Highly Efficient Catalyst for Electrochemical Water Oxidation. ACS Sustainable Chem. Eng. 2017, 5, 11069-11079. 141 Zhu, Y.-h.; Yin, Y.-b.; Yang, X.; Sun, T.; Wang, S.; Jiang, Y.-s.; Yan, J.-M.; Zhang, X. Transformation of Rusty Stainless-steel Meshes into Stable, Low-Cost, and binder-Free Cathodes for High-Performance Potassium-Ion Batteries. Angew. Chem. Int. Ed. 2017, 56, 7881-7885. 142 Wang, L.; Huang, X.; Jiang, S.; Li, M.; Zhang, K.; Yan, Y.; Zhang, H.; Xue, J. M. Increasing Gas Bubble Escape Rate for Water Splitting with Nonwoven Stainless Steel Fabrics. ACS Appl. Mater. Interfaces 2017, 9, 40281-40289. 143 Chen, P.; Xu, K.; Zhou, T.; Tong, Y.; Wu, J.; Cheng, H.; Lu, X.; Ding, H.; Wu, C.; Xie, Y. Strong-Coupled Cobalt Borate Nanosheets/Graphene Hybrid as Electrocatalyst for Water Oxidation Under Both Alkaline and Neutral Conditions. Angew. Chem. 2016, 55, 2488-2492. 144 He, J.; Peng, Y.; Sun, Z.; Cheng, W.; Liu, Q.; Feng, Y.; Jaing, Y.; Hu, F.; Pan, Z.; Bian Q. et al. Realizing High Water Splitting Activity on Co3O4 Nanowire Arrays under Neutral Environment. Electrochim. Acta 2014, 119, 64-71. 145 Zhao, Y.; Chen, S.; Sun, B.; Su, D.; Huang, X.; Liu, H.; Yan, Y.; Sun, K.; Wang, G. Graphene-Co3O4 nanocomposite as electrocatalyst with high performance for oxygen evolution reaction. Sci. Rep. 2014, 5, 7629, 1-7, DOI: 10.1038/srep07629. 146 Schäfer, H.; Chevrier, D. M.; Kuepper, K.; Zhang, P.; Wollschläger, J.; Daum, D.; Steinhart, M.; Hess, C.; Krupp, U.; Müller-Buschbaum, K. et al. X20CoCrWMo10-9//Co3O4: a metal–ceramic composite with unique efficiency values for water-splitting in the neutral regime. Energy Environ. Sci. 2016, 9, 2609-2622. 147 Kanan, M. W.; Nocera, D. G. In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing 2+ Phosphate and Co . Science 2008, 321, 1072-1075. 148 Arico, A. S; Bruce, P; Scrosati, B.; Tarasccon, J.-M.; Schalwijk, W. V. Nanostructured materials for advanced energy conversion and storage devices. Nat. Mater. 2005, 4, 366-377. 149 Xie, X.; Li, Y.; Liu, Z.-Q.; Haruta, M.; Shen, W. Low-temperature oxidation of CO catalyzed by Co3O4 nanrods. Nature 2009, 458, 746-749. 150 Hu, L.; Peng, Q.; Li, Y. Selective Synthesis of Co3O4 Nanocrystal with different shape and Crystal plane effect on catalytic property for methane combustion. J. Am. Chem. Soc. 2008, 130, 16136-16137. 151 Cao, A.-M.; Hu, J.-S.; Liang, H.-P.; Song, W.-G.; Wan, L-J.; He, X.-L.; Gao, X.-G.; Xia, S.-H. Hierarchically Structured Cobalt Oxide (Co3O4): The Morphology Control and Its Potential in Sensors. J. Phys. Chem. B. 2006, 11, 1585815863. 152 Li, W.; Xu, L. N.; Chen, J. Co3O4 nanomaterials in lithium-ion batteries and gas sensors. Adv. Funct. Mater. 2005, 15, 851-857. 153 Na, C. W.; Woo, H. S.; Kim, I. D.; Lee, J. H. Selective detection of NO2 and C2H5OH using a Co3O4-decorated ZnO nanowire network sensor. Chem. Commun. 2011, 47, 5148-5150. 154 Long, M.; Cai, W. M.; Cai, J.; Zhou, B. X.; Chai, X. Y.; Wu, Y. H. Efficient photocatalytic degradation of phenol over Co3O4/BiVO4 composite under visible light irradiation. J. Phys. Chem. B 2006, 110, 20211-20216. 155 Lou, X. W.; Deng, D.; Lee, J. Y.; Feng, J.; Archer, L. A. Self-Supported Formation of Needlelike Co3O4 Nanotubes and Their Application as Lithium-Ion Battery Electrodes. Adv. Mater. 2008, 20, 258-262. 156 Wu, Z.-S.; Ren, W.; Wen, l.; Gao, L.; Zhao, J.; Chen, Z.; Zhou, G.; Li, F.; Cheng, H.-M. Graphene Anchored with Co3O4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance. ACS Nano 2010, 4, 3187-3194. 157 Hamdani, M.; Singh, R. N.; Chartier, P. Co3O4 and Co-Based Spinel Oxides Bifunctional Oxygen Electrodes. Int. J. Electrochem. Sci. 2010, 5, 556-577.


Page 52 of 53

Page 53 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

158

Xu, J.; Gao, P.; Zhao, T. S. Non-precious Co3O4 nan-rod electrocatalyst for oxygen reduction reaction in anionexchange membrane fuel cells. Energy Environ. Sci. 2012, 5, 5333-5339. 159 Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H. Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction. Nat. Mater. 2011, 10, 780-786. 160 Xiong, S.; Yuan, C.; Zhang, X.; Xi, B.; Qian, Y. Controllable Synthesis of Mesoporous Co3O4 Nanostructures with Tunable Morphology for Application in Supercapacitors. Chem. Eur. J. 2009, 15, 5320-5326. 161 Schäfer, H.; Küpper, K., Wollschläger, J.; Kashaev, N.; Hardege, J.; Walder, L.; Beladi-Mousavi, S. M.; HartmannAzanza, B.; Steinhart, M.; Sadaf, S. et al. Oxidized Mild Steel S235: An Efficient Anode for Electrocatalytically Initiated Water-splitting. ChemSusChem 2015, 8, 3099-3110. 162 Su, C.; Li, W.; Liu, X.; Huang, X.; Yu, X. Fe-Mn-sepiolite as an effective heterogeneous Fenton-like catalyst for the decolorization of reactive brilliant blue. Front. Environ. Sci. Eng. 2016, 10, 37-45. 163 Trinh, Q. H.; Mok, Y. S. Non-Thermal Plasma Combined with Cordierite-Supported Mn and Fe Based Catalysts for the Decomposition of Diethylether. Catalysts 2015, 5, 800-814. 164 Lian, Z. H.; Ma, J. Z.; He, H. Decomposition of high-level ozone under high humidity over Mn-Fe catalyst: The influence of iron precursors. Catal. Commun. 2015, 59, 156-160. 165 Sedighi, B.; Feyzi, M.; Joshaghani, M. Response surface methodology as an efficient tool for optimizing the Fischer-Tropsch process over a novel Fe-Mn nano catalyst. RSC Adv. 2016, 6, 80099-80105. 166 Yang, J.; Liu, Y.; Chang, J.; Wang, Y. N.; Bai, L., Xu, Y. Y.; Xiang, H. W.; Li, Y. W.; Zhong, B. Detailed kinetics of Fischer-Tropsch synthesis on an industrial Fe-Mn catalyst. Ind. Eng. Chem. Res. 2003, 42, 5066-5090.


Steel, the Resurrection of a Forgotten Water ... - ACS Publications

Recommend Documents