Highly Active and Stable FeâNâC Catalyst for ... - ACS Publications

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Invited Feature Article

A Highly Active and Stable Fe-N-C Catalyst for Oxygen Depolarized Cathode Applications Jingkun Li, Qingying Jia, Shraboni Ghoshal, Wentao Liang, and Sanjeev Mukerjee Langmuir, Just Accepted Manuscript • Publication Date (Web): 26 Apr 2017 Downloaded from http://pubs.acs.org on April 27, 2017

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.

Langmuir 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 26 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

Langmuir

A Highly Active and Stable Fe-N-C Catalyst for Oxygen Depolarized Cathode Applications Jingkun Lia, Qingying Jiaa, Shraboni Ghoshala, Wentao Liangb, and Sanjeev Mukerjeea,* a

Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts, 02115, United States

b

Department of Biology, Northeastern University, Boston, Massachusetts 02115, United

States *

To whom correspondence should be addressed. E-mail: [email protected]

1

ACS Paragon Plus Environment

Langmuir 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

Page 2 of 26

Abstract Anion immunity towards oxygen reduction reaction (ORR) has tremendous implications in electrocatalysis with applications for fuel cells, metal-air batteries, and oxygen depolarized cathodes (ODCs) in anodic evolution of chlorine. The necessity for exploring ORR catalysts with immunity to anion adsorption is particularly significant considering that platinum group metal (PGM) catalysts are costly and highly vulnerable to impurities such as halides. Herein, we report a metal organic framework (MOF) derived Fe-N-C catalyst that exhibits a dramatically improved half-wave potential of 240 mV compared to the state-of-the-art RhxSy/C catalyst in a rotating disk electrode in the presence of Cl-. The Fe-N4 active sites in Fe-N-C are intrinsically immune to Clpoisoning, in contrast to Pt/C that is severely susceptible to Cl- poisoning. Resultantly, the activity of Fe-N-C decreases only marginally in the presence of Cl-, far exceeding that of Pt/C. The viability of this catalyst as ODCs is further demonstrated in “real life” hydrochloric acid electrolyzers using highly concentrated HCl solution saturated with Cl2 gas as the electrolyte. The introduction of Fe-N-C materials as ODC catalysts here overcomes the limitations of (i) the low intrinsic ORR activity of RhxSy/C as the state-of-the-art ODC catalyst; (ii) the vulnerability to Cl- poisoning of Pt/C as the state-of-the-art ORR catalyst; and (iii) the high cost of precious metals in these two materials, resulting in a cost-effective ODC catalyst with the overall performance exceeding all previously reported materials.

2


Page 3 of 26 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

Langmuir

Introduction The recycling of high-value chlorine gas from abundant aqueous hydrochloride acid is widely used in industry utilizing chlorine gas as a reactant.1-2 The recycling of chlorine gas evolved in the anodic compartment as feedstock to the chemical plant reduces risks emanating from large storage tanks of chlorine gas in industrial plants.3 However, such benefit comes at a price of intensive energy consumption. Typically, a metric ton of chlorine gas consumes ~1500 kWh power based on hydrochloric electrolyzers employing conventional hydrogen evolving cathode under standard conditions,4 and the overall chlorine generation in all its forms (i.e., chlor alkali and HCl recycling) consumes 2% of total energy consumption in United States (or any industrially developed country).5-6 Moreover, safety concerns as a consequence of crossover arising from hydrogen evolving cathode is an ever-present danger especially during uncontrolled shutdown conditions.6-7 Theoretically, these issues can be addressed by the invocation of oxygen depolarized cathode (ODC) technology as a replacement of hydrogen evolution cathodic reaction.2, 4, 6, 8-9

A comparison of the cell configurations with standard hydrogen evolving cathodes and

ODCs are displayed in scheme 1. In comparison with a lowering in thermodynamic cell potential from 1.36 V to 0.13 V via the application of ODC process, a practical cell voltage reduction of ~1 V at 0.3 A cm-2 is expected, entailing an energy saving up to 30% (Scheme 1c).2, 10-11 Translating and sustaining such enormous energy saving via the ODC process however has been challenging owing to both the lack of active ODC electrocatalysts and their long term durability under the highly corrosive and poisonous environments of Cl2 saturated concentrated HCl electrolyte. Hence, new catalysts with high ORR activity, stability, and immunity to Cl- poisoning possess tremendous potential for impact in terms of energy conservation.

3


Langmuir 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

Page 4 of 26

Scheme 1 Schematic illustration of HCl electrolyzers with (a) hydrogen evolving, (b) ODC, and (c) the influence of ODC on the electrode potentials.

The harsh operating conditions of ODC process severely limit the choice of electrocatalysts.12-15 Use of Pt and Pt alloys, the current state-of-the-art ORR catalysts for low and medium temperature in acid,16-19 is ruled out for hydrochloric acid electrolyzers due to the lack of anion immunity and more importantly stability. ORR active noble metals such as platinum are seriously poisoned even in a low concentration of anions, such as PO43- and Cl-, with concomitantly higher overpotentials and poorer kinetics of ORR.20-22 In terms of durability, substantial dissolution of Pt occurs in the highly corrosive Cl2 saturated HCl electrolyte especially during uncontrolled shutdown conditions,23 mandating extreme precautions during well-planned cell shutdowns, any

4


Page 5 of 26 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

Langmuir

uncontrolled shutdown however would “kill” the Pt-based catalysts.4, 8 On the other hand, some non-platinum group metal (non-PGM) catalysts, including transition metal oxides, nitrides oxynitrides, carbonitrides, and metal-free catalysts, exhibit immunity to anion poisoning, however their applications for ODC is limited by their poor ORR activity and/or stability.14 So far, carbon supported rhodium-based chalcogenides (RhxSy/C) pioneered by E-TEK Inc. in early 2000 remains the only electrocatalyst with the ability to survive the corrosive and poisonous environment of HCl electrolyzers while maintaining some degree of ORR activity.4, 8-9 As reported earlier, RhxSy is a composite of three crystalline phases (Rh2S3/Rh3S4/Rh17S15), with the Rh3S4 phase identified as the active site for ORR.24 The non-metallic RhS6 (essentially Rh2S3 phase) octahedra backbones anchor two metallic Rh6 eaves of Rh3S4 phase on either side, and the charge transfer predominately occurs at these metallic eaves separated by a non-metallic phase. Importance of such specific adsorption sites, in contrast to extended surfaces of supported Pt/C catalysts, promotes selectivity towards ORR, hence higher immunity to halide ion adsorption.24-25 Despite improved immunity (compared to Pt/C) there is some degree of susceptibility in this case since local conductivity still resides in the need of contiguous Rh to Rh bond in the Rh3S4 phase. Commercial RhxSy/C due to its higher immunity and durability is the current state-of-the-art catalyst9, 24-25 for ODC despite its much lower inherent ORR activity in acidic electrolytes without impurities. Successful incorporation of RhxSy/C catalysts into a chlorine production plant with an active cell area of more than 1000 m2,4, 24 despite the high cost (~$30-35 g-1) and low availability of Rh, forms the backbone of the current state-of-the-art HCl recycling technology. This provides incentive to replace it with more sustainable alternatives. Recent advances in coordinated Fe-N-C type catalysts have provided for its emergence as the leading non-PGM catalysts for ORR to replace Pt and Pt alloys. Fe-N-C materials with low cost, high activity, and enhanced stability26-32 satisfy all conditions required for the harsh environments in ODC-based HCl electrolyzers. The 5


Langmuir 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

Page 6 of 26

superior ORR activity of Fe-N-C catalysts has been demonstrated in H2/O2 and more practical H2/air polymer exchange membrane fuel cells (PEMFCs).30, 33-36 Our recent in situ x-ray absorption spectroscopy (XAS) and Δµ-x-ray absorption near edge spectroscopy (XANES) studies, together with the density function calculations revealed that Fe-N4 active sites host strong immunity to chloride poisoning and high stability in the harsh electrolytes such as Cl2 saturated HCl (5M) encountered in HCl electrolyzers.9 Metallic Fe nanoparticles in these non-PGM electrocatalyst however are immediately dissolved in this corrosive environment.9 The specific selectivity towards molecular oxygen in such Fe-N4 active sites is quite similar to Rh3S4 active sites in RhxSy/C.9 We have reported a highly active metal organic framework (MOF)-precursor derived ORR catalyst with almost exclusive formation of Fe-N4 coordinated active sites with metallic Fe nanoparticles presence being negligible to none.34 Presence of metallic Fe nanoparticles on the carbon structure provides a fertile ground to create a peroxide initiated free radical formation (i.e., formation of OH and OOH via Fenton’s reaction).37 Hierarchically porous structure derived from the sacrificial MOF precursor provides a combination of abundant active sites and efficient mass transport, ensuring high ORR activity of the catalyst. Based on the density functional theory (DFT) and in situ XAS results, our previous work9 showed that the high immunity of Fe-N4 active sites to Cl- poisoning, which has been demonstrated in rotating ring disk electrode (RRDE) technique, originates from the weak binding energy of Fe-N4-Cl compared to that of Fe-N4-O*, as well as the lack of extended metal surfaces due to the single site configuration in these sites. The extended metal surfaces are necessary for Cl- adsorpion since Cl- binds to the n-fold sites of metal surfaces, which is absent for Fe-N4 moieties. This was supported by the finding that the metallic Fe species in the Fe-based catalyst was poisoned by the Cl-.9 However, the interface properties and the source of the Cl- in a “real-life” HCl electrolyzer are quite different from that in the RDE testing. In this paper, we for the first time study the 6


Page 7 of 26 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

Langmuir

tolerance of Cl- of the state-of-the-art Fe-N-C catalyst with exclusively Fe-N4 moieties as active sites in a “real-life” HCl electrolyzer. The primary objective of this paper is to (a) provide a basis of comparison with the state-of-the-art commercial ODC catalysts based on RhxSy using steady state polarization data from operating electrolyzers, and (b) demonstrate durability when subject to uncontrolled shutdown condition. Considering the cost savings and the transition to more sustainable materials based on Fe, this report provides the basis for significant improvement in HCl recycling process.

Experimental Section Materials Preparation: Detailed synthetic procedure of the FePhenMOF-ArNH3 catalyst has been reported previously.34 In summary, the MOF (ZIF-8) precursor was synthesized through a reactive ball milling approach using zinc oxide (heat treated at 400 oC in air prior to use to remove impurities), 2-methylimidazole, and trace amount of ammonia sulfate and methanol as raw materials. Then iron(II) acetate and 1,10-phenanthroline monohydrate were then mixed with the as prepared ZIF-8 precursors. All the reactants were obtained from Alfa Aesar without further purification. The resulting light pink solid, FePhenMOF, was then subjected to two separate heat-treatments, i.e., in argon at 1050 °C for one hour (denoted as FePhenMOF-Ar) and then ammonia at 1050 °C for 18 minutes (denoted as FePhenMOF-ArNH3). Acid leaching of the catalysts was achieved by boiling the catalyst in 0.1 M hydrochloric acid solution at 80 oC overnight. Electrochemical characterization: All electrochemical measurements were performed at room temperature using rotating disc electrode (RDE) equipment from Pine Instruments connected to an Autolab bipotentiostat (model-PGSTAT 30) in a standard electrochemical cell (Chemglass). The commercial Pt/C (46%) electrocatalyst from Tanaka Kikinzoku International KK (TKK, Japan) with a loading of 15 µgPt cm-2 was used as a reference in this study. ORR polarization curves were measured in in 0.1 M perchloric acid (HClO4) solution bubbled with pure oxygen gas with rotation rates of 400, 7


Langmuir 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

Page 8 of 26

625, 900, and 1,600 rpm with a scan rate of 20 mV s-1. All voltages reported were with respect to a reversible hydrogen electrode (RHE) made from the same solution as the electrolyte. Inks of FePhenMOF-ArNH3 catalyst were prepared by dispersing 3.1 mg catalyst in a 150.2 µL millipore water and 465 µL isopropyl alcohol with 6.2 µL of 5 wt% Nafion® as a binder. After sonication for approximately 60 minutes, 30 µL of the ink solution was pipetted onto a polished glassy carbon RDE (Pine Instrument Co., 0.2476 cm2) to reach a loading of 600 µg cm-2. Inks of Pt/C catalyst were prepared by sonicating 10 mg catalyst, 5 mL deionized water, 5 mL 2-propanol, and 40 µL 5 wt% Nafion® as a binder for 60 min. Then 4.7 µL ink solution was drop casted onto a polished glassy carbon RDE (Pine Instrument Co., 0.2476 cm2) to reach a loading of 15 µg cm-2. All current values are normalized to the geometric area of the glassy carbon disk unless otherwise stated. Cl- poisoning testing: The comparative effects of chloride poisoning experiments were performed by comparing the ORR performances of FePhenMOF-ArNH3 catalyst in 1 M HClO4 (0 M Cl-) and 1 M HCl (1 M Cl-) electrolytes at room temperature using RDE. ORR polarization curves were measured in in 1 M HClO4 and 1 M HCl solutions bubbled with pure oxygen gas with rotation rates of 400, 625, 900, and 1600 rpm with a scan rate of 10 mV s-1. 30 wt% Pt/C (Vulcan XC72 from E-TEK) or 30 wt% RhxSy/C (Denora, Concord, OH, USA) were utilized as references with a loading of 15 µgPt/Rh cm-2. Inks of Pt/C or RhxSy/C catalysts were prepared by sonicating 10 mg catalyst, 5 mL deionized water, 5 mL 2-propanol, and 40 µL 5 wt% Nafion® as a binder for 60 min. Then quantified amount of ink solution was drop casted onto a polished glassy carbon RDE (Pine Instrument Co., 0.196 cm2). The ink preparation for the FePhenMOF-ArNH3 catalyst was the same as mentioned in the “electrochemical characterization” section mentioned above and a loading of 600 µg cm-2 FePhenMOF-ArNH3 catalyst was applied onto a 0.196 cm2 RDE. Ag/AgCl was used as reference electrode and carbon cloth was functioned as counter electrode. All the potentials have been converted to RHE scale. All 8


Page 9 of 26 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

Langmuir

current values are normalized to the geometric area of the glassy carbon disk unless otherwise stated. The geometric kinetic current densities were estimated according to: Ikin=I×Ilim/(Ilim−I). Physical characterization: N2 adsorption analysis was performed on a Quantachrome NOVA 2200e at 77 K. Total surface area was determined by the Brunauer-Emmett-Teller (BET) method. Particle morphology and Fe, C, N elemental mapping were performed on a Hitachi S-4800 field emission scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) with an accelerating voltage of 3-5 keV. Samples were mounted on a carbon-free adhesive stub attached to an aluminum sample stage. For transmission electron microscope (TEM), Karaa JEOL 2010 field emission gun TEM was used at an acceleration voltage of 200 kV with samples deposited on a holey carbon film on a 300 mesh copper grid. Raman spectra were collected using a DXRxi Raman microscope. Thermogravimetric analysis (TGA) were performed on TA Instruments SDT Analyzer Q600 from room temperature to 1,100 oC at a ramping rate of 5 oC min-1 in Ar with a flow rate of 100 mL min-1. HCl electrolysis cell testing: In order to assess the ‘‘real-life’’ activity of the FePhenMOF-ArNH3 electrocatalysts as working ODCs, a standard industrial HCl electrolysis cell (supplied by DeNora, details about the cell configuration have been reported in our previous work4, 8) with an active cell area of 6.25 cm2 was applied. The state of the art dimensionally stabilized anodes (DSAs) were utilized in the cell at anode for Cl2 evolution. The powdered samples were incorporated into gas diffusion electrodes (GDEs) with a loading of 5 mg cm-2 as ODCs via spraying a catalyst ink composed of 4 mL Isopropyl Alcohol, 2 mL dionized water, 200 mg of catalyst and 5 wt% Nafion® with a catalyst to Nafion ratio of 1:1 onto a carbon paper. The ODC cathodes with RhxSy/C as catalysts were prepared by hand painting successive coatings of a catalyst/Teflon®/2-propanol slurry onto a carbon cloth. A Rh metal loading of 1 mg cm-2 was obtained after dried at 80 oC under vacuum. The Nafion® 362 membrane was soaked 9


Langmuir 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

Page 10 of 26

in 1 M HCl solution prior to use. The ODCs and DSAs were both physically contacted with the Nafion® 362 membrane (not hot pressed) by tightening down the Ti current collectors at both cathode and anode sides. The cell was tested at 55 oC with a fed of pure oxygen at the cathodic compartment with no backpressure and a fed of Cl2-saturated 5 M HCl solution at the anodic compartment. After stabilized under these conditions for approximately 3 hrs, polarization curves were measured by holding the cell at a constant current density for more than 10 min to obtain a stable voltage. The effect of uncontrolled shutdowns on the cathode electrocatalysts was evaluated by simply switching off the cell during operation. After more than 12 hrs, the cell was restarted according to the conditions mentioned above, and polarization curves were measured at constant current densities.

Results and Discussion ORR activity with and without the presence of Cl-: The ORR polarizations (Figure 1) of the FePhenMOF-ArNH3 catalyst as determined by rotating disk electrode method are shown at both ends of the pH scale at 1,600 rpm with commercial Pt/C catalyst (Tanaka Kikinzoku International KK (TKK, Japan), 46.7 wt%) used as a reference. As reported earlier,34 the FePhenMOF-ArNH3 catalyst exhibited an onset potential of 0.98 V and a half-wave potential (E1/2) of 0.78 V in 0.1 M HClO4, which is only 55 mV lower compared to commercial Pt/C in terms of half-wave potential. In 0.1 M KOH, it exhibited a more positive onset potential (1.05 V) and half-wave potential (0.87 V), which are higher as compared to commercial Pt/C catalyst. These ORR activities represent the best non-PGM catalysts with preferred 4 or 2+2-electron transfer mechanism (Figure S1-3) in both acidic and alkaline media.5, 15, 26, 29-30, 33, 35 It has been proposed that the high intrinsic ORR activity of the FePhenMOF-ArNH3 catalyst in acidic media originates from the non-planar ferrous Fe-N4 moieties as active sites embedded in distorted carbon matrix with a high Fe2+/3+ redox potential (0.78 V).34

10


Page 11 of 26 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

Langmuir

Extensive in situ XAS studies on various catalysts have proven that the onset potential of these Fe-N-C catalysts are highly correlated to the Fe3+ to Fe2+ redox transition,34, 38-39 associated with a reversible switch of the active sites from an in-plane geometry covered by oxygen adsorbates to an non-planar geometry without the oxygenated adsorbates.34, 39 The biomimetic dynamic nature of the active sites accounts for their weakened Fe-O binding energy and higher Fe2+/3+ redox potential, and is responsible for the superior intrinsic activity in acid. In alkaline pH, it has been demonstrated that the direct chemisorption of O2 on the biomimetic Fe-N4 active sites followed by stabilization of the anionic hydrogen peroxide intermediate (HO2-) lead to a concerted 4e- electron catalytic inner sphere charge transfer reaction mechanism.27 Whereas on Pt surfaces a surface-independent outer sphere electron transfer ORR mechanism without the direct surface adsorption of molecular oxygen is the predominant route, leading to a higher propensity for 2e- peroxide intermediate.40 Such distinctly different reaction mechanisms explain

the

more

positive

on-set

and

enhanced

half-wave

potentials

of

FePhenMOF-ArNH3 and various other Fe-N-C catalysts29, 41 compared to conventional commercial Pt/C in alkaline pH.

11


Langmuir 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

Page 12 of 26

12


Page 13 of 26 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

Langmuir

Figure 1. (a) Rotating disk electrode (RDE) ORR polarization plots collected with FePhenMOF-ArNH3, Pt/C (TKK, 46.7 wt%) in O2-saturated 0.1 M HClO4 (solid lines) and 0.1 M KOH (dashed lines) electrolytes at 20 mV s-1 with a rotation rate of 1,600 rpm at room temperature. (b) Comparative ORR polarization curves collected with FePhenMOF-ArNH3, Pt/C (30 wt% Standard BASF-ETEK, Somerset, NJ) and RhxSy/C (30 wt%, Standard Denora Tech, Concord, OH) in O2-saturated 1 M HClO4 (solid lines) and 1 M HCl (dashed lines) electrolytes, respectively. (RDE: 10 mV s-1, 900 rpm in 1M HClO4 (0 M Cl-) and 1M HCl (1 M Cl-). (Working electrode: glassy carbon; reference electrode: Ag/AgCl; counter electrode: carbon cloth. All the potentials have been converted to RHE scale). (c) The influence of Cl- poisoning on the half-wave potential of FePhenMOF-ArNH3, Pt/C and RhxSy/C.

The effect of Cl- poisoning is represented in figure 1b-c and Table S1, wherein comparison of FePhenMOF-ArNH3 polarization is made with previously reported data9 involving Pt/C (30% Standard BASF-ETEK, Somerset, NJ) and RhxSy/C (30%, Standard Denora Tech, Concord, OH). Higher concentration of acids (1 M HClO4 and 1 M HCl) as electrolytes was used to provide a more realistic comparison with the environment of HCl electrolyzers. In contrast to the expected higher ORR activity exhibited by Pt/C compared to non-PGM catalyst in 1 M HClO4, a substantial performance loss in E1/2 (~ 460 mV) was observed in the presence of 1 M Cl-. This phenomenon is well understood as the Pt sites are vulnerable to Cl- poisoning.4, 9, 21 Competitive and site-specific nature of Cladsorption on Pt has been previously reported by us using in situ XAS and Δµ-XANES techniques.21 It should be noted that the state-of-the-art ODC catalyst in HCl electrolyzers, RhxSy/C, with a better tolerance to halide ions, still exhibited an increase in ORR overpotential of 170 mV, which is in good agreement with previous literature.4, 9 The advantage of FePhenMOF-ArNH3 catalyst over those carbon supported noble metal catalysts is more obvious with the presence of halide ions, where a marginal cathodic shift in half-wave potential of ~20 mV was shown in 1 M HCl comparing to that in 1 M HClO4 (Figure 1b-c). An improvement in half-wave potential of ~240 mV (Table S1) was demonstrated between FePhenMOF-ArNH3 catalyst (0.80 V) and RhxSy/C (0.56 V) in 1 M HCl. The Mössbauer spectroscopy and XAS results suggested that active sites of the FePhenMOF-ArNH3 catalyst are Fe-N4 moieties,34 and our previous in situ XAS and

13


Langmuir 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

Page 14 of 26

Δµ-XANES studies, together with the density function calculations revealed the immunity of such Fe-N4 active sites to chloride poisoning.9 These results indicate that the FePhenMOF-ArNH3 catalyst is a highly promising candidate as ODC catalyst for HCl electrolyzers. Physicochemical characterizations: Physicochemical characterizations were applied to trace the origin of the high ORR activity of FePhenMOF-ArNH3 catalyst. The Brunauer-Emmett-Teller (BET) surface areas and the total pore volumes of the catalyst at different synthetic stages are shown in Table 1. The MOF precursor obtained by reactive ball milling exhibited a comparable BET surface area (~2300 m2 g-1) comparing to that of commercial Basolite Z1200® (~2900 m2 g-1). The rapid rise of the N2 adsorption isotherm curve at low relative pressures exhibited by the MOF precursor (Figure 2a) indicated the presence of micropores in the original MOF structure.36 The addition of FePhen complex reduced the surface area sharply (Table 1), and this can be attributed to blocking effect of the pores by externally coated phenanthroline complex. The first heat treatment in Ar created large number of pores as a result of sublimation of Zn nodes in ZIF-8 (Zeolitic Imidazolate Framework).35 As per thermogravimetric analysis (TGA) shown in Figure 2b, the weight loss experienced below 400 oC can be ascribed to the gasification of phenanthroline. The decomposition of the ZnII-Imidazolate-ZnII linkages in the ZIF-8 structure however is indicated at temperatures above 500 oC. At around 600 o

C the weight loss can be attributed to the release of CN fragments from the imidazolate

linker. Subsequent formation of Zn(CN)2 via the reaction of ZnII and CN fragments is then further decomposed around 800 oC as shown in Figure 2b, resulting in CN fragments and volatile Zn (bpt of 907 oC). The second heat treatment in NH3 further increased the BET area (Table 1) significantly, which was attributed to the etching of disordered carbon by NH3 and the further sublimation of the trapped Zn. Moreover, FePhenMOF-Ar and FePhenMOF-ArNH3 catalysts both exhibited type-IV N2 adsorption isotherms (Figure 2a), suggesting the presence of abundant mesopores in the catalysts.41 14


Page 15 of 26 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

Langmuir

Raman spectra (Figure 2c) of FePhenMOF-ArNH3 catalyst before and after acid wash confirmed the highly disordered nature of the carbon matrix in the catalyst, as the intensity of the D-band (disorder vibration mode, ~1350 cm-1) is higher than that of G-band (graphitic carbon, ~1580 cm-1). Generally, a higher ID/IG ratio represents a more porous structure and/or a higher heteroatom (N in this catalyst) on carbon.34,

42

The

former ensures enough space to hold a high concentration of Fe-N4 active sites and effective mass transportation of reactants and products,31, 35, 43 and the latter provides opportunities for metal ions to form the N-coordinated iron complex as active sites,44 both of which are therefore beneficial to the ORR activity of Fe-N-C catalysts. Table 1 Brunauer-Emmett-Teller (BET) surface area and total pore volume of non-heat treated commercial Basolite Z1200®, MOF synthesized through reactive ball milling approach, FePhenMOF precursor, FePhenMOF-Ar and FePhenMOF-ArNH3.

Basolite Z1200®

MOF

FePhenMOF

FePhenMOF -Ar

FePhenMOF -ArNH3

BET Surface Area (m2 g-1)

1900

2307

61.87

355.2

1362

Total Pore Volume (cc g-1)

1.14

1.00

0.0783

0.498

1.18

15


Langmuir 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

Page 16 of 26

16


Page 17 of 26 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

Langmuir

Figure 2. (a) The nitrogen adsorption isotherm curves of MOF synthesized through reactive ball milling approach, FePhenMOF, FePhenMOF-Ar, and FePhenMOF-ArNH3. (b) Thermogravimetric analysis (TGA) and corresponding derivative weight percentage of 1,10-Phenanthroline, commercial Basolite Z1200® and FePhenMOF precursor. (c) Raman spectrum of FePhenMOF-ArNH3 before and after acid wash.

The highly porous structures with inter-connected hollow channels of the FePhenMOF-Ar and FePhenMOF-ArNH3 catalysts were further confirmed by the SEM and TEM images (Figure 3a-d). The proper hierarchy of micropores (100 nm) ensures the superior ORR activity of FePhenMOF-ArNH3 catalyst, since it is well acknowledged that the majority of Fe-N4 active sites reside within the micropores of the carbon matrix,31,

45-46

and the

mesopores/macropores facilitate the mass transportation of ORR related species and H2O towards and away from the active sites within those micropores.20,

35-36, 43

Figure 3e

presented a representative EDX spectrum of the FePhenMOF-ArNH3 catalyst. The Fe signal could be clearly detected despite the low Fe content (0.5 wt%) as given by ICP. The SEM and TEM images of FePhenMOF-ArNH3 catalyst after acid wash (Figure 3c-d) proved the absence of agglomerated Fe nanoparticles in the catalyst, which is in agreement with the Mössbauer spectroscopy and XAS results reported previously.34 This is

further

supported

by

the

mapping

of

Fe

element

distribution

on

the

FePhenMOF-ArNH3 catalyst section (Figure 3i). The uniform signal intensity of Fe suggested the uniform dispersion of Fe in the catalyst.36 The mapping of N, C element distributions (Figure 3g-h) also confirmed the uniform distributions of N and C atoms. The porous structure with abundant micropores and mesopores/macropores, as well as the selective yield of distorted ferrous Fe-N4 moieties as active sites embedded in disordered carbon matrix with a high Fe2+/3+ redox potential are responsible for the high intrinsic ORR activity of the FePhenMOF-ArNH3 catalyst.

17


Langmuir 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

Page 18 of 26

Figure 3. (a) SEM image of FePhenMOF-Ar; scale bar, 500 nm. (b) TEM image of FePhenMOF-Ar; scale bar, 200 nm. (c) SEM image of FePhenMOF-ArNH3; scale bar, 500 nm. (d) TEM image of FePhenMOF-ArNH3; scale bar, 200 nm. (e) EDX spectrum of FePhenMOF-ArNH3. (f) SEM image of a section of FePhenMOF-ArNH3; scale bar, 2 µm. (g)-(j) Mapping of carbon, nitrogen, iron and a combination of the three elements distributions on the same section of FePhenMOF-ArNH3, respectively.

“Real-life” HCl recycling electrolyzer testing: Figure 4a presents a comparison of full chlorine electrolyzer cell polarization curve with FePhenMOF-ArNH3 and RhxSy/C serving as oxygen depolarized cathodes (ODC) in conjunction with chlorine evolving anode (Dimensionally Stable Anodes (DSA), Denora, Concord, OH, USA), details of the electrode loading and the cell configuration are provided in the experimental section. In a separate experiment comparison of the polarization results from DSA chlorine evolution and a H2 evolving cathode was measured to provide accurate estimation of the lower overvoltage observed in the ODC cathodes. The FePhenMOF-ArNH3 catalysts showed a decrease in overall cell voltage of >600 mV at 3 kA m-2 (the current density used in commercial HCl electrolyzer plants) compared to H2 evolving cathode. The difference in “real-life” cell performance of the FePhenMOF-ArNH3 and RhxSy/C catalysts was

18


Page 19 of 26 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

Langmuir

negligible at the beginning of life (Figure 4a), which contradicted the RDE results shown above. The loss of the tremendous performance gain of FePhenMOF-ArNH3 over RhxSy/C is explained by the fact that the performance of the “real-life” HCl recycling electrolyzers running at a high current region (3 kA m-2) fall in the mass transport limited region of the polarization curve. Such limitation, which has also been observed in PEMFCs utilizing non-PGM catalysts at the cathodes12, is exacerbated by the high loading (3 mg cm-2) and thick electrode of non-PGM catalysts based cathodes. Even through the FePhenMOF-ArNH3 and RhxSy/C catalysts exhibit the same performance in “real-life” HCl electrolyzer, the Fe-based non-PGM catalyst still provides pronounced advantage in terms of cost. In addition, the mass transport limitations can be improved by optimizing the cell configuration and electrode structure, considering the fact that the present cell and electrode structures were originally designed based on RhxSy/C catalysts (hence much thinner micro-porous layers). The higher intrinsic ORR activity and immunity to Cl- poisoning as revealed by RDE suggests that the performance of FePhenMOF-ArNH3 catalyst in HCl electrolyzers has a high potential to achieve a better performance. The stability of ODC catalysts upon uncontrolled shutdown is another key factor for the practical application of the catalysts in HCl electrolyzers since any sudden shift of the cathodic potential has the potential to expose the ODC catalysts to not only the highly corrosive environment of concentrated HCl saturated with Cl2 gas, but also dangerous transition of potentials beyond the stability limits. For platinum group metals and their alloys, any uncontrolled shutdown results in severe metal dissolution, followed by the deactivation of the catalysts.4,

8

In order to determine the viability of the

FePhenMOF-ArNH3 catalyst as ODCs, their response to uncontrolled shutdowns was examined (Figure 4b and Figure S4). The closely mirrored cell performances of FePhenMOF-ArNH3 and RhxSy/C catalysts after three uncontrolled shutdowns proved the high stability of both catalysts. Since most of the Fe present in the FePhenMOF-ArNH3 19


Langmuir 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

Page 20 of 26

catalyst are in the form of Fe-N4,34 it is not surprising that the catalyst showed considerable stability upon uncontrolled shutdowns. Moreover, no obvious changes on the structures of the ODC electrode surfaces before and after those uncontrolled shutdowns were observed according to their SEM images (Figure 4c-d), further supporting the stability of FePhenMOF-ArNH3 catalyst upon uncontrolled shutdowns.

Figure 4. (a) Polarization curves of oxygen depolarized cathodes (ODCs) compared with H2 evolving electrodes for single cell HCl electrolyzer cell run in constant current mode (hold at certain currents for more than 10 minutes). Cell temperature: 55 oC; Anode: 5 M HCl/Cl2, ODC Cathode: O2/H2O with FePhenMOF-ArNH3 (3 mg cm-2) or RhxSy/C (Denora Tech, OH, 1 mgRh cm-2). (b) Polarization curves of oxygen depolarized cathodes with the same electrodes after three uncontrolled shutdowns. (c) SEM image of ODC electrodes with FePhenMOF-ArNH3 catalysts

20


Page 21 of 26 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

Langmuir

before test; scale bar, 3 µm. (d) SEM image of ODC electrodes with FePhenMOF-ArNH3 catalysts after three uncontrolled shutdowns; scale bar, 3 µm.

Conclusions The high ORR activity of the FePhenMOF-ArNH3 catalyst with exclusively Fe-N4 moieties as active sites has been attributed to the amorphous carbon matrix with high BET surface area and appropriate combination of micropores and mesopores/macropores derived from the highly porous ZIF-8. An improved tolerance to Cl- poisoning was demonstrated with both RDE in the presence of Cl- and “real life” hydrochloric acid electrolyzers. The high performance of this catalyst for ODC stems from the effective combination of the high intrinsic activity toward ORR and the immunity to Cl- poisoning. The exclusive formation of Fe-N4 coordinated active sites with negligible uncoordinated Fe present is responsible for the high stability upon uncontrolled shutdowns since uncoordinated Fe nanoparticles facilitate the formation of free radicals initiated by peroxide formation (i.e., formation of OH and OOH via Fenton’s reaction). Our work introduces a new route to synthesize cost-effective and efficient non-PGM materials as ODCs with enhanced stability. Acknowledgements: The authors deeply appreciate financial assistance from the U. S. Department of Energy, EERE (DE-EE-0000459) under which the catalyst materials were developed. Evaluation the FePhenMOF-ArNH3 electrocatalyst for ODC applications were sponsored under a catalyst award provided by the Massachusetts Clean Energy Council (Mass-CEC) and sponsorship by Denora (North America). Dr. Chris Allen at Denora Tech (Concord, OH) and Robert J. Allen are gratefully acknowledged for providing professional advices for the design of HCl electrolysis cell and experimental details. Competing financial interests 21


Langmuir 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

Page 22 of 26

The authors declare no competing financial interests. Supporting Information. Koutecky-Levich plots collected with FePhenMOF-ArNH3 in O2-saturated 0.1 M HClO4 and KOH, the single cell HCl electrolyzer performance upon uncontrolled shutdowns and a table summarizing the RDE studies of the effect of chlorine poisoning are provided as Supporting Information. References 1. Federico, F.; Martelli, G. N.; Pinter, D., Gas-Diffusion Electrodes for Chlorine-Related (Production) Technologies. In Modern Chlor-Alkali Technology, Blackwell Science Ltd: 2007; p 114-127. 2. Pérez-Ramírez, J.; Mondelli, C.; Schmidt, T.; Schlüter, O. F. K.; Wolf, A.; Mleczko, L.; Dreier, T. Sustainable chlorine recycling via catalysed HCl oxidation: from fundamentals to implementation. Energ. Environ. Sci. 2011, 4, 4786-4799. 3. Kuwertz, R.; Martinez, I. G.; Vidaković-Koch, T.; Sundmacher, K.; Turek, T.; Kunz, U. Energy-efficient chlorine production by gas-phase HCl electrolysis with oxygen depolarized cathode. Electrochem. Commun. 2013, 34, 320-322. 4. Gulla, A. F.; Gancs, L.; Allen, R. J.; Mukerjee, S. Carbon-supported low-loading rhodium sulfide electrocatalysts for oxygen depolarized cathode applications. Appl. Catal. A 2007, 326, 227-235. 5. Liang, Y.; Wang, H.; Diao, P.; Chang, W.; Hong, G.; Li, Y.; Gong, M.; Xie, L.; Zhou, J.; Wang, J.; Regier, T. Z.; Wei, F.; Dai, H. Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes. J. Am. Chem. Soc. 2012, 134, 15849-15857. 6. Liu, J. J.; Yang, C.; Liu, C. G.; Wang, F.; Song, Y. Design of Pore Structure in Gas Diffusion Layers for Oxygen Depolarized Cathode and Their Effect on Activity for Oxygen Reduction Reaction. Ind. Eng. Chem. Res. 2014, 53, 5866-5872. 7. Chlistunoff, J. Advanced chlor-alkali technology. Los Alamos, NM, USA 2005. 8. Ziegelbauer, J. M.; Gulla, A. F.; O'Laoire, C.; Urgeghe, C.; Allen, R. J.; Mukerjee, S. Chalcogenide electrocatalysts for oxygen-depolarized aqueous hydrochloric acid electrolysis. Electrochim. Acta 2007, 52, 6282-6294. 9. Tylus, U.; Jia, Q.; Hafiz, H.; Allen, R.; Barbiellini, B.; Bansil, A.; Mukerjee, S. Engendering Anion Immunity in Oxygen Consuming Cathodes Based on Fe-Nx Electrocatalysts: Spectroscopic and Electrochemical Advanced characterizations. Appl. Catal. B 2016, 198, 318-324. 10. Moussallem, I.; Jörissen, J.; Kunz, U.; Pinnow, S.; Turek, T. Chlor-alkali electrolysis with oxygen depolarized cathodes: history, present status and future prospects. J. Appl. Electrochem. 2008, 38, 1177-1194.

22


Page 23 of 26 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

Langmuir

11. Figueiredo, R. S.; Bertazzoli, R.; Rodrigues, C. A. Copper/Carbon/PTFE Oxygen-Depolarized Cathodes for Chlor-alkali Membrane Cells. Ind. Eng. Chem. Res. 2013, 52, 5611-5615. 12. Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature 2012, 486, 43-51. 13. Gasteiger, H. A.; Kocha, S. S.; Sompalli, B.; Wagner, F. T. Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs. Appl. Catal. B 2005, 56, 9-35. 14. Shao, M.; Chang, Q.; Dodelet, J. P.; Chenitz, R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594-3657. 15. Masa, J.; Xia, W.; Muhler, M.; Schuhmann, W. On the Role of Metals in Nitrogen-Doped Carbon Electrocatalysts for Oxygen Reduction. Angew. Chem. Int. Ed. Engl. 2015, 54, 10102-10120. 16. Jia, Q. Y.; Li, J. K.; Caldwell, K.; Ramaker, D. E.; Ziegelbauer, J. M.; Kukreja, R. S.; Kongkanand, A.; Mukerjee, S. Circumventing Metal Dissolution Induced Degradation of Pt-Alloy Catalysts in Proton Exchange Membrane Fuel Cells: Revealing the Asymmetric Volcano Nature of Redox Catalysis. ACS Catal. 2016, 6, 928-938. 17. Tian, X.; Luo, J.; Nan, H.; Zou, H.; Chen, R.; Shu, T.; Li, X.; Li, Y.; Song, H.; Liao, S. Transition metal nitride coated with atomic layers of Pt as a low-cost, highly stable electrocatalyst for the oxygen reduction reaction. J. Am. Chem. Soc. 2016, 138, 1575-1583. 18. Zhang, J.; Sasaki, K.; Sutter, E.; Adzic, R. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007, 315, 220-222. 19. Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J.; Lucas, C. A.; Wang, G.; Ross, P. N.; Markovic, N. M. Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. Nat. Mat. 2007, 6, 241-247. 20. Li, Q.; Wu, G.; Cullen, D. A.; More, K. L.; Mack, N. H.; Chung, H. T.; Zelenay, P. Phosphate-Tolerant Oxygen Reduction Catalysts. ACS Catal. 2014, 4, 3193-3200. 21. Arruda, T. M.; Shyam, B.; Ziegelbauer, J. M.; Mukerjee, S.; Ramaker, D. E. Investigation into the competitive and site-specific nature of anion adsorption on Pt using in situ X-ray absorption spectroscopy. J. Phys. Chem. C 2008, 112, 18087-18097. 22. Marković, N.; Gasteiger, H.; Grgur, B.; Ross, P. Oxygen reduction reaction on Pt (111): effects of bromide. J. Electroanal. Chem. 1999, 467, 157-163. 23. Schmidt, T.; Paulus, U.; Gasteiger, H.; Behm, R. The oxygen reduction reaction on a Pt/carbon fuel cell catalyst in the presence of chloride anions. J. Electroanal. Chem. 2001, 508, 41-47. 24. Ziegelbauer, J. M.; Gatewood, D.; Gullá, A. F.; Guinel, M. J.-F.; Ernst, F.; Ramaker, D. E.; Mukerjee, S. Fundamental investigation of oxygen reduction reaction on rhodium sulfide-based chalcogenides. J. Phys. Chem. C 2009, 113, 6955-6968. 25. Ziegelbauer, J.; Gatewood, D.; Gullá, A.; Ramaker, D.; Mukerjee, S. X-Ray Absorption Spectroscopy Studies of Water Activation on an Rh x S y Electrocatalyst for 23


Langmuir 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

Page 24 of 26

Oxygen Reduction Reaction Applications. Electrochem. Solid-State Lett. 2006, 9, A430-A434. 26. Serov, A.; Artyushkova, K.; Atanassov, P. Fe-N-C oxygen reduction fuel cell catalyst derived from carbendazim: synthesis, structure, and reactivity. Adv. Ehergy Mater.. 2014, 4, 919-926. 27. Ramaswamy, N.; Tylus, U.; Jia, Q.; Mukerjee, S. Activity descriptor identification for oxygen reduction on nonprecious electrocatalysts: Linking surface science to coordination chemistry. J. Am. Chem. Soc. 2013, 135, 15443-15449. 28. Jia, Q.; Ramaswamy, N.; Tylus, U.; Strickland, K.; Li, J.; Serov, A.; Artyushkova, K.; Atanassov, P.; Anibal, J.; Gumeci, C. Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid. Nano Energy 2016, 29, 65-82. 29. Wang, Q; Zhou, Z.Y.; Lai, Y.J.; You, Y.; Liu, J.G.; Wu, X.L.; Terefe, E.; Chen, C.; Song, L.; Rauf, M.; Tian, N.; Sun, S.G. Phenylenediamine-based FeNx/C catalyst with high activity for oxygen reduction in acid medium and its active-site probing. J. Am. Chem. Soc. 2014, 136, 10882-10885. 30. Zitolo, A.; Goellner, V.; Armel, V.; Sougrati, M.-T.; Mineva, T.; Stievano, L.; Fonda, E.; Jaouen, F. Identification of catalytic sites for oxygen reduction in iron-and nitrogen-doped graphene materials. Nat. Mat. 2015, 14, 937-942. 31. Lefèvre, M.; Proietti, E.; Jaouen, F.; Dodelet, J.-P. Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells. Science 2009, 324, 71-74. 32. Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, 443-447. 33. Sa, Y.J.; Seo, D.J.; Woo, J.; Lim, J.T.; Cheon, J.Y.; Yang, S.Y.; Lee, J.M.; Kang, D.; Shin, T.J.; Shin, H.S.; Jeong, H.Y.; Kim, C.S.; Kim, M.G.; Kim, T.Y.; Joo, S.H. Ageneral approach to preferential formation of active Fe-Nx sites in Fe-N/C electrocatalysts for efficient oxygen reduction reaction. J. Am. Chem. Soc. 2016, 138, 15046-15056. 34. Li, J.; Ghoshal, S.; Liang, W.; Sougrati, M.-T.; Jaouen, F.; Halevi, B.; McKinney, S.; McCool, G.; Ma, C.; Yuan, X.; Ma, Z.-F.; Mukerjee, S.; Jia, Q. Structural and mechanistic basis for the high activity of Fe-N-C catalysts toward oxygen reduction. Energ. Environ. Sci. 2016, 9, 2418-2432. 35. Proietti, E.; Jaouen, F.; Lefèvre, M.; Larouche, N.; Tian, J.; Herranz, J.; Dodelet, J.-P. Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells. Nat. Commun. 2011, 2, 416. 36. Shui, J.; Chen, C.; Grabstanowicz, L.; Zhao, D.; Liu, D.-J. Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network. Proc. Natl. Acad. Sci. USA 2015, 112, 10629-10634.

24


Page 25 of 26 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

Langmuir

37. Dodelet, J.-P., Oxygen reduction in PEM fuel cell conditions: heat-treated non-precious metal-N4 macrocycles and beyond. In N4-macrocyclic metal complexes, Springer: 2006; p 83-147. 38. Tylus, U.; Jia, Q.; Strickland, K.; Ramaswamy, N.; Serov, A.; Atanassov, P.; Mukerjee, S. Elucidating oxygen reduction active sites in pyrolyzed metal–nitrogen coordinated non-precious-metal electrocatalyst systems. J. Phys. Chem. C 2014, 118, 8999-9008. 39. Jia, Q.; Ramaswamy, N.; Hafiz, H.; Tylus, U.; Strickland, K.; Wu, G.; Barbiellini, B.; Bansil, A.; Holby, E. F.; Zelenay, P.; Mukerjee, S. Experimental Observation of Redox-Induced Fe-N Switching Behavior as a Determinant Role for Oxygen Reduction Activity. ACS Nano 2015, 9, 12496-12505. 40. Ramaswamy, N.; Mukerjee, S. Influence of inner-and outer-sphere electron transfer mechanisms during electrocatalysis of oxygen reduction in alkaline media. J. Phys. Chem. C 2011, 115, 18015-18026. 41. Strickland, K.; Miner, E.; Jia, Q.; Tylus, U.; Ramaswamy, N.; Liang, W.; Sougrati, M.-T.; Jaouen, F.; Mukerjee, S. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal-nitrogen coordination. Nat. Commun. 2015, 6. 42. Gumeci, C.; Leonard, N.; Liu, Y.; McKinney, S.; Halevi, B.; Barton, S. C. Effect of pyrolysis pressure on activity of Fe–N–C catalysts for oxygen reduction. J. Mater. Chem. A 2015, 3, 21494-21500. 43. Rolison, D. R. Catalytic nanoarchitectures--the importance of nothing and the unimportance of periodicity. Science 2003, 299, 1698-1701. 44. Artyushkova, K.; Serov, A.; Rojas-Carbonell, S.; Atanassov, P. Chemistry of multitudinous active sites for oxygen reduction reaction in transition metal–nitrogen– carbon electrocatalysts. J. Phys. Chem. C 2015, 119, 25917-25928. 45. Jaouen, F.; Lefèvre, M.; Dodelet, J.-P.; Cai, M. Heat-Treated Fe/N/C Catalysts for O2 Electroreduction:   Are Active Sites Hosted in Micropores? J. Phys. Chem. B 2006, 110, 5553-5558. 46. Jaouen, F.; Herranz, J.; Lefevre, M.; Dodelet, J. P.; Kramm, U. I.; Herrmann, I.; Bogdanoff, P.; Maruyama, J.; Nagaoka, T.; Garsuch, A.; Dahn, J. R.; Olson, T.; Pylypenko, S.; Atanassov, P.; Ustinov, E. A. Cross-laboratory experimental study of non-noble-metal electrocatalysts for the oxygen reduction reaction. ACS Appl. Mater. Interfaces 2009, 1, 1623-1639.

25


Langmuir 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

Page 26 of 26

Abstract Graphic

26


Highly Active and Stable FeâNâC Catalyst for ... - ACS Publications

Recommend Documents

Highly Active and Stable FeâNâC Catalyst for ... - ACS Publications