NiFe Layered Double Hydroxides Electrode

Subscriber access provided by UNIVERSITY OF CALGARY

Article

Vertically Aligned FeOOH/NiFe Layered Double Hydroxides Electrode for Highly Efficient Oxygen Evolution Reaction Jun Chi, Hongmei Yu, Bowen Qin, Li Fu, Jia Jia, Baolian Yi, and Zhigang Shao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b13360 • Publication Date (Web): 14 Dec 2016 Downloaded from http://pubs.acs.org on December 16, 2016

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 Applied Materials & Interfaces 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 28

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 Applied Materials & Interfaces

Vertically Aligned FeOOH/NiFe Layered Double Hydroxides Electrode for Highly Efficient Oxygen Evolution Reaction §

§,

§

§

§

§

Jun Chi†, , Hongmei Yu†, *, Bowen Qin†, , Li Fu†, , Jia Jia†, , Baolian Yi and §,

Zhigang Shao * §

Fuel Cell System and Engineering Laboratory, Dalian Institute of Chemical Physics,

Chinese Academy of Sciences, Dalian, 116023, PR China †

University of Chinese Academy of Sciences, Beijing, 100049, PR China

E-mail: [email protected], [email protected]

ABSTRACT: Employing a low-cost and highly efficient electrocatalyst to replace Ir-based catalysts for oxygen evolution reaction (OER) has drawn increasing interest in renewable energy storage. In this work, a vertically aligned FeOOH/NiFe layered double hydroxides (LDHs) nanosheets supported on Ni foam (VA FeOOH/NiFe LDHs-NF) is prepared as a highly effective OER electrode in alkaline electrolyte. The VA FeOOH/NiFe LDHs-NF represents nanosheet arrays on nickel foam with some interspace among them. The vertically aligned and interlayer-structured architecture is binder-free and contributes to facile strain relaxation, relieving the exfoliation of 1 ACS Paragon Plus Environment


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 28

catalysts layer caused by oxygen evolution process. The as-prepared electrode shows current densities of 10, 500 mA cm-2 at overpotentials of 208, 288 mV, and good stability in a half-cell electrolyzer. Besides, the alkaline polymer electrolyte water electrolyzer (APEWE) with this electrode showed 1.71 V at 200 mA cm-2, 2.041 V at 500 mA cm-2, exhibiting corresponding energy efficiency of 86.0% and 72.0%, (based on the lower heating value of hydrogen, LHV), which is better than typical commercial alkaline water electrolyzer.

KEYWORDS: layered double hydroxides, binder-free, oxygen evolution reaction, alkaline polymer electrolyte water electrolyzer, water splitting

1. Introduction

Electrochemical water electrolysis has been regarded as an appropriate technology to reserve the electricity generated by intermittent sources, such as solar and wind

1-2

.

However, the efficiency of electrochemical water electrolysis is restricted by the oxygen evolution reaction (OER) due to its intrinsically sluggish reaction kinetics, which imposes serious overptential requirement of the whole water splitting reaction 3-6

. To improve the reaction rate and efficiency, effective catalysts, which have good

eletrocatalytic activity are required to promote this process. Ir-based and Ru-based materials have excellent OER performance in both acidic and alkaline solutions. However, these rare materials are scarce and very expensive, thus hindered their practical application on a large scale7. For this reason, designing efficient, cheap, and 2 ACS Paragon Plus Environment

Page 3 of 28

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


robust electrocatalysts based on earth-abundant elements without compromising good catalytic activity and stability for OER has become the urgent matter. To date, non-precious metal (Ni, Co, Fe-based) materials are of particular interest for OER owing to the low cost and relative abundance

8-10

. For instance, Feng et al. reported

FeOOH/Co/FeOOH hybrid nanotube arrays supported on Ni foams for water oxidation

11

. Sun et al. reported the fabrication of mono dispersed mesoporous Ni

spheres into a three-dimensionally ordered close-packed array structure 12. Gao et al. developed amorphous Ni–Fe hydroxide nanostructures with a homogeneous distribution of Ni-Fe 13 and Tang et al. reported the fabrication of in situ hydrothermal growth of NiSe nanowires on nickel foam for OER 14, respectively. Besides, Lu et al. electrodeposited amorphous mesoporous Ni-Fe composite nanosheets directly onto porous nickel foam substrates as efficient OER electrode in 1.0 M KOH solution15. However, most of these researches are still confined to basic research. The performance of these reported materials in practical use are rarely mentioned. The development of effective earth-abundant metal OER electrocatalysts to accelerate electrochemical water electrolysis process still remains challenging 10, 16-17.

Iron (Fe) and nickel (Ni) based materials (oxides, hydroxides and oxyhydroxides) are cost-effective electrocatalysts for water oxidation, owing to the relatively high activity, natural abundance, and environmental friendliness

18-24

. These catalysts are

generally prepared into powders, therefore, polymer binders, such as Nafion, are required to interface them with an electrode typically in practical application

13, 25-26

.

Moreover, the resulting electrode usually lacks direct electric contact with the 3 ACS Paragon Plus Environment


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 28

catalysts and substrate, exhibiting poor electrical conductivity and mechanical stability under gas evolution condition27. To solve the problems above, hybridizing these materials with conductive substrates was confirmed as an effective approach to improve the electroactivity

28-30

. Among such improvements, catalysts supported on

nickel foam can enhance the electrical conductivity and improve the mass transport of both reactants and productions

31-33

. Many reports have reported hybrid composites

could be utilized as the electrodes for lithium ion batteries 31, 34-35, super capacitors 32, 36-38

and electrochemical water electrolysis

11, 15, 39-40

. However, with low surface

energy, the hybrid composites tend to stack on the substrate

9, 16, 26

. Fabrication of

orderly hybrid composites is difficult, and the technical key is to control the nucleation and growth of materials.

We herein explored a facile hydrothermal method to synthesize a binder-free and vertically aligned FeOOH/NiFe layered double hydroxides (LDHs) nanosheets supported on Ni foam (VA FeOOH/NiFe LDHs-NF) for effective and stable OER in alkaline electrolyte. The experimental observations indicated the binder-free and vertically aligned nanostructure could enhance the electrochemical surface area significantly, leading to effective chemical/interfacial distributions at nanoscale and fast ion-electron transfer. What’s more, the interspace between the nanosheets relieves the exfoliation of catalysts layer caused by oxygen evolution process, which is beneficial to build a more stable three-phase-interface (catalysts-oxygen-electrolyte). Electrochemical

measurements

showed

that

the

multilayer-structured

VA

FeOOH/NiFe LDHs-NF exhibited high OER activity with low overpotential of 208, 4 ACS Paragon Plus Environment

Page 5 of 28

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


288 mV to reach 10, 500 mA cm-2. In addition, to evaluate the performance of VA FeOOH/NiFe LDHs-NF for OER in practical use, an alkaline polymer electrolyte water electrolyzer (APEWE) with as-prepared electrode was assembled and tested.

2. Experimental Section

Chemicals and Materials: All the reagents were of analytically pure and used without further purification. A piece of Ni foam (NF, 2 cm ×2.5 cm× 1.6 mm) was used as the substrate. Iron nitrate nonahydrate (Fe(NO3)3·9H2O, ≥98 wt.%), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, ≥98 wt.%), ammonium fluoride (NH4F, ≥98 wt.%), urea (CO(NH2)2, ≥98 wt.% ), potassium hydroxide (KOH, ≥85 wt.%), and polyethylene glycol were obtained from Damao Chemicals. All solutions were prepared with deionized water (~18 MΩ, 25 °C). Ir black (99.95 wt.%) was obtained from Johnson Matthey.

Hydrothermal fabrication of VA FeOOH/NiFe LDHs-NF: The fabrication of VA FeOOH/NiFe LDHs-NF was similar as previous reports

41-43

. Nickel oxides was

removed from the NF surface by sonicating in aqueous HCl (30 wt.%) for 10 min, and it was washed successively with deionized water and ethanol, dried in the fume hood. Fe(NO3)2·9H2O (25 mM ), Ni(NO3)2·6H2O (25 mM), NH4F (0.2 M ), polyethylene glycol (1 g) and urea (0.1 M ) were dissolved in deionized water (40 mL), and stirred for 30 min to get a transparent precursor solution. Then transferred the precursor solution into a Teflon-lined stainless steel autoclave (48 mL), and immersed NF vertically into the liquid. After that, sealed the autoclave and transferred it into an 5 ACS Paragon Plus Environment


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 28

electric oven. The reaction was continued for 5 h at 120 °C, then cooled down naturally, rinsed the sample with massive deionized water and ethanol, and dried in the fume hood. The obtained was designated as VA FeOOH/NiFe LDHs-NF.

Hydrothermal fabrication of Ni LDHs-NF: The precursor solution was prepared by dissolving Ni(NO3)2·6H2O (50 mM), NH4F (0.2 M), polyethylene glycol (1 g) and urea (0.1 M ) in deionized water (40 mL) and stirred for 30 min to get a transparent liquid. The Ni LDHs-NF was also fabricated with the similar methods, and accordingly the Ni LDHs-NF were fabricated for the comparative study.

Hydrothermal fabrication of Fe LDHs-NF: The precursor solution was prepared by dissolving Fe(NO3)2·9H2O (50 mM), NH4F (0.2 M), polyethylene glycol (1 g) and urea (0.1 M ) in deionized water (40 mL) and stirred for 30 min to get a transparent liquid. The Fe LDHs-NF was also fabricated with the similar methods, and accordingly the Fe LDHs-NF were fabricated for the comparative study.

Materials Characterizations: The phase analysis of samples was measured by X-ray diffraction (XRD, PANalytical X’Pert PRO) via Cu-Kα tube (40 kV, 40 mA). The scanning rate was 10o min-1 from 10 o to 90 o in 2θ. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectrum analysis (EDS) were performed on a JSM-7800F field emission scanning electron microscope (FE-SEM) with an EDS system. The morphologies of the samples were characterized by high resolution transmission electron microscopy (HR-TEM) on a JEM-2000EX transmission electron microscope, and the acceleration voltage was 120 kV. X-ray photoelectron 6 ACS Paragon Plus Environment

Page 7 of 28

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


spectra (XPS) analysis were performed on an ESCALAB MK II X-ray photoelectron spectrometer, equipped with Mg Kα excitation source. The binding energies obtained from the XPS were corrected by referencing C1s to 284.5 eV. Raman spectra were recorded with Bruker Optic Senterra Raman Spectrometer 750 K with a laser power of 0.5 mW at ambient temperature.

Electrochemical Measurements: All of the electrochemical tests were carried out in a three-electrode system on an electrochemical workstation (Gamry Interface 5000E). The reference electrode was calibrated in a H2 saturated 1.0 M KOH with a platinum foil as the working electrode. Electrochemical impedance spectroscopy (EIS) was carried out on Gamry Interface 5000E in 1.0 M KOH at 1.518 V vs RHE. (See supporting information S2 Electrochemical Measurements section for details).

To study the electrocatalytic activity and stability, the polarization was tested from 0 V to 1 V vs HgO/Hg at 10 mV s-1 in 1.0 M KOH. The chronoamperometry measurements were carried out at 20-200 mA cm-2 in the solution of 1.0 M KOH (pH=14). Prior to all experiments, the electrolyte solution was purged with high purity O2 gas for 30 min. For comparison study, the electrocatalytic activities of NF and FeOOH NTAs-NF were also measured under the similar conditions. All electrochemical measurements were carried out at 25 °C. Unless specifically noted, all results were recorded without iR-correction.

7 ACS Paragon Plus Environment


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

The electrochemical active surface area (ECSA) of electrode is usually studied by the double layer capacitance

44-46

. (See supporting information S2 Electrochemical

Measurements section for details)

Alkaline polymer electrolyte water electrolysis tests: Performance of the prepared catalyst was evaluated in real electrolysis, alkaline polymer electrolyte water electrolyzer (APEWE) (2×2.5 cm2) were assembled. The prepared VA FeOOH/NiFe LDHs-NF was used as the anode. A wet-proof carbon paper loaded with 0.4 mg cm-2 Pt/C (70 wt.% Pt/C, Johnson Matthey) was used as the cathode. An alkaline polymer electrolyte (APE) membrane (home-made) was chosen as the solid polymer electrolyte. The catalyst coated membrane and cathode were then hot-pressed at 60 oC and 0.2 MPa for 1 min. The steady-state i-V tests were conducted at 50 oC in potentiostatic mode. The stability test was performed at 200 mA cm-2 and 50 oC, 1.0 M KOH solution was supplied to the anode compartment at 5 mL min-1.

3. Results and Discussion

3.1. Material Synthesis and Characterization

The fabrication process of the VA FeOOH/NiFe LDHs-NF is shown in Scheme 1. A commercial nickel foam with high specific surface area, good electrical conductivity, and micro-scale pores was employed as substrate. The micro-structure of as-prepared sample was first characterized by the field emission scanning electron microscopy (FE-SEM). The observed images with different magnifications were shown in Figure 1a-b. With careful conditions controlled, uniform vertical aligned 8 ACS Paragon Plus Environment

Page 8 of 28

Page 9 of 28

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


single layer nanosheets were synthesized on the substrate. It is clear that the uniform catalyst layer consists of thin nanosheets with small gaps between them. The vertical aligned nanosheets contact with the nickel framework directly rather than piling up with other nanosheets, which avoids the use of ionomer, and provides an effective and stable pathway for mass transfer. It benefits the electrical conductivity and the mechanical stability of the resulting electrode under gas evolution condition. The diameter and thickness of nanosheets were ~3µm and 30 nm, respectively. Figure 1c shows the cross-sectional view of the catalyst layer, in which the thickness of layer was estimated as ~3 µm, indicating the single layer structure of the catalyst layer. After scraping the green films off the substrate and dispersing in ethanol under ultrasound, the nanosheets were examined by HRTEM, as shown in Figure 1d. The measured interplanar spacings are 0.25 and 0.26 nm. They are consistent with NiFe LDHs (012) and FeOOH (211) lattice fringes, respectively. Moreover, in Figure 2, the element maps demonstrated the homogenous distribution of Ni, Fe and O in the as-prepared sample.

X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were carried out to analyze the phase and electronic structures of VA FeOOH/NiFe LDHs-NF. Figure 3a shows the XRD pattern of the VA FeOOH/NiFe LDHs-NF peaks, such as NiFe LDHs peaks, (003), (006), (101), (012), (015), (018), (110), (113), and (116) (JCPDS 00-040-0215), and FeOOH peaks, such as (110), (200), (220), (130), (211), (301), (411) and (600) (JCPDS 01-075-1594), demonstrating the coexistence of NiFe LDHs and 9 ACS Paragon Plus Environment


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 28

FeOOH in the sample. From observed results to reasons, the substitution of Fe introduces certain strains into the NiFe LDHs framework to make the peaks shift positively (Figure S1). These results proved that Ni and Fe sharing the VA FeOOH/NiFe LDHs-NF crystals position in the crystal lattice to form a new hybrid

47

. It was reported that Fe3+ in Ni1−xFexOOH occupies octahedral

sites with unusually short Fe−O bond distances, which can enhance the OER activity due to the strong electronic interactions between Ni and Fe 48-50.

Besides, the surface chemical states of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF and Fe LDHs-NF were further investigated by XPS (Figure S2). For the Ni 2p3/2 spectrum (Figure 3c) , peaks at 855.4 and 873.0 eV correspond to the main Ni2+, accompanied by two prominent shake-up satellite peaks (861.1 and 879.7 eV)51. The peaks located at 711.5 eV and 724.8 eV, which are usually the typical characteristic peaks of Fe3+ specie (Figure 3c)

13, 52-53

.

Oxyhydroxides formation was further supported by the observed decrement of the M−O component in Figure 3b53. The high-resolution O1s spectrum of the composites reveal five distinct peaks at O1s A (529.7 eV), O1s B (530.36 eV), O1s C (530.9 eV), O1s D (531.5 eV) and O1s E (532.3 eV). O1s A represents the binding energies of oxygen in metal-oxyhydroxide bonds. O1s B, O1s C, O1s D represent OH- bonds, and O1s E stands for absorbed water, respectively (Figure 3d)

54-55

. Compared with Fe LDHs-NF, VA FeOOH/NiFe LDHs-NF

shows negatively shift of ~0.6 eV. When compared with Ni LDHs-NF, this shift comes to ~0.8 eV. These also support the electron interaction between 10 ACS Paragon Plus Environment

Page 11 of 28

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


FeOOH and NiFe LDHs, demonstrating the variable electronic environment altered by the Fe/Ni ratio56.

The detailed information about the vibrational dynamics of nickel (iron) oxyhydroxides (Ni-O and O-H) was investigated by Raman spectroscopy57 (Figure 3e). The prominent peaks at ~450 and ~540 cm-1 attributed to Fe-O vibrations in FeOOH can be clearly seen 58-61. The characteristic peaks obtained at ~300, ~400 cm-1 correspond to the M–O, M–OH symmetric stretching of M(OH) (M=Ni, Fe), respectively56,

58, 62-63

. The above results confirm the

formation of metal (Ni/Fe)-oxyhydroxides.

3.2. Oxygen Evolution Activity in Half-cell Tests

The catalytic activities of all as-prepared samples (VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF, Fe LDHs-NF, and Bare NF) for electrochemical water splitting were investigated in O2-saturated 1.0 M KOH solution. The calibration of the reference electrode was shown in Figure S3

64

In Figure 4a, the linear sweep voltammograms

(LSV) at 10 mV s-1 with iR-correction for all samples were shown. The VA FeOOH/NiFe LDHs-NF sample exhibits the best catalytic activity. An overpotential of only 208 mV is shown for the VA FeOOH/NiFe LDHs-NF sample to reach a current density of 10 mA cm-2 (η10=208 mV, η100=247 mV), which is lower than those of Fe LDHs-NF (η10=251 mV, η100=285 mV), Ni LDHs-NF (η100=360 mV), Bare NF (η10=348 mV, η100=519 mV) (LSV data without iR-correction: Figure S4). Overpotential required to deliver a current density of 10 mA cm-2 is of great 11 ACS Paragon Plus Environment


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 28

importance, because it is approximately the current density expected for a 10% efficient solar water-splitting device46. The corresponding Tafel slope of VA FeOOH/NiFe LDHs-NF is 42 mV dec-1, which is smaller than that of the Fe LDHs-NF (53 mVdec-1) (see Figure S5). Compared the performance of the as-prepared samples with other congeneric catalysts in alkaline media, the performance of VA FeOOH/NiFe LDHs-NF is comparable to or better than most reported electrocatalysts for OER (Table 1). Table S1 summarizes the more detailed catalytic parameters.

Electrochemical impedance spectroscopy (EIS) was performed to analyze the kinetics during the OER process in 1.0 M KOH. EIS results of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF and Fe LDHs-NF were simulated, which showed that the high frequency resistance (RΩ) and charge transfer resistance (Rct) of the VA FeOOH/NiFe LDHs-NF were the smallest, indicating the VA FeOOH/NiFe LDHs-NF possessed the faster charge transfer process (Figure S6-S9, summary of fitted EIS data shown in Table S2 ). Besides, the electrochemical double layer capacitance measurement was conducted to study the electrochemically active surface area (ECSA) of each sample

44, 46

(Cdl; Figure 4b, Figure S10-S12). As shown in Figure

4b, the slopes provide the double layer capacitances of VA FeOOH/NiFe LDHs-NF (42.5 mF), Ni LDHs-NF (30 mF) and Fe LDHs-NF (35.6 mF), respectively. This result represents the inclusion of iron in VA FeOOH/NiFe LDHs-NF resulted in a rougher surface and larger ECSA (see Electrochemical Measurements for details). 12 ACS Paragon Plus Environment

Page 13 of 28

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


Benefited from the particular interlayer architecture, which facilitates the permeation of electrolytes into the catalyst layer, creates many fast paths for ion transportation, and provides more active sites for OER at large current densities to a certain degree. Figure S13 shows the introduction of Fe into Ni increases the potential at which Ni2+-Ni3+ oxidation occurs, and the peak area decreases, which is consistent with the previous reports48, 65. Combining the experimental observation with model analysis, the recent researches identified that Fe in a Ni compound obtains ideal binding energy with −OOH and –OH intermediates 23, 65. From these perspectives, the reason why the VA

FeOOH/NiFe

LDHs-NF

showed

higher

ECSA

value

and

excellent

electrochemical performances could be illustrated well. Additionally, a multi-step chronopotentiometric test of the VA FeOOH/NiFe LDHs-NF was carried out in 1.0 M KOH to screen the mass transport in the electrode interface (Figure 4c). At the start of 10 mA cm-2, the voltage kept nearly constant for 500 s at 1.473 V vs. RHE, indicating the interlayer-structured electrode is highly effective in dissipating the gas bubbles. Similar results were observed for all studied current densities (10-240 mA cm-2). The chronopotentiometric measurement thus reflects the excellent mass transport properties, electric conductivity and mechanical robustness of the VA FeOOH/NiFe LDHs-NF.

Stability is an important parameter for the electrocatalyst. The stability test for OER was carried out by the chronopotentiometry method in 1.0 M KOH. For the VA FeOOH/NiFe LDHs-NF, an overpotential of only 230±1 mV is required to reach a current density of 10 mA cm-2, and the operating voltage was nearly constant for 5 h 13 ACS Paragon Plus Environment


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 28

(Figure 4d). Besides, the stabilities for OER at higher current densities are significant for practical electrolysis. Stability tests with current densities of 100, 300 and 500 mA cm-2 were conducted to evaluate the OER stability of the VA FeOOH/NiFe LDHs-NF for the extra 15 hours (Figure 4d). As the test results showed, the potential remained stable for over 5 h during each 5-h running operation, revealing the good stability of VA FeOOH/NiFe LDHs-NF.

3.3. APEWE tests

A traditional commercial alkaline electrolyzer usually used high concentrations of alkaline solution as electrolyte (4-10 M KOH, NaOH), and carried out at temperatures of around 80‑90 oC, which eroded equipment and increased the capital cost

1, 66-68

.A

compact electrolyzer system based on proton exchange membrane fuel cell structure has been proposed to lower the capital and operating cost of water electrolysis69. The VA FeOOH/NiFe LDHs-NF was directly utilized as the anode catalysts and tested after assembled into an APEWE. (see the Alkaline polymer electrolyte water electrolysis tests for details) Herein, an APEWE was assembled to evaluate the performance of VA FeOOH/NiFe LDHs-NF for OER in practical use. The i-V curve of the home-made APE water electrolyzer at 50 oC in 1.0 M KOH solution was recorded in Figure 5a. The cell voltage of the water splitting was 1.71 V at 200 mA cm-2, 2.041 V at 500 mA cm-2, respectively. And the corresponding energy efficiency was 86.0% and 72.0% (based on the lower heating value of hydrogen, LHV), which is higher than typical alkaline electrolysis cells (about 60-75% 14 ACS Paragon Plus Environment

Page 15 of 28

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


efficient)68. Besides, the cell stability test was performed in a constant current mode at 200 mA cm-2 and 50 oC (Figure 5b). The APEWE voltage ranged from 1.70 V to1.76 V in 60 h running time, confirming the good stability of VA FeOOH/NiFe LDHs-NF for OER in practical use.

4. Conclusion

In summary, we have synthesized an interlayer-structured binder-free VA FeOOH/NiFe LDHs-NF OER electrode by a facile hydrothermal method. Because of the excellent electrochemical activity, electric conductivity and mechanical robustness, the obtained VA FeOOH/NiFe LDHs-NF showed a remarkable OER performance, and the overpotentials is only 216 and 288 mV at 10, and 500 mA cm-2 respectively. The half-cell tests electrolyzer tests reveal that the interlayer-structured VA FeOOH/NiFe LDHs-NF OER electrode shows good catalytic performance in comparison to the non-precious OER electrocatalysts reported to date and good stability even at large current densities. On basis of the physicochemical characterization, the good electrochemical performance can be ascribed to: First, the self-standing nanosheets arrays had numerous interspaces among them, resulting in large specific surface area. Second, the nanosheets directly in-situ formed on the NFs, decreasing electrical contact resistance between the catalyst layer and the substrate. Besides The APEWE evaluations indicate the potential of VA FeOOH/NiFe LDHs-NF for OER in practical use. Based on these results, the as-prepared material shows the potential for OER in the scalable production of low-cost hydrogen from 15 ACS Paragon Plus Environment


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 28

renewable sources. In terms of perspectives, the specific catalytic mechanism of the as-prepared electrode is still need to be elucidated to further improve its OER electrochemical performance.

Supporting Information

Supporting Information is available online.

Images of XRD patterns of as-prepared samples with different mole ration images and XPS spectrum of VA FeOOH/NiFe LDHs-NF as well as Calibration of reference electrode (Figures S1 S2 and S3), i-V curves of VA FeOOH/NiFe LDHs-NF, Fe LDHs-NF, Bare NF, and Ir black without iR-correction (Figures S4), Tafel plots of VA FeOOH/NiFe LDHs-NF, Fe LDHs-NF for OER (Figure S5), Nyquist plots of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF, and Fe LDHs-NF (Figure S6-S9). Cyclic voltammograms in the double layer region of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF and Fe LDHs-NF were recorded at different scan rates (Figure S10−S12). Cyclic voltammograms curves of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF, and Fe LDHs-NF (Figure S13). Summary of results for representative non-precious-metal OER electrocatalysts reported in the literatures (Table S1). Summary of fitted EIS data for VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF, and Fe LDHs-NF (Table S2).


Page 17 of 28

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


Acknowledgements

This work is financially supported by the National Natural Science Foundations of China (No. U1664259, and No. 91434106), CAS-DOE Cooperation Project (No. 121421KYSB20160009), and the Natural Science Foundations of Liaoning Province (No. 2014020088).

References 1. Holladay, J. D.; Hu, J.; King, D. L.; Wang, Y., An Overview of Hydrogen Production Technologies. Catal. Today 2009, 139 (4), 244-260. 2. Turner, J.; Sverdrup, G.; Mann, M. K.; Maness, P. C.; Kroposki, B.; Ghirardi, M.; Evans, R. J.; Blake, D., Renewable Hydrogen Production. Int. J. Energy Research 2008, 32 (5), 379-407. 3. Liu, Y.; Cheng, H.; Lyu, M.; Fan, S.; Liu, Q.; Zhang, W.; Zhi, Y.; Wang, C.; Xiao, C.; Wei, S.; Ye, B.; Xie, Y., Low Overpotential in Vacancy-Rich Ultrathin CoSe2 Nanosheets for Water Oxidation. J. Am. Chem. Soc. 2014, 136 (44), 15670-15675. 4. Abu Sayeed, M.; Herd, T.; O'Mullane, A. P., Direct Electrochemical Formation of Nanostructured Amorphous Co(OH)2 on Gold Electrodes With Enhanced Activity for the Oxygen Evolution Reaction. J. Mater. Chem. A 2016, 4 (3), 991-999. 5. Lee, D. U.; Kim, B. J.; Chen, Z., One-pot Synthesis of a Mesoporous NiCo2O4 Nanoplatelet and Graphene Hybrid and Its Oxygen Reduction and Evolution Activities as an Efficient Bi-functional Electrocatalyst. J. Mater. Chem. A 2013, 1 (15), 4754-4762. 6. Haber, J. A.; Anzenburg, E.; Yano, J.; Kisielowski, C.; Gregoire, J. M., Multiphase Nanostructure of a Quinary Metal Oxide Electrocatalyst Reveals a New Direction for OER Electrocatalyst Design. Adv. Energy Mater. 2015, 5 (10), 1402307/1-1402307/11. 7. Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., A Comprehensive Review on PEM Water Electrolysis. Int. J. Hydrogen Energy 2013, 38 (12), 4901-4934. 8. Kang, D.; Kim, T. W.; Kubota, S. R.; Cardiel, A. C.; Cha, H. G.; Choi, K. S., Electrochemical Synthesis of Photoelectrodes and Catalysts for Use in Solar Water Splitting. Chem. Rev. 2015, 115 (23), 12839-12887. 9. Liu, S.; Hu, L.; Xu, X.; Al-Ghamdi, A. A.; Fang, X., Nickel Cobaltite Nanostructures for Photoelectric and Catalytic Applications. Small 2015, 11 (34), 4267-4283. 10. Wang, F. M.; Shifa, T. A.; Zhan, X. Y.; Huang, Y.; Liu, K. L.; Cheng, Z. Z.; Jiang, C.; He, J., Recent Advances in Transition-metal Dichalcogenide Based Nanomaterials for Water Splitting. Nanoscale 2015, 7 (47), 19764-19788. 17 ACS Paragon Plus Environment


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 28

11. Feng, J. X.; Xu, H.; Dong, Y. T.; Ye, S. H.; Tong, Y. X.; Li, G. R., FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High-Performance Electrocatalysts for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2016, 55 (11), 3694-3698. 12. Sun, T. T.; Xu, L. B.; Yan, Y. S.; Zakhidov, A. A.; Baughman, R. H.; Chen, J. F., Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation. Acs Catalysis 2016, 6 (3), 1446-1450. 13. Gao, Y. Q.; Liu, X. Y.; Yang, G. W., Amorphous Mixed-metal Hydroxide Nanostructures for Advanced Water Oxidation Catalysts. Nanoscale 2016, 8 (9), 5015-5023. 14. 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. Engl. 2015, 54 (32), 9351-9355. 15. Lu, X.; Zhao, C., Electrodeposition of Hierarchically Structured Three-Dimensional Nickel-Iron Electrodes for Efficient Oxygen Evolutikon at High Current Densities. Nat. Commun. 2015, 6, 6616/1- 6616/7. 16. Gao, M. R.; Xu, Y. F.; Jiang, J.; Yu, S. H., Nanostructured Metal Chalcogenides: Synthesis, Modification, and Applications in Energy Conversion and Storage Devices. Chem. Soc. Rev. 2013, 42 (7), 2986-3017. 17. Chen, S; Thind, S. S.; Chen, A. C.; Nanostructured Materials for Water Splitting State of the Art and Future Needs: A Mini-review. Electrochem. Commun. 2016, 6 (3), 10-17. 18. Zeng, G.; Liao, M.; Zhou, C.; Chen, X.; Wang, Y.; Xiao, D., Iron and Nickel Co-doped Cobalt Hydroxide Nanosheets With Enhanced Activity for Oxygen Evolution Reaction. Rsc Advances 2016, 6 (48), 42255-42262. 19. Thenuwara, A. C.; Cerkez, E. B.; Shumlas, S. L.; Attanayake, N. H.; McKendry, I. G.; Frazer, L.; Borguet, E.; Kang, Q.; Remsing, R. C.; Klein, M. L.; Zdilla, M. J.; Strongin, D. R., Nickel Confined in the Interlayer Region of Birnessite: an Active Electrocatalyst for Water Oxidation. Angew. Chem. Int. Ed. Engl. 2016, 55, 1-6. 20. Zhao, Z.; Wu, H.; He, H.; Xu, X.; Jin, Y., Self-standing Non-noble Metal (Ni-Fe) Oxide Nanotube Array Anode Catalysts With Synergistic Reactivity for High-performance Water Oxidation. J. Mater. Chem. A 2015, 3 (13), 7179-7186. 21. Tian, J.; Cheng, N.; Liu, Q.; Sun, X.; He, Y.; Asiri, A. M., Self-Supported Nimo Hollow Nanorod Array: An Efficient 3D Bifunctional Catalytic Electrode for Overall Water Splitting. J. Mater. Chem. A 2015, 3 (40), 20056-20059. 22. Gao, M.; Sheng, W.; Zhuang, Z.; Fang, Q.; Gu, S.; Jiang, J.; Yan, Y., Efficient Water Oxidation Using Nanostructured Alpha-Nickel-Hydroxide as an Electrocatalyst. J. Am. Chem. Soc. 2014, 136 (19), 7077-7084. 23. Tang, C.; Wang, H. F.; Wang, H. S.; Wei, F.; Zhang, Q., Guest-host Modulation of Multi-Metallic (oxy) Hydroxides for Superb Water Oxidation. J. Mater. Chem. A 2016, 4 (9), 3210-3216. 24. Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M., Trends in Activity for the Water Electrolyser Reactions on 3d M(Ni,Co,Fe,Mn) Hydr(oxy)oxide Catalysts. Nat. Mater. 2012, 11 (6), 550-7. 18 ACS Paragon Plus Environment

Page 19 of 28

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


25. Reisner, D. E.; Salkind, A. J.; Strutt, P. R.; Xiao, T. D., Nickel Hydroxide and Other Nanophase Cathode Materials for Rechargeable Batteries. J. Power Sources 1997, (65), 231-233 26. Gong, M.; Wang, D. Y.; Chen, C. C.; Hwang, B. J.; Dai, H. J., A Mini Review on Nickel-Based Electrocatalysts for Alkaline Hydrogen Evolution Reaction. Nano Research 2016, 9 (1), 28-46. 27. Miao, Y.; Ouyang, L.; Zhou, S.; Xu, L.; Yang, Z.; Xiao, M.; Ouyang, R., Electrocatalysis and Electroanalysis of Nickel, Its Oxides, Hydroxides and Oxyhydroxides Toward Small Molecules. Biosens. Bioelectron. 2014, 53, 428-439. 28. Eder, D., Carbon Nanotube-Inorganic Hybrids. Chem. Rev. 2010, 110, 1348-1385. 29. Deng. D., Novoselov. K. S.; Fu, Q.; Zheng, N.; Tian, Z. and Bao. X., Catalysis With Two-Dimensional Materials and Their Heterostructures. Nat. Nanotechnol. 2016, 11, 218-230. 30. Du, P., Eisenberg, Richard, Catalysts Made of Earth-Abundant Elements (Co, Ni, Fe) for Water Splitting: Recent Progress and Future Challenges. Energy Environ. Sci. 2012, 5 (3), 6012-6021. 31. Yang, W.; Cheng, G.; Dong, C.; Bai, Q.; Chen, X.; Peng, Z.; Zhang, Z., NiO Nanorod Array Anchored Ni Foam as a Binder-free Anode for High-rate Lithium Ion Batteries. J. Mater. Chem. A 2014, 2 (47), 20022-20029. 32. Hu, B.; Qin, X.; Asiri, A. M.; Alamry, K. A.; Al-Youbi, A. O.; Sun, X., Fabrication of Ni(OH)2 Nanoflakes Array on Ni Foam as a Binder-free Electrode Material for High Performance Supercapacitors. Electrochim. Acta 2013, 107, 339-342. 33. Shi, Y.; Xu, Y.; Zhuo, S.; Zhang, J.; Zhang, B., Ni2P Nanosheets/Ni Foam Composite Electrode for Long-Lived and pH-Tolerable Electrochemical Hydrogen Generation. ACS. Appl. Mater. Interfaces 2015, 7 (4), 2376-2384. 34. Wang, Y.; Zhang, Y.; Ou, J.; Zhao, Q.; Liao, M.; Xiao, D., Facile Fabrication of Reduced Graphene Oxide Covered ZnCo2O4 Porous Nanowire Array Hierarchical Structure on Ni-foam as a High Performance Anode for a Lithium-Ion Battery. Rsc Advances 2016, 6 (1), 547-554. 35. Li, Q.; Miao, X.; Wang, C.; Yin, L., Three-dimensional Mn-doped Zn2GeO4 Nanosheet Array Hierarchical Nanostructures Anchored on Porous Ni Foam as Binder-Free and Carbon-Free Lithium-Ion Battery Anodes with Enhanced Electrochemical Performance. J. Mater. Chem. A 2015, 3 (42), 21328-21336. 36. Huang, M.; Li, F.; Ji, J. Y.; Zhang, Y. X.; Zhao, X. L.; Gao, X., Facile Synthesis Of Single-Crystalline NiO Nanosheet Arrays on Ni Foam for High-performance Supercapacitors. Cryst. Eng. Comm. 2014, 16 (14), 2878-2884. 37. Eugénio, S.; Silva, T. M.; Carmezim, M. J.; Duarte, R. G.; Montemor, M. F., Electrodeposition and Characterization of Nickel–Copper Metallic Foams for Application as Electrodes for Supercapacitors. J. Appl. Electrochem. 2013, 44 (4), 455-465. 38. Garg, N.; Basu, M.; Ganguli, A. K., Nickel Cobaltite Nanostructures with Enhanced Supercapacitance Activity. J. Mater. Chem. C 2014, 118 (31), 17332-17341. 39. Han, G. Q.; Liu, Y. R.; Hu, W. H.; Dong, B.; Li, X.; Shang, X.; Chai, Y. M.; Liu, Y. Q.; Liu, C. G., Three Dimensional Nickel Oxides/Nickel Structure by in situ 19 ACS Paragon Plus Environment


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 28

Electro-Oxidation of Nickel Foam as Robust Electrocatalyst for Oxygen Evolution Reaction. Appl. Surf. Sci. 2015, 359, 172-176. 40. Trotochaud, L.; Young, S. L.; Ranney, 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 (18), 6744-6753. 41. Xiao, C.; Li, Y.; Lu, X.; Zhao, C., Bifunctional Porous NiFe/NiCo2O4/Ni Foam Electrodes with Triple Hierarchy and Double Synergies for Efficient Whole Cell Water Splitting. Adv. Funct. Mater. 2016, 26 (20), 3515-3523. 42. Fan, K.; Chen, H.; Ji, Y.; Huang, H.; Claesson, P. M.; Daniel, Q.; Philippe, B.; Rensmo, H.; Li, F.; Luo, Y.; Sun, L., Nickel-Vanadium Monolayer Double Hydroxide for Efficient Electrochemical Water Oxidation. Nat. Commun. 2016, 7, 11981/1-11981/9. 43. Liu, Z.; Ma, R.; Minoru, O.; Nobuo, I.; Yasuo, E.; Kazunori, T. and Takayoshi S., Synthesis, Anion Exchange and Delamination of Co-Al Layered Double Hydroxide: Assembly of the Exfoliated Nanosheet/Polyanion Composite Films and Magneto-Optical Studies. J. Am. Chem. Soc. 2006, 128, 4872-4880. 44. McCrory, C. C.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, J. C.; Jaramillo, T. F., Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. J. Am. Chem. Soc. 2015, 137 (13), 4347-4357. 45. Chen, R.; Wang, H.-Y.; Miao, J.; Yang, H.; Liu, B., A Flexible High-Performance Oxygen Evolution Electrode with Three-Dimensional NiCo2O4 Core-Shell Nanowires. Nano Energy 2015, 11, 333-340. 46. McCrory, C. C.; Jung, S.; Peters, J. C.; Jaramillo, T. F., Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135 (45), 16977-16987. 47. Alam Venugopal, N. K.; Joseph, J., Electrochemically Formed 3D Hierarchical Thin Films of Cobalt–Manganese (Co–Mn) Hexacyanoferrate Hybrids for Electrochemical Applications. J. Power Sources 2016, 305, 249-258. 48. Enman, L. J.; Burke, M. S.; Batchellor, A. S.; Boettcher, S. W., Effects of Intentionally Incorporated Metal Cations on the Oxygen Evolution Electrocatalytic Activity of Nickel (Oxy)hydroxide in Alkaline Media. ACS Catalysis 2016, 6 (4), 2416-2423. 49. Smith, A. M.; Trotochaud, L.; Burke, M. S.; Boettcher, S. W., Contributions to Activity Enhancement via Fe Incorporation in Ni-(Oxy)Hydroxide/Borate Catalysts for Near-Neutral pH Oxygen Evolution. Chem. Commun. (Camb) 2015, 51 (25), 5261-5263. 50. Friebel, D.; Louie, M. W.; Bajdich, M.; Sanwald, K. E.; Cai, Y.; Wise, A. M.; Cheng, M. J.; Sokaras, D.; Weng, T. C.; Alonso-Mori, R.; Davis, R. C.; Bargar, J. R.; Norskov, J. K.; Nilsson, A.; Bell, A. T., Identification of Highly Active Fe Sites in (Ni,Fe)OOH for Electrocatalytic Water Splitting. J. Am. Chem. Soc. 2015, 137 (3), 1305-1313. 51. Baptiste, P.; Franck, T.; François, C., Synthesis of Ni-poor NiO Nanoparticles for p-DSSC Applications. Solid State Sci. 2016, 54, 37-42. 20 ACS Paragon Plus Environment

Page 21 of 28

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


52. Wang, R.; Xu, C.; Lee, J. M., High Performance Asymmetric Supercapacitors: New NiOOH Nanosheet/Graphene Hydrogels and Pure Graphene Hydrogels. Nano Energy 2016, 19, 210-221. 53. Ali-Löytty, H.; Louie, M. W.; Singh, M. R.; Friebel, D., Ambient-Pressure XPS Study of a Ni−Fe Electrocatalyst for the Oxygen Evolution Reaction. J. Phys. Chem. C 2016, 120, 2247-2253. 54. Takei, T.; Fuse, H.; Miura, A.; Kumada, N., Topotactic Transformation of Ni-based Layered Double Hydroxide Film to Layered Metal Oxide and Hydroxide. Appl. Clay Sci. 2016, 124 (125), 236-242. 55. Yan, F.; Zhu, C.; Wang, S.; Zhao, Y.; Zhang, X.; Li, C.; Chen, Y., Electrochemically Activated-Iron Oxide Nanosheet Arrays on Carbon Fiber Cloth as a Three-Dimensional Self-Supported Electrode for Efficient Water Oxidation. J. Mater. Chem. A 2016, 4 (16), 6048-6055. 56. Kwong, W. L.; Lee, C. C.; Messinger, J., Transparent Nanoparticulate FeOOH Improves the Performance of a WO3 Photoanode in a Tandem Water-Splitting Device. J. Phys. Chem. C 2016, 120 (20), 10941-10950. 57. Michael, J. D.; Demeter, E. L.; Illes, S. M.; Fan, Q.; Boes, J. R.; Kitchin, J. R., Alkaline Electrolyte and Fe Impurity Effects on the Performance and Active-Phase Structure of NiOOH Thin Films for OER Catalysis Applications. J. Phys. Chem. C 2015, 119 (21), 11475-11481. 58. Jiang, J.; Zhang, C.; Ai, L., Hierarchical Iron Nickel Oxide Architectures Derived from Metal-Organic Frameworks as Efficient Electrocatalysts for Oxygen Evolution Reaction. Electrochim. Acta 2016, 208, 17-24. 59. Hermet, P.; Gourrier, L.; Bantignies, J. L.; Ravot, D.; Michel, T.; Deabate, S.; Boulet, P.; Henn, F., Dielectric, Magnetic, and Phonon Properties of Nickel Hydroxide. Phys. Rev. B 2011, 23 (84), 235211/1-235211/10. 60. Klaus, S.; Louie, M. W.; Trotochaud, L.; Bell, A. T., Role of Catalyst Preparation on the Electrocatalytic Activity of Ni1-xFexOOH for the Oxygen Evolution Reaction. J. Phys. Chem. C 2015, 119 (32), 18303-18316. 61. 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 (33), 12329-12337. 62. Bantignies, J. L.; Deabate, S.; Righi, A.; Rols, S.; Herme, P.; Sauvajol, J. L. and Henn, F., New Insight into the Vibrational Behavior of Nickel Hydroxide and Oxyhydroxide Using Inelastic Neutron Scattering, Far/Mid-Infrared and Raman Spectroscopies. J. Phys. Chem. C 2008, 112, 2193-2201. 63. Klaus, S.; Cai, Y.; Louie, M. W.; Trotochaud, L.; Bell, A. T., Effects of Fe Electrolyte Impurities on Ni(OH)2/NiOOH Structure and Oxygen Evolution Activity. J. Phys. Chem. C 2015, 119 (13), 7243-7254. 64. Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T. and Dai, H., Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction. Nat. Mater. 2011, 10, 780-786.



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 28

65. Bates, M. K.; Jia, Q. Y.; Doan, H.; Liang, W. T.; Mukerjee, S., Charge-Transfer Effects in Ni-Fe and Ni-Fe-Co Mixed-Metal Oxides for the Alkaline Oxygen Evolution Reaction. Acs Catalysis 2016, 6 (1), 155-161. 66. Marini, S.; Salvi, P.; Nelli, P.; Pesenti, R.; Villa, M.; Berrettoni, M.; Zangari, G.; Kiros, Y., Advanced Alkaline Water Electrolysis. Electrochim. Acta 2012, 82, 384-391. 67. Pletcher, D.; Li, X., Prospects for Alkaline Zero Gap Water Electrolysers for Hydrogen Production. Int. J. Hydrogen Energy 2011, 36 (23), 15089-15104. 68. Sequeira, D. M.; Sequeira, C. A. C.; Figueiredo, J. L., Hydrogen Production by Alkaline Water Electrolysis. Quim. Nova 2013, 36 (8), 1176-1193. 69. Leng, Y.; Chen, G.; Mendoza, A. J.; Tighe, T. B.; Hickner, M. A.; Wang, C. Y., Solid-State Water Electrolysis with an Alkaline Membrane. J. Am. Chem. Soc. 2012, 134 (22), 9054-9057.

Scheme 1. Schematic illustration of the formation process of the porous VA FeOOH/NiFe LDHs-NF electrodes. 22 ACS Paragon Plus Environment

Page 23 of 28

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


Figure 1. a, b) SEM images of VA FeOOH/NiFe LDHs-NF with different magnifications (inset in a: higher magnification); c) cross view of a typical VA FeOOH/NiFe LDHs-NF; d) HR-TEM image of VA FeOOH/NiFe LDHs (scraped from the VA FeOOH/NiFe LDHs-NF).



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 28

Figure 2．． HRTEM images of the corresponding elemental mapping of Ni, Fe and O, respectively.


Page 25 of 28

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


Figure 3. a) XRD patterns of VA FeOOH/NiFe LDHs; b) XPS spectra of Fe2p of VA FeOOH/NiFe LDHs and Fe LDHs; c) XPS spectra of Ni2p of VA FeOOH/NiFe LDHs and Ni LDHs; d) XPS spectra of O1s of VA FeOOH/NiFe LDHs; e) Raman spectra of the VA FeOOH/NiFe LDHs after electrolysis.



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 28

Figure 4. Electrocatalysis studies of VA FeOOH/NiFe LDHs-NF, Ni LDHs-NF, Fe LDHs-NF, and Bare NF, a) Polarization curves of as-prepared samples for OER with iR-correction at 25 oC. b) Cyclic voltammograms in the double layer region (-0.05~0.05 V vs open circuit potential) at different scan rates at 25 oC. c) Multi-step chronopotentiometric test in 1.0 M KOH at different current densities (10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, 180, 200, 220 and 240 mA cm-2) for every 500 s at 25 oC. d) Stability tests of VA FeOOH/NiFe LDHs-NF in half cell at 25 oC.


Page 27 of 28

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


Figure 5. a) Polarization curves of an APE water electrolyzer at 50 oC; b) Stability test of the APE water electrolyzer with the nickel/cobalt oxide OER catalyst at 200 mA cm-2 and 50 oC.

Table 1. Comparison of catalytic parameters of VA FeOOH/NiFe LDHs-NF and some latest publications. Catalyst

Overpotential at 10 mA cm−2, η10 [mV] a)

Reference

Fe LDHs-NF

208 216 258

This work

Ir black

270

This work

VA FeOOH/NiFe LDHs-NF

FeOx/CFC

431

a)

330

a)

CoMnP nanoparticles

This work

250(η21) 350(η199)

FeOOH/Co/FeOOH HNTAs-NF

[34] [48] [8]

a) Data with iR-compensation.



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 28 of 28

Table of Contents Graphic


NiFe Layered Double Hydroxides Electrode

Recommend Documents