Benzoate Anions-Intercalated Layered Nickel Hydroxide Nanobelts

Oct 9, 2017 - The design and fabrication of earth-abundant and highly efficient water oxidation electrocatalysts are important for water splitting sys...
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Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX-XXX

Benzoate Anions-Intercalated Layered Nickel Hydroxide Nanobelts Array: An Earth-Abundant Electrocatalyst with Greatly Enhanced Oxygen Evolution Activity Min Ma,† Ruixiang Ge,† Xuqiang Ji,† Xiang Ren,† Zhiang Liu,‡ Abdullah M. Asiri,§ and Xuping Sun*,† †

College of Chemistry, Sichuan University, Chengdu 610064, Sichuan China College of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, Shandong, China § Chemistry Department, King Abdulaziz University, Jeddah 21589, Saudi Arabia ‡

S Supporting Information *

ABSTRACT: The design and fabrication of earth-abundant and highly efficient water oxidation electrocatalysts are important for water splitting systems associated with the energy conversion and storage. In this work, we report an intercalation strategy to expand interlayer spacing of the layered structure and thus achieve great enhancement for water oxidation activity. Layered-structured nickel benzoate hydroxide nanobelts arrays on nickel foam (benzoate-Ni(OH)2/NF) are prepared by a one-step hydrothermal method. As-prepared benzoate-Ni(OH)2/NF exhibits outstanding oxygen evolution performance with the need of only 242 mV overpotential to drive a current density of 60 mA cm−2 in 1.0 M KOH, 126 mV lower than that for Ni(OH)2/ NF. This catalyst electrode also has good stability with the maintenance of its catalytic activity for 27 h. KEYWORDS: Benzoate-Ni(OH)2, Nanobelts array, Intercalation, Oxygen evolution reaction, Alkaline electrolyte

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INTRODUCTION Water electrolysis is currently acknowledged as an attractive approach for hydrogen production, which can well relieve the global energy crisis and environmental deterioration caused by increased depletion of fossil fuels.1,2 However, electrocatalytic water splitting is seriously limited by the intrinsically sluggish kinetics of oxygen evolution reaction (OER) as the energy intensive step.3,4 Hence, effective catalysts are demanded to accelerate the OER process and thus decrease the overpotential requirement. Ru and Ir oxides are the most active OER catalysts, but they suffer from scarcity, high cost, and instability during long-term electrolysis in alkaline medium, which hinders their large-scale applications.5,6 Accordingly, extensive efforts have been devoted to the development of high-efficiency alternatives made from cost-effective materials. Layered metal hydroxides (LMHs) with brucite-like structures have emerged as promising earth-abundant materials with excellent electrochemical activity,7−12 and various strategies have been proposed to further improve the electrochemical performance of LMHs.13−17 Jin and co-workers reported layered α-cobalt hydroxide intercalated by large charge-balancing anions for the expansion of its interlayer spacing, and the larger interlayer distance allows for more accessible surface areas leading to enhanced capacitive performance.17 Some work also demonstrates that LMHs with expanded interlayer spacing catalyze water oxidation more efficiently.18−21 Additionally, previous reports have verified that more effective electrocatalysis © XXXX American Chemical Society

can be achieved by directly growing catalyst nanoarrays on current collectors because of decreased series resistance, more exposed active sites, and facilitated diffusion of electrolytes.22,23 Our recent work also indicates that benzoate anions are effective intercalators for layered cobalt hydroxide nanoarrays toward efficient OER electrocatalysis.24 Given the Ni is more earthabundant than Co, it is interesting to investigate the intercalation effect of benzoate anions on the OER activity of Ni-based LMHs nanoarrays, which, however, has not been explored before. In this work, we report layered nickel hydroxide intercalated by benzoate ions (0.7 nm in length) via a simple hydrothermal process to expand its interlayer spacing. Such benzoateintercalated layered nickel hydroxide nanobelts arrays on nickel foam (benzoate-Ni(OH)2/NF) show greatly enhanced OER performance. Behaving as a 3D durable electrocatalyst for water oxidation in 1.0 M KOH, benzoate-Ni(OH)2/NF requires the overpotential of only 242 mV to afford 60 mA cm−2, and much increased overpotential (368 mV) is demanded for Ni(OH)2/ NF. Also, its catalytic activity can be maintained for at least 27 h.

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EXPERIMENTAL SECTION

Materials. NF was purchased from Shenzhen Green and Creative Environmental Science and Technology Co., Ltd. HCl, Ni(NO3)2· Received: July 27, 2017 Revised: September 21, 2017 Published: October 9, 2017 A

DOI: 10.1021/acssuschemeng.7b02557 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering

evolution from water; F is the Faradaic constant (96,485 C mol−1); m is the number of active sites (mol).

6H2O, and C6H5COONa were purchased from Aladdin Ltd. in Shanghai. Hexamethylenetetramine (HMT) was provided by Beijing Chemical Works. Ethanol was purchased from Tianjin Chemical Corporation. KOH was purchased by Chengdu Kelon Chemical Reagent Factory. RuCl3·3H2O and Nafion (5 wt %) were bought from Sigma-Aldrich Chemical Reagent Co., Ltd. All chemical regents were used as received without further purification. The water used throughout all experiments was purified through a Millipore system. Preparation of Catalysts. Benzoate-Ni(OH)2/NF was prepared using a traditional hydrothermal method. A piece of NF (2 cm × 3 cm) was first treated with ethanol, HCl, and deionized water by sonication sequentially to obtain a clean surface before use. First, 24 mL of Ni(NO3)2 solution (0.2 mol L−1) was mixed with 36 mL of C6H5COONa solution (0.267 mol L−1) under continuous stirring at room temperature. Then, the mixture was put into an autoclave and hydrothermally treated at 95 °C for 48 h. Subsequently, the resulting green product was washed with distilled water several times and dried in a vacuum oven at 60 °C for 2 h to obtain benzoate-Ni(OH)2/NF finally. The loading of as-prepared benzoate-Ni(OH)2 was determined to be 7.51 mg cm−2 using a high precision microbalance. Ni(OH)2/NF was synthesized as described below. Ni(NO3)2·6H2O (1.45 g) and HMT (1.4 g) were dissolved in 36 mL of water under vigorous stirring for 30 min. Then, the solution was transferred to a 50 mL Teflon-lined stainless-steel autoclave in which a piece of NF with a clean surface was immersed into the solution. The autoclave was sealed and maintained at 100 °C for 10 h in an electric oven to obtain the Ni(OH)2/NF product with a loading of 7.49 mg cm−2. RuO2 was prepared according to reported work. Briefly, 2.61 g of RuCl3·3H2O and 1.0 mL KOH (1.0 M) were added into 100 mL of distilled water and stirred for 45 min at 100 °C. Then, the above solution was centrifuged for 10 min and filtered. The precipitates were collected by centrifugation and washed with water several times, followed by drying at 70 °C. Finally, the product was annealed at 300 °C for 3 h under an air atmosphere. RuO2 ink was prepared by dispersing 20 mg of catalyst into 490 μL of water/ethanol (v/v = 1:1) and 10 μL of 5 wt % Nafion using sonication for 30 min. Then, 47 μL of the RuO2 ink (containing 1.88 mg of RuO2) was loaded onto bare NF of 0.25 cm−2 in geometric area (loading: 7.52 mg cm−2). Characterizations. Powder X-ray diffraction (XRD) patterns were performed using a RigakuD/MAX 2550 diffractometer with Cu Kα radiation (λ = 1.5418 Å). Scanning electron microscope (SEM) measurements were recorded on a XL30 ESEM FEG scanning electron microscope at an accelerating voltage of 20 kV. X-ray photoelectron spectroscopy (XPS) data of the samples were collected on an ESCALABMK II X-ray photoelectron spectrometer using Mg as the exciting source. Infrared spectroscopy was collected on a Nicolet-6700 Fourier transform infrared (FTIR) spectrometer using the potassium bromide pellet method. Electrochemical Measurements. Electrochemical tests were performed with a CHI 660E electrochemical analyzer (CH Instruments, Inc., Shanghai) in a standard three-electrode system. BenzoateNi(OH)2/NF was used as the working electrode. A graphite plate and Hg/HgO were used as the counter electrode and the reference electrode, respectively. The temperature of solution was kept at 25 °C for all the measurements via the adjustment of air conditioning and heating support, which ensured the variation of diffusion coefficient below 1%. The potentials reported in this work were calibrated to RHE other than specifically explained, using the following equation: E (RHE) = E (Hg/HgO) + (0.098 + 0.059 pH) V. Calculations of Turnover Frequency (TOF). To calculate TOF, we need to quantify the surface concentration of active sites using the following equation: slope = n2F2m/4RT, where slope is obtained from the linear relationship between the oxidation peak current and scan rate; n is the number of electrons transferred (n is 1, assuming an oneelectron process for oxidation of Ni centers in benzoate-Ni(OH)2); F is the Faradaic constant; m is the number of active sites (mol); R and T are the ideal gas constant and the absolute temperature, respectively. Then, TOF values can be calculated from the formula: TOF = JA/4Fm, where J is current density (A cm−2) at defined overpotential during the LSV measurement in 1.0 M KOH; A is the geometric area of the electrode; 4 indicates the mole of electrons consumed for one mole of oxygen

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RESULTS AND DISCUSSION Benzoate-Ni(OH)2/NF was synthesized through a facile hydrothermal process (see Experimental Section for more details). Figure 1a shows the XRD pattern for benzoate-Ni(OH)2

Figure 1. XRD patterns for (a) benzoate-Ni(OH)2 and (b) Ni(OH)2 powder. (c) FT-IR spectra for benzoate-Ni(OH)2 and Ni(OH)2 powder. SEM images of (d) Ni(OH)2/NF and (e) benzoateNi(OH)2/NF. (f) The corresponding EDX elemental mapping images of Ni, C, and O elements for benzoate-Ni(OH)2/NF.

powder. The powder product presents a series of diffraction peaks at 5.95° (1.48 nm), 11.85° (0.75 nm), and 17.78° (0.50 nm) indexed to (001), (002), and (003) planes of crystalline Ni(C6H5COO)1.17(OH)0.83·0.59H2O phase (JCPDS No. 421835), respectively, which corresponds to the reported work.25 Combined with the thickness of a brucite-like octahedral sheet (0.48 nm)26 and the interplanar d-spacing of 1.48 nm indexed to (001) plane for benzoate-Ni(OH)2, we can confirm the formation of a stacked bilayer-like structure for benzoate anions (0.7 nm).27 The XRD pattern of Ni(OH)2 is displayed in Figure 1b, revealing the formation of the crystalline Ni(OH)2 phase (JCPDS No. 14-0117). FTIR measurement is carried out to further analyze the structure of benzoate-Ni(OH)2. As displayed in Figure 1c, the narrow absorption band at 3606 cm−1 is ascribed to the O−H vibration from M−OH groups with a brucite-like structure, and the broad one at 3448 cm−1 can be attributed to the stretching vibration of interlayer water molecules.28 The three absorption bands at 1602 (CC stretching mode) and 711 and 687 cm−1 (C−H antiplane bending mode) imply the presence of aromatic rings.27 Another two strong absorption bands located at 1401 and 1562 cm−1 correspond to symmetric and antisymmetric vibrations of carboxylate groups from intercalated benzoate anions, respectively. 27 The lowest B

DOI: 10.1021/acssuschemeng.7b02557 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering absorption band at 455 cm−1 arises from an Ni−O vibrational stretching in Ni(OH)2.29 We also recorded the FT-IR spectrum of Ni(OH)2 as a comparison (Figure 1c), and the test result is consistent with the previous report.30 The SEM images of Ni(OH)2/NF show the full coverage of nanosheets arrays on NF (Figure 1d). Figure 1e presents the SEM images of benzoateNi(OH)2/NF, indicating that the entire NF is completely covered with nanobelts arrays with widths of about 0.45 μm (inset). The energy-dispersive X-ray (EDX) spectrum (Figure S1) verifies the presence of Ni, C, and O elements, and corresponds to elemental mapping images (Figure 1f) further confirming the uniform distribution of Ni, C, and O elements in this product. To confirm the chemical composition and valence states for benzoate-Ni(OH)2, we recorded the XPS spectra. Figure 2a

Figure 3. (a) LSV curves of RuO2/NF, benzoate-Ni(OH)2/NF, Ni(OH)2/NF, and bare NF for OER. (b) Corresponding Tafel plots of RuO2/NF, benzoate-Ni(OH)2/NF, and Ni(OH)2/NF. (c) Capacitive currents at 0.21 V vs Hg/HgO versus scan rates for benzoateNi(OH)2/NF and Ni(OH)2/NF. (d) Time-dependent current density curve at fixed overpotential of 230 mV. All experiments were tested in 1.0 M KOH.

oxidation. To achieve a catalytic current density of 60 mA cm−2, Ni(OH)2/NF demands an overpotential of 368 mV, and greatly improved OER overpotential (242 mV) is required for benzoateNi(OH)2/NF. Expectedly, RuO2/NF has outstanding OER performance with the requirement of 212 mV overpotential to drive the same current. It is noted that such benzoate-Ni(OH)2/ NF also outperforms other non-noble metal OER electrocatalysts working in 1.0 M KOH solution. A detailed comparison is listed in Table S1. The corresponding Tafel plots derived from polarization curves for as-obtained catalysts are presented in Figure 3b. Benzoate-Ni(OH)2/NF has a Tafel slope of 97 mV dec−1 comparable to RuO2/NF (95 mV dec−1) and smaller than that for Ni(OH)2/NF (103 mV dec−1). It suggests that such an intercalated electrode possesses more rapid catalytic kinetics for water oxidation.33 We tested the double layer capacitance (Cdl) at the solid/liquid interface for as-prepared catalysts to estimate the electrochemical active surface area (ECSA). The Cdl is measured by cyclic voltammetry technique, in accordance with a previous report.34 Figure S2 presents the cyclic voltammograms (CVs) collected in the region of 0.16−0.26 V vs Hg/HgO. CDL is determined by the the equation ic = v × Cdl, which means CDL is equal to the slope of a straight line yielded by current density (ic) versus scan rate (v). Thus, we obtain the Cdl of 6.0 mF cm−2 for benzoate-Ni(OH)2/ NF, and lower Cdl (3.1 mF cm−2) is calculated for Ni(OH)2/NF (Figure 3c). This result indicates that benzoate-Ni(OH)2/NF has a larger ECSA and thus can afford more catalytically active sites for oxygen evolution,35 which could be rationally attributed to its expanded interlayer spacing and more accessible surface area. Figure S3 displays the electrochemical impedance spectroscopies. It is observed that benzoate-Ni(OH)2/NF has a smaller radius of a semicircle in comparison with Ni(OH)2/NF, revealing a lower charge−transfer resistance that can make great contributions to rapid OER catalysis on a benzoateNi(OH)2/NF electrode.36 The multistep chronopotentiometric curve is presented in Figure S4, showing that the potential immediately levels off at 0.57 V vs Hg/HgO for the start current of 50 mA cm−2 and

Figure 2. (a) XPS survey spectrum for benzoate-Ni(OH)2. XPS spectra of benzoate-Ni(OH)2 in the (b) Ni 2p, (c) C 1s, and (d) O 1s regions.

presents the XPS survey spectrum, further testifying the existence of Ni, C, and O elements in this product. As presented in Figure 2b, the binding energies (BEs) at 856.5 and 874.2 eV in the Ni 2p region can be assigned to Ni 2p3/2 and Ni 2p1/2, respectively, which implies the presence of Ni2+ from Ni(OH)2.31 Another two peaks centered at 862.3 and 880.9 eV with two shakeup satellites are also associated with Ni2+. Figure 2c displays the high-resolution C 1s spectrum. The peak at 284.7 eV and another one at 288.3 eV can be attributed to carbon components in aromatic rings and carboxylate groups in benzoate anions, respectively.18 In the O 1s region (Figure 2d), two peaks at 531.2 and 532.5 eV are observed, which can be assigned to hydroxyl groups (O−H) and carboxylate groups (O−CO) in intercalated products, respectively.32 All of the above-stated results clearly support the successful formation of benzoateNi(OH)2 nanobelts arrays. We measured the electrochemical OER behavior for benzoateNi(OH)2/NF with a scan rate of 2 mV s−1 in 1.0 M KOH. Bare NF, RuO2 on NF (RuO2/NF), and Ni(OH)2/NF were also examined for comparisons. Because as-examined currents cannot directly reveal the intrinsic performance for catalysts owing to the influence of ohmic resistance, we applied ohmic potential drop (iR) corrections to all initial data except those particularly explained.33 Figure 3a shows the polarization curves. As observed, bare NF is poorly active for electrocatalytic water C

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theoretically calculated oxygen. As observed in Figure S7, the approximate agreement of the measured value and calculated one demonstrates a FE of 94.6% for oxygen evolution on the benzoate-Ni(OH)2/NF electrode.

remains constant for the remaining 500 s. All other steps also give similar results, proving the excellent mass transportation property, conductivity, and mechanical robustness on such an intercalated electrode.33,37 Since long-term stability is another pivotal parameter determining the practicability of an electrocatalyst, we probed the durability of benzoate-Ni(OH)2/NF by bulk electrolysis at a settled overpotential of 230 mV in 1.0 M KOH (Figure 3d). It shows no decrease in current, implying that benzoate-Ni(OH)2/NF can maintain its catalytic activity for 27 h. To further investigate the effect of benzoate ions on the catalytic activity, we also measured the OER performance of Ni(OH)2/NF in 1.0 M KOH containing 10 mM benzoate ions, and corresponding LSV curves are shown in Figure S5. It is found that Ni(OH)2/NF exhibits similar catalytic behavior for OER with the presence or absence of benzoate ions, implying that the great improvement in catalytic ability for benzoate-Ni(OH)2/NF can be ascribed to expanded interlayer spacing rather than the synergistic effect between benzoate species and Ni(OH)2. TOF was also employed for further assessment of as-prepared catalysts at varied overpotentials. TOFs are calculated based on the assumption that Ni ions in our product are catalytically active.38 For the TOF calculation, we quantified the surface concentration of active sites using the electrochemistry technique.39 The CVs under different scan rates for benzoateNi(OH)2/NF (Figure 4a) and Ni(OH)2/NF (Figure 4b)

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CONCLUSIONS In summary, benzoate-Ni(OH)2/NF has been successfully prepared by the intercalation of layered Ni(OH)2/NF using a traditional hydrothermal method. The expansion of interlayer spacing increased from 0.46 to 1.48 nm and leads to remarkably improved OER performance for benzoate-Ni(OH)2/NF. To achieve a catalytic current density of 60 mA cm−2, such an intercalated nanoarray catalyst only needs an overpotential of 242 mV, which is a 126 mV improvement compared to Ni(OH)2/NF (368 mV) in 1.0 M KOH. It also exhibits strong long-term electrochemical durability. This study not only provides us a high performance and stable nanoarray catalyst material for water electrolysis in alkaline media, but also gives an attractive strategy to the significant enhancement in catalytic activity for layered hydroxide-based electrocatalysts.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b02557. EDX spectrum, CVs, nyquist plots, multicurrent process curve, LSV curves, plots of TOF, amount of oxygen versus time, and comparison of OER performance. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Abdullah M. Asiri: 0000-0001-7905-3209 Xuping Sun: 0000-0001-5034-1135 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 21575137).

Figure 4. CVs of (a) benzoate-Ni(OH)2/NF and (b) Ni(OH)2/NF under different scan rates increasing from 5 to 25 mV s−1 in 1.0 M KOH. Linear relationship of the oxidation peak currents versus scan rates for (c) benzoate-Ni(OH)2/NF and (d) Ni(OH)2/NF.

REFERENCES

(1) Symes, M. D.; Cronin, L. Decoupling Hydrogen and Oxygen Evolution during Electrolytic Water Splitting Using an ElectronCoupled-Proton Buffer. Nat. Chem. 2013, 5, 403−409. (2) Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G. Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds. Chem. Rev. 2010, 110, 6474−6502. (3) Sartorel, A.; Carraro, M.; Toma, F. M.; Prato, M.; Bonchio, M. Shaping the Beating Heart of Artificial Photosynthesis: Oxygenic Metal Oxide Nano-Clusters. Energy Environ. Sci. 2012, 5, 5592−5603. (4) DeKrafft, K. E.; Wang, C.; Xie, Z.; Su, X.; Hinds, B. J.; Lin, W. Electrochemical Water Oxidation with Carbon-Grafted Iridium Complexes. ACS Appl. Mater. Interfaces 2012, 4, 608−613. (5) Lee, Y.; Suntivich, J.; May, K. J.; Perry, E. E.; Shao-Horn, Y. Synthesis and Activities of Rutile IrO2 and RuO2 Nanoparticles for Oxygen Evolution in Acid and Alkaline Solutions. J. Phys. Chem. Lett. 2012, 3, 399−404. (6) Guo, S.; Yang, Y.; Liu, N.; Qiao, S.; Huang, H.; Liu, Y.; Kang, Z. One-Step Synthesis of Cobalt, Nitrogen-Codoped Carbon as Nonpre-

suggest that the oxidation peak current for redox species is linearly dependent on scan rates. The corresponding slope is fitted to this following formula: slope = n2F2m/4RT (see Experimental Section for calculation detailes). As shown in Figure 4c and d, the slopes for benzoate-Ni(OH)2/NF and Ni(OH)2/NF are 1.5498 and 1.1936, respectively. As a result, the TOF for benzoate-Ni(OH)2/NF is determined to be 0.18 s−1 at the overpotential of 330 mV, much higher than that of Ni(OH)2/ NF (0.018 s−1) at the same overpotential. More detailed comparsions for TOF values at different settled overpotentials are shown in Figure S6. Such contrast may be ascribed to the intercalated 3D nanoarray structure, realizing sufficient exposure for nickel active sites toward enhanced water oxidation activity.The Faradaic efficiency (FE) was also determined by comparing the quantity of experimentally measured oxygen with D

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An Efficient Electrocatalyst for Oxygen Evolution Reaction. ChemSusChem 2017, DOI: 10.1002/cssc.201701358. (25) Xu, J.; Xue, Y.; Cao, J.; Wang, G.; Li, Y.; Wang, W.; Chen, Z. The Carbon Quantum Dots/Nickel Oxide (CQDs/NiO) Nanorods with High Capacitance for Supercapacitor. RSC Adv. 2016, 6, 5541−5546. (26) Kooli, F.; Chisem, I. C.; Vucelic, M.; Jones, W. Synthesis and Properties of Terephthalate and Benzoate Intercalates of Mg-Al Layered Double Hydroxides Possessing Varying Layer Charge. Chem. Mater. 1996, 8, 1969−1977. (27) Guo, X.; Wang, L.; Yue, S.; Wang, D.; Lu, Y.; Song, Y.; He, J. Single-Crystalline Organic-Inorganic Layered Cobalt Hydroxide Nanofibers: Facile Synthesis, Characterization, and Reversible Water-Induced Structural Conversion. Inorg. Chem. 2014, 53, 12841−12847. (28) Li, F.; Liu, J.; Evans, D. G.; Duan, X. Stoichiometric Synthesis of Pure MFe2O4 (M = Mg, Co, and Ni) Spinel Ferrites from Tailored Layered Double Hydroxide (Hydrotalcite-Like) Precursors. Chem. Mater. 2004, 16, 1597−1602. (29) Freitas, M. Nickel Hydroxide Powder for NiO·OH/Ni(OH)2 Electrodes of the Alkaline Batteries. J. Power Sources 2001, 93, 163−173. (30) Fu, G. R.; Hu, Z. A.; Xie, L. J.; Jin, X. Q.; Xie, Y. L.; Wang, Y. X.; Zhang, Z. Y.; Yang, Y. Y.; Wu, H. Y. Electrodeposition of Nickel Hydroxide Films on Nickel Foil and Its Electrochemical Performances for Supercapacitor. Int. J. Electrochem. Sci. 2009, 4, 1052−1062. (31) Vedrine, J. C.; Hollinger, G.; Duc, T. M. Investigations of Antigorite and Nickel Supported Catalysts by X-ray Photoelectron Spectroscopy. J. Phys. Chem. 1978, 82, 1515−1520. (32) Mu, J.; Shao, C.; Guo, Z.; Zhang, Z.; Zhang, M.; Zhang, P.; Chen, B.; Liu, Y. High Photocatalytic Activity of ZnO-Carbon Nanofiber Heteroarchitectures. ACS Appl. Mater. Interfaces 2011, 3, 590−596. (33) Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X. NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem., Int. Ed. 2015, 54, 9351−9355. (34) McCrory, C. C. L.; Jung; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977−16987. (35) Lei, F.; Liu, W.; Sun, Y.; Xu, J.; Liu, K.; Liang, L.; Yao, T.; Pan, B.; Wei, S.; Xie, Y. Metallic Tin Quantum Sheets Confined in Graphene toward High-Efficiency Carbon Dioxide Electroreduction. Nat. Commun. 2016, 7, 12697. (36) Guo, C.; Zhang, L.; Miao, J.; Zhang, J.; Li, C. DNA-Functionalized Graphene to Guide Growth of Highly Active Pd Nanocrystals as Efficient Electrocatalyst for Direct Formic Acid Fuel Cells. Adv. Energy Mater. 2013, 3, 167−171. (37) Lu, X.; Zhao, C. Electrodeposition of Hierarchically Structured Three-Dimensional Nickel−Iron Electrodes for Efficient Oxygen Evolution at High Current Densities. Nat. Commun. 2015, 6, 6616. (38) Surendranath, Y.; Kanan, M. W.; Nocera, D. G. Mechanistic Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate Catalyst at Neutral pH. J. Am. Chem. Soc. 2010, 132, 16501−16509. (39) Li, Y.; Zhang, L.; Xiang, X.; Yan, D.; Li, F. Engineering of ZnCoLayered Double Hydroxide Nanowalls toward High-Efficiency Electrochemical Water Oxidation. J. Mater. Chem. A 2014, 2, 13250−13258.

cious Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions. Science Bulletin 2016, 61, 68−77. (7) Gong, M.; Dai, H. A Mini Review of NiFe-Based Materials as Highly Active Oxygen Evolution Reaction Electrocatalysts. Nano Res. 2015, 8, 23−39. (8) Gong, M.; Li, Y.; Wang, H.; Liang, Y.; Wu, J. Z.; Zhou, J.; Wang, J.; Regier, T.; Wei, F.; Dai, H. An Advanced Ni−Fe Layered Double Hydroxide Electrocatalyst for Water Oxidation. J. Am. Chem. Soc. 2013, 135, 8452−8455. (9) 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, 6744−6753. (10) Li, Z.; Shao, M.; Yang, Q.; Tang, Y.; Wei, M.; Evans, D. G.; Duan, X. Directed Synthesis of Carbon Nanotube Arrays Based on Layered Double Hydroxides toward Highly-Efficient Bifunctional Oxygen Electrocatalysis. Nano Energy 2017, 37, 98−107. (11) Wang, Z.; Zeng, S.; Liu, W.; Wang, X.; Li, Q.; Zhao, Z.; Geng, F. Coupling Molecularly Ultrathin Sheets of NiFe-Layered Double Hydroxide on NiCo2O4 Nanowire Arrays for Highly Efficient Overall Water-Splitting Activity. ACS Appl. Mater. Interfaces 2017, 9, 1488− 1495. (12) Varadwaj, G. B. B.; Nyamori, V. O. NiMn Layered Double Hydroxides as Efficient Electrocatalysts for the Oxygen Evolution Reaction and Their Application in Rechargeable Zn−Air Batteries. Nano Res. 2016, 9, 3598−3621. (13) Zhang, C.; Zhao, J.; Zhou, L.; Li, Z.; Shao, M.; Wei, M. Layer-byLayer Assembly of Exfoliated Layered Double Hydroxide Nanosheets for Enhanced Electrochemical Oxidation of Water. J. Mater. Chem. A 2016, 4, 11516−11523. (14) Song, F.; Hu, X. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nat. Commun. 2014, 5, 4477. (15) Yu, X.; Zhang, M.; Yuan, W.; Shi, G. A High-Performance ThreeDimensional Ni−Fe Layered Double Hydroxide/Graphene Electrode for Water Oxidation. J. Mater. Chem. A 2015, 3, 6921−6928. (16) Jia, G.; Hu, Y.; Qian, Q.; Yao, Y.; Zhang, S.; Li, Z.; Zou, Z. Formation of Hierarchical Structure Composed of (Co/Ni)Mn-LDH Nanosheets on MWCNT Backbones for Efficient Electrocatalytic Water Oxidation. ACS Appl. Mater. Interfaces 2016, 8, 14527−14534. (17) Wang, L.; Dong, Z. H.; Wang, Z. G.; Zhang, F. X.; Jin, J. Layered α-Co(OH)2 Nanocones as Electrode Materials for Pseudocapacitors: Understanding the Effect of Interlayer Space on Electrochemical Activity. Adv. Funct. Mater. 2013, 23, 2758−2764. (18) Huang, L.; Jiang, J.; Ai, L. Interlayer Expansion of Layered Cobalt Hydroxide Nanobelts to Highly Improve Oxygen Evolution Electrocatalysis. ACS Appl. Mater. Interfaces 2017, 9, 7059−7067. (19) Li, X.; Hao, X.; Wang, Z.; Abudula, A.; Guan, G. In-Situ Intercalation of NiFe LDH Materials: An Efficient Approach to Improve Electrocatalytic Activity and Stability for Water Splitting. J. Power Sources 2017, 347, 193−200. (20) Luo, M.; Cai, Z.; Wang, C.; Bi, Y.; Qian, L.; Hao, Y.; Li, L.; Kuang, Y.; Li, Y.; Lei, X.; Huo, Z.; Liu, W.; Wang, H.; Sun, X.; Duan, X. Phosphorus Oxoanion-Intercalated Layered Double Hydroxides for High-Performance Oxygen Evolution. Nano Res. 2017, 10, 1732−1739. (21) Ge, X.; Gu, C. D.; Wang, X. L.; Tu, J. P. Ionothermal Synthesis of Cobalt Iron Layered Double Hydroxides (LDHs) with Expanded Interlayer Spacing as Advanced Electrochemical Materials. J. Mater. Chem. A 2014, 2, 17066−17076. (22) Tian, J.; Liu, Q.; Cheng, N.; Asiri, A. M.; Sun, X. Self-Supported Cu3P Nanowire Arrays as an Integrated High-Performance ThreeDimensional Cathode for Generating Hydrogen from Water. Angew. Chem., Int. Ed. 2014, 53, 9577−9581. (23) Ren, Z.; Botu, V.; Wang, S.; Meng, Y.; Song, W.; Guo, Y.; Ramprasad, R.; Suib, S. L.; Gao, P. Monolithically Integrated Spinel MxCo3‑xO4 (M = Co, Ni, Zn) Nanoarray Catalysts: Scalable Synthesis and Cation Manipulation for Tunable Low-Temperature CH4 and CO Oxidation. Angew. Chem., Int. Ed. 2014, 53, 7223−7227. (24) Ge, R.; Ren, X.; Ji, X.; Liu, Z.; Du, G.; Asiri, A. M.; Sun, X.; Chen, L. Benzoate Anions-Intercalated Layered Cobalt Hydroxide Nanoarray: E

DOI: 10.1021/acssuschemeng.7b02557 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX