Nanoporous CoP3 Nanowire Array: Acid Etching Preparation and

enhanced performance with the need of overpotential of 76 mV (j=10 mV cm-2), ... Acid Etching Preparation, Hydrogen Evolution Reaction, Alkaline Solut...
1 downloads 0 Views 571KB Size
Download PDF
Subscriber access provided by Kaohsiung Medical University

Letter

Nanoporous CoP3 Nanowire Array: Acid Etching Preparation and Application as a High-Active Electrocatalyst for Hydrogen Evolution Reaction in Alkaline Solution Yuyao Ji, Li Yang, Xiang Ren, Guanwei Cui, Xiaoli Xiong, and Xuping Sun ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b01714 • Publication Date (Web): 30 Jul 2018 Downloaded from http://pubs.acs.org on July 30, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a 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 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.

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 5 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 Sustainable Chemistry & Engineering

Nanoporous CoP3 Nanowire Array: Acid Etching Preparation and Application as a High-Active Electrocatalyst for Hydrogen Evolution Reaction in Alkaline Solution Yuyao Ji,† Li Yang,# Xiang Ren,# Guanwei Cui,§ Xiaoli Xiong,†,* and Xuping Sun#,* †

College of Chemistry and Materials Science, Sichuan Normal University, Chengdu 610068, Sichuan, China #Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu 610054, China,§College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan 250014, Shandong, China * E-mail: [email protected] (X.S.); [email protected] (X.X.) ABSTRACT: Transition metal phosphides have been intensively and extensively studied as earth-abundant catalysts for effective hydrogen evolution electrocatalysis, but it is highly desired to explore new strategy to improve the catalytic activity. In this work, nanoporous CoP3 nanowire array on Ti mesh (np-CoP3/TM) was derived from MnO2-CoP3/TM by acid etching of MnO2 that acts as a pore-forming agent. As a non-noble-metal catalyst for the hydrogen evolution reaction, the resulting np-CoP3/TM demonstrates enhanced performance with the need of overpotential of 76 mV (j=10 mV cm-2), 45 mV less that needed by MnO2-CoP3/TM. Moreover, it also shows a good durability for at least 60 h.

KEYWORDS: Nanoporous, Nanowire Array, Acid Etching Preparation, Hydrogen Evolution Reaction, Alkaline Solution.

INTRODUCTION Recently, much attention has been focused on finding green and sustainable ways in order to deal with the environmental problems caused by fossil fuel.1,2 Hydrogen is considered as an abundant such candidate.3,4 Water electrolysis is an attractive carbon-neutral technique for hydrogen production but requires efficient electrocatalyst to achieve high current density at low overpotential for hydrogen evolution reaction (HER).5-7 The most active Pt catalyst however suffers from scarcity, stimulating the researchers to search earth-abundant alternatives.8-10 As a vital class of compounds with metalloid properties, transition-metal phosphides (TMPs) have been widely used for hydrodesulfurization reaction.11,12 In recent years, considerable research attention has also focused on exploring TMPs as lowcost catalysts for efficient hydrogen evolution electrocatalysis, and among such catalysts, Co phosphides attracts a lot of attention because of high activity.7,8,13-18 Both element doping1921 and surface/interface energinerring22 are proven effectively to improve the HER activity of such catalysts. Porous nanostructures have obvious advantages of high surface area,23,24 providing good benefit to improve the electrocatalytic HER performance. It is thus believed that creating nanopores would be a good way to boost the HER activity of Co phosphide catalysts, which, however, has not been explored before. Herein, we show the nanoporous CoP3 nanowire array on Ti mesh (np-CoP3/TM) derived from MnO2-CoP3/TM via an acid etching strategy. The central ideal lies in the fact that MnO2 and CoP3 are different in stability again oxalic acid and the

selective etching of MnO2 as the pore-forming agent produces nanoporous CoP3 nanowire. The resulting np-CoP3/TM shows superior HER activity over MnO2-CoP3/TM and it needs an overpotential of 76 mV (j=10 mV cm-2). Moreover, it also exhibits strong stability to maintain 60 h for HER.

RESULTS AND DISCUSSION X-ray diffraction (XRD) patterns for MnO2-CoP3 and np-CoP3 scratched down from TM are shown in Figure 1a. The CoP3 presents six peaks at 27.4°, 32.5°, 40.3°, 44.6°, 70.2°, and 76.4° indexed to the (210), (240), (245), (420), (540), and (630) facets of CoP3 (JCPDS No.30-0443). The diffraction peaks at 44.7° and 65.7° are indexed to (360) and (400) lattice plane, respectively. In contrast, np-CoP3 only shows diffraction peaks characteristic of CoP3 (JCPDS No.42-1169), suggesting the successful etching of MnO2 by oxalic acid.25 The SEM image shows the MnO2-CoP3 nanowire arrays are anchored on TM (Figure 1b). Note that the resulting np-CoP3/TM still preserves its nanowire array feature (Figure 1c). Cross-section analysis for np-CoP3/TM shows the nanoarray is about 1.7 µm in height (Figure S1). Further transmission electron microscopy (TEM) analysis reveals the nanoporous CoP3 nanowire after oxalic acid etching. Figure 1d and Figure 1e show that the High-resolution TEM (HRTEM) provides the interplanar distance of 0.404 nm matching with (220) plane of CoP3 (Figure 1f). The EDX images (Figure 1g) further show the presence of Co and P elements. As shown from the Brunauer-EmmettTeller (BET) pore-size distribution curves of MnO2-CoP3 and np-CoP3 (Figure 1h), np-CoP3 shows a broad peak centering at 9.6 nm, correlating quite well with TEM observations. From

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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 corresponding nitrogen adsorption/desorption isotherm plots (Figure 1i), the BET surface areas for MnO2-CoP3 and np-CoP3 were determined as 67.7 and 206.6 m2 g−1, respectively. As shown in Figure S2, the Fourier transform infrared spectroscopy (FTIR) spectrum for the product only shows peaks characteristic of CoP3,26 suggesting the complete removal oxalic acid after acid etching. All these data strongly support the successful formation of MnO2-CoP3 derived nanoporous CoP3 nanowires with high surface area after acid etching.

CoP3/TM is also efficient to electrochemically catalyze the HER and needs overpotential of 121 mV (j=10 mV cm-2). And the np-CoP3/TM has superior catalytic activity to MnO2CoP3/TM and requires overpotential of only 76 mV (j=10 mV cm-2). Our np-CoP3/TM outperforms reported Co-based HER catalysts like CoP nanowire/CC,8 Co2P nanorods,15 FeCoP/Ti,18 CoP3 NAs/CFP,31 CoOx@CN,32 Co-PP/Au,33 and CoP2/RGO,34 etc. More detailed comparison is listed in Table S1. As shown in Figure S3, CoP3/TM with a lower CoP3 loading (1.2 mg cm-2 ) needs a much larger overpotential of 142 mV to afford 10 mA cm-2, suggesting catalyst loading has heavy influence on the catalytic performance. Figure 3b shows the Tafel plots of Pt/C on TM (32 mV dec-1), np-CoP3/TM (45 mV dec-1) and MnO2-CoP3/TM (50 mV dec-1), respectively. We also probed the oxygen-evolving activity of np-CoP3/TM in 1.0 M KOH. It suggests that the np-CoP3/TM is also active for water oxidation electrocatalysis with the need of overpotential of 336 mV to achieve 10 mA cm-2 (Figure S4a). Using this bifunctional catalyst as both cathode and anode, we constructed a two-electrode water electrolyzer. In 1.0 M KOH, this system requires a cell voltage of 1.68 V (j=10 mV cm-2) water-splitting current (Figure S4b). We investigated the HER activity of np-CoP3/TM in 1.0 M PBS and 0.1 M KOH and this catalyst needs the overpotentials of 121 and 134 mV (j=10 mV cm-2), respectively (Figure S5 and S6).

Figure 1. (a) XRD patterns for MnO2-CoP3 and np-CoP3. SEM images of (b) MnO2-CoP3/TM and (c) np-CoP3/TM. TEM images taken from one single nanowire of (d) MnO2-CoP3 and (e) npCoP3. (f) HRTEM image taken from np-CoP3. (g) EDX elemental mapping images of np-CoP3/TM. (h) BJH pore-size distribution curves and (i) nitrogen adsorption/desorption isotherm plots of MnO2-CoP3 and np-CoP3.

Figure 2a shows the two peaks Co 2p region for np-CoP3. 27 Two peaks at 796.7 and 795.2 eV can indexed to to the binding energies (BEs) of Co 2p1/2 and Co 2p3/2. The BE of P 2p1/2 and P 2p3/2 appear at 133.7 and 129.3 eV, respectively.28 It shows that the Co has partial positive charge but P partial negative charge, so it implies that the electron density is transferred from the Co to P.29,30 The POx or P-O species at 134.5 eV may be due to air exposure resulting in surface oxidation of CoP3.31

Figure 2. (a) XPS spectra for np-CoP3 in the (a) Co 2p and (b) P 2p regions. We also examined the electrochemical HER activity for np-

CoP3/TM (CoP3 loading quality: 1.8 mg cm-2). Bare TM, MnO2-CoP3/TM and Pt/C on TM were also tested for comparison. As observed, Pt/C on TM shows excellent HER activity, but bare TM shows negligible property. MnO2-

Figure 3. (a) The LSV of MnO2-CoP3/TM, np-CoP3/TM, Pt/C on TM and bare TM. (b) Tafel plots of MnO2-CoP3/TM, npCoP3/TM and Pt/C on TM. (c) LSV of np-CoP3/TM before and after 500 cyclic voltammetry cycles. (d) Chronopotentiometry curve for np-CoP3/TM at overpotential of 86 mV.

After 500 cyclic voltammetry cycles, there is almost no loss changes (Figure 3c), confirming its superior stability. Figure 3d shows that np-CoP3/TM exhibits excellent long-term stability for maintaining 60 h for HER. SEM (Figure S7), XRD (Figure S8) and XPS (Figure S9) analyses conclude that the catalyst can maintain its nanoarray feature and also is still np-CoP3 in nature after HER electrolysis. In order to evaluate the effective surface area of MnO2CoP3/TM and np-CoP3/TM, the bilayer capacitance of two electrodes at the solid/liquid interface were measured.35 The capacitance for MnO2-CoP3/TM and np-CoP3/TM was estimated as 2.3 and 9.8 mF cm-2, respectively, The electrochemically active surface areas (ECSAs) for MnO2-

ACS Paragon Plus Environment

Page 2 of 5

Page 3 of 5 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 Sustainable Chemistry & Engineering

CoP3/TM and np-CoP3/TM were calculated to be 0.09 and 0.17 m2, (Figure 4c). Compared with MnO2-CoP3/TM, npCoP3/TM has much larger surface area.35 Nyquist plots (Figure 4d) show a smaller charge-transfer resistance (Rct) of this MnO2-CoP3/TM than that of np-CoP3/TM, indicating a better electron-transporting capability.36,37 To estimate the intrinsic activity of np-CoP3/TM, turnover frequency (TOF) normalized by per surface site is evaluated.38 As shown in Figure S10, npCoP3/TM shows a higher value of 0.13 s-1 than that of MnO2CoP3/TM (0.06 s-1) at overpotential of 100 mV, revealing its superior intrinsic activity.

REFERENCES (1)

(2)

(3)

(4)

(5)

(6)

(7) Figure 4. CVs of (a) MnO2-CoP3/TM and (b) np-CoP3/TM at the different scan rates (from inner to outer 10, 50, 90, 130, 170). Corresponding capacitive currents at 0.09 V vs. Ag/AgCl as a function of scan rates for (c) MnO2-CoP3/TM and np-CoP3/TM. (d) Nyquist plots.

(8)

CONCLUSIONS In summary, selective acid etching is proposed as an effective strategy to fabricate nanoporous CoP3 nanowire array with superior catalytic activity for HER. Such np-CoP3 nanoarray drives 10 mV cm-2 with the need of overpotential of 76 mV. This study is of significance because it not only gives us an attractive catalyst for full water splitting, but opens up an exciting new opportunity to rational design of porous TMPs nanostructures for applications.

ASSOCIATED CONTENT

(9)

(10)

(11)

Supporting Information SEM image; FTIR spectra; LSV curves; XRD pattern; XPS spectra; TOFcalculation; Tables S1; This material is available free of charge via the Internet at http://pubs.acs.org.

(12)

AUTHOR INFORMATION (13)

Corresponding Author * E-mail: [email protected] (X.S.); [email protected] (X.X.)

Notes The authors declare no competing financial interest.

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

(14)

Service, R. F. Hydrogens Cars: Fad or the Future? Science 2009, 324, 1257–1259. DOI: 10.1126/science.3241257. 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. DOI: 10.1021/cr100246c. Dresselhaus, M. S.; Thomas, I. L. Alterbative Energy Technologies. Nature 2001, 414, 332–337. DOI: 10.1038/35104599. Du, H.; Xia, L.; Zhu, S.; Qu, F.; Qu, F. Al-Doped Ni2P Nanosheet Array: a Superior and Durable Electrocatalyst for Alkaline Hydrogen Evolution. Chem. Commun. 2018, 54, 2894–2897. DOI: 10.1039/c7cc09445k. Wang, J.; Cui, W.; Liu, Q. Xing, Z.; Asiri, A. M.; Sun, X. Recent Progress in Cobalt-Based Heterogeneous Catalysts for Electrochemical Water Splitting. Adv. Mater. 2016, 28, 215–230. DOI: 10.1002/adma.201502696. Shi, Y.; Zhang, B. Recent Advances in Transition Metal Phosphide Nanomaterials: Synthesis and Applications in Hydrogen Evolution Reaction. Chem. Soc. Rev. 2016, 45, 1529–1541. DOI: 10.1039/C5CS00434A. Zou, X.; Zhang, Y. Noble Metal-Free Hydrogen Evolution Catalysts for Water Splitting. Chem. Soc. Rev. 2015, 44, 5148–5180. DOI: 10.1039/C4CS00448E. Tian, J.; Liu, Q.; Asiri A. M.; Sun, X. Self-Supported Nanoporous Cobalt Phosphide Nanowire Arrays: An Efficient 3D Hydrogen-Evolving Cathode over the Wide Range of pH 0-14. J. Am. Chem. Soc. 2014, 136, 7587−7590. DOI: 10.1021/ja503372r. Du, H.; Zhang, X.; Tan, Q.; Kong, R.; Qu, F. A Cu3P– CoP Hybrid Nanowire Array: a Superior Electrocatalyst for Acidic Hydrogen Evolution Reactions. Chem. Commun. 2017, 53, 12021–12015. DOI: 10.1039/c7cc07802a. Zhang, X.; Si, C.; Guo, X.; Kong, R.; Qu, F. A MnCo2S4 Nanowire Array as an Earth-Abundant Electrocatalyst for An Efficient Oxygen Evolution Reaction Under Alkaline Conditions. J. Mater. Chem. A 2017, 5, 17211–17215. DOI: 10.1039/c7ta04804a. Vigil, J. A.; Lambert, T. N. Nanostructured Cobalt Phosphide-Based Films as Bifunctional Electrocatalysts for Overall Water Splitting. RSC Adv. 2015, 5, 105814–105819. DOI: 10.1039/C5RA24562A. Carenco, S.; Portehault, D.; Boissière, C.; Mèzailles N.; Sanchez, C. Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives. Chem. Rev. 2013, 113, 7981–8065. DOI:10.1021/cr400020d. Liu, Q.; Tian, J.; Cui, W.; Jiang, P.; Cheng, N.; Asiri, A. M.; Sun, X. Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non-Noble-Metal Nanohybrid Electrocatalyst for Hydrogen Evolution. Angew. Chem. Int. Ed. 2014, 53, 6710–6714. DOI: 10.1002/anie.201404161. Popcaun, E. J.; Read, C. G.; Roske, C. W.; Lewis N. S.; Schaak, R. E. Highly Active Electrocatalysis of the Hydrogen Evolution Reaction by Cobalt Phosphide

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

Nanoparticles. Angew. Chem. Int. Ed. 2014, 53, 5427– 5430. DOI： 10.1002/ani.201402646. Huang, Z.; Chen Z.; Chen, Z.; Lv, C.; Humphrey, M. G.; Zhang, C. Cobalt Phosphide Nanorods as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction. Nano Energy. 2014, 9, 373–382. DOI: 10.1016/j.nanoen.201408013. Yang, H.；Zhang, Y.；Hu, F.；Wang, Q. Urchin-like CoP Nanocrystals as Hydrogen Evolution Reaction and Oxygen Reduction Reaction Dual-Electrocatalyst with Superior Stability. Nano Lett. 2015, 15, 7616– 7620. DOI: 10.1021/acs.nanolett.5b03446. Yang, X.；Lu, A.-Y.；Zhu, Y.；Hedhili, M. N.；Min, S.；Huang, K. W.；Han Y.；Li, L. J. Cop Nanosheet Assembly Grown on Carbon Cloth: A Highly Efficient Electrocatalyst for Hydrogen Generation. Nano Energy 2015, 15, 634–641. DOI: 0.1016/j.nanoen.201505026. Zhang, C.; Huang, Y.; Yu, Y.; Zhang, J.; Zhuo S.; Zhang, B. Sub-1.1 Nm Ultrathin Porous Cop Nanosheets with Dominant Reactive {200} Facets: A High Mass Activity and Efficient Electrocatalyst for the Hydrogen Evolution Reaction. Chem. Sci. 2017, 8, 2769–2775. DOI: 10.1039/C6SC05687C. Liu, T.; Ma, X.; Liu, D.; Hao, S.; Du, G.; Ma, Y.; Asiri A. M.; Sun X.; Chen, L. Mn Doping of CoP Nanosheets Array: An Efficient Electrocatalyst for Hydrogen Evolution Reaction with Enhanced Activity at All pH Values. ACS Catal. 2017, 7, 98−102. DOI: 10.1021/acscatal.6b02849. Tang, C.; Zhang, R.; Lu, W.; He, L.; Jiang, X.; Asiri, A. M.; Sun, X. Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation. Adv. Mater. 2016, 29, 1602441. DOI: 10.1002/adma.201602441. Liu, T.; Liu, D.; Qu, F.; Wang, D.; Zhang, L.; Ge, R.; Hao, S.; Ma, Y.; Du, G.; Asiri, A. M.; Chen L.; Sun, X. Enhanced Electrocatalysis for Energy-Efficient Hydrogen Production over CoP Catalyst with Nonelectroactive Zn as a Promoter. Adv. Energy Mater. 2017, 7, 1700020. DOI: 10.1002/aenm.201700020. Zhang, R.; Ren, X.; Hao, S.; Ge, R.; Liu, Z.; Asiri, A. M.; Chen, L.; Zhang Q.; Sun, X. Selective Phosphidation: An Effective Strategy Toward Cop/Ceo2 Interface Engineering for Superior Alkaline Hydrogen Evolution Electrocatalysis. J. Mater. Chem. A 2018, 6, 1985–1990. DOI: 10.1039/C7TA10237B. Zhang, Q.; Uchaker, E.; Candelaria S. L.; Cao, G. Nanomaterials for Energy Conversion and Storage. Chem. Soc. Rev. 2013, 42, 3127–3171. DOI: 10.1039/C3CS00009E. Xia, X.; Zhang, Y.; Chao, D.; Guan, C.; Zhang, Y.; Li, L.; Ge, X.; Bacho, I. M.; Tu, J.; H. Fan, J. Nanoscale 2014, 6, 5008–5048. DOI: 10.1039/C4NR00024B. Zhou, X. Yu, L.; Lou, X. W. Nanowire-Templated Formation Of SnO2/Carbon Nanotubes with Enhanced Lithium Storage Properties. Nanoscale 2016, 8, 8384– 8389. DOI: 10.1039/C6NR01272H. Leszczynski, J.; Malecki, A. L.; Wojciechowski, T. K. Proceedings of the 5th European Conference on Thermoelectrics, Odessa, Ukraine, 2007, September 10–12. Wu, T.; Pi, M.; Wang, X.; Zhang D.; Chen, S. ThreeDimensional Metal-Organic Framework Derived

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

(37)

(38)

Page 4 of 5

Porous CoP3 Concave Polyhedrons as Superior Bifunctional Electrocatalysts for the Evolution of Hydrogen and Oxygen. Phys. Chem. Chem. Phys. 2017, 19, 2104–2110. DOI: 10.1039/C6CP07294A. Liu, T.; Xie, L.; Yang, J.; Kong, R.; Du, G.; Asiri, A. M.; Sun, X.; Chen, L. Self-Standing CoP Nanosheets Array: A Three-Dimensional Bifunctional Catalyst Electrode for Overall Water Splitting in both Neutral and Alkaline Media. ChemElectroChem 2017, 4, 1840–1845. DOI: 10.1002/celc.201700392. Liu, T.; Wang, K.; Du, G.; Asiri, A. M.; Sun, X. SelfSupported CoP Nanosheet Arrays: A Non-Precious Metal Catalyst for Efficient Hydrogen Generation from Alkaline NaBH4 Solution. J. Mater. Chem. A 2016, 4, 13053–13057. DOI: 10.1039/C6TA02997C. Grosvenor, A. P.; Wik, S. D.; Cavell R. G.; Mar, A. Examination of the Bonding in Binary TransitionMetal Monophosphides MP (M = Cr, Mn, Fe, Co) by X-Ray Photoelectron Spectroscopy. Inorg. Chem. 2005, 44, 8988–8998. DOI: 10.1021/ic051004d. Wu, T.; Pi, M.; Zhang D.; Chen, S. 3D Structured Porous CoP3 Nanoneedle Arrays as an Efficient Bifunctional Electrocatalyst for the Evolution Reaction of Hydrogen and Oxygen. J. Mater. Chem. A 2016, 4, 14539–14544. DOI: 10.1039/C6TA05838H. Jin, H.; Wang, J.; Su, D.; Wei, Z.; Pang Z.; Wang Y. In Situ Cobalt–Cobalt Oxide/N-Doped Carbon Hybrids as Superior Bifunctional Electrocatalysts for Hydrogen and Oxygen Evolution. J. Am. Chem. Soc. 2015, 137, 2688–2694. DOI: 10.1021/ja5127165. Vigil, J. A.; Lambert, T. N. Nanostructured Cobalt Phosphide-Based Films as Bifunctional Electrocatalysts for Overall Water Splitting. RSC Adv. 2015, 5, 105814–105819. DOI: 10.1039/C5RA24562A. Wang, J.; Yang, W.; Liu, J. CoP2 Nanoparticles on Reduced Graphene Oxide Sheets as a Super-Efficient Bifunctional Electrocatalyst for Full Water Splitting. J. Mater. Chem. A 2016, 4, 4686−4690. DOI: 10.1039/C6TA00596A. Ji, Y.; Ma, M.; Ji, X.; Xiong, X.; Sun, X. NickelCarbonate Nanowire Array: An Efficient and Durable Electrocatalyst for Water Oxidation under Nearly Neutral Conditions. Front. Chem. Sci. Eng. DOI: 10.1007/s11705-018-1717-8. Guo, C.; Zhang, L.; Miao, J.; Zhang, J.; Li, C. M. 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. DOI: 10.1002/aenm.201200527. Xiong, X.; Ji, Y.; Xie, M.; You, C.; Yang, L.; Liu, Z.; Asiri, A. M.; Sun, X. MnO2-CoP3 Nanowires Array: An Efficient Electrocatalyst for Alkaline Oxygen Evolution Reaction with Enhanced Activity. Electrochem. Commun. 2018, 86, 161–165. DOI: 10.1016/j.elecom.2017.12.008. Kibsgaard, J.; Tsai, Charlie.; Chan Karen.; Benck J. D., Nørskov, J., Abild-Pedersen F.; Jaramillo T. Designing an Improved Transition Metal Phosphide Catalyst for Hydrogen Evolution Using Experimental and Theoretical Trends. Energy Environ. Sci. 2015, 8, 3022–3029. DOI: 10.1039/C5EE02179K.

For Table of Contents Use Only ACS Paragon Plus Environment

Page 5 of 5 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 Sustainable Chemistry & Engineering

Nanoporous CoP3 nanowire array on Ti mesh (np-CoP3/TM) derived from MnO2-CoP3/TM via an acid etching shows enhanced catalytic activity for hydrogen evolution reaction. Such np-CoP3/TM affords 10 mA cm–2 at overpotential of 76 mV, 45 mV less that for MnO2-CoP3/TM.

ACS Paragon Plus Environment

5