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Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis.

ABSTRACT: Electrochemical water splitting into hydrogen and oxygen is a promising technology for sustainable energy storage. The development of earth-abundant transition metal phosphides (TMPs) to catalyze the hydrogen evolution reaction (HER) and TMP-derived oxy-hydroxides to catalyze the oxygen evolution reaction (OER) has recently drawn considerable attention. However, most monolithically integrated metal phosphide electrodes are prepared by laborious multi-step methods and their operational stability at high current densities has been rarely studied. Herein, we report a novel vapor-solid synthesis of single-crystalline cobalt phosphide nanowires (CoP NWs) on a porous Co foam and demonstrate their use in overall water splitting. The CoP NWs grown on the entire surface of the porous Co foam ligaments have a large aspect ratio, and hence are able to provide a large catalytically accessible surface over a given geometrical area. Comprehensive investigation shows that under the OER conditions CoP NWs are progressively and conformally converted to CoOOH through electrochemical in situ oxidation/dephosphorization; the latter serving as an active species to catalyze the OER. The in situ oxidized electrode shows exceptional electrocatalytic performance for the OER in 1.0 M KOH, delivering 100 mA cm^-2 at an overpotential (?) of merely 300 mV and a small Tafel slope of 78 mV dec^-1 as well as excellent stability at various current densities. Meanwhile, the CoP NW electrode exhibits superior catalytic activity for the HER in the same electrolyte, affording -100 mA cm^-2 at ? = 244 mV and showing outstanding stability. An alkaline electrolyzer composed of two symmetrical CoP NW electrodes can deliver 10 and 100 mA cm^-2 at low cell voltages of 1.56 and 1.78 V, respectively. The CoP NW electrolyzer demonstrates exceptional long-term stability for overall water splitting, capable of working at 20 and 100 mA cm^-2 for 1000 h without obvious degradation.

SUBMITTER: Li W

PROVIDER: S-EPMC5376710 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis.

Li Wei W Gao Xuefei X Xiong Dehua D Xia Fang F Liu Jian J Song Wei-Guo WG Xu Junyuan J Thalluri Sitaramanjaneya Mouli SM Cerqueira M F MF Fu Xiuli X Liu Lifeng L

Chemical science 20170123 4

Electrochemical water splitting into hydrogen and oxygen is a promising technology for sustainable energy storage. The development of earth-abundant transition metal phosphides (TMPs) to catalyze the hydrogen evolution reaction (HER) and TMP-derived oxy-hydroxides to catalyze the oxygen evolution reaction (OER) has recently drawn considerable attention. However, most monolithically integrated metal phosphide electrodes are prepared by laborious multi-step methods and their operational stability ...[more]

PMID: 28451361

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Project description:A new synthetic method to grow O-deficient rutile TiO2(s) nanorods (NRs) and nanowires (NWs) by a vapor-solid reaction growth method is developed. TiCl4(g) was employed to react with commercially supplied CaTiO3(s) (size 2-4 ?m) at 973 K under atmospheric pressure to generate TiO2(s) NRs (diameters 80-120 nm, lengths 1-4 ?m). The reaction employing TiCl4(g) and CaO(s) at 973 K also generated CaTiO3(s) (size 4-13 ?m) as the intermediate which reacted further with TiCl4(g) to produce NWs (diameters 80-120 nm, lengths 4-15 ?m). This is the first report of 1D rutile TiO2(s) nanostructure with such a high aspect ratio. Both of the NRs and the NWs, with compositions TiO1.81 and TiO1.65, respectively, were single crystals grown in the [001] direction. Their morphology was affected by the reaction temperature, the concentration of TiCl4(g), and the particle size of CaTiO3(s). The NRs and the NWs were investigated as anode materials for Li+-ion batteries. At constant current rates 1, 2, and 5 C (1 C = 170 mA g-1) for 100 cycles, the cycling (1.0-3.0 V) performance data of the NRs were 146, 123, and 104 mA h g-1, respectively. On the other hand, the cycling performance data of the NWs were 120, 80, and 52 mA h g-1, respectively. This is attributed to the high Li+ ion diffusion rate (D Li+ ) of the NRs (29.52 × 10-15 cm2 s-1), which exceeds that of the NWs (8.61 × 10-15 cm2 s-1). Although the [001] growth direction of the NR crystals would provide the fastest channels for the diffusion of Li+ ions and enhance the battery capacity, the extremely long channels in the NWs could hamper the diffusion of the Li+ ions. The O-deficiency in the structure would increase the conductivity of the electrode material and improve the stable cycling stability of the batteries also. The long-term cycling test at 2 C for the battery constructed from the NRs retained 121 mA h g-1 after 200 cycles and 99.2 mA h g-1 after 800 cycles. The device has an excellent long-term cycling stability with a loss of only 0.04% per cycle.

Dataset Information

Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis.

Publications

Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis.

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