The effect of phosphating time on the electrocatalytic activity of nickel phosphide nanorod arrays grown on Ni foam
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Recently, highly active, easy-to-make, and efficient bifunctional electrocatalysts have attracted tremendous attention because of their potential applications in clean energy. Herein, we report a simple, one-step approach for fabricating three-dimensional (3D) Ni–P nanorod arrays by direct phosphorization of commercial nickel foam (Ni foam) with different times. When used as a 3D electrode for oxygen evolution reaction, the obtained Ni–P nanorods with two hours of phosphatization treatment display high activity with an overpotential of 270 mV required to generate a current density of 30 mA/cm2 and excellent stability in 1.0 M KOH. Additionally, the Ni–P nanorod arrays are also highly active for electrocatalyzing the hydrogen evolution reaction in the alkaline media. As a result, the bifunctional Ni–P catalysts enabled a highly performed overall water splitting, in which a low applied external potential of 1.6 V led to a stabilized catalytic current density of 10 mA/cm2 over 12 h.
I. INTRODUCTION
The increasing global energy demand and accompanying climate changes as well as environmental issues are driving scientists to search for sustainable and environmentally friendly alternative sources of energy to replace exhaustible fossil fuels.1 Hydrogen has been considered as an efficient and clean energy resource to replace the depleting fossil fuel in the 21st century.2,3 Recently, the electrocatalytic water splitting for generating hydrogen and oxygen has attracted extensive attentions because this process provides a promising approach for the production of a sustainable, secure, and clean hydrogen-fuel energy.4–6 This electricity-driven process can be divided into two half-reactions, namely, the four-electron oxygen evolution reaction (OER) and the two-electron hydrogen evolution reaction (HER).7,8 Thereinto, the OER is thermodynamically and kinetically sluggish due to the four proton-coupled electron transfer process.9 Thus, it still remains a great challenge to develop the efficient and high-active bifunctional electrocatalysts for overall water splitting. Currently, the state-of-the-art electrocatalysts are the precious metal and their composites such as Pt, RuO2, and IrO2.10,11 However, the high cost and limited availability of noble metals potentially obstruct their large-scale applications in overall water splitting. In this case, tremendous research efforts have been focused on Contributing Editor: Yao Zheng a) Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2017.399
the low-cost and earth-abundant catalysts as alternatives to the noble metal. For example, Yang’s group reported the iron-nickel sulfide (INS) ultrathin nanosheets (NSs) that enabled a catalytic current density of 10 mA/cm2, an even lower overpotential of 105 mV at 10 mA/cm2, and a smaller Tafel slope of 40 mV/dec for HER.12 Also, Sun’s group synthesized new hierarchically multifunctional porous nickel sulfide superstructures (h-NiSx) through electrodeposition of porous metallic Ni microsphere
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