Cobalt Phosphide Nanowire Arrays on Conductive Substrate as an Efficient Bifunctional Catalyst for Overall Water Splitting

Hydrogen production via water splitting is a promising pathway to a clean energy resource. Herein we report the direct growth of cobalt phosphide (CoP) nanowires on conductive nickel foam (CoP@NF) as an efficient bifunctional catalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium. CoP@NF electrodes were facilely synthesized by a one-pot hydrothermal method followed by a phosphorization step. For HER, the CoP@NF electrode showed excellent catalytic activity with a low overpotential of only ∼100 mV to reach 10 mA/cm2, a low Tafel slope of 57 mV/dec, and long-term durability in 1.0 M KOH. Interestingly, anodic activation of the CoP@NF electrode led to the formation of a CoP/CoO core–shell structure. The CoP/CoO core–shell structure exhibited a low overpotential of 300 mV to reach 10 mA/cm2 for OER and a Tafel slope of 64 mV/dec was achieved with good durability in 1.0 M KOH. Furthermore, CoP@NF and CoP/CoO@NF electrodes were used to construct a water splitting electrolyzer, which can perform overall water splitting activity with a current density of 10 mA/cm2 under a voltage of 1.62 derived by a commercial solar cell.