Hierarchically Porous Urchin-Like Ni2P Superstructures Supported on Nickel Foam as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

The development of high-performance nonprecious electrocatalysts with both H-2 and O-2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize three-dimensional hierarchically porous urchin-like Ni2P microsphere superstructures anchored on nickel foam (Ni2P/Ni/NF) as bifunctional electrocatalysts for overall water splitting. The Ni2P/Ni/NF catalysts were prepared by template-free electro-deposition of porous nickel microspheres on nickel foam followed by phosphidation. The hierarchically macroporous E (V) superstructures with 3D configuration can reduce ion transport resistance and facilitate the diffusion of gaseous products (H-2 and O-2). The optimal Ni2P/Ni/NF exhibited remarkable catalytic performance and outstanding stability for both the HER and OER in alkaline electrolyte (1.0 M KOH). For the HER, Ni2P/Ni/NF afforded a current density of 10 mA cm(-2) at a low overpotential of only -98 mV. When it served as an OER electrocatalyst, Ni2P/Ni/NF was partially oxidized to nickel oxides/hydroxides/oxyhydroxides (mainly NiO) on the catalyst surface and exhibited excellent OER activity with small overpotentials of 200 and 268 mV to reach 10 and 100 mA cm(-2), respectively. Furthermore, when Ni2P/Ni/NF was employed as the electrocatalyst for both the cathode and anode, a water splitting electrolyzer was able to reach 10 and 100 mA cm(-2) in 1.0 M KOH at cell voltages of 1.49 and 1.68 V, respectively, together with robust durability. Various characterization techniques and controlled experiments indicated that the superior activity and strong stability of Ni2P/Ni/NF for overall water splitting originated from its electrochemically active constituents, 3D interconnected porosity, and high conductivity.