Hierarchical CoP/Ni 5 P 4 /CoP microsheet arrays as a robust pH-universal electrocatalyst for efficient hydrogen generation

Highly active catalysts composed of earth-abundant materials, performing as efficiently as Pt catalysts, are crucial for sustainable hydrogen production through water splitting. However, most efficient catalysts consist of nanostructures made via complex synthetic methods, making scale-up quite challenging. Here we report an effective strategy for developing a very active and durable pH-universal electrocatalyst for the hydrogen evolution reaction (HER). This catalyst is constructed using a sandwich-like structure, where hierarchical cobalt phosphide (CoP) nanoparticles serve as thin skins covering both sides of nickel phosphide (Ni5P4) nanosheet arrays, forming self-supported sandwich-like CoP/Ni5P4/CoP microsheet arrays with lots of mesopores and macropores. The as-prepared electrocatalyst requires an overpotential of only 33 mV to achieve a benchmark of 10 mA cm−2, with a very large exchange current density and high turnover frequencies (TOFs) in acid media, superior to most electrocatalysts made of metal phosphides, well-known MoS2 and WS2 catalysts, and it performs comparably to state-of-the-art Pt catalysts. In particular, this electrocatalyst shows impressive operational stability at an extremely large current density of 1 A cm−2, indicating its possible application toward large-scale water electrolysis. Additionally, this electrocatalyst is very active in alkaline electrolyte (71 mV at 10 mA cm−2), which demonstrates its pH universality as a HER catalyst with outstanding catalytic activity. This simple strategy does not involve any solvothermal and hydrothermal processes, paving a new avenue toward the design of robust non-noble electrocatalysts for hydrogen production, aimed at commercial water electrolysis.