Hierarchically porous nickel–cobalt phosphide nanoneedle arrays loaded micro-carbon spheres as an advanced electrocatalyst for overall water splitting application

Due to the easy recyclability and pollution-free nature of hydrogen fuel, its highly purified production through electrochemical water splitting process has been attracting increasing attention. In this work, a hybrid of hierarchical porous nickel–cobalt phosphide nanoneedle arrays supported micro-carbon spheres was successfully synthesized and employed as robust bifunctional electrocatalyst for overall water splitting. The optimized Ni₁Co₃–P@CSs displayed catalytic activity with a low overpotential (η) of 57 mV at 10 mA cm⁻² for hydrogen evolution and a η of 330 mV at 20 mA cm⁻² for oxygen evolution, along with good stability after testing for 30 h. The water splitting cell of the Ni₁Co₃–P@CSs delivered smaller cell voltage at a current density of 50 mA cm⁻² and much better durability than a similar device based on RuO₂/C and Pt/C. The enhanced performance was assumed to the unique hierarchical three-dimensional urchin nanostructure of bimetallic phosphide nanoneedles, which resulted in the synergetic effects to modulate electronic properties and electroactive surface area. These improved the reactant's intermediates adsorption energy, number of exposed active sites, and various shortened channels for charge transfer and reactant/electrolyte diffusion. Our finding offers an attractive electrocatalyst with low cost and high catalytic activity for efficient water electrolysis.