Nitrogen Engineering on 3D Dandelion-Flower-Like CoS2 for High-Performance Overall Water Splitting.

Searching for highly efficient and stable bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable for the practical application of water electrolysis under alkaline electrolyte. Although electrocatalysts based on transition metal sulfides (TMSs) are widely studied as efficient (pre)catalysts toward OER under alkaline media, their HER performances are far less than the state-of-the-art Pt catalyst. Herein, the synthesis of nitrogen doped 3D dandelion-flower-like CoS2 architecture directly grown on Ni foam (N-CoS2 /NF) is reported that possesses outstanding HER activity and durability, with an overpotential of 28 mV to obtain the current density of 10 mA cm-2 , exceeding almost all the documented TMS-based electrocatalysts. Density functional theory calculations and experimental results reveal that the d-band center of CoS2 could be efficiently tailored by N doping, resulting in optimized adsorption free energies of hydrogen (ΔG*H ) and water , which can accelerate the HER process in alkaline electrolyte. Besides, the resulting N-CoS2 /NF also displays excellent performance for OER, making it a high-performance bifunctional electrocatalyst toward overall water splitting, with a cell voltage of 1.50 V to achieve 10 mA cm-2 .