Bifunctionality and Mechanism of Electrodeposited Nickel-Phosphorous Films for Efficient Overall Water Splitting

Efficient, stable, and low-cost electrocatalysts are crucial for realizing large-scale water splitting. Herein, we report that electrodeposited nickel-phosphorous (Ni-P) films can act as efficient bifunctional electrocatalysts for overall water splitting. The as-prepared Ni-P films exhibit remarkable catalytic performance for both H-2 and O-2 evolution reactions (HER and OER) in alkaline media, achieving a current density of 10 mAcm(-2) at overpotentials of -93 mV for HER and 344 mV for OER with Tafel slopes of 43 and 49 mVdec(-1), respectively, rivaling the performance of Pt and IrO2. Various techniques were employed to probe the composition and morphology of the Ni-P films prior to and post catalysis, revealing the major composition of the as-prepared and post-HER films as metallic nickel and nickel phosphide, which partially transform to nickel oxides during OER. It was also found that the catalytic rate of OER catalyzed by Ni-P was first order in the activity of the hydroxide anion.