Modulating the active sites of nickel phosphorous by pulse-reverse electrodeposition for improving electrochemical water splitting

This study introduces how pulse-reverse electrodeposition (PRED) affects the properties of nickel phosphorus (NiP) films and improves the performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The impact of electrochemical parameters in PRED on HER and OER activities is explored, indicating that changes in two activities of PRED dissolution step are opposite. An increase in dissolution amount during PRED enhances OER while decreasing HER activity. The Mott-Schottky analysis reveals that improvement in HER by adopting PRED is due to an increase in the reactivity of active sites. On the contrary, OER is enhanced due to the number of active sites on the surface of NiP films increased by the excess dissolution during PRED. Surface analyses suggest that the opposite response of HER and OER is caused by different factors; uniform formation of NiP governs HER activity while removability of phosphate determines the exposure of OER-active Ni oxide phases.