Anomalous in situ Activation of Carbon-Supported NiP Nanoparticles for Oxygen Evolving Electrocatalysis in Alkaline Media.

Electrochemical water splitting is one of the most promising systems by which to store energy produced from sustainable sources, such as solar and wind energy. Designing robust and stable electrocatalysts is urgently needed because of the relatively sluggish kinetics of the anodic reaction, i.e. the oxygen evolution reaction (OER). In this study, we investigate the anomalous in situ activation behaviour of carbon-supported NiP nanoparticles (NiP/C) during OER catalysis in alkaline media. The activated NiP/C shows an exceptionally high activity and stability under OER conditions in which the overpotential needed to achieve 10 mA cm was reduced from approximately 350 mV to approximately 300 mV after 8,000 cyclic voltammetric scans. In situ and ex situ characterizations indicate that the activity enhancement of NiP catalysts is due to a favourable phase transformation of the Ni centre to β-NiOOH, including increases in the active area induced by structural deformation under the OER conditions. These findings provide new insights towards designing transition metal/phosphide-based materials for an efficient water splitting catalyst.