N2 plasma-activated NiO nanosheet arrays with enhanced water splitting performance.

NiO is a promising electrocatalyst for electrochemical energy conversion due to its rich redox sites, low cost, and ease of synthesis. However, hindered by low electrical conductivity and limited electrocatalytic active sites, bare NiO usually exhibits poor electrochemical performance towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we develop an N2 plasma activation approach to simultaneously improve both HER and OER activity of NiO by constructing heterostructured Ni/Ni3N/NiO nanosheet arrays on Ni foam. The optimized N2 plasma-activated NiO nanosheet arrays for HER and OER (denoted as P-NiO-HER and P-NiO-OER) only need an overpotential of 46 and 294 mV, respectively, to achieve 10 mA cm-2. Moreover, for overall water splitting, the assembled electrolysis cell with P-NiO-HER and P-NiO-OER as the cathode and anode, respectively, only requires a small voltage of 1.57 V to deliver 10 mA cm-2. Remarkably, the plasma-activated NiO nanosheet arrays exhibit excellent stability for up to 50 h for HER, OER, and full water electrolysis. The strategy developed here to activate the electrocatalytic performance of metal oxides opens a new door for water splitting.