Revealing the effects of oxygen defects on the electro-catalytic activity of nickel oxide

Low-cost transition metal oxides (TMO) has received extensive attention as new generation oxygen evolution reaction (OER) catalysts. In recent years, introducing oxygen defects via various strategies emerged as an efficient way to increase electro-catalytic activity of TMO. Despite many successful examples, the physical and chemical origin of such enhanced OER activity induced by oxygen defects is still not well understood. In this work, we systematically investigate the correlation between the concentration of oxygen vacancies and OER activity by using a NiO thin film model system grown by pulsed laser deposition. Oxygen vacancies are introduced into NiO thin films by Ar plasma treatments with different power (50 W, 100 W, and 150 W). The OER activities of NiO thin films are found to be significantly enhanced after plasma treatment. The improvement in electrochemical OER performance is attributed to the creation of oxygen defects, which lead to the strongly modified surface adsorption properties, as confirmed by X-ray photoelectron spectroscopy and contact angle measurements. Our results demonstrate that plasma treatment as a promising method for precisely tuning physical and chemical properties of TMO through oxygen defects engineering to obtain high performance electro-catalysts. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.