Enhancing oxygen evolution reaction activity of Co4N1-x film electrodes through nitrogen deficiency

Efficient and cheap oxygen evolution reaction (OER) catalysts play an important role in electrochemical energy storage and conversion devices. Transition metal nitrides (TMNs) show excellent OER performance mainly because of their unique electronic structure and high electrical conductivity. In this paper, we report a systematic study in order to explore the relationship between nitrogen deficiency and the OER activity of well-defined Co4N1-x (x > 0) thin film electrodes prepared by magnetron sputtering. The nitrogen deficiency is regulated by changing the Ar-N2 flow ratio and annealing at high temperatures. We find that by decreasing nitrogen content, the surface of Co4N1-x film is more prone to be oxidized with forming a surface Co–N–O layer. The electrochemical measurements imply that the OER activity can be improved by introducing nitrogen deficiency. The above results could be ascribed to better bulk electrical conductivity and a higher surface ratio of Co3+ in more nitrogen-deficient electrocatalysts. These results possibly provide a new and facile route to promote the OER activity by tuning the nitrogen deficiency in TMNs.