The Development of Pseudocapacitive Molybdenum Oxynitride Electrodes for Supercapacitors

Mo oxynitride was developed as pseudocapacitive electrode material for supercapacitors. A thin film Mo oxynitride was produced by first electrodeposition of Mo oxide on a Ti substrate followed by a low-temperature (400 oC) heat treatment in N2 environment. XPS analyses showed that the surface of the Mo oxynitride film was composed of a mixture of MoO3, MoO2 and less than 20 at.% Mo2N. However, the electrochemical behavior of the Mo oxynitride film was significantly different from that of Mo oxide but much similar to the behavior of pure Mo2N, a known pseudocapacitive material. The cycle life and stability of the Mo oxynitride were much improved over the Mo oxide. A two-electrode symmetric cell using the developed Mo oxynitride electrodes was demonstrated and showed high rate performance. An asymmetric cell using a Mo oxynitride as negative electrode and a carbon as positive electrode was also established and showed an extended voltage window and, thus, an increased energy density.