New Insight in the Charge Storage Mechanism of Vanadium Nitride as a Pseudocapacitve Electrode

More than 10 years after the initial studies on the pseudocapacitive performance of molybdenum nitride electrode in acid media ^1,2,a specific capacity of 1340F/g was reported for a vanadium nitride electrode in alkaline electrolyte^3,4. This impressive specific capacity and the high electronic conductivity of VN make it very attractive for energy storage application in electrochemical capacitor.  Accordingly, new synthesis methods such as high energy milling of Li₃N and V₂O₃⁵, xerogel^6–8, nanotubes coating^9,10 or TiN/VN core/shell nanostructure¹¹ have been developed.

On one hand, Choi et al. suggested that the pseudocapacitive behavior of VN can be explained by an equilibrium reaction involving the adsorption of OH^- ions and a redox reaction of an oxidized surface, formed by oxidation of VN. While Pande et al. confirmed the role of OH^- anions in the redox reaction¹², only few studies were aimed at getting an understanding of the charge storage mechanism. On the other hand, significant differences in specific capacity and cyclability have been reported in the literature ^6,8,10,13. These differences can be explained by the diversity in the synthesis methods, which often use oxide precursors leading to oxy-nitrides more than nitrides. However, most studies show a lack of understanding in the different charge storage mechanisms which could help determining the conditions that will insure a long cycle life when use in electrochemical capacitor.

This presentation will describe the synthesis of a model material VN with various thicknesses that will be followed by an electrochemical investigation assisted with in-situ and ex-situ characterizations. The major aim of this work is to get some insights in the different redox reactions involved in the charge storage mechanism and to determine the suitable conditions for utilization of VN as active electrode material.  Our results show a capacity retention of up to 96% after 10 000 cycles.

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