Nitride Supercapacitors: Contribution of Surface Oxide to Charge Storage

With the growing interest in alternative energy sources and the cognitive recognition of the benefits of green energy, there is clearly a pressing need for the development of sustainable and clean energy storage systems (1-3). The scope of electrochemical charge storage devices extends beyond mobile devices into large scale grid level charge storage(4). Load leveling and power quality management applications would be perfectly served by storage of excess charge generated from renewable energy sources in supercapacitors. Supercapacitors are unique electrochemical energy storage devices with high power density and long cyclability. State of the art materials such as high surface area carbons, hydrated ruthenium oxide (5-7) and MnO₂ (3, 8-10) suffer from either poor capacity or rate capability.

 We have previously demonstrated excellent charge storage behavior of nanoparticulate vanadium nitride on account of the surface reactions occurring on the surface of the oxide exo-shell. However, there is limited understanding into the exact nature of the charge storage behavior and its dependence on the synthesis and processing route. In the present work, we explore the effect of materials processing and electrode properties on the capacitive charge storage in VN based supercapacitors. Dependence of capacitance on particle and electrode properties are evaluated and reported here-in. Tailoring the particle size, crystallinity and porosity are of paramount importance to achieve high capacitances at high scan rates. To gain a fundamental understanding into the charge storage mechanism of nitride materials shown in Figure 1, slurries of the nitride were cast on nickel current collectors and characterized used various materials and electrochemical characterization techniques including X-ray photo-electron spectroscopy (XPS), cyclic voltammetry and electrochemical impedance spectroscopy. Results of these studies will be presented and discussed.

References

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Figure 1 caption: TEM image of nanoparticulate VN evaluated extensively using various electrochemical methods