Enhanced electrochemical performance of CNx/Co3O4 multilayer electrodes prepared by a hybrid non-thermal plasma/sol-gel method for energy storage applications

In this work, we report a direct study of the enhanced electrochemical performance of CNx/Co3O4 nano-composite multilayer electrodes which demonstrate great promise as valuable electrode materials for energy storage applications. CNx/Co3O4 electrodes were prepared by a novel hybrid non-thermal plasma/sol-gel deposition technique combining dielectric barrier discharge plasma with a C2H4/N2 gas mixture and sol-gel spin-coating methods. The results indicated that the rough and porous CNx (a-C:H:N) layer consisting of various N species (especially graphitic, pyrrolic and pyridinic N) generated by nitrogen plasma improves electrical conductivity and facilitates ion diffusion in the a-C:H:N/Co3O4 electrode. Furthermore, the synergistic effects arising from interleaving redox active Co3O4 interlayers between CNx layers involving numerous nano-pores led to the remarkable electrochemical activity of the composite electrodes. It was found that the CNx layers noticeably overcame the poor cyclic stability of Co3O4 by protecting it from dissolution in the electrolyte and these composite electrodes remained significantly stable after a very long charge-discharge time. The areal capacitance of 203.4 mF/cm2 at 3 mA/cm2 of the a-C:H:N/Co3O4 multilayer electrode enhanced by 9.7 % of the initial capacitance after 450 CD cycles and stayed stable afterward. This unique hybrid architecture showed intriguing electrochemical properties including rapid redox reactions, wide potential window of 2.73 V, high surface activity and favorable cyclic stability as well as proper reversibility of a-C:H:N/Co3O4 multilayer electrode which makes it a valuable low-cost candidate for electrochemical applications such as energy storage electrodes and biosensors.