Performance evaluation of zero-gap vanadium redox flow battery using composite electrode consisting of graphite and buckypaper

A composite electrode consisting of graphite felt and buckypaper (GF-BP) was developed. GF-BP is used for fabricating a zero-gap structure for all-vanadium redox flow battery (VRFB), which minimizes the distance between two electrodes. With this zero-gap structure, performance of VRFBs is improved, while its flexible design becomes possible. GF and BP are used as base and reinforced materials to combine the proper porous structure of GF and the excellent redox reactivity of vanadium ions promoted by BP. The properties of GF-BP electrode and its applicability to VRFB were evaluated electrochemically and spectroscopically. As a result, its total pore volume and double layer capacitance (0.200 cm³ g⁻¹, 1,547.95 mF g⁻¹) are higher than those of pristine GF electrode (0.040 cm³ g⁻¹, 94.59 mF g⁻¹). When the optimized GF-BP electrode and zero-gap structure are adopted, performance of the zero-gap VRFB using the optimized GF-BP electrode is excellent with energy efficiency (EE) of 60% and discharge capacity of 14.6 Ah L⁻¹ at 160 mA cm⁻², while the EE (67.8%) is 20% better than that using pristine GF electrode (72.4%) at 120 mA cm⁻². The significant increase in actual active sites of the optimized GF-BP electrode is the main reason for the performance enhancement of the zero-gap VRFB using this.