Synergistic Effect of Carbon Nanofiber/Nanotube Composite Catalyst on Carbon Felt Electrode for High-Performance All-Vanadium Redox Flow Battery

Carbon nanofiber/nanotube (CNF/CNT) composite catalysts grown on carbon felt (CF), prepared from a simple way involving the thermal decomposition of acetylene gas over Ni catalysts, are studied as electrode materials in a vanadium redox flow battery. The electrode with the composite catalyst prepared at 700 °C (denoted as CNF/CNT-700) demonstrates the best electrocatalytic properties toward the V2+/V3+ and VO2+/VO2+ redox couples among the samples prepared at 500, 600, 700, and 800 °C. Moreover, this composite electrode in the full cell exhibits substantially improved discharge capacity and energy efficiency by ∼64% and by ∼25% at 40 mA·cm–2 and 100 mA·cm–2, respectively, compared to untreated CF electrode. This outstanding performance is due to the enhanced surface defect sites of exposed edge plane in CNF and a fast electron transfer rate of in-plane side wall of the CNT.