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 catalysis, are studied as electrode materials in a vanadium redox flow battery. The electrode with the composite catalyst prepared at 700 degrees 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 degrees C. Moreover, this composite electrode in the full cell exhibits substantially improved discharge capacity and energy efficiency by similar to 64% and by similar to 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.