High Performance Metal Oxide–Reduced Graphene Oxide Electrocatalyst for All Vanadium Redox Flow Batteries

Abstract

Vanadium redox flow battery (VRFB) is one of the most favorable technologies for large-scale energy storage applications owing to its numerous gorgeous features, such as flexible design, high safety, and long cycle life. In this study, metal oxide (MOx)–reduced graphene oxide (rGO) nanohybrid was successfully synthesized via a facile hydrothermal route followed by annealing and employed as an electrocatalyst to modify the graphite felt (GF) electrode material for all-vanadium redox flow batteries (VRFBs) application. The as-synthesized MOx–rGO nanohybrid reveals good electrocatalytic reversibility and higher anodic and cathodic peak current density for V3+/V2+ and VO2 +/VO2+ redox couples compared with those of rGO and MOx samples. The voltage efficiency of the VRFB using MOx–rGO nanohybrid reaches 84% at 80 mA cm−2, which is 4% and 13% higher than the VRFBs using the rGO-loaded GF electrode and the pristine GF electrode, respectively. It still shows the voltage efficiencies of 76% and 70% at relatively high current densities of 120 mA cm−2 and 140 mA cm−2, respectively, but other samples have no effective discharge. This improvement is accredited to the uniform distribution of MOx nanoparticles on the rGO surfaces, avoiding the restacking of the rGO sheets and conquering nanoparticles aggregation, which might boost the effective active surface area and improve mass transport at the electrode-electrolyte interfaces. Besides, the existence of oxygen vacancies on MOx, the high electrical conductivity of rGO, and the high content of oxygen functional groups play the prodigious roles to facilitate the reversibility of vanadium ions redox reactions.