Oxygen-Vacancy-Rich Cubic CeO₂ Nanowires as Catalysts for Vanadium Redox Flow Batteries

Abstract

A novel, low-cost, and powerful cerium-oxide nanowire (CeO2NW) electrode decorated with graphite felt (GF) through a one-step hydrothermal method was proposed in this study. Subsequently, hydrogen annealing was conducted to create defective-hydrogen-annealed CeO2NWs decorated with GF (H–CeO2NWs–GF) for use in vanadium redox flow batteries (VRFBs). The electrochemical results show that the H–CeO2NWs–GF reveals excellent electrocatalytic effects toward the VO2+/VO2+ redox process in VRFBs at the positive electrode to facilitate the electrochemical kinetics of the VRFBs. The VRFBs using different electrode materials were compared with a VRFB using H–CeO2NWs–GF. The results revealed that the VRFB using H–CeO2NWs–GF exhibits the highest voltage efficiency of 90.4% at a current density of 40 mA cm–2, which is significantly higher than those using pristine GF (81.1%) and a CeO2NW electrode decorated with GF (88.4%). The significant improvement in the electrochemical performance of H–CeO2NWs–GF might be mostly ascribed to the defect-rich H–CeO2NWs on the GF surface, which acts as active sites and reduces the electrochemical polarization of the redox reaction. Moreover, the one-dimensional nature of H–CeO2NWs is favorable for the charge-transfer process and improves the accessibility, thus improving the electrode performance.