Preparation and Electrocatalytic Activity of a Cobalt Mixed Nitrogen 3D Carbon Nanostructure @ Carbon Felt toward an All-Vanadium Redox Flow Battery

All-vanadium redox flow batteries (VRFBs), with good operation flexibility and scalability, have been regarded as one of the most competitive substitutes for large-scale energy storage. However, because of the low electrochemical activities of traditional electrodes such as carbon felt and graphite felt, they will impede the interfacial charge transfer processes and decrease the efficiencies of VRFBs. In this work, Co-MOF (ZIF-67) was prepared as a precursor, and a cobalt mixed nitrogen 3D carbon nanostructure and carbon felt (Co-CN@CF) was prepared by chemical reaction and used in VRFBs as electrodes. With the unique structure and high efficiency catalyst on the carbon felt, the Co-CN@CF exhibited excellent electrochemical activity toward the VO2+/VO2+ redox couple in the VRFB, with an average cell voltage efficiency (VE) of 86% and an energy efficiency (EE) of 82% at 80 mA cm−2, which was increased by more than 10% compared with the traditional carbon felt. VRFBs with a Co-CN@CF electrode also showed much better long-term stability (over 1000 cycles) compared with the battery with a pristine CF electrode