Enhancing Vanadium Redox Flow Battery Negative Electrodes with Vanadium Nitride Nanorod-Assembled Microspheres Modified Graphite Felt

Abstract

The slow kinetics of carbon-based negative electrodes limit the widespread engineering applications of vanadium redox flow batteries (VRFBs). In this study, we developed a method to prepare vanadium nitride (VN) nanorod-assembled microspheres uniformly loaded on graphite felt (GF) fibers. Vanadium dioxide (VO₂) nanorod microspheres were first in-situ grown on GF fibers and then converted into VN microspheres through a nitridation process. The resulting VN@GF electrode demonstrated high performance as a negative electrode for VRFBs. Electrochemical and single-cell performance tests confirmed the significant catalytic effect of VN microspheres on the V³⁺/V²⁺ redox pair. At a current density of 150 mA cm^-2, the VN@GF electrode improved voltage efficiency (VE) and energy efficiency (EE) by 19% and 18%, respectively, compared to the GF electrode. Additionally, after 300 charge-discharge cycles at 200 mA cm^-2, the battery retained 75% of its discharge capacity, with stable EE and VE. The enhanced performance is attributed to the VN microspheres on the electrode surface, which increase the contact area between the electrode and the electrolyte, while also improving the adsorption of reactive ions, thereby enhancing the electrode's electrochemical properties. Moreover, the VN@GF electrode demonstrates excellent stability and emerge as a promising candidate for VRFB negative electrode application.