Synergistic catalytic effects of oxygen and nitrogen functional groups on active carbon electrodes for all-vanadium redox flow batteries

Abstract

All-vanadium redox flow batteries (VRFBs) have attracted a great deal of attention as large-scale energy storage devices. However, VRFBs suffer from unfavorable energy efficiency, originating from large polarization effects that influence the redox reaction of the vanadium ions. Although the catalytic effects of the oxygen and nitrogen functional groups in carbon-based electrodes on the redox reactions of the vanadium ion have been documented in several reports, the specific catalytic effects are not understood due to the lack of systematic studies. In this study, pyroproteins having dual functionality (i.e., nitrogen and oxygen functional groups) were coated onto the surface of conventional carbon felts (the composite is hereafter termed P-CFS) and their catalytic effects on the V2+/V3+ redox reaction were characterized and compared with those of carbon felts possessing a coating layer with only oxygen or nitrogen functional groups. The synergistic catalytic effects of nitrogen and oxygen in the pyridonic structure of the P-CFS led to the lowest anodic and cathodic peak potential separation of ∼0.17 V among all the evaluated samples, having various chemical configurations with oxygen or nitrogen only. This study provides insight for the design of carbon-based active electrode materials in VRFBs and their feasibility was demonstrated in VRFB full-cells.