Vanadium redox flow batteries: Exploring stability with in-situ electrochemically produced nitric acid pretreated enhanced graphene-coated pencil graphite electrodes

Abstract

In this investigation, we explore diverse techniques for pre-treating pencil graphite electrodes (PGE) to optimize their performance in vanadium redox flow batteries (VRFBs). Our objective is to provide researchers with two straightforward yet effective methods for preparing the PGE surface for reduced graphene oxide (RGO) deposition. The graphene deposition process employs cyclic voltammetry (CV) in a 5 M HNO3 (Nitric Acid) solution. Introducing graphene oxide (GO) into the system before CV enables a more substantial conversion of graphite to RGO, enhancing the electrode’s performance and stability under VRFB working conditions, surpassing the efficacy of electrodes pretreated using a basic water washing method. Comparison results highlight the superiority of the HNO3 pre-treated PGE, achieving a peak reduction value of −0.73 A/cm² compared to −0.46 A/cm² for the Water PGE. The GO coated Pencil Graphite Electrode (GOPGE-2 days) exhibits a comparable −0.72 A/cm², signifying an almost 60 % improvement in performance characteristics over the Water PGE. Additionally, characterization using LiClO4 demonstrates a remarkable 83 % increase in the charge-carrying capacity of the electrodes, extending to anodic and cathodic current density as well as redox capacity. Cyclic stability assessments in VOSO4 reveal a remarkable 274 % enhancement in charge-carrying capacity. This paper underscores the significance of a streamlined, one-step pre-treatment method, not only for optimal laboratory experimentation but also for superior performance in VRFBs and potentially other battery chemistries utilizing Graphene-Coated Pencil Graphite Electrodes (GPGE) as electrodes.