Exploration of reduced graphene oxide microparticles as electrocatalytic materials in vanadium redox flow batteries

Abstract

Augmenting reaction rates on porous carbon electrodes is critical for reducing the cost of all-vanadium redox flow batteries (VRFBs). To this end, reduced graphene oxide (rGO) based carbons hold promise, demonstrating high specific surface area, chemomechanical stability, and electrochemical activity. While initial efforts have shown that rGOs can enhance VRFB performance, the range of unique processing conditions leads to a collection of materials with disparate elemental composition and porous structure, thus obscuring performance-determining characteristics behind redox reactions and frustrating the development of generalizable design principles. Here, we generate rGO electrocatalysts of nearly identical chemical composition but different textures (i.e., surface area and pore structure) by varying the drying step in the graphene synthesis (i.e., vacuum-drying vs. carbon dioxide critical point drying). We apply spectroscopic and electrochemical techniques on the synthesized rGOs, observing a three-fold increase in BET surface area using critical point drying. We subsequently decorate carbon felt electrodes – both pristine and thermally activated – with rGO microparticles via a flow deposition procedure, and evaluate their performance and durability in a VRFB cell. The synthesis approach and findings described in this work inform and complement efforts to advance the material science and engineering of rGO electrocatalysts.