Nanostructured copper foam electrodes boost redox kinetics and suppress chemical side reactions of viologen anolytes in pH-neutral aqueous organic redox flow batteries

Abstract

Viologen derivatives hold great promise as anolytes in pH-neutral aqueous organic redox flow batteries (AORFBs). However, sluggish charge transfer kinetics at traditional carbon felt electrodes limit their performance. Herein, we report on the development of nanostructured copper foams as advanced electrocatalysts for the redox reaction of methyl viologen dichloride (MVCl₂) anolyte in pH-neutral AORFBs. By galvanostatic oxidation of commercial copper foams, porous nanostructures are grown on the framework of copper foams, which are then reduced to copper via a potentiostatic reduction approach. The obtained nanostructured copper foams are demonstrated to be highly active for the electrochemical reaction of MVCl₂, achieving a considerable decrease in area-specific resistance (ASR) and overpotential during both charge and discharge processes, thereby improving efficiency and capacity utilization in AORFB applications. The observed enhancements of catalytic activity are attributed to improved mass transport and favorable surface structure effects. Notably, we demonstrate for the first time that copper foam electrodes can suppress the chemical side reactions of viologen radicals, leading to significant improvements in cycle stability.