Self-assembled heteropolyacid on nitrogen-enriched carbon nanofiber for vanadium flow batteries

Abstract

A novel polyoxometalate-based electrode was developed by incorporating phosphotungstic acid (PWA) in nylon-6,6 nanofiber, followed by carbonization. The developed PWA-carbon nanofiber (PWA-CNF) showed the characteristics of the dual-scale porosity of micro- and mesoporous substrate with surface area of around 684 m² g⁻¹. The compound exhibited excellent stability in vanadium electrolyte and battery cycling. Evaluation of electrocatalytic properties toward V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox couples indicated promising advantages in electron transfer kinetics and increasing energy efficiency, particularly for the VO²⁺/VO₂⁺ couple. Moreover, the developed electrode exhibited substantially improved energy efficiency (14% higher than that of pristine carbon felt) in the single cell vanadium redox flow battery. This outstanding performance was attributed to high surface area and abundant oxygen-containing linkages in the developed electrode.