Investigation of local environments in Nafion-SiO2 composite membranes used in vanadium redox flow batteries

► Spectroscopic analysis of a Nafion-SiO2 composite membrane used in a vanadium redox flow battery. ► Bonding environment between Nafion sulfonic groups, silica particles and diffused vanadyl ion are indentified and analyzed. ► Explains the origin of performance degradation of the Nafion-SiO2 composite membrane in vanadium redox flow batteries.