Atomic iron on porous graphene films for catalyzing the VO²⁺/VO₂⁺ redox couple in vanadium redox flow batteries

The electrocatalytic activity of the electrode materials towards the vanadium redox couples is a major factor in determining the performance of vanadium redox flow batteries (VRFBs). Herein, we report the employment of iron single atoms supported on a monolithic porous graphene film (Fe₁-PGF) as electrodes for catalyzing the VO²⁺/VO₂⁺ redox couple. The high intrinsic catalytic activity of the atomic Fe sites, the superior surface hydrophilicity, along with the enhanced mass transfer efficiency and exposure of active sites benefited from the porous structure, endow the Fe₁-PGF electrode with improved electrochemical performance compared to metal-free PGF counterpart and commercial graphite felt electrode. Consequently, the single-cell battery assembled with Fe₁-PGF exhibits a high voltage efficiency (77.96%) and energy efficiency (70.27%) at the current density of 60 mA cm⁻² as well as lower overpotential and higher rate capability compared to the control samples. This study demonstrates that single atom catalysts (SACs) are promising candidates for catalyzing the vanadium redox couples in VRFBs and motivates the exploration of SACs in other types of redox flow batteries.