Surface engineered carbon felt toward highly reversible Fe anode for all-iron flow batteries

Low-cost all-iron flow batteries recently promise a great alternative to conventional flow battery technologies for large-scale energy storage. However, inferior Fe deposition/dissolution reversibility at anode largely impedes further advance of all-iron flow battery in application. Here, we report a surface engineered carbon felt with abundant carbon defects, which realizes highly reversible Fe deposition/dissolution for all-iron flow batteries. By introducing nano-scale pores on carbon fibers via a multistep electrode treatment approach, the modified carbon felt features a high degree of defects and proves effective in promoting Fe/Fe2+ kinetics and improving Fe nucleation and growth morphology, which is beneficial for both uniform Fe deposition and complete Fe dissolution rendering a substantially enhanced reversibility for Fe anode. Theoretical calculations further ascribe the enhanced Fe/Fe2+ reversibility to strong adsorption and intensified hybridization between Fe2+ and carbon defects, while all-iron flow cell tests adopting the modified carbon felt finally demonstrates a high power density of 80 mW cm-2 as well as stable charge-discharge operation over 250 cycles with a Coulombic efficiency of 99 %, which highlights the importance of electrode design in developing stable Fe anode for use in highperformance all-iron flow batteries.