Selective Fe(TEA) complexation on eco-friendly N-doped graphite felt for high-performance all-soluble all-iron flow batteries

All-soluble all-iron redox flow batteries (RFBs) are among the most promising energy storage technologies due to their low cost, dendrite-free operation, and decoupled capacity and power. In particular, the Fe(TEA) 3+/2+ redox couple has attracted significant attention owing to its appropriate redox potential, fast kinetics, and excellent reversibility. However, the instability of Fe(TEA) chelates, caused by the competitive adsorption of free TEA ligands, remains a major challenge that limits cycling stability and energy efficiency. Herein, we propose a green and efficient strategy to fabricate Nitrogen-doped graphite felt (N@GF) as the anode for the Fe(TEA)-based system and identify the optimal doping concentration. The abundant nitrogen-containing functional groups endow the felt with synergistic electronic modulation and surface coordination capabilities, enabling selective Fe(TEA) complexation while suppressing the undesired adsorption of free TEA ligands by occupying the limited active sites. This tailored interfacial regulation stabilizes Fe(TEA) complexes and enhances charge-transfer efficiency. As a result, the battery employing 5 %N@GF as the anode operates stably for over 950 deep charge–discharge cycles (near 260 h) at 80 mA cm −2 , exhibits significantly reduced polarization compared to pristine GF, achieves a peak energy efficiency above 78 % and a capacity utilization exceeding 83 %. This work offers an eco-friendly and effective material design strategy for improving both the energy efficiency and cycle life of all-soluble all-iron redox flow batteries.