Neutralized Fe–Cr redox flow battery with symmetric DTPA-Ligand electrolytes: mitigating cross-contamination and enhancing cycling stability

Iron-chromium redox flow batteries (ICRFBs) have emerged as a promising candidate for large-scale energy storage due to their cost-effectiveness, long cycle life, power-energy decoupling, and inherent safety. However, conventional ICRFBs using acidic FeCl₂ + CrCl₃ + HCl electrolytes face critical challenges, including severe material corrosion, active species cross-contamination, and parasitic hydrogen evolution reactions. To address these issues, we propose a neutral chelated Fe/Cr electrolyte system utilizing the identical ligand, 1,3-diaminopropanetetraacetic acid (DTPA), for both half-cells. This symmetric ligand design effectively suppresses metal ion crossover while enhancing redox kinetics, as confirmed by Fourier transform infrared (FTIR) and ultraviolet–visible (UV–vis) spectroscopy. The DTPA-complexed electrolytes exhibit high solubility (up to 1.0 mol/L) and environmental benignity, eliminating the need for corrosive acids. The resulting ICRFB demonstrates outstanding performance: a discharge energy density of 12.1 Wh/L, an average capacity decay rate of 0.13% per cycle over 300 cycles, and a coulombic efficiency approaching 100% at 50 mA/cm 2 , with a round-trip energy efficiency of 60%. These metrics are comparable to those of traditional acidic systems but with significantly reduced material degradation and operational risks. Our work validates the chelation strategy as a viable pathway to develop low-cost, long-lifetime ICRFBs, accelerating their practical deployment in grid-scale energy storage applications. Graphical