Gluconic acid additives for ultra-mild and long-life acidic zinc‑iron flow batteries: Hydrolysis inhibition and cross-blocking

As clean and environmentally friendly renewable energy gradually replaces traditional fossil energy, which is highly polluting and non-renewable, flow batteries serve as scalable storage systems that balance energy input and output. Zinc–iron redox flow batteries (ZIRFBs) combine low cost with strong prospects for large-scale deployment. Acidic ZIRFBs benefit from higher Fe solubility and non-toxic electrolytes. However, environmental and operational challenges persist, including electrolyte cross-permeation, component corrosion, and the requirement for strong acids (leading to low pH) to inhibit Fe 3+ hydrolysis. Theoretical calculations indicate that environmentally friendly gluconic acid (GA), with its strong affinity for Fe 3+ , can prevent hydrolysis and transmembrane crossover, serving as an alternative to strong acids. Unlike previous acidic ZIRFBs with pH < 1 or even pH < 0, introducing GA into the cathode electrolyte facilitated the battery running stably under milder pH = 3–4 conditions for 133 cycles, with a running time of more than 125 h. The life of this battery could be extended to 215 % of the original one. The addition of GA is cost-effective and environmentally friendly, significantly enhancing battery performance. Crucially, it eliminates the need for traditional acidic ZIRFBs to operate in highly corrosive media, thereby creating new opportunities for their development.