Benefiting from the uniform zinc plating and materials optimization, the areal capacity of zinc-based flow batteries has been remarkably improved, e.g., 435 mAh cm -2 for a single alkaline zinc-iron flow battery, 240 mAh cm -2 for an alkaline zinc-iron flow battery cell stack , 240 mAh cm -2 for a single zinc-iodine flow battery .
The history of zinc-based flow batteries is longer than that of the vanadium flow battery but has only a handful of demonstration systems. The currently available demo and application for zinc-based flow batteries are zinc-bromine flow batteries, alkaline zinc-iron flow batteries, and alkaline zinc-nickel flow batteries.
The ultralow cost neutral Zn/Fe RFB shows great potential for large scale energy storage. Zinc-based flow batteries have attracted tremendous attention owing to their outstanding advantages of high theoretical gravimetric capacity, low electrochemical potential, rich abundance, and low cost of metallic zinc.
Authors to whom correspondence should be addressed. Zinc–iron redox flow batteries (ZIRFBs) possess intrinsic safety and stability and have been the research focus of electrochemical energy storage technology due to their low electrolyte cost.
Among which, zinc-iron (Zn/Fe) flow batteries show great promise for grid-scale energy storage. However, they still face challenges associated with the corrosive and environmental pollution of acid and alkaline electrolytes, hydrolysis reactions of iron species, poor reversibility and stability of Zn/Zn 2+ redox couple.
Neutral zinc–iron flow batteries (ZIFBs) remain attractive due to features of low cost, abundant reserves, and mild operating medium. However, the ZIFBs based on Fe (CN) 63– /Fe (CN) 64– catholyte suffer from Zn 2 Fe (CN) 6 precipitation due to the Zn 2+ crossover from the anolyte.