A Stable and High-Capacity Redox Targeting-Based Electrolyte for Aqueous Flow Batteries

Summary Aqueous redox flow batteries (ARFBs) have received considerable attention for large-scale energy storage because of their salient feature of decoupled energy storage and power generation; however, their deployment is critically constrained by low energy density and relatively high cost. Here, we report a low-cost, high-capacity ferrocyanide/ferricyanide ([Fe(CN)6]4−/3−)-based electrolyte system via the redox targeting reactions with Prussian blue (Fe4[Fe(CN)6]3, PB). The [Fe(CN)6]4−/3−-PB electrolyte exhibits an excellent capacity retention of 99.991% per cycle and an unprecedented capacity of 61.6 Ah L−1. A Zn/[Fe(CN)6]3−-PB flow cell with energy density of 97.4 Wh L−1 at 20 mA cm−2 and a [Fe(CN)6]4−/3−/Br− flow cell with PB as the sole solid material were demonstrated. The battery chemistry and associated redox targeting reactions were scrutinized with computational, neutron diffraction, and spectroscopic studies. The ultra-stable and capacity-intensive [Fe(CN)6]4−/3−-PB electrolyte system presents an intriguing paradigm for advanced cost-effective large-scale energy storage.