Fig. 4: Flow battery performance of Zn-I FBs with ZMC-IMS membranes.

a CE and EE of Zn-I FB cell (5 ml of 6 M KI + 3 M ZnBr₂ | ZMC-IMS membrane | 5 ml of 3 M ZnBr₂ + 3 M KCl, 4 cm² membrane area) under 10, 20, 30 and 50 mA cm⁻² at 50% SOC. The inset shows the prototype of Zn-I FBs flow-cell stack (5 ml of electrolytes, 4 cm² membrane area, for illustration). b Galvanostatic cycling of Zn-I FBs cell with ZMC-IMS and pristine N117 membranes. c Long cycling of high-energy Zn-I FB flow-cell (5 mL of 6 M KI + 3 M ZnBr₂ | ZMC-IMS membrane | 5 mL of 3 M ZnBr₂ + 3 M KCl, 4 cm² membrane area) at 30 mA cm⁻² with the designated discharge duration (energy to power ratio, E/P) of 2.23 h. The insets show the representative voltage profiles over cycling, CE, and volumetric/areal capacity during 500 cycles (2050 h). d Self-discharging performance of Zn-I FB flow-cell after charging to 50% SOC for static flowing 24 h and 168 h. e Comparison of Zn-based FBs in terms of CE, working time, and areal/volumetric capacity, where the symbol size and color scale show the corresponding areal capacity and volumetric capacity, respectively. All battery tests were charged from 0% to either 20% or 50% SOC.