Fig. 3: Cell test for aqueous Fe redox flow battery.

a Full cell test of 0.67 M Fe-NTMPA₂ anolyte paired with 0.67 M Fe-CN catholyte at 20 mA·cm⁻² for 1000 cycles. Capacity and Coulombic efficiency (C.E.) plots vs. cycle number. b Comparison for the representative charge and discharge voltage profiles over 1000 cycles. c Capacity response vs. different current densities (5–100 mA·cm⁻²). d The charging/discharging voltage profiles for the different currents densities (5–100 mA·cm⁻²). Black arrow indicates voltage set-ups appeared for higher current densities. e Capacity response from asymmetric current densities for the charge and discharge, respectively. For asymmetric charge (black), the discharging current is fixed at 20 mA·cm⁻², while the charging current increases from 5–100 mA·cm⁻². Conversely, for asymmetric discharging (red), the charging current remains fixed at 20 mA·cm⁻² while the discharging current varies in the same range. f Cell discharge voltage (100% SOC) and discharging power density plots vs. current density. Discharging power densities are shown for the depth-of-discharge (DoD) at 0, 50 and 100%, respectively.