The effects of design parameters on the charge-discharge performance of iron-chromium redox flow batteries

•The effects of design parameters on the ICRFB performance are investigated.•The energy efficiency of the present ICRFB reaches 80.5% at 480 mA cm−2.•The power density reaches 1077 and 694 mW cm−2 at 65 and 25 °C, respectively.•The dominant loss of ICRFBs operating at 25 and 65 °C is the ohmic loss.

The objective of this work is to understand and identify key design parameters that influence the battery performance of iron-chromium redox flow batteries (ICRFBs). The investigated parameters include the membrane thickness, electrode compression ratio, electrode pretreatment and catalyst loading. Results show that: (i) with a thin NR-211 membrane and a high electrode compression ratio of 62.5%, the operating current density of the ICRFB can reach as high as 480 mA cm−2 at an energy efficiency of higher than 80%; (ii) the bismuth catalyst loading has insignificant effect on the battery performance in the range of 0.52-10.45 mg cm−2; (iii) the moderately oxidative thermal pretreatment of the electrode improves the energy efficiency compared to the as-received electrode while the electrode prepared with a harsh pretreatment deteriorates the battery performance; and (iv) for the present ICRFBs operating at both 25 °C and 65 °C, the dominant loss is identified to be ohmic loss rather than kinetics loss.