Due to the advantages of low cost and good stability, iron-chromium flow batteries (ICRFBs) have been widely used in energy storage development. However, issues such as poor Cr³⁺/Cr²⁺ activity still need to be addressed urgently. To improve the slow reaction kinetics of the Cr redox pairs, we propose a method of preparing nano bismuth catalyst modified carbon cloth electrode (TBCC) based on intrinsic defect assisted catalyst attachment. By utilizing the carbon thermal reaction to firmly adhere the bismuth catalyst to the electrode surface, the electrochemical performance and reaction kinetics of the TBCC electrode are significantly improved. It proved that the polarization of the battery assembled with the modified electrode was reduced, and the energy efficiency was significantly improved compared to the original carbon cloth electrode. Charging and discharging tests were conducted at a high current density of 140 mA/cm², achieving average energy efficiency of up to 82.9%, and even achieving ultra-high energy efficiency of 88.95% at the current density of 80 mA/cm². This provides broad prospects for the commercialization of ICRFBs.