The effect of adding Bi³⁺ on the performance of a newly developed iron-copper redox flow battery

In this paper, we propose a new, abundant, cost-effective, non-toxic, and environmentally benign iron-copper redox flow battery (Fe/Cu RFB), which employs Fe²⁺/Fe³⁺ and Cu⁺/Cu⁰ as the positive and negative electrolytes, respectively. The effect of graphite felt (GF) electrode modification and addition of Bi³⁺ into the electrolytes on the performance of the Fe/Cu RFB were investigated. It was found that the cell containing Bi³⁺ in the electrolytes revealed higher coulombic efficiency (89.18%) and energy efficiency (35.24%) than the cell without Bi³⁺ (CE = 84.10% and EE = 34.43%) at 20 mA cm^-2. This is because after adding Bi³⁺, Cu metal precipitation was not observed on the electrode surface, which indicates that the deposition process was potentially reversible on the electrode material, thus leading to enhanced performance of the battery. Furthermore, the efficiencies of the battery are stable over 10 cycles, which demonstrates that Fe/Cu RFB exhibits good stability on the microwave heat treated GF plus one layer microwave heat treated carbon paper (HT-GF + HT-CP) electrode after adding Bi³⁺ into the electrolytes.