Low-Cost and Sustainable All-Iron Redox Flow Battery Energy Storage

Redox flow batteries are promising grid-scale energy storage devices as they are able to decouple battery power and capacity as either property can be independently scaled. Herein a novel all aqueous all-iron redox flow battery was developed. Iron was selected because of its low cost and due to its low-toxicity, the all-iron RFB is likely to have minimal detrimental effect on the environment. Using ferrocyanide as the redox active material in the positive electrolyte and iron triethanolamine in the negative electrolyte a columbic efficiency of >80% was achieved. A redox flow battery using ferrocyanide in the positive electrolyte and iron triisopropanolamine in the negative electrolyte was also developed which achieved >81% columbic efficiency. Capacity loss was seen over 25 cycles in all battery experiments, this was found to be due to the crossover of the negative redox active material over the membrane. Both Nafion-117 and BTMA membranes were evaluated to attempt mitigation of crossover. Further scale up of the design is hindered by limiting solubility of the negative electrolyte redox active material, however, future work into improving the solubility by adding additives to the electrolytes may improve efficiency. Additives may also improve the stability of the redox active material during the charging and discharging process and avoid crossover of species