A High Efficiency Iron-Chloride Redox Flow Battery for Large-Scale Energy Storage

We report advances on a novel membrane-based iron-chloride redox flow rechargeable battery that is based on inexpensive, earth-abundant, and eco-friendly materials. The development and large-scale commercialization of such an iron-chloride flow battery technology has been hindered hitherto by low charging efficiency resulting from parasitic hydrogen evolution at the negative electrode and high overpotential losses. We have demonstrated a high charging efficiency of 97% by maintaining the negative electrolyte at a pH value of 2 and by using indium chloride as an electrolyte additive. The high charging efficiency of the negative electrode was found to be stable over at least 50 cycles. Further, we have demonstrated that with a graphite felt electrode, the overpotential losses were substantially mitigated at the positive and negative electrodes allowing the electrodes to be operated at current densities as high as 100 mA/cm 2 . With these technical advancements, the iron-chloride redox flow battery has an increased prospect of being a sustainable and efficient solution for large-scale energy storage.