High performance of zinc-ferrum redox flow battery with Ac−/HAc buffer solution

A green low-cost redox flow battery using Zn/Zn 2+ redox couple in HAc/NaAc medium and Fe 2+ /Fe 3+ redox couple in H 2 SO 4 medium was first proposed and investigated for potential stationary energy storage applications . The presence of HAc/NaAc in the negative electrolyte can keep the pH between 2.0 and 6.0 even when a large amount of H + ions move into negative electrolyte from positive electrolyte through ion exchange membrane . In the pH range of 2.0–6.0, the chemical reaction of Zn species with H + species is very insignificant; furthermore, the electroreduction of H + ion on the negative electrode is significantly suppressed at this pH range. The zinc-ferrum redox flow battery (Zn/Fe RFB) operated within a voltage window of 0.5–2.0   V with a nearly 90% utilization ratio, and its energy efficiency is around 71.1% at room temperature. These results show that Zn/Fe RFB is a promising option as a stationary energy storage equipment.