The Recycling of Waste Per-Fluorinated Sulfonic Acid for Reformulation and Membrane Application in Iron-Chromium Redox Flow Batteries

Abstract

Iron–chromium redox flow batteries (ICRFB) possess the advantage of low raw material cost, intrinsic safety, long charge–discharge cycle life, good life-cycle economy, and environmental friendliness, which has attracted attention from academia and industry over time. The proton exchange membrane (PEM) is an important part of the ICRFB system, impacting the efficiency and lifetime of the battery. Currently, the most widely used PEMs in the market are per-fluorinated sulfonic acid (PFSA) membranes, which possess high electrolyte stability and achieve the separation of positive and negative electrolytes. In addition, the complex preparation process and extremely high market price limited the usage of PEM in ICRFB. In this paper, we developed a remanufactured membrane (RM) strategy from waste PFSA resins. The RM has higher electrical conductivity and better proton transport ability than the commodity membrane N212. In the cell performance test, the RM exhibits similar coulombic efficiency (CE) as N212 at different current densities, which is stabilized at over 95%. Furthermore, the voltage efficiency (VE) and energy efficiency (EE) of the RM are improved compared to N212. At a current strength of 140 mA cm−2, the degree of energy loss is lower in the RM, and after 60 cycles, the capacity decay rate is lower by only 16.66%, leading to long-term battery life. It is a cost-effective method for membrane recovery and reformulation, which is suitable for large-scale application of ICRFB in the future.