Quan Xu,Xinyi Chen,Siyang Wang,Chao Guo,Yingchun Niu,Runguo Zuo,Ziji Yang,Yang Zhou,Chunming Xu
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.
Interfacial interactions profoundly influence the proton conductivity and ion selectivity of ion-exchange membranes. However, previous studies on membranes primarily focus on enhancing the selective-conductive properties of the secondary phase while neglecting interfacial regulation. In this study, PFSA/CF 3 SO 3 -M heterogeneous membrane is successfully fabricated by incorporating CF 3 SO 3 -M nanosheets—derived from organic Lewis acid (trifluoromethanesulfonic acid) etching of Ti 3 AlC 2 —into perfluorosulfonic acid resin (PFSA). Compared to PFSA/HF-M hybrid membrane containing fillers etched by inorganic acid (HF), the PFSA/CF 3 SO 3 -M heterogeneous membrane exhibits superior proton conductivity, reduces vanadium ion permeability, and the highest ion selectivity (11.7 S min cm −3 ) among all tested membranes. This enhancement arises from two mechanisms: the development of heterointerface proton transport channels between filler and PFSA matrix and the pH-responsive Donnan exclusion effect inherent to the filler. Electrochemical evaluations demonstrate that the PFSA/CF 3 SO 3 -M membrane outperforms conventional Nafion membrane in vanadium redox flow battery (VRFB) applications, achieving 98.1% coulombic efficiency and 84.2% energy efficiency after 800 cycles. Cost analysis reveals that the PFSA/CF 3 SO 3 -M heterogeneous membrane demonstrates a 59.8% reduction in membrane cost compared to Nafion 212 in a 2 MW × 6 h VRFB system. This work establishes an effective strategy for designing MXene-based ion-selective membranes through rational interfacial engineering.
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