Interfacial Engineering of MXene‐Based Heterogeneous Membranes with Enhanced Ion Selectivity in Vanadium Redox Flow Battery

Abstract 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.