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

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.