Constructing Heterogeneous Metal Nodes in Metal–Organic Framework Lamellar Membranes for High Proton Conduction in Fuel Cells

Precisely defining proton transport channels and regulating the chemical microenvironment of proton carriers are critical for high-performance proton exchange membranes (PEMs). Beyond optimizing carrier type and density, modulation of electron density distribution offers an underexplored route to enhance intrinsic proton conductivity. Herein, a series of ZnM-BDC-COOH nanosheets are synthesized by partial substitution of Zn²⁺ with a second metal ion in Zn-BDC frameworks and subsequent −COOH modification. The optimized ZnCu-BDC-COOH achieves a high intrinsic proton conductivity of 361.5 mS cm^–1 over 16 times that of the pristine Zn-BDC (22.2 mS cm^–1) at 80 °C and 98% RH using comb electrodes. Density functional theory and molecular dynamics simulations reveal that the introduced Cu²⁺, with higher electronegativity, withdraws more electrons from adjacent −COOH groups and Zn ions, generating asymmetric electron cloud distribution within the O–H bonds and the heterogeneous Zn₃CuO(COO)₆ nodes. This electron asymmetry facilitates rapid H⁺ release and establishes a strong local potential gradient that lowers the proton transport barrier. The resulting ZnCu-BDC-COOH lamellar membrane achieves a peak power density of 0.92 W cm^–2, outperforming Nafion-117 (0.28 W cm^–2), and maintains good durability over 100 h of open-circuit voltage (OCV) under 80 °C and 100% RH in fuel cells.