H 2 O‐Induced Transformation of Superstructured MOFs into Self‐Standing, Superprotonic Conducting Membranes for Hydrogen Fuel Cells

Abstract Metal–organic frameworks (MOFs) represent an emerging class of crystalline materials characterized by high porosity, vast surface area, and structural variability. Despite the potential for sustainable energy applications, challenges remain in designing and engineering MOF powders with limited mechanical robustness and integrity into self‐standing, durable membranes while retaining their functionality. Inspired by unique structure of natural vascular bundles, an approach is developed to fabricating MOF membranes via dimensional reduction of superstructures. Interestingly, structural water‐flexibility of MOF superstructure led to homogeneous gelation, which can encapsulate a substantial amount of water molecules within porous structures, forming micro/nano‐scale channels for efficient proton transport. Hierarchical channel ensures super‐protonic conductivity values ranging from 0.07 S cm −1 (40% RH) at 293 K to 0.14 S cm −1 (90% RH) at 353 K. For the first time, it demonstrates relevant hydrogen fuel cell performance, achieving a peak power density of 48 mW cm −2 . This study paves the way for engineering all‐MOF‐based materials as proton‐conducting membranes for low‐temperature hydrogen fuel cells.