Steric Modulation Enables Superionic Proton Conduction in Metal‐Bis(Dithiolene) Frameworks for Fuel Cells

The rational design of coordination polymers (CPs) with exceptional proton conductivity remains a pivotal challenge for advancing energy conversion technologies. Herein, we report a steric modulation strategy involving the functionalization of a nickel bis(dithiolene) ligand with meta ‐carboxylate groups, yielding two isostructural CPs, Mn‐CP and Cd‐CP . Benefiting from the synergy between uncoordinated carboxylate groups acting as proton donors and unsaturated metal centers serving as Lewis acid sites to dynamically coordinate and activate water molecules, these CPs establish an extensive hydrogen‐bonding network that enables efficient proton transport. This architecture affords a remarkable proton conductivity of 1.36 S cm − 1 , outperforming the isostructural tetrathiafulvalene‐based framework and ranking among the top tier of reported CPs/MOFs. Deuterium isotope effect experiments, coupled with density functional theory (DFT) calculations, elucidate the underlying proton conduction mechanism. Crucially, we demonstrate the practical utility of Mn‐CP in proton exchange membrane fuel cells, which deliver an exceptional open‐circuit voltage of 0.94 V and a maximum power density of 870 mW cm −2 . The derived proton conductivity under operando conditions was determined to be 0.21 S cm − 1 , reflecting the intrinsic conductivity of the material. This work establishes a pioneering crystal design strategy, providing a robust paradigm for the development of next‐generation high‐performance proton‐exchange membranes.