Tuning Pore Confinement and Chemistry of Fluorine-Free Membranes.

The design of low-temperature fuel cells and electrolyzers involving proton exchange membranes (PEMs) has been dominated by the exceptional performance and industrial dominance of Nafion. With emerging regulations banning the use of fluorinated compounds, the search for F-free alternatives must be accelerated. Here, we optimize a fluorine-free, sustainable, and low-cost liquid crystalline poly(epichlorohydrin)membrane, based on the identification of key descriptors for proton mobility obtained using machine learning interatomic potentials (MLIPs) derived from first-principles calculations for extensive molecular dynamics. Proton transfer is controlled by the interplay between water confinement and internal pore chemistry. This allows us to modify the active functional groups so that they directly participate in the proton diffusion process, increasing three times the diffusion rate in the membrane, thus being closer to Nafion standards. This work provides key descriptors for a targeted design approach essential for catalyzing the commercial development of next-generation fluorine-free PEMs.