Construction of unimpeded proton-conducting pathways in solution-processed nanoporous polymer membranes

Developing proton-conducting membranes with three-dimensional conductivity and expedited interfacial contact is requested in the field of fuel cells. Here, we present a design strategy by combining solution processing and material flexibility into amorphous and porous polymers. We design a nanoporous polymer whose skeleton contains dihydrophenazine as a proton-accepting site, and subsequently protonate these sites to produce abundant charges on the polymer skeletons, which enables ionic polymers to be well dispersed in organic solvents and guarantees that they can be fabricated into uniform and amorphous membranes in a solution-processed manner. Importantly, after protonation, the dihydrophenazines change to proton-donating sites, which exhibit dynamic local motions that assist proton exchange on the polymer skeletons and thus construct three-dimensional and unimpeded proton-conduction pathways, with a striking proton conductivity of 0.30 S cm^-1 (298 K and 90% relative humidity), a low resistance of 3.02 Ω, and a H⁺ transport number of 0.98 that was very close to the upper limitation of 1.0.