Conjugated Microporous Polymers with Dense Sulfonic Acid Groups as Efficient Proton Conductors

Proton-exchange membrane fuel cells, emerging as green and sustainable energy sources, have attracted extensive attention in recent decades. Porous organic polymers, which feature in high surface area values, tunable pore sizes, excellent thermal and chemical stabilities, and the flexibility to incorporate specific functional groups, have recently displayed their striking images as potential electrolytes for fuel cells. In this work, BO-CMP-1 and BO-CMP-2 that possess rich π-structure and permanent porosity and have high thermal and chemical stability were synthesized through Suzuki-Miyaura coupling reaction. Owing to their rigid structures and abundant electrophilic substitution positions, these two novel porous polymers were covalently decorated with dense sulfonic acid groups by postsulfonation, as denoted by SBO-CMP-1 and SBO-CMP-2. The proton conductivity of SBO-CMPs is systematically studied to evaluate their performance as proton-conductive materials. It was found that their performance is highly humidity- and temperature-dependent and they show relatively high proton conductivity. For SBO-CMP-1 and SBO-CMP-2, their proton conductivities are 1.29 × 10^-2 and 5.21 × 10^-3 S cm^-1, respectively, at 70 °C and 100% relative humidity. Low activation energy values of 0.32 eV for SBO-CMP-1 and 0.40 eV for SBO-CMP-2 suggest the Grotthuss mechanism for proton conduction.