Drastic Enhancement of Proton Conductivity in a Porous Organic Polymer Conductor via Dual Postsynthetic Acidifications

While strategies for proton conductivity enhancement are required, appropriate synthetic procedures are still sought. Herein, we synthesized a porous organic polymer, POP-Me40, through the judicial selection of functional groups with varying electronic effects. Postsynthetic sulfonation of POP-Me40 was conducted to produce POP-Me40-S. This material demonstrates a high conductivity of 1.42 × 10-1 S cm-1 at 80 °C and 90% relative humidity along with a low activation energy of 0.094 eV, consistent with the Grotthuss proton conduction mechanism. Subsequent impregnation of sulfonic acid groups in POP-Me40-S afforded a doubly acidified polymer, POP-Me40-S-SA, showing an exceptional proton conductivity of 1.91 × 10-1 S cm-1 under the same conditions. This value represents a 780000-fold increase in conductivity with respect to its unmodified precursor, POP-Me40, setting a record among porous materials. Furthermore, POP-Me40-S-SA exhibits an activation energy of 0.063 eV, one of the lowest reported, indicating the formation of highly efficient proton transport pathways within its framework channels.