Highly Proton Conductive Phosphoric Acid Porous Organic Polymers via Knitting Method

Abstract

Phosphoric acid group, which possesses a low energy barrier for proton conduction and high water bonding energy, favors proton conduction and water retention. In this study, a phosphoric acid porous organic polymer (PAPOP) with high proton conductivity was synthesized. The diethyl benzylphosphonate (DBP) monomer and the benzyl monomer were directly knitted via the Friedel–Crafts alkylation reaction to form a porous scaffold. The phosphate ester group on DBP not only enhanced the monomer reactivity but also realized the in situ introduction of the phosphoric acid group precursor during the formation of the porous scaffold. It is found that p-dichloroxylene (DCX) monomer, due to its higher electrophilic activity, is easier to react with DBP and thus easier to introduce phosphoric acid groups. The higher ratio of DCX leads to a more continuous hydrogen-bond network within the scaffold, which facilitates the proton-conducting process. The resultant porous organic polymers exhibited high hydrophilicity and excellent stability in strong acid as well as antiswelling ability in water. The highest ion-exchange capacity reached 2.68 mmol g–¹, much higher than that of most reported polymers. The proton conductivity of powders reached the highest value of 7.09 × 10–² S cm–¹ at 348 K and 98% relative humidity.