Phosphonic acid loaded covalent imine networks for proton-conducting membranes

Triazine-based covalent organic polymers (COPs) have substantially concerned as a hopeful proton-conducting medium. Generally, encapsulating protonphore molecules into porous COPs is a potential tactics to improve the proton conductivity (PC). Herein, the COP-based proton conductor is fabricated by immobilizing nitrilotrimethylphosphonic acid (NTP) molecules into the pores of nitrogen-rich covalent imine network (CIN) to give NTP/CIN, further followed by blending NTP/CIN as filler into chitosan (CS, a deacetylated form of chitin) to form hybrid membranes (NTP/CIN@CS). NTP/CIN@CS possesses relatively higher PC of 7.8 × 10−3 S cm−1 under ~98% RH at 328 K, ranging in the most conductive COF-based hybrids, which is 71- and 17-folds than those of pristine CS and CIN@CS. The basic functional units contained from CIN backbone, phosphate groups derived from NTP and amino and hydroxyl groups at CS matrix, along with water, conduct the transfer of proton in the hybrid membrane. The relatively high water uptake (W.U.) and ion exchange capacity (IEC) of NTP/CIN@CS also contribute to form continuous and steady H-transport channel, and thus greatly enhance PC. The inspiration that nitrogen-rich COF framework federated with proton carrier tenders a new path to discern solid-state electrolyte.