Designing continuous proton-conductive channels for direct methanol fuel cell through the sulfonated poly(ether ether ketone)/carbon quantum dot/graphitic carbon nitride nanosheet

Abstract

In this research, new nanocomposite membranes were fabricated based on sulfonated poly(ether ether ketone)/carbon quantum dot/graphitic carbon nitride nanosheet (SPEEK/CQD/g-C3N4). It was found that anchoring CQD onto g-C3N4 provides a new proton transport pathway in the design of proton exchange membranes for high-performance fuel cell applications. The uniform distribution of CQDs on the nanosheets and the interaction of hydrophilic groups such as the –NH2 and CO with the -SO3H of the polymer matrix creates a hydrogen bond transfer network and facilitates the protons transfer based on the Grotthuss mechanism. The incorporation of CQD/g-C3N4 in the polymer matrix has increased the proton conduction from 0.023 S/cm for SPEEK at 20 °C and 100 % R.H. to 0.052 S/cm for the SPEEK/CQD/g-C3N4-3 %wt. The proton conduction for the nanocomposite membrane containing 3 wt% CQD/g-C3N4 improved at higher temperatures (0.128 S/cm at 80 °C) and also, this membrane showed better thermal properties (maximum Tg at 176 °C). Compared to the SPEEK membrane, the nanocomposite membrane with 3 wt% CQD/g-C3N4 had a better single-cell direct methanol fuel cell (DMFC) test performance.