Fabrication of water-insoluble phosphotungstic acid-carbon nitride nanohybrids for promoting proton transport of nanocomposite proton exchange membranes

Abstract Incorporation of heteropolyacids (HPAs) could greatly improve proton conductivity of composite proton exchange membranes (PEMs). However, HPA leaching, due to their high solubility in water, remains one of the major problems hindering the further development of these composite PEMs. In this work, we have prepared water-insoluble P–C3N4 nanohybrids via the hydrothermal reactions between phosphotungstic acid (HPW) and graphitic carbon nitride (g-C3N4) nanosheets, in which HPW is chemically bonded with g-C3N4. The introduction of P–C3N4 nanohybrids promotes the proton transport by providing the strong acidity of HPW and the continuous 2D proton transport pathways, resulting in the proton conductivity reaching up to 0.086 S cm−1 in liquid water and 0.91 × 10−3 S cm−1 at 45% RH at 20 °C for the sulfonated poly(ether ether ketone) (SPEEK) nanocomposite membrane, which are 50% and 6000% higher than the SPEEK control membrane (0.056 S cm−1 and 1.5 × 10−5 S cm−1), respectively. The fuel cell performance for the MEA based on the SPEEK/P–C3N4 nanocomposite membrane is significantly improved, achieving a 38.1% increase in the peak power density at 80 °C under 92% RH. Therefore, our study demonstrates a facile and promising approach to prepare water-insoluble solid proton conductor with HPW components, which could be further applied to fabricate high performance nanocomposite PEMs.