As a novel 2D nanomaterial, graphitic carbon nitride (g-C3N4) has been actively explored in photocatalysis and heterogeneous chemical catalysis, however, its application in proton exchange membranes (PEMs) remained unexplored. Different from other 2D nanomaterials, g-C3N4possesses periodic vacancies in the lattice which could allow hydrated proton to selectively pass through. This molecular sieving effect could lead to a decrease in methanol crossover and more direct proton transfer pathways.
In this study, g-C3N4 nanosheets were incorporated into sulfonated poly(ether ether ketone) (SPEEK) for the first time to prepare nanocomposite membranes. The resultant nanocomposite membrane showed increased proton conductivity and decreased methanol crossover, which indicated that g-C3N4 nanosheets could serve as efficient methanol barriers; meanwhile, incorporation of g-C3N4 nanosheets in PEMs led to better connectivity of the ionic groups, triggered the acid-base pair effect and provided more continuous pathways for protons. In addition, the ultimate tensile strength of the control SPEEK membrane was increased by 68 %, arisen from the superior intrinsic mechanical stability of the g-C3N4 nanosheets, as well as the interfacial interactions between the g-C3N4 nanosheets and the SPEEK matrix. This study suggested the application potential of g-C3N4nanosheets as novel and versatile fillers to prepare high performance nanocomposite membranes for direct methanol fuel cells.