Novel polybenzimidazole/graphitic carbon nitride nanosheets composite membrane for the application of acid-alkaline amphoteric water electrolysis

Abstract It is a great challenge to develop membrane materials with high performance and long durability for acid-alkaline amphoteric water electrolysis. Hence, the graphitic carbon nitride (g-C3N4) nanosheets were compounded with the (2,2′-m-phenylene)-5,5′-benzimidazole (m-PBI) matrix for the preparation of m-PBI/g-C3N4 composite membranes. The synthesis of g-C3N4 nanosheets and m-PBI matrix have been confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscoy (TEM) and 1H nuclear magnetic resonance spectra (1H NMR), respectively. The fourier transform infrared spectroscopy (FT-IR) and SEM of the composite membranes showed the g-C3N4 nanosheets were well dispersed in the m-PBI/g-C3N4 composite membrane. The mechanical properties test exhibited the good mechanical strength, and the TGA curves of m-PBI showed the high thermal stability of composite membranes. Besides, the m-PBI/g-C3N4 composite membrane showed excellent proton and hydroxide ion conductivity, which was higher than pure m-PBI and Nafion 115 membrane. The acid-alkaline amphoteric water electrolysis test showed m-PBI/1% g-C3N4 composite membrane has the best performance with a current density of 800 mA cm−2 at cell voltage of 1.98 V at 20 °C. It showed that m-PBI/g-C3N4 composite membrane has a good application prospect for acid-alkaline amphoteric water electrolysis.