Construction of wide-temperature-range proton exchange membrane by regulating proton transfer channels based on phosphate-functionalized carbon nanotubes

Abstract

Phosphoric acid (PA) doped polybenzimidazole (PBI) high-temperature proton exchange membrane is favored because it can achieve faster proton transfer at 180 °C without additional humidification. However, the PA-PBI membrane is faced with slow PA proton conduction kinetics below 100 °C, and failing rapid start-up of fuel cells. Herein, carbon nanotubes functionalized with phosphate groups (P-CNT) and sulfonated poly [2,2'-(p-hydroxydibenzene)-5,5′-benzimidazole] (SOPBI) composite membranes are prepared as proton exchange membranes with wide temperature range (40–180 °C). Based on the regulation of monophosphate and bisphosphate groups on P-CNT, the bisphosphate group can strengthen the vehicular mechanism of proton transport by accelerating the formation and diffusion of H3O+ at low temperature/high humidity, and the Grotthuss mechanism of proton transport by constructing dense hydrogen bond network at high temperature/low humidity. The 2P-CNT(6 %)/SOPBI composite membrane shows excellent proton conductivity (131.8 mS cm−1 at 80 °C/90%RH, 170.5 mS cm−1 at 180 °C/0%RH) and peak power density (378 mW cm−2 at 80 °C/100 % RH, 531 mW cm−2 at 160 °C/0 % RH) under wide temperature conditions, surpassing SOPBI membrane and other composite membranes. Furthermore, the 2P-CNT(6 %)/SOPBI composite membrane exhibits high proton conduction and fuel cell stability at both 80 °C/100 % RH and 160 °C/0 % RH.