Phosphination-modified Polyborosiloxane/chitosan composite membrane for high temperature proton exchange membranes

Phosphoric acid (PA)-doped membranes have emerged as promising electrolyte candidates for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Nevertheless, their commercial adoption has been limited by durability challenges, particularly PA leaching. Herein, we developed composite proton-exchange membranes by blending phosphonated polyborosiloxane (PA-PBS) with chitosan (CS). The phosphonic groups were grafted onto polyborosiloxane chains via N-C-P bonds, which effectively reduces proton carrier loss. The microporous structure of membranes provides channels for internal water transfer. The membranes exhibit 3.5% weight loss at 150 °C. The membrane with the optimal PA ratio (PA:APTES = 2:1) achieves a proton conductivity of up to 67 mS/cm at 140 °C, and a maximum single-cell output power density of 435.1 mW/cm 2 at 140 °C, demonstrating its potential for high-temperature, low-humidity applications.