ABSTRACT
High-temperature (typically 120°C-200°C) polymer electrolyte membrane (PEM) fuel cells (HT-PEMFCs) have attracted considerable attention in the past decades because they possess many advantages such as high CO tolerance of electrodes, easy water management, and fast electrochemical kinetics [1,2]. For use in HT-PEMFCs, an ideal PEM must meet the following requirements: (1) high proton conductivity at elevated temperatures without humidi–cation (low humidities), (2) excellent chemical and electrochemical stability atelevated temperatures, (3) high mechanicalstrength and toughness, and (4) high thermal stability. Sulfonated polymers can hardly be used as the PEMs in HT-PEMFCs because of their very low proton conductivities(<10−2 S cm−1) at low relative humidities (e.g., <30%) resulting from the insuf–cient water molecules as the carrier for proton transport. In contrast, phosphoricacid (PA)–doped polybenzimidazole (PBI) membranes have been reported to have high proton conductivities (>0.01 Scm−1) at low relative humidities or even under complete anhydrous condition atelevated temperatures, which makes them very suitable for use in HT-PEMFCs. The PA-doped PBI membranes as PEMs were –rst reported by Litt, Savinell and coworkers [1], and since then, ahuge number of research articles have been published.
