Performance of the Polymer Electrolyte Membranes Impregnated with Some Room-temperature Ionic Liquids at Elevated Temperature

Abstract

The Nafion membrane impregnated with various room-temperature ionic liquids have been prepared and characterized as the electrolytes for polymer electrolyte fuel cells (PEFCs) operated at elevated temperature (100∼200°C). The continuous proton transportation in the membrane was confirmed under dry hydrogen atmosphere at 160°C. The ionic conductivity of the membrane was determined by both DC and AC measurements under dry hydrogen atmosphere and found to reach the order of 10⁻² S cm⁻¹ at 200°C without humidification. It is suggested that the high ionic conductivity of the membrane is caused mainly by free ionic liquids in the membranes. The continuous operation of the PEFC using the membrane was found to be possible without humidification at 120°C. However, the overpotential at the cathode was found to be large compared with the anode probably due to the sluggish electrode reaction and/or the slow diffusion of HTFSI in the membranes.