High-Temperature Polymer Electrolyte Fuel Cells Based on Protic Ionic Liquids

A hydrogen-based energy system will be the backbone of a future energy grid using renewable energies. It is widely accepted that polymer electrolyte membrane fuel cells (PEMFCs) are promising converters of chemical energy stored as hydrogen into electrical energy. An increase of the operation temperature from below 80°C to above about 160°C is considered beneficial, as it would allow for much simpler water management and the use of waste heat. Here, we are investigating protic ionic liquids (PILs) immobilized in a polybenzimidazole polymer as electrolytes for high-temperature PEMFCs. Ionic liquids are promising for fuel cell applications as they provide high thermal and chemical stability and high proton conductivity. In contrast to aqueous electrolytes, ionic liquids form a dense layered structure at the electrode–electrolyte interface that depends on the potential and on the content of residual water in the electrolyte. We investigate how PILs interact with the host polymer of the membrane revealing that porous polymer structures can be formed by solution casting, which allows for an encapsulation of the ionic liquid within the pores. After doping the polymer with small amounts of phosphoric acid, the membranes showed reasonable conductivity and fuel cell performance.