Superprotonic Solid Acid Membranes: Alternative Proton Conductors for Fuel Cells

Sustained efforts in the engineering of fuel cells based on polymer electrolyte membranes have resulted in the development of practical systems for vehicular, portable, and stationary applications. However, the low operation temperature of PEMFCs requires stringent management of liquid water content and fuel purity, increasing ultimate system cost and raising barriers to widespread adoption. The so-called superprotonic solid acids (SSAs)1 have recently emerged as a possible alternative to polymer electrolytes. Essentially chemical intermediates of acids and salts, SSAs are distinguished by thermally-activated polymorphic phase transitions at intermediate temperatures (140 °C to 230 °C) to phases with proton conductivity approaching that of polymers (~0.03 S cm-1). By operating at elevated temperatures, solid acid fue