Alternative electrochemical storage and conversion devices
Fuel cells are among the enabling technologies toward a safe, reliable, and sustainable energy solution. Yet the lack of clean hydrogen sources and a sizable hydrogen infrastructure limits the fuel-cell applications today. Due to their elevated operating temperature, between 150°C and 180°C, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on phosphoric acid doped polybenzimidazole (H3PO4/PBI) membranes can tolerate fuel contaminants such as carbon monoxide (CO) and hydrogen sulfide (H2S) without considerable performance loss. These are typical byproducts of the steam reforming process, which produces hydrogen from hydrocarbon fuels such as methanol or natural gas. So it is an appealing concept to couple a HT-PEMFC stack directly with a fuel processor, which can be used as auxiliary power units (APUs). These APUs use the fossil fuel resources more efficiently and help reduce emission of CO2. This might also be a good strategy for the wide deployment of fuel cells before the hydrogen infrastructure is established. The fuel cell system’s efficiency can be further increased by reusing the exhaust heat produced during electrical power generation.
The slow oxygen reduction reaction in concentrated phosphoric acid remains a major technological challenge for future development of HT-PEMFCs. The slow reaction rate is believed to be related to strong adsorption of phosphoric acid species on the surface of the platinum catalyst. It is generally accepted that adsorption of molecular or anionic species from the concentrated phosphoric acid electrolyte hinders ORR by blocking active sites on the catalyst surface. To gain a better understanding of the adsorption mechanisms we conduct systematic studies employing various types of perfluoroalkylated derivatives of phosphoric acid. We evaluated these model electrolytes for their adsorption behavior and influence on ORR on a polycrystalline platinum surface.