Advances in solid acid electrolytes for fuel cell applications

Fuel cells represent a class of high-efficiency energy conversion devices that are expected to play a major role in reducing the environmental pollution in hydrogen economy. These cells typically employ polymer membranes as electrolytes for protonic conduction that are operable only under humid conditions. This requirement limits their operating temperature range to 373 K. Solid acids are a relatively new class of electrolytes that allow protonic conduction at temperatures above 373 K and are thereby free from water management issues. Each solid acid has a specific transition temperature beyond which its protonic conductivity increases. Unlike polymer membranes, they do not require hydration for proton conduction and follow Grotthus mechanism which makes them a promising candidate for further research. In the last decade, significant amount of attention has been paid to these compounds and the results have been encouraging. Addition of additives like SiO₂ to solid acids has been found to be an effective method to increase their conductivity and lower the superprotonic transition temperature. This work describes the recent developments and the future challenges in the field of solid electrolytes for fuel cell applications.