Fuels

The primary fuels that can be directly utilized within fuel cell stacks today include natural gas, biogas, and hydrogen depending upon the fuel cell type. PEMFC operate most effectively on high-purity hydrogen. PAFCs can also operate directly on hydrogen, but with lower requirements for purity. As a result, PAFC have been traditionally deployed on natural gas reformed through an external reformer. While MCFCs and SOFCs can in principle operate on hydrogen, commercial systems are designed to operate on natural gas (due to the wide availability) with reformation internal to the fuel cell given the availability of high quality heat. As society reduces its dependency on natural gas, all fuel cell types are available to operate directly on zero-carbon renewable hydrogen. Parenthetically, the presence of sulfur (the mercaptan odorant in natural gas, for example) is not tolerated by fuel cells in general and that the SOFC is the most inherently fuel flexible of the fuel cell types. MCFC units are also quite fuel flexible.