ABSTRACT
Although hydrogen is the most abundant element in the universe it is never found in the free, elemental state on Earth. Indeed, the preceding chapters have addressed thermochemical methods for synthesizing hydrogen from methanol (with or without water) for precisely this reason. However, the reaction products invariably in-clude high concentrations of carbon dioxide and carbon monoxide, and perhaps low concentrations, or even trace concentrations, of a wide range of organic byproducts. Low-temperature PEMFC stacks require a relatively high de-gree of hydrogen purity. For instance, Ballard specifies1 that hydro-gen for consumption in their low-temperature fuel cell be at least 99.95% pure with <0.2 ppmv carbon monoxide and no more than trace levels (parts-per-billion) of functionalized organic compounds. AFC stacks additionally require very low concentrations of carbon dioxide due to adverse reaction of carbon dioxide with the alkaline electrolyte.Fuel cells operating at higher temperature (e.g., SOFC and MCFC) are not required to use such a high purity of hydrogen. Even PAFC stacks can operate adequately with hydrogen containing up to a few percent carbon monoxide, but the presence of sulfur compounds and reactive organic contaminants will still cause degradation in fuel cell performance.
