Theoretically, there are several me

Theoretically, there are several methods that can be usedto remove CO from hydrogen-rich gases [5–8]. As for theapplications of PEFCs to transportation vehicles, residential cogenerators and portable devices, however, the feasible choicemay be only between the preferential CO oxidation (PROX)and selective CO methanation (SMET) because of the limitedavailable spaces and low operating pressures in such applicationsystems. The PROX has so far been extensively tested [9–11]since it is somehow reliable to remove CO down to 10 ppm byraising the oxygen consumption unlimitedly. Nonetheless, thetechnology requires a closely controlled low O2 supply to keepthe possibly lowest H2 oxidation and a generally narrow window of suitable working temperatures. This, while making themethod costly and complicated, obviously hinders its application to low-power PEFCs where very small oxidant flows haveto be provided by use of well-refined expensive flow meters,such as mass flow meters. On the other hand, the fuel cells withpower of tens of watts to a few kilowatts (