However, a Pt also tends to absorb CO molecules into its surface and thereby cause significant CO poisoning at lower temperatures. Tests show that a minor change in CO concentration (i.e.,0e200 ppm) in hydrogen fuel stream will cause a major reduction in a PEMFC's power output (0.65e0.13 W cm2 at 0.65 V) [20]. Cells operated at higher temperatures (i.e., >60 C) showed greater CO tolerance than those operated at lower temperatures. In the lower voltage range (i.e.,