Although crossover of both fuel (e.g., hydrogen) and oxidant (oxygen) takes place, the latter generally occurs at a lower rate. For instance, it has been found that under the same conditions, the crossover rate of oxygen is about half the rate of hydrogen through Naœon 125 membrane (with a thickness of 125 µm) at 25°C (Ogumi et al., 1984a). In addition, based on Weber’s simulation (Weber, 2008), it has also been demonstrated that hydrogen crossover is more detrimental to cell operation than oxygen crossover, due to the facile kinetics of hydrogen oxidation and the fact that most fuel gases are pure hydrogen. šerefore, fuel crossover is most o§en the main issue of interest, and has been investigated by various research groups (Ogumi et al., 1984a,b; Sakai et al., 1985; Broka et al., 1997; Inaba et al., 2006).