An in situ study of the effects of Na + , Mg 2+ and Cr 3+ on direct methanol fuel cell (DMFC) performance is reported. The result showed that dramatic decrease of the cell voltage was mainly ascribed to the increase of the cathode overpotential. Meanwhile, the different contamination effects by introducing Na + , Mg 2+ and Cr 3+ to the anode and the cathode were compared. When the same molar concentration of different cations was added to the anode feed, the contamination effect on the cell

more »

... ormance followed the order of Na + N Mg 2+ N Cr 3+ . Owing to the fast transfer speed and the low affinity to the sulfonic acid groups in the ionomer phase, the low-valent cations may cause much more proton losses than the high-valent cations in the cathode catalyst layer (CCL) within the same time. So the low-valent cations led to the higher cathode overpotential than the high-valent cations. When the same molar concentration of cations was directly added to the CCL, the contamination effects on the cell voltage showed an opposite trend which is Na + b Mg 2+ b Cr 3+ . This is presumably because a high-valent cation can exchange more protons than a low-valent cation in the CCL.