Electrochemical properties of platinum/carbon ink electrodes for direct methanol polymer electrolyte fuel cells

Oxygen reduction on an ink type electrode and the influence of methanol on oxygen reduction were investigated in a mini fuel cell using Nafion(R) memb rane at 60 degrees C and at rotating disc electrode (RDE) in 0.1 M H2SO4. V arious loadings of platinum (Pt) supported on three types of carbon materia ls having different surface areas (e.g. Shawinigan Acetylene Black, XC-72, and Black Pearls) were employed. The results reported here suggest that the type of carbon supporting material does not have any significant influence on oxygen reduction. Mass activity for catalysts of the same Pt loading do es not depend on Pt particle size or carbon support. On the other hand in t he high density region where mass transfer effects are seen, the mass activ ity of oxygen reduction decreases with an increase in Pt loading. This is b ecause the limiting current does not depend on the amount of Pt in the elec trode. Although methanol oxidation takes place around 0.5 - 0.8 V vs. RHE, methanol oxidation or its products does not significantly influence the kin etics or mechanisms of oxygen reduction. However the mixed potential effect still lowers the oxygen cathode potential when methanol is present.