Palladium-based alloys, such as Pd–Co, Ni, and Cr, have been developed as a novel methanol-tolerant oxygen reduction electrocatalyst for direct methanol fuel cells. The Pd alloy electrocatalysts were fabricated by a rf sputtering method. Their electrochemical characteristics for the oxygen reduction reaction (ORR) were determined in sulfuric acid solution with and without methanol at 30°C . The Pd alloys showed a higher ORR electrocatalytic activity than Pd, although lower than Pt. The Pd alloys also had no electrocatalytic activity for methanol oxidation in the presence of methanol. The maximum electrocatalytic activities for ORR were observed for the alloy composition of ca. 60 atom % Pd in all the Pd alloys. Based on the X-ray photoelectron surface analysis, it was confirmed that the filling of the Pd d-band by alloying decreased the density of states (DOS) at the Fermi level. The decreased DOS inhibited the formation of Pd oxide on the surface of the electrocatalyst. This result should contribute to the improvement of the ORR activity of the Pd alloy electrocatalysts.

The consumption rate of Pt in sulfuric acid under potential cycling has been investigated in 1 mol dm −3 H 2 SO 4 at 40°C as a basic study to understand the consumption rate of the electrocatalyst of polymer electrolyte fuel cells. With a higher potential limit, E H was 1.5 V vs reversible hydrogen electrode ͑RHE͒, the consumption rate was a few ng cm −2 cycle −1 for rectangular and symmetric triangular waves, and the consumption rate increased with the E H up to 1.8 V vs RHE. Among the triangular waves between 0.5 to 1.8 V vs RHE, the consumption rate of symmetric waves and fast cathodic asymmetric triangular waves were a few ng cm −2 cycle −1 . However, the slow cathodic triangular wave, which were 20 V s −1 anodic and 0.5 V s −1 cathodic, showed 24 ng cm −2 cycle −1 consumption rate. The ratio in the difference of charge to the consumption showed that the electron transfer number was about 2 for the slow cathodic triangular wave, and that of the electron transfer number was about 4 for the symmetric waves and the fast cathodic triangular waves. Therefore, PtO 2 + 4H + + 2e − → Pt 2+ + 2H 2 O that follows the Pt oxidation, Pt + 2H 2 O → PtO 2 + 4H + + 4e − would occur under the enhanced condition, and Pt → Pt 4+ + 4e − would occur under symmetric conditions.

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