Methanol-Tolerant Oxygen Reduction Electrocatalysts Based on Pd-3D Transition Metal Alloys for Direct Methanol Fuel Cells

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 . 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.