Low temperature preparation of carbon-supported Pd-Co alloy electrocatalysts for methanol-tolerant oxygen reduction reaction

Carbon-supported Pd-Co alloy electrocatalysts of different Pd/Co atomic ratios were simply prepared in an aqueous solution at room temperature with NH₄ as a complexing agent and H₃BO₃ as a buffer, followed by NaBH₄ reduction. As-prepared Pd-Co bimetallic nanoparticles show a single-phase face-centered-cubic (fee) disordered structure, and the mean particle size is found to decrease with increase in Co content. TEM images demonstrated that the as-prepared Pd-Co alloy nanoparticles are well dispersed on the surface of the carbon support with a small particle size and a relatively narrow particle size distribution. For example, the average particle size of a Pd₂Co₁/C catalyst is ca. 3.0 nm, which is much smaller than that of the Pd-Co/C bimetallic nanoparticles reported by others. An activity evaluation of the oxygen reduction reaction (ORR) on as-prepared Pd-Co/C catalysts with a rotating disk electrode (RDE) technique indicated that the maximum ORR mass activity was observed for a Pd: Co atomic ratio of 4:1, but the highest specific activity was found on a Pd:Co atomic ratio of 2:1. Kinetic analysis reveals that the ORR on Pd-Co/C catalysts follows a four-electron process leading to water. Moreover, the Pd-Co/C catalyst exhibited much higher methanol tolerance during the ORR than the Pt/C catalyst, assessing that it may function as a methanol-tolerant cathode catalyst in a direct methanol fuel cell (DMFC).