Electrodeposited Pd Sub-Monolayers on Carbon-Supported Au Particles of Few Nanometers in Size: Electrocatalytic Activity for Hydrogen Oxidation and CO Tolerance Vs. Pd Coverage

摘要

A series of Pd-Au/C catalysts were obtained by selective electrodeposition of various amounts of Pd metal from a H2PdCl4 solution onto the carbon-supported Au nanoparticles (mainly below 5 nm in diameter) synthesized by "cationic adsorption" technique. The catalytic performance of the Pd-Au particles with both the clean and carbon monoxide (CO)-blocked surfaces for the hydrogen oxidation reaction (HOR) at 25 and 60 °C was tested as a function of the Pd coverage (θ_(Pd)) expressed in effective monolayer (ML) units, using a rotating disk electrode (RDE). The RDE studies demonstrate superior HOR activity (per unit of Pd surface area) of Pd deposited at the submo-nolayer level (θ_(Pd)<0.65 ML) onto the finely dispersed Au particles in comparison to those observed for the low-dispersed Pd-Au/C catalysts described earlier by other authors and for the monometallic Pd particles. The dependencies of the HOR activity and CO tolerance of the finely dispersed Pd-Au particles on their surface composition are discussed in terms of occurrence of various Pd sites on the surface of bimetallic particles differing in their ability to catalyze HOR and adsorb CO. The relative contribution of various factors to the rise of CO tolerance observed for Pd deposited on Au at varying θ_(Pd) was estimated bycomparison of the HOR activities measured with the fresh and CO-poisoned Pd-Au/C catalysts.