Palladium Monolayer Electrocatalysts

Abstract

In this chapter, a Pd monolayer electrocatalyst has been described, showing that, in principle, other metals, not only Pt, can serve as monolayer electrocatalysts. When supported by adequate cores, these electrocatalysts can have platinum-like stability. In alkaline fuel cells, Pd as non-platinum catalyst that can have high stability, activity, and selectivity. The applications of these catalysts can be expected in oxidation and reduction of organic compounds, syntheses of pharmaceuticals, where these properties have high importance. The activity of Pd monolayers increased in the following order: Pd/Ru(0001) < Pd/Ir(111) < Pd/Rh(111) < Pd/Au(111) < Pd/Pt(111. It was correlated with their d-band centers, which were calculated using density functional theory. The volcano-type dependence of activity on the energy of the d-band center of Pd monolayers, with Pd/Pt(111) at the top of the curve, was found. Analysis of the origin of this dependence is presented. A descriptor of surface reactivity was the calculated Pd d-band center (relative to the Fermi level). These data provide guidance for designing Pd-based alloy catalysts. The alloying element should facilitate the decrease in energy of the d-band center. Hydrogen adsorption and formic acid oxidation on pseudomorphic monolayer of Pd on Au(111), Pt(111), PtRu(111), Rh(111) results are in agreement with the d-band model.