Effect of Co doping on catalytic activity of small Pt clusters

Platinum is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no platinum content is one of the grand challenges in fuel cell research. Here, we investigate electronic structures of Pt4 and Pt3 Co clusters and report a comparative study of adsorption of H2, O2, and CO molecules on the two clusters using density functional theory. The adsorption studies show that H2 undergoes dissociative chemisorption on the tetrahedral clusters in head on and side on approaches at Pt centers. O2 dissociation occurs primarily in three and four center coordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O2 is found to be higher for the Co doped cluster. For CO, the Pt atop orientation is preferred for both Pt4 and Pt3 Co tetrahedral clusters. Adsorption of CO molecule on tetrahedral Pt3 Co in side on approach leads to isomerization to planar rhombus geometry. An analysis of Hirshfeld charge distribution shows that the clusters become more polarized after adsorption of the molecules.