Electrochemical adsorption of hydrogen on mixed Pd₂Pt nanostructures

Abstract

In the present contribution we have focused on the electrochemical adsorption of a proton from the solution-the Volmer reaction-on a variety of systems based on bimetallic nanostructures-clusters and wires-of Pd and Pt deposited on a surface of Au(111). We have calculated the free energy surface for the electron transfer step by a combination of DFT calculations, MD simulations and the theory of electrocatalysis. We analyze in detail the interaction of the metal d band with the valence orbital of the hydrogen and its effect on the catalytic activity as well as several aspects that influence the electrode reactivity such as spatial arrangements of the nanostructures, the solvation shell and chemical factors. We found that the mixed Pd 2 Pt wire interacts strongly with hydrogen, and retains an almost complete solvation shell, which is reflected in a substantially reduced activation energy for the Volmer step. Thus, Pd 2 Pt wires on Au(111) are predicted to be efficient electrocatalysts for the reaction.

Models of Electron Transfer at Different Electrode Materials

“…Figure 2 shows the situation for a solvated proton approaching either a Pd(111) surface or a Pd 4 cluster on Au(111). 25 In the latter case, the pmf starts to increase farther from the adsorption site.…”

“…Usually, such potentials of mean force are calculated for flat surfaces; however, on steps or clusters the situation can be different due to the geometry of the adsorption site. Figure shows the situation for a solvated proton approaching either a Pd(111) surface or a Pd 4 cluster on Au(111) . In the latter case, the pmf starts to increase farther from the adsorption site.…”

“…Santos et al , investigated the adsorption of hydrogen on monatomic wires of the coin metals and on platinum and compared it with the adsorption on the (111) surfaces of these metals at 0 V NHE. In all cases, the adsorption energy is more favorable on the wires than on the (111) surface (see Table ).…”

“…In a similar vein, Schulte et al investigated hydrogen adsorption on Pt 2 Pd nanowires supported on gold. They not only calculated the interaction of a hydrogen atom with these clusters but also calculated the potential of mean force for the approach of the proton to the adsorption site.…”

“…The letters A and C correspond to positions on the free-energy surfaces shown in Figure . Adapted from ref .…”