Density Functional Theory Comparison of Water Dissociation Steps on Cu, Au, Ni, Pd, and Pt

Abstract

We report a plane-wave, supercell density functional theory (DFT) investigation of the adsorption and dissociation of water on (111) surfaces of Cu, Au, Pt, Pd, and Ni, five metals of potential interest in the context of water gas shift (WGS) catalysis. Binding energies, preferred adsorption sites, and configurations for H2O and its dissociation products (OH, H, and O) are determined on all five metals, as are the minimum energy paths (MEPs) and activation energies for H−OH and O−H dissociation. Results are compared with the diverse computational literature on H2O dissociation over these metals. Both dissociation steps are found here to be highly endothermic on Au(111) and slightly endothermic on Pt(111) and Pd(111). The first H abstraction from adsorbed H2O is exothermic on Cu(111) and Ni(111), but subsequent OH dissociation is endothermic on Cu(111) and slightly exothermic on Ni(111). Using a simple Langmuir equilibrium model, we show that under the high H2 background pressures typical of low-temperature WGS, the surface coverage of OH is expected to be several orders of magnitude higher than that of O, consistent with a significant role of OH in surface CO oxidation.