First Principles Investigation of Water Dissociation on Cu, Au, and Pt-Group Metals

We report a periodic self-consistent density functional theory investigation of the adsorption and dissociation of water on (111) surface of Cu, Au, Pt, Pd and Ni. We determined the binding energies, preferred adsorption sites and configurations, and vibrational frequencies for H₂O and its dissociation products (OH, H, and O) on these metals. We also examined the thermochemistry and calculated activation energy barriers for steps in the sequential two-step water dissociation. We find that both the dissociation steps are endothermic on Au(111), Pt(111) and Pd(111). Furthermore, first H abstraction from adsorbed H₂O is exothermic on Cu(111) and Ni(111). Subsequent OH dissociation is endothermic on Cu(111) and slightly exothermic on Ni(111). Among the metals studied, Cu(111) provides an optimum pathway for H₂O dissociation. Using a simple Langmuir equilibrium model, we show that, under typical low temperature water-gas shift conditions, surface coverage of OH is several orders of magnitude higher than that of O.