Active sites for H2 and H2O activation over bifunctional ZnO-Pt(111) model catalysts

•Construction of submonolayer or multilayer Zn oxide (ZnOx) structures on Pt(1 1 1).•Hydroxylation of ZnOx suface via H2 dissociation on bare Pt and spillover of H species to ZnOx.•Hydroxylation of ZnOx surface via dissociation of H2O on oxide surface.•O/Zn ratio in the ZnOx layer determines either H2O or H2 is dominant in the surface hydroxylation.