High coverage H2O adsorption on CuAl2O4 surface: A DFT study

Investigation into the interaction between water and surface is important for many reactions. Periodic DFT calculations were performed to investigate the adsorption of nH2O (n = 1–8) on the CuAl2O4 (1 0 0) and (1 1 0) surfaces. The results show that single water molecule is adsorbed on the CuAl2O4 (1 0 0) and (1 1 0) surfaces via dissociative adsorption with adsorption energies of −103 and −170 kJ/mol. On O-defective CuAl2O4 surfaces, the O atom of the water molecule prefers to insert into the O vacancy, leaving two isolated H atoms bonds to surface O atoms forming two in-surface hydroxyls. For nH2O (n = 2–8) on CuAl2O4 surfaces, molecular and dissociative water adsorption can coexist. The interaction of H2O with CuAl2O4 (1 1 0) surface is much stronger than with the (1 0 0) surface. The PDOS analysis revels that the adsorption of water on the surfaces is accompanied by charge transfer. Water adsorption on the CuAl2O4 surfaces leads to the decreases of the work function at low water coverage, while higher water coverage results in the increase of the work function. The phase diagrams of the water adsorption on the CuAl2O4 spinel surfaces show that water will desorb from the CuAl2O4 surfaces at higher temperature and lower H2O pressure.