Density functional study of the interaction of CO with undoped and Pd doped SnO2(1 1 0) surface

Density functional theory calculations with the generalized gradient approximation, together with pseudopotentials and plane-wave basis sets, have been performed for the interaction of CO with undoped and Pd doped SnO2 (1 1 0) surface. Four top adsorption models of CO on undoped SnO2 (1 1 0) surface were investigated: adsorption on 5-fold tin, on 6-fold tin, on bridging oxygen, and on plane oxygen, respectively. The results show that the adsorption of CO is weak to the undoped SnO2 (1 1 0) surface, and the energy gap has no remarkable change, except a shift of the Fermi level. Two doping models were considered for the Pd doped surface: Pd substituted 5-fold tin and Pd substituted 6-fold tin. The results reveal that Pd substituted 5-fold tin forms a stable doping structure, and doping induces some new electronic states in the band gap they may lead to the changes of the surface properties. By contrasting the adsorption energies and electronic population of CO adsorption on undoped and Pd doped SnO2 (1 1 0) surface, it is found that Pd doping can obviously enhance the adsorption of CO, which theoretically verified the experimental fact that Pd doping can greatly increase the SnO2 gas sensors’ sensitivity to CO gas.