Role of Cu Doping in SnO2 Sensing Properties Toward H2S

Adsorption properties of H2S on SnO2 (110) surface and effects of Cu-doping on SnO2 sensitivity toward H2S have been studied by means of the first-principles calculations based on the density functional theory. It has been found that H2S is dissociatively adsorbed on the SnO2 (110) surface with one H atom converged to abridging oxygen atom while the complex HS is bonded to a five-fold coordinated Sn atom. H2S adsorption has no change on the electrical conductivity of SnO2, which indicates that SnO2 has weak sensitivity toward H2S. Cu tends to be doped close to the surface region and prefers the five-fold coordinated Sn site. Cu-doping can directly improve the sensitivity of SnO2 toward H2S because of the increase in surface electrical conductivity. In addition, Cu-doping can greatly improve the formation of surface oxygen vacancies in SnO2, and the formation energy is in relation to Cu depth from surface. Molecular O-2 can be exothermically adsorbed on the reduced SnO2 surface, which also underlies the mechanism of enhanced SnO2 sensitivity toward H2S due to Cu-doping.