A DFT study of the CO adsorption and oxidation at ZnO surfaces and its implication for CO detection

Abstract

Recently, ZnO-based gas sensors have been successfully fabricated and widely studied for their excellent sensitivity and selectivity, especially in CO detection. However, detailed explorations of their mechanisms are rather limited. Herein, aiming at clarifying the sensing mechanism, we carried out density functional theory (DFT) calculations to track down the CO adsorption and oxidation on the ZnO(101¯0) and (112¯0) surfaces. The calculated results show that the lattice O of ZnO(101¯0) is more reactive than that of ZnO(112¯0) for CO oxidation. From the calculated energetics and structures, the main reaction product on both surfaces can be determined to be CO2 rather than carbonate. Moreover, the surface conductivity changes during the adsorption and reaction processes of CO were also studied. For both ZnO(101¯0) and (112¯0), the conductivity would increase upon CO adsorption and decrease following CO oxidation, in consistence with the reported experimental results. This work can help understand the origins of ZnO-based sensors’ performances and the development of novel gas sensors with higher sensitivity and selectivity.