Ab Initio Studies of Work Function Changes Induced by Single and Co-Adsorption of NO, CO, CO2, NO2, H2S, and O3 on ZnGa2O4(111) Surface for Gas Sensor Applications

In this study, first-principles density functional theory (DFT) calculations were employed to investigate the effects of single and binary gas adsorption of NO, CO, CO2, NO2, H2S, and O3 on the ZnGa2O4(111) surface. For single-gas adsorption, O3 adsorbed on surface Ga sites induces a pronounced work-function increase of 0.97 eV, whereas H2S adsorption at surface O sites yields the strongest adsorption energy (−1.21 eV), highlighting their distinct electronic interactions with the surface. For binary co-adsorption, the NO2-O3 pair adsorbed at Ga-coordinated sites produces the largest work-function shift (1.88 eV), while adsorption at Zn sites results in the most stable configuration, with an adsorption energy reaching −3.98 eV. These results indicate that co-adsorption of highly electronegative gases can significantly enhance charge transfer and sensing response. In contrast, mixed oxidizing–reducing gas pairs, such as NO2-H2S, lead to a markedly suppressed work-function variation (−0.02 eV), suggesting reduced sensor sensitivity due to compensating charge-transfer effects. Overall, this work demonstrates that gas-sensing behavior on ZnGa2O4(111) is governed not only by individual gas–surface interactions but also by cooperative and competitive effects arising from binary co-adsorption, providing insights into realistic multi-gas sensing environments.