# 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

## TL;DR

This study uses computer simulations to show how different gases affect the electronic properties of a ZnGa2O4 surface, which is important for improving gas sensor performance.

## Contribution

The study reveals how co-adsorption of gases, especially O3 and NO2, enhances sensor sensitivity through significant work function changes.

## Key findings

- Co-adsorption of O3 and NO2 on ZnGa2O4(111) leads to the largest work function shift and adsorption energy.
- H2S is the only gas that decreases the work function upon adsorption on ZnGa2O4(111).
- Mixed oxidizing–reducing gas pairs like NO2-H2S reduce work function variation due to compensating charge-transfer effects.

## Abstract

What are the main findings?
Co-adsorption of O3 and NO2 on ZnGa2O4(111) significantly enhances electron transfer, leading to the most significant work function variation and adsorption energy, thereby improving gas sensor sensitivity.H2S is the only gas among those studied that decreases the work function upon adsorption on the ZnGa2O4(111) surface.

Co-adsorption of O3 and NO2 on ZnGa2O4(111) significantly enhances electron transfer, leading to the most significant work function variation and adsorption energy, thereby improving gas sensor sensitivity.

H2S is the only gas among those studied that decreases the work function upon adsorption on the ZnGa2O4(111) surface.

What are the implications of the main findings?
When H2S forms a binary co-adsorption with other gases, the overall work function variation is reduced.These results highlight the unique role of H2S in modulating surface electronic properties during gas co-adsorption.

When H2S forms a binary co-adsorption with other gases, the overall work function variation is reduced.

These results highlight the unique role of H2S in modulating surface electronic properties during gas co-adsorption.

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.