Ab initio thermodynamic study of SnO$_2$(110) surface in an O$_2$ and NO environment: a fundamental understanding of gas sensing mechanism for NO and NO$_2$

TL;DR

This study uses ab initio thermodynamics to analyze the SnO$_2$(110) surface in O$_2$ and NO environments, revealing stable surface phases and providing insights into the gas sensing mechanism for NO and NO$_2$ gases.

Contribution

It presents a detailed ab initio thermodynamic analysis of SnO$_2$(110) surfaces in gas environments, elucidating stable surface phases and the sensing mechanism for NO and NO$_2$ gases.

Findings

Identified stable surface phases under different oxygen and NO conditions.

Determined the most stable NO-adsorbed surfaces in NO-rich environments.

Provided electronic structure insights into gas adsorption and sensing mechanisms.

Abstract

For the purpose of elucidating the gas sensing mechanism of SnO$_2$ for NO and NO$_2$ gases, we calculate the phase diagram of SnO$_2$(110) surface in contact with an O$_2$ and NO gas environment by means of {\it ab initio} thermodynamic method. Firstly we build a range of surface slab models of oxygen pre-adsorbed SnO$_2$(110) surfaces using (1$\times$1) and (2$\times$1) surface unit cells and calculate their Gibbs free energies considering only oxygen chemical potential. The fully reduced surface containing the bridging and in-plane oxygen vacancies in the oxygen-poor condition, while the fully oxidized surface containing the bridging oxygen and oxygen dimer in the oxygen-rich condition, and the stoichiometric surface in between, were proved to be most stable. Using the selected plausible NO-adsorbed surfaces, we then determine the surface phase diagram of SnO$_2$(110) surfaces in ($\Delta\mu_\text{O}$, $\Delta\mu_\text{NO}$) space. In the NO-rich condition, the most stable surfaces were those formed by NO adsorption on the most stable surfaces in contact with only oxygen gas. Through the analysis of electronic charge transferring and density of states during NO$_x$ adsorption on the surface, we provide a meaningful understanding about the gas sensing mechanism.