A computational chemist approach to gas sensors: Modeling the response of SnO₂ to CO, O₂, and H₂O Gases

Abstract

A general bottom-up modeling strategy for gas sensor response to CO, O(2), H(2)O, and related mixtures exposure is demonstrated. In a first stage, we present first principles calculations that aimed at giving an unprecedented review of basic chemical mechanisms taking place at the sensor surface. Then, simulations of an operating gas sensor are performed via a mesoscopic model derived from calculated density functional theory data into a set of differential equations. Significant presence of catalytic oxidation reaction is highlighted.

Identifying the Active Oxygen Species in SnO2 Based Gas Sensing Materials: An Operando IR Spectrsocopy Study

“…As observed already in synthetic air, no carbonyl-like donor species are formed. All in all, our results confirm the theoretical results reported recently 8,9 : the sensing of representative reducing gases, including humidity, seems to be governed by the interplay between surface reduction and reoxidation, which depends on the composition of the surrounding atmosphere, and will result in a certain concentration of oxygen vacancies i.e. surface charge and in the end sensor resistance.…”

“…Besides the obvious consequences for the transduction -this switch has major implications on the effect of band bending changes onto the measured sensing layer resistance -there are significant implications also for the 3 reception: additional to the reaction with ionosorbed oxygen species we have to take into consideration also the direct reaction between the reducing gases and the SnO 2 surface. In the absence of experimental evidence, a good starting point is the theory: recent DFT calculations for SnO 2 (101) and (110) surfaces, published by J.-M. Ducéré et al 8 and X. Wang et al 9 respectively, give a detailed description of the charge-transfer associated with CO oxidation. Consistently, it was found that CO reacts with 2-fold coordinated (bridging) oxygen forming CO 2 and an oxygen vacancy (equation 1), which acts as an adsorption site for molecular and atomic oxygen species (equation 2).…”

“…Adsorbed molecular oxygen may dissociate into two atomic oxygen species (equation 3a) or react with CO forming CO 2 and bridging oxygen (equation 3b). The formation and healing of oxygen vacancies is coupled with a charge transfer of approximately one electron per site (α = 1) 8,9 between SnO 2 and the adsorbed oxygen species. The chemical equations are simplified by disregarding the adsorption and desorption steps of the reaction educts/products.…”

“…Based on the theoretical calculations 8,9 and our experimental findings we have developed the following general model for the SnO 2 surface reaction using CO as an example for a simple reducing gas …”

Ab initio thermodynamic study of the SnO2(110) surface in an O2 and NO environment: a fundamental understanding of the gas sensing mechanism for NO and NO2

“…Compared to the CO sensing mechanism of SnO 2 (110) surface [43][44][45][46][47], the sensing properties strongly depends upon the concentration of oxygen in the ambient atmosphere: CO reacts with either directly stoichiometric surface or oxygen species O − 2 or O − , accompanying the release of electrons to the surface with or without formation of CO 2 [43].…”