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New Insight into H2S Sensing Mechanism of Continuous SnO2–CuO Bilayer Thin Film: A Theoretical Macroscopic Approach

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journal contribution
posted on 2016-04-01, 00:00 authored by Zhoubin Boroun, Mohammad Ghorbani, Ali Moosavi, Raheleh Mohammadpour
SnO2–CuO is one the most promising systems for detection of detrimental H2S gas. Although previous experimental research has suggested a sulfidation reaction to explain selectivity toward H2S, little is known about the origin of change of electrical response of this system by changing the H2S gas concentration. In this study the relation between sensing response of continuous SnO2–CuO bilayer thin film and H2S gas concentration is computed based on changeability of chemical composition of covellite CuxS. For this purpose, chemical activity of sulfur as a function of atomic fraction in covellite copper sulfide is estimated using Gibbs energies of formation and chemical thermodynamics. By considering equilibrium between covellite and H2S, a relationship between chemical composition of the copper sulfide and concentration of the gas at 150 °C is obtained. Utilizing electronic physics and finite difference method, electrical response of the sensor as a function of H2S concentration is computed. Results show that increasing H2S concentration from 0.053 ppm to saturation value of 455 ppm changes chemical composition of the upper conductive covellite layer from Cu1.5S to CuS, which increases the response of the system. The model explains why SnO2–CuO systems can detect H2S gas from sub-ppm levels to hundreds of ppm without involving oxygen adsorption/desorption phenomena. Finally, the theoretical response–concentration curve is compared with the previous experimental curve. Despite a few differences, the theoretical curve matches relatively well with the experimental one.

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