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

Abstract

SnO 2 −CuO is one the most promising systems for detection of detrimental H 2 S gas. Although previous experimental research has suggested a sulfidation reaction to explain selectivity toward H 2 S, little is known about the origin of change of electrical response of this system by changing the H 2 S gas concentration. In this study the relation between sensing response of continuous SnO 2 −CuO bilayer thin film and H 2 S gas concentration is computed based on changeability of chemical composition of covellite Cu x S. 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 H 2 S, 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 H 2 S concentration is computed. Results show that increasing H 2 S concentration from 0.053 ppm to saturation value of 455 ppm changes chemical composition of the upper conductive covellite layer from Cu 1.5 S to CuS, which increases the response of the system. The model explains why SnO 2 −CuO systems can detect H 2 S 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.

Ultrafine nanoparticles of W-doped SnO2for durable H2S sensors with fast response and recovery

“…The kinetics of a tandem process is usually determined by the rate of the slowest reaction which may differ in the response and recovery process. 48 However, our discussion is far from satisfactory and further experiments are needed to fully illustrate the picture behind the complicated sensing behavior.…”

Importance of N-P-N Junction in H2S Sensing Process of SnO2-CuO Heterostructures: A Theoretical Macroscopic Approach

“…The previous 2D thin bilayer model explained some aspects of H 2 S sensing process of SnO 2 -CuO system [22], [23], however, entirely new issues will be addressed in this paper, which as follows:…”

“…Although experimental reports about H 2 S sensing performance of SnO 2 -CuO system are abundant, very few theoretical works have been reported in this regard [22], [23]. In previous theoretical model, role of CuS and how its electrical conductivity affects Response-Concentration [22] and Response-Temperature [23] curves in H 2 S sensing performance of SnO 2 -CuO thin bilayer, were discussed. Fig.…”

“…1 demonstrates the role of CuS according to the thin bilayer model. Even though CuS layer is not in direct contact with electrodes, it's electrical conductivity determine the resistance of thin bilayer system [22].…”

H2S Sensing by Hybrids Based on Nanocrystalline SnO2 Functionalized with Cu(II) Organometallic Complexes: The Role of the Ligand Platform

“…These hybrid materials can be considered as a model system in which the central ion provides selectivity in H 2 S detection, and the choice of an organic ligand allows for varying the magnitude of the signal. Surface modification of n -type SnO 2 with p -type CuO is a well-known method for the selective increase of SnO 2 sensitivity to H 2 S [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. The selectivity mechanism for the CuO/SnO 2 system was first proposed in the earliest works of Yamazoe and co-workers [ 8 ] and confirmed for materials obtained in different forms: ceramics and thick films [ 11 , 15 , 22 ], thin films [ 9 , 12 , 13 , 16 ], planar thin film heterostructures [ 10 , 23 ], and 1D nanostructures [ 14 , 17 , 18 , 19 , 20 , 21 ].…”