Enhancement of SnO2-Based Gas Sensor Performance through WO3 Receptor Surface Modification
Authors: Ren Tao , Suematsu Koichi , Watanabe Ken , Shimanoe Kengo 
Published: December 2024

The widespread application of SnO2-based semiconductor gas sensors stems from their exceptional sensitivity and stability in detecting various gases, including volatile organic compounds (VOCs). The fundamental mechanism involves the interaction between the semiconductor material's surface and oxidizing or reducing gases, resulting in a change in electrical resistance. Additionally, the receptor function stands out as a pivotal factor influencing the sensing performance of chemical sensors [1]. Modification of the surface of SnO2 with acidic or basic oxides has been shown to effectively alter its catalytic properties, thereby changing the reaction pathways during ethanol oxidation. This study focuses on an acidic oxide, WO3, which is a promising candidate receptor for improving gas selectivity due to its property of not adsorbing oxygen as well as its high sensitivity to VOC gases. Our previous results demonstrated that similar ethanol consumption rates are observed between neat SnO2 and WO3-loaded SnO2 within the range of 150 to 350℃ during catalytic combustion. Over neat SnO2, dehydrogenation is primarily observed, resulting in CH3CHO being the main product at 150℃, with peak production occurring at 250℃, gradually transitioning to CO2. Furthermore, CO2 generation is initiated at 250℃ and rapidly increases at higher temperatures, attributed to the high catalytic activity of SnO2. Conversely, loading WO3 onto the surface of SnO2 successfully modifies the reaction pathway of ethanol oxidation, with the primary reaction shifting from dehydrogenation to dehydration and selectively generating C2H4 at temperature exceeding 300℃. When materials synthesized by different compositing methods are applied in thick film sensors, the interaction between WO3 and SnO2 significantly influences their sensing properties, with the fine dispersion of WO3 playing a crucial role. Both WO3-loaded and mixed SnO2 exhibited higher responses compared to neat SnO2, with the loaded group showing the highest response to ethanol and acetone. Additionally, 3 mol% WO3-loaded SnO2 demonstrated selective detection properties, with the highest response to 20 ppm acetone at 250℃, which was 22.8 times higher than that of neat SnO2.

Efforts have also been made to enhance the gas sensing properties of VOC gases by integrating thermal modulation techniques into miniaturized gas sensors, known as MEMS sensors. These sensors enable operation in a pulse-driven mode [2,3], where the microheater is capable of rapidly heating and cooling the sensor device. Such a driving mode offers selectivity due to the gas adsorption and combustion properties occurring during the heating and cooling phases. By utilizing the pulse-driven mode, it is suggested that during the low-temperature heat-off phase, VOC gases adsorb to the surface of particles, followed by their combustion during the high-temperature heat-on phase. This gas detection model facilitates enhancements in both sensitivity and selectivity, capitalizing on the gas adsorption, diffusion, and catalytic combustion properties on the particle surface. Such developments offer significant improvements in gas detection based on catalytic combustion properties. These insights are crucial for the development of high-performance volatile organic compound gas sensor materials.

References

[1] Yamazoe, N. and Shimanoe, K., Sens. Actuators B Chem., 138(1), 100-107 (2009)

[2] Suematsu, K., Harano, W., Yamasaki, S., Watanabe, K., and Shimanoe, K., ACS Applied Electronic Materials, 2(12), 4122-4126 (2020).

[3] Suematsu, K., Hiroyama, Y., Harano, W., Mizukami, W., Watanabe, K., and Shimanoe, K., ACS sensors, 5(11), 3449-3456 (2020).