Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors—The Influence of Humidity

Cristian E Simion,Ionel Mercioniu,Catalina G Mihalcea,Ovidiu G Florea,Adelina Stanoiu,Daniela Ghica,Corneliu Ghica,Simona Somacescu

doi:10.3390/chemosensors9090244

Cristian E Simion, Ionel Mercioniu + Show 6 more

Open Access

https://doi.org/10.3390/chemosensors9090244

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Abstract

Polycrystalline NiO thick film-based gas sensors have been exposed to different test gas atmospheres at 250 °C and measured via simultaneous electrical resistance and work function investigations. Accordingly, we decoupled different features manifested toward the potential changes, i.e., work function, band-bending, and electron affinity. The experimental results have shown that the presence of moisture induces an unusual behavior toward carbon monoxide (CO) detection by considering different surface adsorption sites. On this basis, we derived an appropriate detection mechanism capable of explaining the lack of moisture influence over the CO detection with NiO-sensitive materials. As such, CO might have both chemical and dipolar interactions with pre-adsorbed or lattice oxygen species, thus canceling out the effect of moisture. Additionally, morphology, structure, and surface chemistry were addressed, and the results have been linked to the sensing properties envisaging the role played by the porous quasispherical–hollow structures and surface hydration.

Highlights

Nickel oxide (NiO) was obtained by a hydrothermal synthesis method starting from Ni(NO3 )2 hydrated as inorganic precursors, water as the solvent, ethylene glycol (EG) as the template, and ethylenediaminetetraacetic acid (EDTA) as the complexing agent
No secondary phase has been observed in the X-ray diffraction (XRD) pattern, within the detection limit of 1–2%
NiO-based gas sensors operated under in-field conditions

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Metal oxide-based gas sensors (MOX) are among the foremost versatile type of sensors, being capable of detecting a wide variety of gases under in-field operating conditions [1–4]. The operating principle of MOX gas sensors relies on the electrical resistance changes with respect to the gas-surface interaction processes. When operated at the optimum gas detection temperature, the appearance of a reducing gas (such as carbon monoxide—CO)

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Conclusion