Abstract
In this work, p-type oxide semiconductors, Co3O4 and complex oxides NixCo3−xO4 (x = 0.04, 0.07, 0.1), were studied as materials for sub-ppm H2S sensing in the temperature range of 90–300 °C in dry and humid air. Nanocrystalline Co3O4 and NixCo3−xO4 (x = 0.04, 0.07, 0.1) were prepared by coprecipitation of cobalt and nickel oxalates from nitrate solutions and further annealing at 300 °C. The surface reactivity of the obtained materials toward H2S both in dry and humid atmosphere (relative humidity at 25 °C R.H. = 60%) was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Sensor measurements showed a decrease in sensor signal toward 1 ppm H2S with an increase in Ni content because of a decrease in chemisorbed surface oxygen species. On the other hand, sensor signal increases for all samples with increasing the relative humidity that depends on reactivity of the surface hydroxyl groups, which stimulate the decomposition of surface sulfites and provide better surface regeneration at higher temperature. This assumption was additionally confirmed by the faster saturation of the conductivity curve and a decrease in the sensor response time in humid air.
Highlights
Hydrogen sulfide is a highly toxic, reactive and flammable gas that is found in various technological processes
It is extremely important to monitor its concentration in the air at a level below 100 ppm of H2 S, which is considered to be immediately dangerous to life and health (IDLH)
Semiconductor gas sensors based on n-type metal oxides are one of the most commonly used commercial hydrogen sulfide detectors [1]
Summary
Hydrogen sulfide is a highly toxic, reactive and flammable gas that is found in various technological processes. Semiconductor gas sensors based on n-type metal oxides are one of the most commonly used commercial hydrogen sulfide detectors [1]. For this type of devices, the problem of the negative influence of ambient humidity often arises [2,3]. The effect of humidity had been actively studied for the most common oxides used in gas sensors, such as SnO2 [4,5], WO3 [6], ZnO [7], In2 O3 [8]. The blocking effect of adsorbed water on WO3 can be overcome by aging processes, leading to the appearance of surface hydroxyl groups [9]
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