Ethanol gas sensing mechanisms of p-type NiO at room temperature
Conductometric gas sensors based on metal oxide semiconductors (MOS) usually require high temperature operation, increasing their energy consumption and limiting their applicability. However, room temperature operation with these devices still remains a challenge in many sensor-analyte systems due in part to the low or null response and recovery speeds obtained at this temperature. In this work, the conductometric response of p- type NiO ceramic samples to ethanol is studied under room temperature operation. An anomalous response consisting in an unexpected resistance decrease upon ethanol exposure is observed depending on sample texturing, which is tuned by changing the temperature at which the samples are synthesized. This anomalous response is characterized by fast response and recovery times. A model based on two competing mechanisms, consisting in either an electron transfer from NiO to the ethanol molecule or the catalytic decomposition of adsorbed ethanol, is proposed to explain the observed anomalous response. Extending this model to other MOS could pave the way for fast sensors operating at room temperature.
This work was supported by the V-PRICIT of Comunidad de Madrid through the research project PR65/19-22335 and by the RTI2018- 097195-B-I00 project supported by MCI/AEI/FEDER, UE. Authors thank the ESCA-microscopy staff at the Elettra Synchrotron for their help during XPS and additional sensitivity measurements. J.B. acknowledges financial support from the Comunidad de Madrid through the Talento fellowship 2017-T2/IND-5617.
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