Electrochemical detection of volatile organic compounds using a Na3Zr2Si2PO12/Bi2Cu0.1V0.9O5.35 heterojunction device

A fast sodium ion conductor, NASICON (Na3Zr2Si2PO12), has been widely used for gas sensor applications. In this study, we demonstrate that a device combining NASICON with an oxygen-ion conductor of BiCuVOx (Bi2Cu0.1V0.9O5.35) can electrochemically detect volatile organic compounds (VOCs), such as ethanol, formaldehyde, and toluene. The sensing electrode made of BiCuVOx was attached onto a sintered NASICON disk at high temperature to produce an interfacial layer that had a different morphology and composition from those of NASICON and BiCuVOx, as observed by scanning electron microscopy-energy dispersive X-ray spectroscopy analysis. The device in which NASICON was fitted with the BiCuVOx-based electrode was found to efficiently detect VOCs in ppm concentrations. The sensor signal (electromotive force) exceeded 100 mV in response to 10 ppm HCOH at 400 °C, demonstrating the high sensitivity of the device. It also exhibited a relatively quick response, reproducible and stable sensor signals, and high selectivity to VOCs. The sensor responses followed behavior typical for mixed-potential-type gas sensors based on oxygen-ion conductors. It was thus suggested that the electrochemical oxidation of VOCs with oxide ions took place at the interfacial oxygen ion-conductive layer that was formed by the reaction of NASICON with BiCuVOx.

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► A device combining a sodium ion conductor of NASICON (Na3Zr2Si2PO12) with an oxygen ion conductor of BiCuVOx (Bi2Cu0.1V0.9O5.35) was fabricated.
► The device can electrochemically detect volatile organic compounds (VOCs).
► The electrochemical oxidation of VOCs with oxide ions occurred as the sensing reaction.
► The formation of an oxygen ion-conductive layer at the interface between NASICON and BiCuVOx was suggested.