Non-ohmic current-voltage and impedance characteristics of electroadsorptive Zn2SnO4

Although Zn2SnO4 is known as a CO-selective gas sensor that responds to CO gas more sensitively than to H-2 gas, non-ohmic I-V curves and thus voltage-dependent sensitivity were observed when used with Pt electrodes. In order to study the observed voltage-dependent resistance, one side of Zn2SnO4 was contacted with ZnO (or SnO2). In this configuration, the asymmetric I-V curve was shown due to the ohmic interface between ZnO (or SnO2) and Zn2SnO4, and the non-ohmic interface between Pt and Zn2SnO4. The impedance spectra of the ZnO/Zn2SnO4 layered sample also indicated that the interfacial resistance of (-) Pt/Zn2SnO4(+) increased with applied bias. The time-dependent current and potential measurements showed the slowly increasing resistance when Zn2SnO4 was positively biased, (-) Pt/Zn2SnO4(+). This observation was explained by the field-induced adsorption of oxygen gas (or the electroadsorptive effect). (C) 2001 The Electrochemical Society.