Selectivity improvement towards hydrogen and oxygen of solid electrolyte sensors by dynamic electrochemical methods

摘要

Solid electrolyte sensors (SES) based on yttria-stabilized zirconia (YSZ) can exhibit improved selectivity to redox active gases when they are operated with dynamic electrochemical methods like cyclic voltammetry (CV) or impedance spectroscopy (IS). To clarify basic electrochemical processes at the measuring electrode, experiments in the temperature range 650-750 degrees C with precise control of hydrogen, oxygen, and water vapor concentrations in non-equilibrated gas mixtures have been conducted. The results show that it is possible to detect hydrogen and oxygen selectively in oxidizing and in reducing gas mixtures with SES operated with CV at different scan rates and polarization ranges.Hydrogen-related peaks appear during anodic scan direction at potentials between -0.4 and -0.2 V vs. Pt/air reference and scan rates between 10 and 100 mV/s. Their heights increase with H-2-concentration, temperature, and negative shift of the negative CV limit, providing a lower limit of detection below 5 vol.-ppm and an upper limit of detection at around 100 vol.-ppm at 700 to 750 degrees C. Oxygen-related peaks arise in cathodic scan direction at potentials between -0.1 and -0.4 V and scan rates between 100 and 1000 mV/s. Their heights also increase with O-2-concentration and temperature, providing a lower limit of detection below 5 vol.-ppm and an upper limit of detection above 200 vol.-ppm at 650 degrees C. Water vapor causes decreasing H-2-related peak heights, suggesting an occupation of electrode surface places needed for H-2 reaction. In contrast to that, additionally conducted impedance spectroscopy experiments in the frequency range from 0.2 to 10(5) Hz did not provide further information about the selective detection of hydrogen and oxygen in non-equilibrated gas mixtures.