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. Solid electrolyte gas sensors (SESs) based onyttria-stabilized zirconia (YSZ) are suitable to detect traces of redox componentsin inert gases. Usually, their signals are generated as a voltage betweentwo electrodes at open circuit potential or as a current flowing betweenconstantly polarized electrodes. In these rather stationary modes ofoperation, SESs often lack the desired selectivity. This drawback can becircumvented if SESs are operated in dynamic electrochemical modes thatutilize the differences of electrode kinetics for single components todistinguish between them. Accordingly, this contribution is directed to theinvestigation of cyclic voltammetry and square-wave voltammetryas methods to improve the selectivity of SESs. For this, a commercial SES of the type “sample gas, Pt | YSZ | Pt, air” was exposed to mixtures containing NO and O2 in N2 in the temperature range between 550 and 750  ∘ C. On cyclic voltammograms (CVs), NO-related peaks occur in the cathodic directionat polarization voltages between −0.3 and −0.6  V at scan rates between100 and 2000 mV s −1 and temperatures between 550 and 750  ∘ C.Their heights depend on the NO concentration, on the temperature and on thescan rate, providing a lower limit of detection below 10 ppmv, with thehighest sensitivity at 700  ∘ C. The O2 -related peaks,appearing also in the cathodic direction between −0.1 and −0.3  V at scanrates between 100 and 5000 mV s −1 , are well separated from theNO-related peaks if the scan rate does not exceed 2000 mV s −1 . Square-wave voltammograms (SWVs) obtained at a pulse frequency of 5 Hz, pulses of 0.1 mV andsteps of 5 mV in the polarization range from 0 to −0.6  V also exhibitNO-related peaks at polarization voltages between −0.3 and −0.45  Vcompared to the Pt–air (platinum–air) electrode. In the temperature range between 650 and750  ∘ C the highest NO sensitivity was found at 700  ∘ C. O2 -related peaks arise in the cathodic direction between −0.12 and −0.16  V,increase with temperature and do not depend on the concentration of NO.Since capacitive currents are suppressed with square-wave voltammetry, this method providesimproved selectivity. In contrast to cyclic voltammetry, a third peak was found with square-wave voltammetry at −0.48  V and a temperature of 750  ∘ C. This peak does not depend on theNO concentration. It is assumed that this peak is due to the depletion of anoxide layer on the electrode surface. The results prove the selectivedetection of NO and O2 with SESs operated with both cyclic voltammetry and square-wave voltammetry.

journal of sensors and sensor systems

Cyclic and square-wave voltammetry for selective simultaneous NO and O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; gas detection by means of solid electrolyte sensors