Mixed-potential gas sensor with layered Au,Pt-YSZ electrode: Investigating the sensing mechanism with steady state and dynamic electrochemical methods

- Layered Au,Pt-YSZ mixed potential sensing electrodes with different Au layer of two different thicknesses were studied by open circuit potentiometry (OCP) and cyclic voltammetry (CV).
- The combination of the steady-state (OCP) and the dynamic (CV) electrochemical methods brings a more comprehensive view of potential forming processes at the electrode.
- The Layered Au,Pt-YSZ electrode with thicker Au layer showed a reduced catalytic activity for oxygen reduction reaction, but a better sensing response to CO.

Mixed potential gas sensors with layered Au,Pt-YSZ electrode comprising a thick-film Pt-YSZ electrode and a covering thin-film Au layer deposited in two different thicknesses, respectively, were studied in this work. It was shown by GD-OES analysis that the Au layer is not uniformly admixed with the Pt-YSZ bulk after firing treatment at 850 °C, but results in a gradient of Au from top over the thickness of the electrode. Surprisingly, also this kind of layered electrode exhibits a mixed-potential characteristic, which was confirmed by open circuit potential measurement. Better sensitivity to CO was found for the electrode with thicker Au layer, and was attributed to the reduced catalytic activity for the oxygen reduction reaction by addition of Au. This aspect was investigated by cyclic voltammetry, and the dependence of electrochemical behaviors of the electrodes on temperature was studied as well. Over all, the experiments have clearly shown, that mixed potential formation at the Au,Pt-YSZ MPE can be dominated by a relatively thin Au,Pt-layer in the top part of the porous electrode material.