Oxygen detection using junctions based on thin films of yttria-stabilized zirconia doped with platinum nanoparticles and pure yttria-stabilized zirconia

Here we develop new types of ceramic junctions composed of two plane-parallel ceramic electrodes: one of them consists of yttria-stabilized zirconia (YSZ), the other one is composed of YSZ doped with platinum nanoparticles. The bottom electrode is either of pure YSZ or of doped YSZ + Pt with the top electrode being of the opposite material. The concentration of platinum has been varied at 2.5, 4.5 and 6.5 mol%. The tests are made in an experimental setup allowing the exchange of gas atmosphere with variable oxygen content at fixed temperature or the gradual change in the temperature up to about 400 °C in a pure nitrogen medium. For YSZ/YSZ + Pt junctions the potential difference is positive, while for YSZ + Pt/YSZ junctions it is negative. At a fixed temperature we investigate the rough response to oxygen of different structures by periodically exchanging the oxygen from 0.9% (technical grade nitrogen) to 21% (air). Good reproducibility of the results is maintained both in the regime of nitrogen flowing and air flowing. The detailed investigation of the kinetics of potential relaxation revealed that it is governed by the diffusion of oxygen in the ceramics. The fastest response is detected with the junctions YSZ + Pt/YSZ with 6.5 mol% of platinum. We also study the potential difference at varying oxygen concentration by tuning the ratio between air and nitrogen. The functional dependence is Nernstian type like in potentiometric gas sensors, which is well-described by the respective equation if the junction is considered as a sort of thermocouple with the electrodes being the contact point. This makes our junctions promising as oxygen sensors at low working temperature and very low oxygen content.