Electrochemical characteristics of limiting current sensors with LSM-YSZ and LSM-CGO-YSZ composite electrodes

Abstract

Limiting current gas sensors with Pt electrodes are widely used to detect gaseous species, such as O2, CO, HC, and NOx, from exhaust gases generated by the incomplete combustion of fossil fuels. In this study, aperture-type limiting current sensors were fabricated based on La0.8Sr0.2MnO3 (LSM)–yttria-stabilized zirconia (YSZ) and LSM–Gd0.1Ce0.9O2-d (CGO)–YSZ composites. The potential of these composites as alternative electrodes for O2 and CO sensing was evaluated. The composite electrodes exhibited current–voltage curves that are typical for limiting current sensors. LSM–CGO–YSZ registered higher limiting current values than those of the commercial Pt and LSM–YSZ electrodes in O2 and CO atmospheres. The formation of a resistive secondary La2Zr2O7 phase at the LSM/YSZ interface of LSM–YSZ deteriorates the electrochemical reaction and increases the polarization resistance of the electrode in the CO environment. The addition of CGO prevented the formation of the secondary phase, which lowered the ohmic and polarization resistances of LSM–CGO–YSZ compared to that of the LSM–YSZ composite. However, increasing the CGO concentration from 10 to 40 wt% weakened the adhesion of LSM and reduced the triple phase boundaries, which increased the electrode polarization resistance in both O2 and CO atmospheres.