Novel solid-state manganese oxide-based reference electrode for YSZ-based oxygen sensors

Various Mn-based oxides have been screened to find a suitable all-solid-state gas-insensitive reference-electrode (RE) for yttria-stabilized zirconia (YSZ)-based potentiometric oxygen sensor. The experimental observation of tubular YSZ-based sensors attached with each of the outer Mn-based oxide sensing electrodes (SEs) and the inner Pt-RE revealed that Mn2O3-SE was insensitive to all gases including oxygen at operating temperatures below 550 °C. Thus, the planar-like rod-type YSZ-based sensor using Pt-SE, Au-SE and Mn2O3-RE was then fabricated and its sensing performances were evaluated at 550 °C. As a result, the planar sensor using a couple of Pt-SE and Mn2O3–RE exhibited excellent responses to oxygen in the concentration range of 0.05–21 vol.% obeying Nernst equation and gave negligible responses to other co-existing gases. Close similarity of the results for tubular and planar sensors operated in a wide range of air/fuel (A/F) ratio indicated that the tubular YSZ-based sensor using the inner Pt-RE could be successfully miniaturized to the planar one using Mn2O3-RE without sacrificing its performance.