Solution-based synthesis of efficient WO3 sensing electrodes for high temperature potentiometric NOx sensors

Electrode nanostructures as well as species at electrode–electrolyte interfaces have substantial influence on the sensitivity, response and recovery times of electrochemical sensors. YSZ-based potentiometric NOx sensors with WO3 sensing electrodes have shown considerable promise for enhanced sensitivity. In this study, we present a solution-based method using peroxytungstate solutions to fabricate WO3 electrodes. UV-ozone treatment of the YSZ was necessary for effective bonding of the WO3 to the YSZ. The resulting WO3 electrode was found to exhibit different surface nanostructures, better mechanical stability, faster recovery times, and better sensitivity than devices made from conventional ceramic WO3 powders. Upon UV-ozone treatment, the YSZ surfaces become more reactive towards the acidic peroxytungstate solution and results in monoclinic ZrO2 formation at the electrode–electrolyte interface, which, based on earlier studies, we propose to be responsible for the improved sensor sensitivity. Better adhesion of the peroxytungstate-based WO3 electrode to the YSZ electrolyte is related to the improved recovery times.