Study on the aging pattern of Pt-Au alloy oxygen-pumping electrode of NOx sensor

Abstract

The catalytic activity of the oxygen-pumping electrode in automotive nitrogen oxide sensors has an essential effect on the final measurement accuracy of nitrogen oxides. To investigate the variation pattern of catalytic activity of Pt-Au alloy oxygen-pumping electrode affected by Au content and aging time, the corresponding three samples with various Au content were prepared by high-temperature co-fired ceramic (HTCC) process. All samples were subjected to long-term and high-temperature aging in a simulated automotive exhaust atmosphere, and the electrodes at different aging stages were tested for AC impedance and characterized for morphology. The results of testing show that the catalytic activity of the Pt-Au alloy electrodes decreases with the increase of Au content. At the same time, the catalytic activity of the electrodes also decays exponentially with the increasing aging time and stabilizes at about three weeks. The explanation is that as the Au content increases and aging proceeds, the electrochemical reaction triple phase boundaries (TPBs) decrease, and the catalytic activity of the electrodes decreases.