Journal Article

Periodically Pulsed Polarization Gas Sensors Based on Au|YSZ: Mechanism of NOsub.x Detection

Moos, Ralf, Zosel, Jens, Donker, Nils, Schönauer-Kamin, Daniela

2026

Overview

What are the main findings? * Pulsed polarization with Au electrodes on YSZ shows that NO[sub.2] accelerates self-discharge from the beginning, while NO, CO, and H[sub.2] slow down discharge in the late stage. C[sub.3]H[sub.6] does not affect the discharging behavior. * A lower O[sub.2] content slows down discharge and intensifies the NO[sub.2] effect. Pulsed polarization with Au electrodes on YSZ shows that NO[sub.2] accelerates self-discharge from the beginning, while NO, CO, and H[sub.2] slow down discharge in the late stage. C[sub.3]H[sub.6] does not affect the discharging behavior. A lower O[sub.2] content slows down discharge and intensifies the NO[sub.2] effect. What are the implications of the main findings? * Oxygen supply and surface exchange at the triple-phase boundary are rate-determining during pulsed polarization. * NO and NO[sub.2] might be selectively distinguished from each other by choosing appropriate electrode materials. Oxygen supply and surface exchange at the triple-phase boundary are rate-determining during pulsed polarization. NO and NO[sub.2] might be selectively distinguished from each other by choosing appropriate electrode materials. Pulsed polarization of Au|YSZ gas sensors is examined to clarify the mechanism of NO[sub.x] detection under dynamic operation and to disentangle catalytic surface effects from electrochemical relaxation. Using gold electrodes with substantially lower catalytic activity than platinum explicitly enables this mechanistic separation. During pulsed polarization, periodic voltage pulses are followed by self-discharge under open-circuit conditions, and the response is measured based on the self-discharge rate. NO[sub.2] consistently accelerates the self-discharge from the beginning, whereas NO slows the relaxation predominantly at later times. CO and H[sub.2] produce similar delaying effects, and C[sub.3]H[sub.6] shows no measurable influence under the tested conditions. Decreasing ambient O[sub.2] slows the discharge and amplifies the NO[sub.2] effect, which indicates that oxygen supply and surface exchange at the triple-phase boundary are rate determining. A Pt-containing catalytic overlayer drives local NO/NO[sub.2] interconversion toward equilibrium so that both gases yield to an accelerated self-discharge. These findings support a mechanistic picture in which NO[sub.2] provides effective oxygen equivalents that accelerate discharge, whereas NO, CO, and H[sub.2] consume oxygen and slow down discharge. Overall, this establishes a materials-based approach for distinguishing between NO and NO[sub.2] and evaluating the underlying mechanism during pulsed polarization.

• Publisher: MDPI AG
• Subject: Sensors