Microheater-based catalytic hydrogen sensor: Operando X-ray absorption spectroscopy study of Pd–Pt catalyst chemistry

Microheater-based catalytic combustion gas sensors are currently available in stock and are expected to dominate the market in the near future. To increase the sensor response and maintain long-term stability, the catalyst chemistry under operating conditions is being studied extensively. Here we report an operando X-ray absorption spectroscopy study of a microheater catalytic hydrogen sensor based on anodic alumina with a Pd : Pt molar ratio of 3 : 1 in the catalyst. When the sensor operates in air, palladium oxidation blocks hydrogen combustion. Only after the reduction of PdO to metallic Pd in presence of hydrogen at 38 °C, the hydrogen catalytic oxidation manifests itself as a sharp increase in sensor response from 0 to 15 mV/vol% H2. The observed feature is important for detecting low hydrogen concentration with no response lag, decreasing the operating temperature of the sensor, and measuring in pulsed mode.