Rhodium Oxide Surface-Loaded Gas Sensors.

Area of Science:

• Materials Science
• Chemical Engineering
• Sensor Technology

Background:

• Metal oxides are widely used in gas sensors, often enhanced by noble metal surface-loading for improved stability and sensing.
• While empirical evidence shows noble metals significantly alter sensor performance, the underlying mechanisms remain poorly understood.

Purpose of the Study:

• To systematically investigate the sensing mechanisms of rhodium-loaded metal oxide sensors (WO₃, SnO₂, In₂O₃).
• To elucidate the role of rhodium cluster oxidation state in gas sensing performance.

Main Methods:

• Utilized X-ray diffraction (XRD), high-resolution scanning transmission electron microscopy (HR-STEM), and direct current (DC) resistance measurements.
• Employed operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and operando X-ray absorption spectroscopy (XAS) for in-situ analysis.

Main Results:

• Rhodium clusters were found to be oxidized under normal sensing conditions, dominating sensing via Fermi-level pinning.
• A mechanism switch was observed in low-oxygen environments, where reduced metallic rhodium clusters led to altered resistance and gas-surface interactions.
• Identified generalities and sample-specific aspects in rhodium-loaded sensor mechanisms.

Conclusions:

• The study clarifies the dual sensing mechanisms in noble metal-loaded metal oxide sensors based on the metal cluster's oxidation state.
• Findings provide a deeper understanding of how noble metal loading influences gas sensor performance, crucial for designing advanced gas detection systems.