Embedding Pd into SnO₂ drastically enhances gas sensing

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Combustion aerosol processes enable unique noble metal integration into semiconducting particles.
• Tin dioxide (SnO2) is a widely studied semiconductor for gas sensing applications.
• Noble metals like palladium (Pd) are known to enhance the catalytic and sensing properties of metal oxides.

Purpose of the Study:

• To synthesize monocrystalline SnO2 particles embedded with palladium (Pd) and/or palladium oxide (PdO) using flame spray pyrolysis (FSP).
• To investigate the effect of embedded Pd/PdO on the gas sensing performance of SnO2-based sensors.
• To correlate the synthesis parameters with particle characteristics and sensor response.

Main Methods:

• Flame spray pyrolysis (FSP) for synthesizing Pd-embedded SnO2 particles.
• Post-synthesis treatments including air annealing and nitric acid leaching.
• Characterization using nitrogen adsorption, high-resolution electron microscopy, and X-ray photoelectron spectroscopy (XPS).
• Gas sensing measurements of acetone and carbon monoxide (CO) at 350 °C and 50% relative humidity.

Main Results:

• Monocrystalline SnO2 particles with embedded Pd/PdO were successfully synthesized, with crystal size controlled by precursor concentration.
• The embedded fraction of Pd ranged from 30-80%, tunable by FSP parameters.
• Pd/PdO embedding significantly boosted sensor response to 1 ppm acetone and CO, by 2-6 times at low Pd content (0.2 mol%) and up to two orders of magnitude at higher content (1 mol%).
• Baseline resistance measurements indicated altered transducing properties due to Pd atoms in the SnO2 lattice or Pd/PdO clusters.

Conclusions:

• Flame spray pyrolysis is an effective method for creating SnO2 particles with embedded noble metals.
• Embedding Pd/PdO into SnO2 dramatically enhances gas sensor sensitivity and response.
• The enhanced sensing is attributed to the catalytic activity and nanoelectrode effects of the embedded Pd/PdO species within the SnO2 matrix.