Palladium Oxide

palladium oxide is a highly insoluble thermally stable source of palladium suitable for glass, optic and ceramic applications. It is immune to acids but reverts to palladium metal and oxygen gas above about 900 °C.

Stable nanoparticles of palladium oxide were obtained by dissolving palladium nitrate in water at a concentration around 10-4 M. They were characterized by different techniques, including TEM microscopy, XRD, XPS, UV-visible absorption spectroscopy and Raman spectroscopy, in conjunction with DFT calculations. The colloidal stability of the obtained nanoparticles was confirmed by zeta-potential measurements.

Optical properties of palladium oxide have been investigated by measuring the optical absorption and photoconductivity in thin films. These films are oxidized by air and show an extrapolated band gap of 2.13+-0.03 eV and 2.67+-0.13 eV (Figure 1).

PdO thin film sensors have been prepared and tested for ozone detection. Depending on the thickness of the PdO film, oxidation temperature and humidity, a sensor response can be achieved in 7-8 times.

The p-type conductivity of palladium oxide is determined by the thermo-power (Seebeck coefficient S). In a comparison with ultrathin palladium oxide films, it can be shown that films with thickness of about 35 nm are characterized by higher values of sensor response.

DFT calculations reveal a short hydrogen bond distance O – – – H-O-H (1.631 A) in the PdO/H2O complex, along with a significant negative charge-transfer from PdO to H2O (-0.085 e). The presence of this species points to a form of palladium oxide strongly coordinated to water.