Composition, structure, and electrochemical behavior of sol-gel derived nanoparticulate Pt thin films

A Pt sol was formed using a sol-gel derived methodology. This sol, and films formed from it, were characterized using various techniques. The nanoparticulate phase, seen by transmission electron microscopy (TEM), exhibited a notable temperature dependence, with the particles averaging 1-3 nm diam when dried at room temperature and 3-6 nm diam when dried at 400 deg C. X-ray photoelectron spectroscopy (XPS) confirmed the presence of metallic Pt in these films. The charge density of films deposited on Au also exhibited a temperature dependence, with maximum charge densities being exhibited at ca. 200 deg C. The increase from room temperature to 200 deg C can be attributed to thermal conversion of residual oxidized Pt in the film to metallic Pt, as well as improved electrical connectivity between the particles due to sintering. Above 200 deg C, sintering becomes a major contributor to the loss of charge density, as it reduces the electroactive surface area. The efficiency of use of the metallic Pt was examined using electrochemistry and the quartz crystal microbalance technique, and was found to be 20-25%. A second phase, consisting of larger crystallites, was also found in as-formed films by both TEM and scanning electron microscopy. While this phase could be removed by rinsing with acid, it could not be identified by either X-ray diffraction or XPS.