Michal Václavů

Platinum-Doped CeO2 Thin Film Catalysts Prepared by Magnetron Sputtering

The interaction of Pt with CeO(2) layers was investigated by using photoelectron spectroscopy. The 30 nm thick Pt doped CeO(2) layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) substrate, multiwall carbon nanotubes (CNTs) supported by a carbon diffusion layer of a polymer membrane fuel cell and on CNTs grown on the silicon wafer by the CVD technique. The synchrotron radiation X-ray photoelectron spectra showed the formation of cerium oxide with completely ionized Pt(2+,4+) species, and with the Pt(2+)/Pt(4+) ratio strongly dependent on the substrate. The TEM and XRD study showed the Pt(2+)/Pt(4+) ratio is dependent on the film structure.

Anode Material for Hydrogen Polymer Membrane Fuel Cell: Pt – CeO2 RF-Sputtered Thin Films

The interaction of Pt with CeO 2 layers was investigated using photoelectron spectroscopy. Pt-doped CeO 2 layers 30 nm thick were deposited by radio-frequency (rf) magnetron sputtering using a composite CeO 2 -Pt target on a carbon diffusion layer of micropolymer membrane fuel cell covered by double-wall carbon nanotubes. The laboratory X-ray photoelectron spectroscopy and synchrotron radiation soft X-ray photoemission spectra showed the formation of cerium oxide with completely ionized species Pt 2+,4+ embedded in the film. A small amount of Pt 0 is present on the film surface only. Hydrogen/air fuel cell activity measurements normalized to the amount of used Pt revealed specific power up to 30 W/mg(Pt). The activity of this material is explained by high activity of embedded Pt 2+,4+ cations toward H 2 dissociation and formation of protonic hydrogen. Very high specific power and low cost together with planar deposition techniques make the material promising for microfabrication of fuel cells to power mobile systems.

Au+ and Au3+ ions in CeO2 rf-sputtered thin films

The interaction of gold with CeO2 layers was investigated using photoelectron spectroscopy. 65 nm thick Au doped CeO2 layers were deposited by rf-magnetron sputtering on a Si(0 0 1) substrate by using a composite CeO2–Au target. The laboratory XPS and synchrotron radiation soft x-ray and hard x-ray photoemission spectra showed the formation of stoichiometric Ce4+ (CeO2) and the appearance of new Au+,3+ states with ionized Au species in excess of 50% of the total Au amount. Depth resolved measurements, by varying the emission angle or photon energy, indicated the formation of an Au0 overlayer and deeper Au+,3+ species. The formation of Au+,3+ ions was found to be strongly dependent on the cerium oxide stoichiometry. The amount of ionized Au can be reversibly decreased and increased by surface reduction (removal of O by sputtering) and subsequent surface re-oxidation.

Nanoporous Ptn+–CeOx catalyst films grown on carbon substrates

Deposition of the Pt doped cerium oxide catalyst layers on carbon nanotubes and flat carbon substrates by magnetron sputtering leads to growth of solid solution films composed of nanorods oriented perpendicularly to the substrate surface forming fractal like highly porous structure. The films contain only cationic Pt2+ and Pt4+. Cerium oxide is partially reduced. The catalyst films reveal high catalytic activity as anode catalyst in proton exchange membrane fuel cells. Preparation of nanoporous structures by sputtering shows that this technique is suitable for preparation of catalyst for micro fuel cell systems made by planar technology.