Roman Fiala

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.

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.

Mn doped GaN thin films and nanoparticles

Magnetically doped GaN in the form of thin films and nanoparticles has been investigated. The Mn doped GaN layers were grown on sapphire substrates by MOVPE. The influence of deposition condition on surface morphology, magnetic and structural properties was investigated. GaN:Mn epitaxial layers exhibit magnetic moment persisting up to room temperature. The magnetically doped layers were also prepared by ion implantation of GaN layers by Mn. The influence of free carrier concentration and other parameters on magnetic properties were investigated. The pure and transition metal (Cr, Mn and Fe) doped GaN nanoparticles were synthesised by decomposition of fluoride–based complex compound in ammonia atmosphere. Mn doped nanoparticles exhibit pure paramagnetic behaviour.

Mass Spectrometry of Polymer Electrolyte Membrane Fuel Cells

The chemical analysis of processes inside fuel cells under operating conditions in either direct or inverted (electrolysis) mode and their correlation with potentiostatic measurements is a crucial part of understanding fuel cell electrochemistry. We present a relatively simple yet powerful experimental setup for online monitoring of the fuel cell exhaust (of either cathode or anode side) downstream by mass spectrometry. The influence of a variety of parameters (composition of the catalyst, fuel type or its concentration, cell temperature, level of humidification, mass flow rate, power load, cell potential, etc.) on the fuel cell operation can be easily investigated separately or in a combined fashion. We demonstrate the application of this technique on a few examples of low-temperature (70°C herein) polymer electrolyte membrane fuel cells (both alcohol- and hydrogen-fed) subjected to a wide range of conditions.