On the 28 August at 14.00 Heiki Erikson will defend his PhD thesis „Electrochemical reduction of oxygen on nanostructured palladium and gold catalysts“ in chemistry in the Faculty on Science and Technology in the University Tartu (Chemicum, Ravila 14a-1021).
Associate Professor Kaido Tammeveski (PhD), University of Tartu
Senior Research Fellow Ave Sarapuu (PhD), University of Tartu
Opponent: Professor Elisabet Ahlberg (PhD), University of Gothenburg (Sweden)
Nanostructured palladium and gold catalysts. This process is essentially important in the low-temperature fuel cells. Platinum is the most active metal for the ORR, but due to the lower price and similar properties palladium has been proposed for its substitution. For the characterisation of studied materials, several surface analysis methods (scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectronspectroscopy, energy dispersive X-ray spectroscopy) and electrochemical methods (cyclic voltammetry, the rotating disk electrode method) were used. The studied nanostructured electrodes were prepared using various methods including electron beam evaporation, electrochemical deposition and chemical synthesis. The ORR activity of the catalysts was evaluated in sulphuric acid and in potassium hydroxide solutions. In general the studied nanostructured Pd and Au had higher electrocatalytic activity in alkaline media where the oxygen reduction reaction on Pd-based catalysts proceeded mainly via a four-electron pathway that is preferred in the fuel cells, while on Au-based catalysts the main product was hydrogen peroxide, which was further reduced to water. In acid solutions the ORR on gold-based catalysts yielded hydrogen peroxide, on palladium-based catalysts it depended more strongly on the morphology of the catalyst. On Pd nanocubes and Pd-Au alloys the number of electrons transferred per oxygen molecule was closer to 4 than the other studied catalysts. The studied catalysts were evaluated also by calculating the specific activities that was found to be the highest for nanocubes in both electrolytes. For all nanostructured electrocatalysts studied the mechanistic pathway of the ORR was similar to that of the respective bulk electrodes.