RATIONAL DESIGN OF OXYGEN REDUCTION REACTION AND HYDROGEN PEROXIDE CATALYSTS: FROM SURFACE SCIENCE TO NANOPARTICLES.

摘要

There is a strong demand for improving the anode material of the Proton Exchange Membrane Fuel Cell, either by increasing the activity and thereby being able to reduce the loading or by replacing Pt entirely. Recently we have found a new class of alloys, which are very active towards the Oxygen Reduction Reaction (ORR). The first catalyst were predicted in a DFT screening study which pointed for activity and stability towards Pt3Sc and Pt3Y and the latter proved particular active by a factor 4-6 times as active as polycrystalline Pt [1]. Initially we have tested the activity of poly crystalline-samples in a rotating disk setup. We have since expanded the number of catalyst to also include Zr, Hf and La [2, 3] and subsequently a systematic study on the trends in activity of nine novel Pt-lanthanide and Pt-alkaline earth electrodes (Pt5Ca, Pt5Sr, Pt5La, Pt5Ce, Pt5Sm, Pt5Gd, Pt5Tb, Pt5Dy and Pt5Tm). The materials are highly active, presenting a 3 to 6-fold activity enhancement over Pt [4-5], Pt5Tb being the most active polycrystalline Pt-based catalyst. The ORR activity versus the lattice parameter obtained by X-ray diffraction measurements follows a volcano relationship, but the most active and stable catalyst seem to be Pt5Ga [5]. All this would be in vain if we cannot make it into nanoparticles. We have therefore used mass selected nanoparticles cluster source to first establish a base for pure Pt [6] and subsequently showed that PtY [7] and PtGd [8] nanoparticles display high activity per mass.