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 ofrnthe Proton Exchange Membrane Fuel Cell, either by increasing thernactivity and thereby being able to reduce the loading or by replacingrnPt entirely. Recently we have found a new class of alloys, which arernvery active towards the Oxygen Reduction Reaction (ORR). The firstrncatalyst were predicted in a DFT screening study which pointed forrnactivity and stability towards Pt_3Sc and Pt_3Y and the latter provedrnparticular active by a factor 4-6 times as active as polycrystalline Ptrn[1]. Initially we have tested the activity of poly crystalline samples inrna rotating disk setup. We have since expanded the number of catalystrnto also include Zr, Hf and La [2, 3] and subsequently a systematicrnstudy on the trends in activity of nine novel Pt-lanthanide and Ptalkalinernearth electrodes (Pt_5Ca, Pt_5Sr, Pt_5La, Pt_5Ce, Pt_5Sm, Pt_5Gd,rnPt_5Tb, Pt_5Dy and Pt_5Tm). The materials are highly active, presentingrna 3 to 6-fold activity enhancement over Pt [4-5], Pt_5Tb being the mostrnactive polycrystalline Pt-based catalyst. The ORR activity versus thernlattice parameter obtained by X-ray diffraction measurements followsrna volcano relationship, but the most active and stable catalyst seem tornbe Pt_5Ga [5]. All this would be in vain if we cannot make it intornnanoparticles. We have therefore used mass selected nanoparticlesrncluster source to first establish a base for pure Pt [6] and subsequentlyrnshowed that PtY [7] and PtGd [8] nanoparticles display high activityrnper mass.