Controlling Near-Surface Ni Composition in OctahedralPtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen ReductionReaction Catalyst

We report and study the translation of the high catalytic oxygen electroreduction activities of nanostructured Molybdenum-doped octahedrally-shaped PtNiMo particles from conventional thin-film rotating disk electrodescreenings (3.43 ± 0.35 A mgPt-1 at 0.9 VRHE) to Membrane Electrode Assembly(MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mgPt-1 at 0.9 Vcell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopywith energy dispersive X-ray analysis (STEM-EDX) evidences that Mo preferentially occupies the Pt rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, combining in situ wide angle X-ray spectroscopy, X-ray fluorescence and STEM-EDX elemental mapping with electrochemical measurements we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodi...