Pt-Ni and Pt-Cu Nanocrystals with Enhanced Oxygen Reduction Reaction Electrocatalytic Activity Toward Proton Exchange Membrane Fuel Cells

The growing demand for hydrogen-based clean energy has prompted the development of high-performance proton exchange membrane fuel cells (PEMFCs), that convert hydrogen fuel to electricity. The sluggish kinetic on the cathode where the Oxygen Reduction Reaction (ORR) occurs requires a catalyst material. Platinum and Pt-alloys are the most used and available catalysts materials, because of their high activity toward the ORR. One of their disadvantages is the high material cost, leading several research groups to develop more efficient materials that allow lowering the amount of platinum loading on the catalyst. In this work, we present Pt-Ni and Pt-Cu nanocrystals from colloidal synthesis with shape, size and composition control that have shown high ORR activity.

We could observe a transition from octahedral to cuboctahedral morphology of 5 nm Pt-Ni nanocrystals. The Pt-Ni octahedral and the Pt-Ni cuboctahedral nanoparticles lead to high activity toward ORR (>5 times of commercial Pt/C catalyst). These results were verified by rotation disk electrode (RDE) and characterized by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), Transition Electron Microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS).

In addition, we demonstrate that the ratio of surfactant can tune the size of core-shell Pt-Cu nano-octahedra from 8 to 18 nm with homogeneous size and shapes on carbon support. The core-shell structure has been determined using HAADF-STEM and EDS. The Pt rich shell exhibits an increasing compressive strain with increasing of the surface in the {111} facets. The compressive strain enhances the ORR of the Pt-Cu nano-octahedra with the highest activity observed for 18 nm octahedra.