Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts

Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this, scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.

P.S. acknowledges financial support by the German Research Foundation (DFG) through grant STR 596/5-1 (“Nanoscale Pt Alloy electrocatalysts with well-defined shapes”). Partial funding by the German Ministry of Education and Research (BMBF) grant “LOPLAKAT” is gratefully acknowledged. Also, this work was financially supported by the MICINN (Spain) (project 2013-44083-P). R.M.A.A. thanks the funding received from MICINN (EEBB-I-14-08240) to carry out a predoctoral stay in a foreign R&D center. M.H. thanks the Deutsche Forschungsgemeinschaft (DFG) for financial support within the grant HE 7192/1-1.