Designed synthesis of highly catalytic Ni-Pt nanoparticles for fuel cell applications

A modified alcohol reduction process by controlling the complexation and reduction of metallic ions was developed to obtain compositionally and structurally controlled Ni-Pt nanoparticles (NPs) with sizes less than 20 nm in a high yield. The characterization of NPs synthesized under different experimental conditions suggested that the reduction of Pt and subsequent formation of cubic-shaped Ni-Pt NPs were strongly dependent on the formation of Pt-oleylamine (OAm) complexes. Thus, prior to the synthesis of Ni-Pt NPs, the formation and reduction process of Pt complexes in the solution-state were investigated by in situ UV-Visible and X-ray spectroscopies. The complexation of Pt ions along with their reduction prior to the formation of Pt metal and their influence on the size and the elemental distribution of Pt within the Ni-Pt NPs were revealed. Then, the above findings were actively utilized to design and to obtain Pt(core)-Ni(shell), Ni-Pt alloy, and Ni(core)-Pt(shell) nanostructures by regulating the OAm concentration in the system. The specific distribution of Pt on the Ni-Pt surface was confirmed by decolorization of methylene blue. Furthermore, Ni-Pt NPs with a Pt concentration of 10 at.% exhibited a mass activity four times larger than that of commercial Pt during the oxygen reduction reaction (ORR).