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

Abstract

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).

Magneto-Plasmonic Co@Pt@Au Nanocrystals for Biosensing and Therapeutics

“…% (Figure (d)). Similar diffusion behavior has been observed in the cases of Pt-based bimetallic NP systems. − The segregation of Pt atoms at the NP surface is assumed through the diffusion of Pt, a phenomenon already experimentally observed in the case of Ni–Pt NPs synthesized by an alcohol reduction method. − This phenomenon becomes intense at higher Co concentration, and at 70 at. % Co almost all the Pt atoms are diffused to the surface to form a Pt-rich shell around the Co-rich core (Figure (d)).…”

“…However, the experimental results suggest the reverse. This is believed to be due to the delayed reduction of Pt due to strong complexation between OAm and Pt than those between OAm and Co . This was confirmed by the calculation of the binding energies for Pt (29.94 kcal/mol) and Co (19.83 kcal/mol) with OAm (Figure S3).…”

“…Therefore, to obtain uniform Co–Pt NPs, it is essential to reduce Co and Pt ions simultaneously. This could be achieved only by delaying the reduction of Pt appropriately by modifying the OAm/Pt ratio . Based on the above reasoning, a scheme for coreduction is proposed as shown in Figure (a).…”

“…To facilitate the coreduction of Co and Pt, therefore, it is necessary to delay the reduction of Pt until the system reaches the temperature appropriate for the reduction of Co. Here, control over the formation of the Pt complex was attempted as a means to delay the reduction of Pt . In addition, delayed injection of Co salt was also considered.…”

“…The controllability of reaction using the alcohol reduction technique is much superior to that of the thermal decomposition. Moreover, the coreduction of the Ni–Pt system, where the difference in reduction potential between Ni 2+ and Pt 4+ is quite large, has been successfully demonstrated in the alcohol reduction method using 1-heptanol as the reducing agent and oleylamine as the complexing agent. − Therefore, the coreduction of Co and Pt also holds enough possibility using this technique, and so here we report the synthesis of Co–Pt NPs based on the alcohol reduction technique adapted for Ni–Pt NPs, using a proper complexing agent, oleylamine, to delay the reduction of Pt …”