Carbon Monoxide-Assisted Size Confinement of Bimetallic Alloy Nanoparticles

Abstract

Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 °C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of ∼4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations.

The Space Confinement Approach Using Hollow Graphitic Spheres to Unveil Activity and Stability of Pt‐Co Nanocatalysts for PEMFC

“…Moreover, the shape of the Pt/TKK CO-stripping CV suggests a change in particle size distribution, probably originating from the agglomeration of the nanoparticles (see Figures S19-S21, Supporting Information). [27] For a comparison of HGS and Vulcan, the SFC coupled with an online electrochemical mass spectrometer (SFC-OLEMS) [39] was employed (see Figure S21, Supporting Information). [6] Furthermore, the presence of partial graphitization within the HGS supports (see XRD in Figure 1b) is expected to have a positive influence on the stability of the support and thus the catalyst itself.…”

Octahedral Pd@Pt1.8Ni Core–Shell Nanocrystals with Ultrathin PtNi Alloy Shells as Active Catalysts for Oxygen Reduction Reaction

“…It should be pointed out that the ORR catalytic activity showed a typical degradation over extended test times, which may arise from the dealloying of PtNi with Ni leaching during the long-term test. [29][30][31][32] In order to verify the conjecture, we measured the content of Ni during the whole process. As shown in Figure S10, the atomic percentage of Ni was decreased by 10% approximately throughout the 6,000 cycles, which indicates the existence of dealloying.…”

Size‐Controlled Synthesis of Sub‐10 nm PtNi3 Alloy Nanoparticles and their Unusual Volcano‐Shaped Size Effect on ORR Electrocatalysis

“…One key factor toward this achievement was to control the particle size below a critical value (e.g., 10 nm) to form nonporous core–shell NPs. These NPs were unique in that they were able to retain large fractions of their initial base metal in the lattice‐contracted alloy core thereby exerting sustained compressive surface lattice strain and ORR activity . Despite these progresses, a critical question concerning how particle size affect the activity and stability of nonporous sub‐10 nm PtNi 3 NPs still remains unaddressed.…”