Synthesis and Characterization of Stable Cu–Pt Nanoparticles under Reductive and Oxidative Conditions

Abstract

We report a synthesis method for highly monodisperse Cu−Pt alloy nanoparticles. Small and large Cu−Pt particles with a Cu/Pt ratio of 1:1 can be obtained through colloidal synthesis at 300 °C. The fresh particles have a Pt-rich surface and a Cu-rich core and can be converted into an intermetallic phase after annealing at 800 °C under H 2 . First, we demonstrated the stability of fresh particles under redox conditions at 400 °C, as the Pt-rich surface prevents substantial oxidation of Cu. Then, a combination of in situ scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, and CO oxidation measurements of the intermetallic CuPt phase before and after redox treatments at 800 °C showed promising activity and stability for CO oxidation. Full oxidation of Cu was prevented after exposure to O 2 at 800 °C. The activity and structure of the particles were only slightly changed after exposure to O 2 at 800 °C and were recovered after re-reduction at 800 °C. Additionally, the intermetallic CuPt phase showed enhanced catalytic properties compared to the fresh particles with a Pt-rich surface or pure Pt particles of the same size. Thus, the incorporation of Pt with Cu does not lead to a rapid deactivation and degradation of the material, as seen with other bimetallic systems. This work provides a synthesis route to control the design of Cu−Pt nanostructures and underlines the promising properties of these alloys (intermetallic and non-intermetallic) for heterogeneous catalysis.

Structure and Stability of Core–Shell Cu–Pt Nanoparticles for Catalytic Applications

“…35−37 Nevertheless, the catalytic testing and the in situ experiments underline the promising overall stability of core−shell Cu−Pt particles provided that the temperature remains below a limit (which in our in situ experiment was 450 °C, still relevant for many catalytic processes). 26,38 If Cu 0.75 Pt 0.25 particles are exposed to H 2 at elevated temperatures (Figure 4c), the core−shell configuration is partly converted into an intermetallic CuPt phase with a Cu:Pt ratio of (1:1), consistent with other investigations of Cu−Pt particles. 26 Atomic resolution imaging shows atomic rows with high brightness (Pt atoms) and low brightness (Cu), typical for an intermetallic phase with a 1:1 ratio between the two metals.…”

“…26,38 If Cu 0.75 Pt 0.25 particles are exposed to H 2 at elevated temperatures (Figure 4c), the core−shell configuration is partly converted into an intermetallic CuPt phase with a Cu:Pt ratio of (1:1), consistent with other investigations of Cu−Pt particles. 26 Atomic resolution imaging shows atomic rows with high brightness (Pt atoms) and low brightness (Cu), typical for an intermetallic phase with a 1:1 ratio between the two metals. Excess Cu can be found on the surface of the carbon support.…”

“…16−19 For instance, Pt nanoparticles are used for the oxygen reduction reaction (ORR) or hydrogen evolution reaction (HER) 20−24 but do not optimize each gram of Pt used in the structure. Instead, core− Pt-shell particles are ideal candidates for new catalyst development, 25,26 as they expose the maximum number of Pt atoms on the particle surface without making the particles so small that they become unstable in catalysis reaction conditions. Thus, the development of new synthesis methods to produce Pt-shell nanoparticles is a key area of investigation for heterogeneous catalyst research.…”

Scalable Synthesis of Low-Pt PtCu3 Intermetallic Oxygen Reduction Electrocatalysts via Sulfur-Containing Inorganic Salt-Assisted Strategy

“…Meanwhile, compared to monometallic Pt, the Pt–M alloy has a weaker oxygen binding energy ( E O ) owing to the strain and/or ligand effects, which can consequently promote the ORR activity. − Relative to random alloy counterparts, atomically ordered Pt–M intermetallic compound (IMC) nanoparticles exhibited higher catalytic activity, as a result of optimized strain effect and thus weakened adsorption strength toward ORR adsorbates. , In particular, compared to the conventional Pt-richer IMCs (such as Pt 3 M, PtM, etc. ), low-Pt IMC catalysts with a stoichiometry of PtM 3 (M = Cu, Co, Fe, Ni) show higher ORR activities because the higher non-noble-metal content can induce more pronounced strain effect. − Furthermore, ordered Pt–M IMCs potentially exhibit enhanced electrochemical stability under corrosive fuel cell conditions, which stemmed from a greater formation enthalpy induced by the strong 3d–5d orbital interactions between M and Pt. ,, …”

“…17−19 Furthermore, ordered Pt−M IMCs potentially exhibit enhanced electrochemical stability under corrosive fuel cell conditions, which stemmed from a greater formation enthalpy induced by the strong 3d−5d orbital interactions between M and Pt. 15,16,20 When downsized to the nanoscale, Pt-based IMC catalysts can exhibit a higher active surface area (a larger number of active sites per mass) and expose more active sites, accelerating the ORR kinetic process. However, the preparation of IMC catalysts generally needs the time-consuming and hightemperature annealing process to overcome the high activation barrier of atom ordering, leading to catalyst sintering and thus relatively low mass-based activity (MA).…”