Ordered Intermetallic PtCu Catalysts Made from Pt@Cu Core/Shell Structures for Oxygen Reduction Reaction

Abstract

Platinum-based ordered intermetallic compounds are promising low-Pt catalysts toward the oxygen reduction reaction (ORR) for high-performance fuel cells. However, the synthesis of ordered intermetallic catalysts usually requires high-temperature annealing to overcome the energy barrier for atom diffusion, which leads to inevitable sintering of catalysts and greatly reduced mass-specific activity. Herein, we developed a new strategy to synthesize PtCu-ordered intermetallic catalysts by the generation of the Pt@Cu core/shell nanoparticles (Pt@Cu NPs) by Pt-assisted H2 reduction of Cu2+ with subsequent annealing at 500–1000 °C. Compared to the commonly used wet-impregnation method, the core/shell structure starts to form ordered PtCu alloys at a lower annealing temperature (500 °C). The Pt@Cu core/shell structure avoids the necessary process of Cu atoms diffusing to Pt NPs across the carbon supports occurred during high-temperature annealing in the wet-impregnation method, which ensures the formation of PtCu NPs with higher ordering degree while annealing at the same temperature. The highly ordered small-sized PtCu catalysts prepared by the core/shell strategy exhibit higher mass activity and specific activity compared to those prepared by the wet-impregnation method. Moreover, a positive correlation between the ORR activity and the ordering degree of the intermetallic PtCu NPs is identified, which could be associated with the increase of compressive strain with the ordering degree.

Recent progress in intermetallic nanocrystals for electrocatalysis: From binary to ternary to high‐entropy intermetallics

“…Forth, instead of directly conducting thermal treatment on substrate-supported metal precursors or disordered alloys, heterostructures, such as core-shell [90][91][92][93][94] and dimer 95 structures, can be prepared first via wet-chemical methods, which are subsequently transformed into intermetallic nanoparticles via thermal annealing. Metal oxides are usually synthesized as the shell, such that during thermal annealing in the reductive environment, rich oxygen vacancies can be generated, promoting the inter-diffusion between core and shell.…”

Targeted Intermetallic Nanocatalysts for Sustainable Biomass and CO2 Valorization

“…In addition, the XRD pattern can also be used to identify the ordered structure of IMCs. Ye and his colleagues used XRD to inspect the evolution of the crystalline phase of the prepared PtCu NPs after annealing at different temperatures (Figure d) . The XRD spectrum of the PtCu–H 2 sample annealed at 300 °C shows a shift of the diffraction peaks to higher angles, which indicates the beginning of the formation of disordered alloys; after the sample was annealed at 500 °C, (021) superlattice peaks appear in its XRD spectrum at 20.4°, confirming the formation of ordered PtCu NP.…”

“…Ye and his colleagues used XRD to inspect the evolution of the crystalline phase of the prepared PtCu NPs after annealing at different temperatures (Figure 6d). 54 The XRD spectrum of the PtCu−H 2 sample annealed at 300 °C shows a shift of the diffraction peaks to higher angles, which indicates the beginning of the formation of disordered alloys; after the sample was annealed at 500 °C, (021) superlattice peaks appear in its XRD spectrum at 20.4°, confirming the formation of ordered PtCu NP. The alternating layers consisting of periodic bright spots (Pt) and weak spots (Cu) in the HAADF-STEM image, as shown in Figure 6e, again demonstrate the ordered layer-by-layer arrangement of Pt and Cu atoms based on the Z-contrast.…”

“…(f) Enlarged HAADF-STEM view of PtCu–H 2 in (e). Reproduced from ref . Copyright 2022 American Chemical Society.…”

Electrochemical Synthesis of Nanostructured Ordered Intermetallic Materials under Ambient Conditions

“…In a solid-solution alloy the atoms are randomly positioned onto the lattice sites, and thus the system contains only short-range atomic ordering . While many solid-solution alloy NPs have shown increased catalytic performance for various reactions, − it is still unclear how these reactions proceed on the NP surface since the active sites are poorly defined due to the heterogeneous distributions of atoms within the material. In contrast, ordered intermetallics display long-range ordering which minimizes the free energy between constituent atoms, leading to increased catalytic performances and stability, and well-defined active sites. , …”