The development of proton exchange membrane fuel cells (PEMFCs) is mainly limited by the high cost Pt-based electrocatalysts^1,2. Despite progress in the development of non-noble metal electrocatalysts, Pt-based catalysts are currently the state-of-the-art electrocatalysts in practical PEMFCs.

Binary Pt-based 3d transition metals electrocatalysts (such as Pt-Co, Pt-Cu, and Pt-Ni) is a promising approach to improve the catalyst activity and reduce the Pt loading in fuel cells. Compared to other alloy elements, Cu is more stable against electrochemical oxidation than other solute metals (for example, Ni, Co), and Cu can be stabilized in the second Pt laye. Besides, Pt-Cu alloy can be used to distinguish strain effects and ligand effects^3,4. Besides, numerous results have suggested that the {111}-terminated Pt-alloy nano-octahedra could be very promising electrocatalysts for use as the cathode of PEMFCs. However, the synthesis of most Pt-based nano-octahedra involve bulky capping agents, which are necessary to stabilize and to prevent aggregation of nanocrystals during synthesis. However, the capping agents can reduce the free accessible surface site for O₂ reaction, leading to the undesirable decrease in ORR activity. While the removal of capping agents will inevitably affect the size or morphology of the particles, which in-turn alters their ORR activity. Thus, a surfactant-free synthesis of Pt-based alloys with high activity for ORR is urgent for the development of PEMFCs.

Herein, we reported the synthesis of Pt-Cu nnao-octahedra of size about 7.2 nm by a facile surfactant-free strategy, which enhances the surface exposure and their catalytic activity for ORR. In a typical synthesis of Pt-Cu octahedra, DMF was used as solvent and reducing agent, while Pt(acac)₂ and Cu(acac)₂ were used as precursor. Unusually, we found that low reaction temperature favors the formation of nanocrystal with (111) facets and small size. The electrochemical surface area of synthesized Pt-Cu octahedra were determined by the CO stripping. The area-specific ORR activity activity of Pt-Cu nano-octahedra was 4.25 mA cm^-2 at 0.90 V, that is about 20 times higher than that of commerical Pt/C (0.2 mA cm^-2). This study provides a strategic design of Pt-based efficient catalysts for fuel cells.

Acknowledgments. This work is supported by NSFC (21222310 and 21573183).

Reference:

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