Ultrafine L10 PtFeZn intermetallics via a two-step annealing process for oxygen reduction reaction: Decoupling alloying and ordering stages

In this paper, we report the design of ultrafine ordered PtFeZn ternary intermetallics uniformly supported on ZIF-8-derived Zn,N-codoped graphitic carbon (ZnNC) via a green aqueous impregnation method followed by a two-step annealing protocol (H 2 /Ar, 600 and 800 °C) to circumvent the sintering issues imposed by conventional thermodynamics. Physical characterizations (X-ray diffraction, high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy) and theoretical calculations reveal that low-temperature annealing at 600 °C stabilizes sub-nano disordered PtFe alloys via the strong metal-support interactions (SMSI) between Zn in ZnNC and Pt precursors, while high-temperature treatment at 800 °C promotes Zn diffusion from the support into the alloy bulk and simultaneously triggers the disorder-to-order phase transition. The as-prepared ZnNC-15PtFeZn exhibits an initial mass activity of 0.769 mA/μg Pt and retains 61.7% of its activity after 30000 cycles of accelerated stress testing (AST). Notably, when used as a cathode catalyst in MEA, ZnNC-15PtFeZn achieves superior power density (2.018 W/cm 2 under H 2 -O 2 ) at half the Pt loading (0.05 mg/cm 2 ) of state-of-the-art commercial Pt/C, highlighting its potential for low-Pt PEMFCs. Density functional theory confirms that Fe enhances ORR activity via ligand effects, while Zn strengthens Pt-Fe/Zn bonding (elevating vacancy formation energies), thereby improving structural stability. This mild, scalable aqueous impregnation strategy offers a general approach for synthesizing multi-component ordered alloys in electrocatalysis.