Unveiling the Atomic Diffusion Pathway for the In Situ Formation of Size-Controlled Intermetallic Pt on Co–N–C with Exceptional PEMFC Performance

The integration of an intermetallic Pt alloy and single-atom M-N-C support is an intriguing strategy to combine the advantages of both counterparts and further lower Pt usage at higher power output. Despite prior attempts, the fuel cell performance is still unsatisfactory, and the atomic diffusion/alloying pathway between the Pt alloy and M-N-C is still not clear. Here, we control the Co amount in the CoNC and present the atomic-diffusion pathway for the in situ formation of Pt-based intermetallic catalysts with size-controlled nanoparticles (NPs). The synthesized Pt₃Fe-Co@5CoNC demonstrates excellent performance in half-cell ORR tests. Under H₂-air conditions, the membrane electrode assembly exhibits low Pt usage (0.175 g kW^-1), good stability with a 12.5 mV loss at 0.8 A cm^-2 at the end of the test, and an ultrahigh power density of 1.717 W cm^-2 at 0.429 V. Comprehensive experimental results and DFT calculations show the atomic pathway of diffusion and alloying for low-coordinated Co-N₃-C into L1₂-Pt₃Fe NPs. In comparison, high-coordinated Co-N₄-C remains stable and contributes to the stability of the intermetallic Pt alloy through the strong Pt-Co-N₄ interaction. This work demonstrates important progress in the integration of intermetallic Pt alloy and single-atom CoNC for ORR and can be extended to other single-atom supports, including Ni-NC, Fe-NC, and Cu-NC.