Intermetallic electrocatalysts have demonstrated significant potential in facilitating the cathodic oxygen reduction reaction (ORR) in fuel cells with enhanced activity and durability. However, it is still an enormous challenge to the facile synthesis of Pt-based intermetallic catalysts with uniform size and high ordering degree. Here, we innovatively fabricate the core-shell structured L1 0 -PtFe intermetallics with Pt skins supported on N-doped porous carbon matrix through one-step pyrolysis of PtFe Hofmann-type metal-organic frameworks (denoted as L1 0 -PtFe/NC). Under the constraints of the porous structure and cyano-ligand bonding, most Fe atoms are alloyed with Pt to form uniform-ordered PtFe intermetallics, while some Fe atoms are atomically dispersed in the carbon framework to form FeN x moieties. Notably, a series of intermetallic PtFe catalysts with different ordering degrees are successfully constructed by adjusting the pyrolysis temperature, which verified that the increase of ordering degree is beneficial to promote the electrocatalytic performance. In particular, the ordered L1 0 -PtFe/NC-800 exhibits superb ORR activity with both mass and specific activities, which are 2.7-folds higher than those of commercial Pt/C. Moreover, after an accelerated durability test, L1 0 -PtFe/NC-800 retains over 90 % mass activity. This work provides a promising approach for the development of efficient Pt-based intermetallic electrocatalysts for fuel cells.
In the pursuit of high-performance proton exchange membrane fuel cells (PEMFCs), obtaining durable Pt-based intermetallic catalysts with small particle sizes for oxygen reduction reaction (ORR) stands as a crucial yet challenging topic. Herein, we propose an idea of catalyst design utilizing Fe-phenanthroline (Phen) complex as precursor to integrate metal-nitrogen-carbon (M-N-C) with the strong anchoring effect into carbon shells, synthesizing highly ordered and small-sized (3.59 nm) PtFe intermetallic catalyst coated with iron-nitrogen-carbon (FeNC) shells (L1 0 -PtFe@FeNC). The strong Fe-Phen interaction ensures the uniform dispersion of Fe species on Pt seeds so as to form protective shells suppressing the agglomeration and dissolution of PtFe nanoparticles (NPs) under the high-temperature annealing or harsh operational conditions. It exhibits excellent mass activity (MA) that is about five-fold increase compared to the commercial Pt/C, as well as the significantly improved MA retention after 30,000 potential cycles (68.2% vs. 45.3%). Nitrogen-doped carbon (NC) shells and pure carbon (C) shells are used as comparison to demonstrate the advantages of FeNC shells. Durability test results show that NC and C shells obviously degrade after potential cycles, while well-preserved FeNC shells guarantee catalyst stability. Theoretical calculations reveal that the strong binding between FeNC shells and the Pt surface enhances the stability of both the nanoparticles and the FeNC shells.
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