Leaching- and sintering-resistant hollow or structurally ordered intermetallic PtFe alloy catalysts for oxygen reduction reactions†
Carbon supported Pt-based alloy materials that have been developed for proton exchange membrane fuel cells (PEMFCs) are vulnerable to deactivation due to the loss of non-noble metal components (leaching) or detachment, migration and aggregation of active nanoparticles (sintering). Until now some methods have been developed to inhibit leaching or sintering individually. However, a route able to avoid leaching and sintering simultaneously is still lacking. Herein, we develop a thermally driven interfacial diffusion alloying route that allows for the direct evolution of solid Pt nanoparticles (NPs) supported on carbon (Pt/C) into a Pt-skin-like hollow PtFe alloy or a structurally ordered intermetallic PtFe alloy, together with in situ encapsulation of PtFe alloy NPs with a thin layer porous nitrogen-doped carbon (NC) shell. The robust NC shells not only effectively prevent Pt-based NPs from detachment, migration, and aggregation during accelerated durability tests but also allow smoother access of electrolyte to the Pt surface, thus allowing the catalysts to well preserve their high catalytic activity. The well-defined shape and atomic arrangement of PtFe alloy NPs exhibit over 600% increase in mass activity and specific activity when compared with that of the pristine Pt/C catalyst. Stability tests confirm that the ordered PtFe alloy is more electrochemically stable than the disordered hollow PtFe alloy and Pt/C catalysts due to its ordered atomic arrangement and the robust NC shell.