Tailored Lattice Compressive Strain of Pt-Skins by the L1₂ -Pt₃ M Intermetallic Core for Highly Efficient Oxygen Reduction.

Abstract

The sluggish kinetics of oxygen reduction reaction (ORR) and unsatisfactory durability of Pt-based catalysts are severely hindering the commercialization of proton-exchange-membrane fuel cells (PEMFCs). In this work, the lattice compressive strain of Pt-skins imposed by Pt-based intermetallic cores is tailored for highly effective ORR through the confinement effect of the activated nitrogen-doped porous carbon (a-NPC). The modulated pores of a-NPC not only promote Pt-based intermetallics with ultrasmall size (average size of <4 nm), but also efficiently stabilizes intermetallic nanoparticles and sufficient exposure of active sites during the ORR process. The optimized catalyst (L1₂ -Pt₃ Co@ML-Pt/NPC₁₀ ) achieves excellent mass activity (1.72 A mg_Pt ^-1 ) and specific activity (3.49 mA cm_Pt ^-2 ), which are 11- and 15-fold that of commercial Pt/C, respectively. Besides, owing to the confinement effect of a-NPC and protection of Pt-skins, L1₂ -Pt₃ Co@ML-Pt/NPC₁₀ retains 98.1% mass activity after 30 000 cycles, and even 95% for 100 000 cycles, while Pt/C retains only 51.2% for 30 000 cycles. Rationalized by density functional theory, compared with other metals (Cr, Mn, Fe, and Zn), L1₂ -Pt₃ Co closer to the top of "volcano" induces a more suitable compressive strain and electronic structure on Pt-skin, leading to an optimal oxygen adsorption energy and a remarkable ORR performance.