A unique ligand effect in Pt-based core–shell nanocubes to boost oxygen reduction electrocatalysis

Abstract

Pt-based core–shell nanocrystals are a fantastic catalyst to enhance the catalytic performance for the oxygen reduction reaction (ORR). Pursuing further enhancement in ORR properties requires an unconventional interaction between the components of a catalyst. Here Pb is selected to alloy with Pd cores and Pt shells for generating Pd₃Pb@Pt_mPb (m = 3 and 4) nanocubes. Both nanocubes are much more active and stable for the ORR relative to commercial Pt/C, with Pd₃Pb@Pt₃Pb nanocubes being the better one. Specifically, Pd₃Pb@Pt₃Pb nanocubes achieved record-breaking mass (4.69 A mg_Pt⁻¹) and specific (6.69 mA cm⁻²) activities in alkaline media, which are ∼40.4 and 25.3 times as high as those of commercial Pt/C, respectively. Furthermore, these nanocubes are highly stable with only 9.3% loss in mass activity after 10 000 cycles, as compared to a big decrease of 59.9% for commercial Pt/C. From geometrical phase analysis (GPA) combined with theoretical calculation data, the strain effect in such nanocubes contributes only ∼4% enhancement in ORR activity and the ligand effect is prominent due to the negligible lattice mismatch between Pd₃Pb and Pt_mPb. Besides electronic coupling between Pt and Pd, density functional theory (DFT) calculations show that the strong p–d orbital hybridization between Pt and Pb is critical to downshift the d-band center of Pt and dramatically boost the ORR activity.