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

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@PtmPb (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 similar to 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 similar to 4% enhancement in ORR activity and the ligand effect is prominent due to the negligible lattice mismatch between Pd3Pb and PtmPb. 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.