Precise Pt-skin manipulation of strain and ligand effects for oxygen reduction

Nanostructured platinum (Pt)-skin alloys are promising electrocatalysts for oxygen reduction reaction (ORR) due to their tunable strain and ligand effects which essentially regulate the surface electronic structures. In addition to the chemical nature of alloying elements, the layer numbers of Pt-skin crucially determine the strain and ligand effects. So far, the effects of Pt-skin layer numbers have been generally investigated through vapor deposition on bulk metals and alloys with extended surfaces, while the precise Pt-skin control of nanostructured alloy electrocatalysts in wet chemical synthesis remains fairly challenging. Herein, we develop a Pt-skin engineering strategy to construct a family of dendrite-like porous PtCu@Pt nL nanospheres (NSs) with precisely controlled Pt-skin layers by adjusting the reducibility of Cu ions. Density functional theory calculations and X-ray photoelectron spectroscopy-based valence band spectra results indicate a concave parabolic trend of d -band center with varying the Pt-skin layer from 0 to 5, jointly resulting from the skin layer-dependent electron transfer numbers and compression strain. The two-layer Pt-skin alloy, PtCu@Pt 2L NS, is identified to have the lowest d -band center and therefore locates at the summit of ORR activity volcano. Accordingly, this carbon supported PtCu@Pt 2L NSs catalyst achieves excellent ORR electrocatalysis in H 2 –O 2 proton exchange membrane fuel cells. Pt-skinned porous PtCu@Pt nL nanospheres (n ​= ​0, 1, 2, 3, 5) with precisely designed skin layers enable effective tuning of surface electronic structure and ORR activity, with the two-layer Pt-skin exhibiting the lowest d -band center by a consociation of strain and ligand effects, and top electrocatalytic activity accordingly. • Precise control of Pt-skin layer number has been achieved for the dendrite-like porous network PtCu@Pt nL NSs. • Both strain and electronic effects together manipulate a concave parabolic trend of d -band center. • A volcanic relationship between ORR activity and Pt-skin layers shows peak activity at two-layer Pt-skin at the summit. • The optimal PtCu@Pt 2L NSs/C catalyst exhibits excellent activity and stability in half-cells and H 2 –O 2 fuel cells.