Optimization of atomic layer deposited Pt-shell thickness of PtCu3@Pt/C catalyst for oxygen reduction reaction

Abstract

A series of PtCu3@Pt/C catalysts with core@shell structure applicable to oxygen reduction reaction (ORR) were successfully synthesized by combining wet chemistry method for supported PtCu3/C preparation and atomic layer deposition (ALD) technique for Pt-shell covering PtCu3 nanoparticles. The oxygen adsorption energy on the surface of model PtCu3@Pt(111) based on density functional theory calculation revealed that the optimal oxygen adsorption strength suitable for ORR appears on the PtCu3@Pt(111) having few layers of Pt-shell. For this purpose, the Pt-shell thickness was precisely adjusted by varying the number of ALD cycles between 1 and 6, and four ALD cycles were found to deposit approximately one layer of Pt atoms on the surface of PtCu3 nanoparticles. In-depth investigation through material characterization verified the formation of PtCu3 alloy and the adjustability of Pt-shell thickness. Strain effect and electronic effects were observed between the PtCu3 core and Pt-shell, manifested as lattice compression of the Pt-shell and electron transfer from Pt band to Cu, both of which can downshift d-band center of the Pt-shell thus weakening the adsorption of oxygen species. The electrocatalytic performance of various PtCu3@PtALD-n/C (n = 1–6) catalysts was tested in the ORR process using rotating disk electrode approach. PtCu3@PtALD-4/C exhibited the maximum mass and specific activity among all catalysts, being 3.2 and 2.6 times higher than a commercial Pt/C catalyst, and much better as well than the PtCu3/C without Pt-shell. The durability of the PtCu3@PtALD-4/C catalyst was also superior to that of the PtCu3/C and Pt/C catalysts.