Understanding oxygen reduction reaction activity of Pt-based nanoparticles from Pt atomic layers to Pt single atom alloy

The development of Pt -based atomic layer alloy and Pt -based single atom alloy (SAA) catalysts for oxygen reduction reaction (ORR) has received extensive attention. A comprehensive insight into how Pt distribution on nanoparticle surface affects ORR kinetics is still unclear. Here, we employ density functional theory calculation, current-potential polarization curve simulations and Wulff construction principle to study ORR on a series of Au@PtnL nanoparticles with diverse Pt loading from three atomic layers to dilute concentration of single -atom (n = 3, 2, 1, 1/4, 3/16, 1/8, 1/16). The ORR rate -determining step and activity of Au@PtnL nanoparticles can be described by a three-dimensional volcano plot spanned by the adsorption free energies of Delta G(O2*) and Delta G(OH*), where high density Pt SAA (Au@Pt1/4L) presents highest Pt atom catalytic efficiency. The simulations reveal that thinner Pt atomic layers on Au@PtnL possess higher d -band energy level due to stretch strain, leading the stronger OH* intermediate binding and suppressed protonation kinetics of OH*, in good agreement with available experimental data. When Pt atoms become isolated by Au host on Au@PtnL, Pt single -atom is converted into a free atom -like electronic structure due to the ligand effect of Au full coordination. A much narrower d band of Pt single -atom results in more filling of the sigma* anti -bond, which brings about a much weakened OH* adsorption strength and superior ORR activity of Pt SAA. An excessive diluter concentration of Pt SAA suffers from declined ORR kinetics impeded by O2 adsorption as the rate -determining step. This work shed light on the adjustment mechanism of the coordination environment of Pt active sites on ORR activity and attributed it to a combined ligand effect and geometry strain effect, which provides guidance for the future engineering of Ptbased nanoparticles with high Pt atom catalytic efficiency.