Modulating the intrinsic properties of platinum–cobalt nanowires for enhanced electrocatalysis of the oxygen reduction reaction

Abstract

The ability to improve the intrinsic activity of nanoalloy electrocatalysts is essential for designing highly efficient electrocatalysts by optimizing the basic physical properties of the nanoalloy. This report describes that the electrocatalytic performance of ultrathin Pt_nCo_100−n alloy nanowires (Pt_nCo_100−n NWs) toward the oxygen reduction reaction (ORR) is enhanced by regulating the lattice strain, highly active facets, and the electronic structure of the alloy, which can be achieved by optimizing the ratio of platinum-to-cobalt in alloys. The catalyst of Pt_nCo_100−n nanoalloy NWs features subtle lattice strain and (111) facets. The electrochemical results show excellent activity and durability toward ORR at a Pt : Co ratio of ∼70 : 30, which suggests compressively-strained single-phase alloy state revealed by X-ray diffraction (XRD) results. The correlation of facets, lattice strain, electronic structure, and activity is evaluated by the theoretical model based on the density functional theory (DFT) calculations of nanoalloy clusters, which show electron transfer from the PtCo alloy to oxygen. There is a relatively low energy difference between the HOMO of the PtCo nanoalloy and the LUMO of oxygen as the Pt : Co atom ratio is 70 : 30. By analyzing the adsorption of OH, O, and OOH intermediates on the surface of PtCo(111) facets of different compositions, it is observed that the adsorption energy of the Pt₂Co₈ cluster (Pt : Co20 : 80) is the strongest, resulting in low activity. Interestingly, the adsorption energy of the Pt₇Co₃ cluster is between that of the Pt₆Co₄ and Pt₁₀ cluster, which is thought to be related to the highest catalytic activity of the nanoalloy when the Pt : Co atom ratio is ∼70 : 30. This finding will provide a new strategy for studying the relationship between the structure and the catalytic activity of nanocatalysts.