Roles of Mo Surface Dopants in Enhancing the ORR Performance of Octahedral PtNi Nanoparticles

Abstract

Doping with a transition metal was recently shown to greatly boost the activity and durability of PtNi/C octahedral nanoparticles (NPs) for the oxygen reduction reaction (ORR), but its specific roles remain unclear. By combining electrochemistry, ex situ and in situ spectroscopic techniques, density functional theory calculations, and a newly developed kinetic Monte Carlo model, we showed that Mo atoms are preferentially located on the vertex and edge sites of Mo-PtNi/C in the form of oxides, which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides stabilize adjacent Pt sites, hereby stabilizing the octahedral shape enriched with (111) facets, and lead to increased concentration of Ni in subsurface layers where they are protected against acid dissolution. Consequently, the favorable PtNi(111) structure for the ORR is stabilized on the surface of PtNi/C NPs in acid against voltage cycling. Significantly, the unusual potential-dependent oxygen coverage trend on Mo-doped PtNi/C NPs as revealed by the surface-sensitive Δμ analysis suggests that the Mo dopants may also improve the ORR kinetics by modifying the coordination environments of Pt atoms on the surface. Our studies point out a possible way to stabilize the favorable shape and composition established on conceptual catalytic models in practical nanoscale catalysts.

Tungsten as “Adhesive” in Pt2CuW0.25 Ternary Alloy for Highly Durable Oxygen Reduction Electrocatalysis

“…The peaks centered at 40.8°, 47.6°, 69.7°, and 84.0° (2θ) agree well with the constructive interferences of (111), (200), (220), and (311) facets of face-centered-cubic (fcc) crystal structure. 25 shows the positive shift compared with that of Pt 2 Cu and Pt 2 W NPs, which may originate from the smaller radius of W(δ+) ions, which will be discussed later. 25 shows the positive shift compared with that of Pt 2 Cu and Pt 2 W NPs, which may originate from the smaller radius of W(δ+) ions, which will be discussed later.…”

“…The Pt 4f spectra collected for the Pt 2 W, Pt 2 Cu, and Pt 2 CuW 0.25 catalysts show two peaks designated to core-level photoemission of the 4f 5/2 and 4f 7/2 . 25 NPs, the W(+6) valence is the dominating component with the binding energy lower than that in Pt 2 W (Figure 2d), indicating that W atom may accept electron from other elements. The Pt 4f 5/2 can be fit with the similar deconvolution into Pt(2+) and Pt(0), echoing with the 4f 7/2 peak to indicate the existence of partially oxidized Pt atoms on the surface.…”

“…[22] Chorkendorff et al studied the effect of subsurface transition metal atoms on the ORR activity of Pt (named as near-surface alloy) on singlecrystalline Pt(111) surface, and confirmed that the subsurface Cu layer can weaken the binding of Pt surface to OH* and achieves an eightfold enhancement in ORR activity over Pt(111) surface. [24,25] However, the Pt x Cu y -based alloy catalysts still suffer from severe stability issue due to the low redox potential nature of Cu element. Sun et al, focusing on the stability issue, demonstrated the effectiveness of doping Au atoms into the octahedral PtCu alloy nanocrystals (NCs) at trace amount in prolonging the high ORR activity.…”

Phase Modulating of Cu–Ni Nanowires Enables Active and Stable Electrocatalysts for the Methanol Oxidation Reaction

“…To date, Pt‐based catalysts are regarded as primarily alternative catalysts for the MOR, although high costs and sluggish kinetics are vital factors to hamper their wide commercialization . In addition, the unsatisfied stability with a tendency to aggregate as well as poor tolerance to CO or other carbonaceous intermediates are tremendous problems in methanol oxidation . Searching for advanced candidates with both highly activity and stability becomes extremely meaningful.…”

Morphological, Structural, and Compositional Evolution of Pt–Ni Octahedral Electrocatalysts with Pt‐Rich Edges and Ni‐Rich Core: Toward the Rational Design of Electrocatalysts for the Oxygen Reduction Reaction

“…Different annealing treatments on Pt–Ni NPs as well as the addition of a third transition metal, on top of the Pt 3 Ni composition has led to the report of unprecedented ORR activity and durability. In most of the reports, the octahedral nanocrystals are Pt 3 Ni alloys and the third transition metal is located mainly on the surface …”