Why Does Pt Shell Bearing Tensile Strain Still Have Superior Activity for the Oxygen Reduction Reaction?

Abstract

Nanoparticles with a 55 nm Au core and a few monolayers of Pt shell (denoted as Au@Pt x ML, x = 1–4) are found to have superior activity toward the oxygen reduction reaction (ORR) compared to commercial Pt nanoparticles and polycrystalline Pt (pc-Pt) electrodes in 0.1 M HClO4. The half-wave potential for ORR at Au@Pt1 ML is ca. 20 mV positively shifted. With the decrease of the Pt shell thickness from 4 to 1 monolayer, both the extent of enhancement of the ORR activity and the adsorption strength of oxygen-containing species increase; the latter is confirmed by results from surface-enhanced Raman spectroscopy (SERS) and X-ray photon emission spectroscopy (XPS). Furthermore, SERS results also reveal that adsorbed CO on such catalysts displays a blue shift in Pt–CO and a red shift in C–O stretching frequencies compared to that at pc-Pt under otherwise identical conditions. Positive double layer effects induced by diminishing surface charge density, which leads to the less rigid first layer of water, are suggested to be the origin of the superior ORR performance of Au@Pt x ML to that of commercial Pt/C catalysts.

In Situ SERS Probing the Effect of Additional Metals on Pt-Based Ternary Alloys toward Improving ORR Performance

“…16−18 This strategy has been successfully applied to in situ study the ORR mechanism of Pt-based catalysts, and direct spectral evidence of oxygencontaining adsorbents such as *OOH has been observed. 19,20 However, the evolution of the *OOH adsorption configuration has yet to be reported. Herein, the borrowing strategy was prolonged to study the configuration change of surface adsorbents on Pt-based alloys during ORR (Figure 1a).…”

“…Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive technique for detecting surface oxygen-containing species, especially in the low wavenumber region. , The extended SERS “borrowing” strategy based on core–shell nanoparticles (NPs) broke the limit of traditional SERS technology on the universality of the substrate and greatly expanded the application scope of SERS. − This strategy has been successfully applied to in situ study the ORR mechanism of Pt-based catalysts, and direct spectral evidence of oxygen-containing adsorbents such as *OOH has been observed. , However, the evolution of the *OOH adsorption configuration has yet to be reported. Herein, the borrowing strategy was prolonged to study the configuration change of surface adsorbents on Pt-based alloys during ORR (Figure a).…”

Cobalt-Doped Pd@Pt Core–Shell Nanoparticles: A Correlative Study of Electronic Structure and Catalytic Activity in ORR

“…Recently, palladium has been widely used as a substrate for platinum deposition in core–shell catalysts due to their close lattice match, and both theoretical and experimental studies have shown that the activity can be enhanced as a result of electronic coupling between Pd and Pt. Another strategy for obtaining a decent ORR performance in platinum would be hindering its shape to some specific facets and optimizing the surface structure through shape-controlled synthesis, as ORR is a structure-sensitive reaction. , The specific activity of Pd@Pt core@shell catalyst has shown to increase in the order of (100) < (110) < (111). – In all cases, the Pt d-band center will be downshifted, resulting in reduced oxygen binding energy on platinum. – Stamenkovic et al have demonstrated that the d-band center has an optimum value, and the highest specific activity follows a volcano plot in relation to oxygen binding energy. , Despite the sole incorporation of all these techniques in previous studies and reports showcasing the successful synthesis of Pt-based catalysts with remarkable activity toward ORR, practical use is still confined due to their low durability in the corrosive operating conditions of ORR. The low durability is mainly attributed to the thermodynamically unstable structures, which are necessary for highly active catalysts, but result in rapid performance losses.…”

Electrocatalysis of Oxygen Reduction on Te-Modified Platinum Stepped Crystal Surfaces

“…6 For that, it is necessary to understand the ORR mechanism and factors that affect ORR kinetics on the electrocatalysts. 7 However, the complex catalyst structure in practical electrode materials limits the in-depth study of ORR kinetics. 8−10 Singlecrystal electrodes with well-defined surfaces and a controlled atomic arrangement 11−18 are of great help in elucidating the reaction mechanism and unraveling the structure−activity relationship.…”

“…Polymer electrolyte membrane fuel cells (PEMFCs) are promising technologies for the extensive use of sustainable energy due to their high energy conversion efficiency and the wide range of potential applications with different power density scales. − However, the high overpotential of oxygen reduction reaction (ORR) at the cathode of PEMFCs requires a high loading of precious Pt group catalysts which limits large-scale application. , Thus, developing cathode catalysts with high electrocatalytic activity is of significant importance . For that, it is necessary to understand the ORR mechanism and factors that affect ORR kinetics on the electrocatalysts . However, the complex catalyst structure in practical electrode materials limits the in-depth study of ORR kinetics. − Single-crystal electrodes with well-defined surfaces and a controlled atomic arrangement − are of great help in elucidating the reaction mechanism and unraveling the structure–activity relationship.…”