Nanoengineered Ir_core@Pt_shell Nanoparticles with Controlled Pt Shell Coverages for Direct Methanol Electro-Oxidation

Abstract

The design and application of bimetallic alloy nanoparticles (NPs) for electrocatalytic applications are challenged by the need to clearly identify and understand the individual effect of each component. In the present work, the focus has been on PtIr NPs, with alloyed NPs being previously shown to be active toward the methanol oxidation reaction (MOR), but for which the mode of action of the Ir component remains uncertain. We have therefore nanoengineered a family of Ir@Pt NPs, using a modified polyol method, to control the Pt shell coverage (up to 2 monolayers) and thus to allow the separation of the bifunctional and electronic effects of Ir on the Pt activity. It is shown that the Ir core size and crystallinity do not change with the deposition of the Pt shell, as confirmed by transmission electron microscopy and X-ray diffraction. CO stripping and hydrogen underpotential deposition/removal were used for the first time to determine the surface composition of the Ir@Pt NPs. It is shown that the Ir enhances the MOR activity of the Pt primarily through the bifunctional effect, with an optimum Pt coverage of 0.4 of a monolayer. At 60 °C, an additional electronic effect of Ir on Pt can be discerned, causing an inhibition in the MOR rate by weakening the adsorption of methanol on the Pt, thus helping to remove the adsorbed CO intermediate from the shell surface.

Hydrogen evolution reaction on bimetallic Ir/Pt(poly) electrodes in alkaline solution

“…Since Pt and Ir have very similar atomic weights, EDS mapping was not able to easily distinguish these two peaks. Similar overlapping of Ir and Pt peaks was found for IrPt alloy nanoparticles designed for electrocatalytic applications [44].…”

Compressive Strain in Core–Shell Au–Pd Nanoparticles Introduced by Lateral Confinement of Deformation Twinnings to Enhance the Oxidation Reduction Reaction Performance

“…Although noble metal-based nanoparticles (NPs) as electrocatalysts have been widely studied in the field of fuel cells, the rare content in nature and expensive price limit their applications. − Thus, a series of strategies are developed to reduce the cost but enhance the electrocatalytic performance of the resulting NPs meanwhile by controlling their structure, , morphology, , elemental composition, , strain effect, , and so forth. For instance, core–shell (CS)-structured Au–Pd NPs were fabricated by epitaxial growth of the ultrathin Pd layer on Au NPs, which not only reduced the cost by increasing the utilization of Pd but also enhanced the electrocatalytic performance. , However, the electrocatalytic performance of common CS Au–Pd NPs is not very ideal because the adsorption ability of reactants and the desorption ability of reactive intermediates on their surfaces cannot be well balanced (Schemes S1 and S2).…”

Effect of Rh Coverage on CO-Adsorption and -Stripping Behaviors of Rhodium-Adlayer-Modified Platinum Electrodes

“…However, for bimetallic alloy nanoparticles (NPs), the surface composition does not always coincide with the bulk composition. − Core/shell NPs have attracted considerable attention as a new class of bimetallic electrocatalysts. In particular, one or two monolayers of precious metals such as Pt are often used as shells to maintain or improve catalytic activity and reduce precious metal consumption in applications such as fuel cell catalysts. − …”

“…The activities of the core/shell NP catalysts are also influenced by the coverage of the shell. ,− For example, the shell coverage of Ru core/Pt shell nanoparticles has been estimated as monolayer equivalent, which was a conceptual number . On the other hand, the coverage of a metal layer coated on a metal electrode has been evaluated using surface characterization techniques such as phase atomic force microscopy, , Rutherford backscattering spectrometry (RBS), Auger electron spectroscopy, , X-ray photoelectron spectroscopy (XPS), − low-energy ion scattering spectroscopy (LEISS), , and scanning tunneling microscopy (STM) .…”