Electronic metal-support interactions in vacuum vs. electrolyte

Abstract

I n our communication 1 , we have investigated Pt nanoparticles supported on high surface area carbons (Pt/C) and boron carbide composites (Pt/BC). We showed that purely electronic interactions between the nanoparticulate catalyst and its support have bearings on electrocatalytic activity for the oxygen reduction reaction in acidic media and catalyst stability. This has been achieved by interrogating the electronic states of the supported Pt catalysts in an electrochemical environment via X-ray absorption near edge structure (XANES), which showed a relatively more positive charge on Pt nanoparticles if supported on BC compared to very similar Pt nanoparticles supported on C. Similarity of the Pt nanoparticle size distribution and morphology was established by transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS), respectively, to exclude other factors contributing to the electrocatalytic characteristics.We also investigated the two catalysts ex situ under ultra-high vacuum (UHV) conditions by X-ray photoelectron spectroscopy (XPS), which has shown a shift to higher binding energies of the Pt 4f signal relative to the reference C 1s signal for the Pt/BC catalyst. Following the band filling argument put forward by Watanabe et al. 2 , we have tentatively interpreted this change with a relatively more negative charge of Pt supported on BC compared to Pt on C under UHV conditions. A fuller account of the reasoning is contained in the published reviewer file of our original communication.This led us to point out that the relative state of charge of the Pt nanoparticles on the two supports (i.e., more negative or more positive) appears different under potentiostatic control in aqueous electrolyte than under UHV conditions. In an attempt to rationalise this observation, we have argued that the overall work function of the heterogeneous electrode surfaces should be different for the Pt/C and Pt/BC systems, which leads to a shift of the potential of zero charge (pzc) 3 of the heterogeneous Pt/BC electrode surface relative to Pt/C. An additional positive charge has, therefore, to be accommodated by the Pt/BC electrode if held at the same potential, because it is further away from the pzc.Binninger addressed this minor point 4 . In an attempt to show that "no inversion of the relative charge transfer between support and Pt nanoparticle can be deduced", Binninger has put forward an electrostatic argument. He investigates the potential at which the nanoparticle electrolyte-facing, external surface has zero charge in the limit of infinitely strong screening (i.e., where the Debye length is much shorter than the catalyst particle size) in the electrolyte in detail and concludes that this potential is the same as is found for an extended Pt electrode under the same conditions. This result is unsurprising given that the assumption of infinite screening will quench all electrostatic interaction between nanoparticle and support through the electrolyte. Binninger then qualitatively expands his co...

Electronic Metal–Support Interactions for Electrochemiluminescence Signal Amplification

“…Metal–support interactions play an important role in the improvement of the catalytic activity of supported metal catalysts. , In 2012, a new type of metal–support interaction, electronic metal–support interaction (EMSI), had attached increasing attention since it was first proposed by Campbell . Recently, much attention has been paid to the fabrication of novel catalysts by the EMSI effect. − For example, Lu and his co-workers developed an atomical Au on two-dimensional VO 2 nanobelt catalysts for the efficient Fenton-like reaction . They concluded that the strong EMSI between Au atoms and VO 2 nanobelt supports could rapidly activate S 2 O 8 2– to generate SO 4 •– radicals to remove various recalcitrant organic pollutants; Datta et al realized the tuning of the EMSI between Ru nanoparticles and CuO nanowire supports by increasing multiple twinned Ru nanoparticle population, and they demonstrated that the defect-assisted EMSI could improve the catalyst activity and stability for oxygen evolution reaction at neutral condition; Wei’s group reported that EMSI from Co­(OH) 2 to Pt nanoparticles could form electron-rich Pt nanoparticles, leading to the improvement of the catalytic activity toward CO oxidation .…”