The direct optical monitoring of electron transfer on single nanoparticles during chemical reactions with gas molecules is one of the main challenges in materials science. Gases interacting with complex surfaces are enormously challenging situations to describe but are core to the understanding and the advancement of heterogeneous catalysis. Often the mechanism which a gas molecule undergoes to become attached to a solid surface is intricate, elusive, and consists of multiple steps. A particularly important case where this is utterly true is H2 adsorption. In this fundamental heterogeneous catalysis study we use dark field microscopy to demonstrate that single gold nanorods (Au NRs) act as a localized optical probe for electron transfer processes when embedded in thin films which H2 can dissociatively adsorb to. The peak position, the full width at half maximum and the relative intensity of the surface plasmon resonance of individual Au NRs embedded in TiO2, TiO2-Pt, ZnO, ZnO-Pt, SiO2 and SiO2-Pt thin films were monitored in real-time during repeated cycles of N2-H2-N2 and air-H2-air to qualitatively infer the rate and number of electrons transferred. From these results we show that dissociated hydrogen species migrate (‘spillover’) from 10 nm platinum nanoparticles (Pt NPs) to a supporting matrix at room temperature. The spillover process produces delocalized electrons that are injected into Au NRs in contact directly with Pt NPs or with a semiconducting support (TiO2 or ZnO). Additionally, we demonstrate with this technique that H2 does not dissociate on gold nanorods (13 nm × 40 nm) but it will dissociate directly on the surface of TiO2 when oxygen ions are adsorbed to the surface. These findings enable us to propose gas interaction mechanisms for different samples with distinct oxide supports and evaluate in real-time the direction of local charge transport at complex metal/oxide interfaces.

Electron transfer between single gold nanocrystals and oxide supports during hydrogen adsorption: A surface plasmon spectroscopy study

249th National Meeting (2015)

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