(488e) Plasmons Increase Catalytic Reduction By Metal Nanoparticles Reduced on Monolayer Transition Metal Dichalcogenide

Electrochemical reduction of gold nanoparticles (GNP) onto monolayer tungsten disulfide (a two-dimensional (2D) transition metal dichalcogenide, TMD) to form a GNP-2DTMD heterostructure was recently shown to enhance catalytic activity over ten-fold relative to bare 2DTMD. However, characterization of the unique properties of GNP-2DTMD heterostructures via largely empirical methods has not elucidated or quantified the underlying physical, chemical, or electromagnetic contributions to this enhancement. As a result, refinement of this intriguing development and its possible extension to other metal-nanocrystal pairs has to date remained a trial-and-error experimental process, limiting its utility and applicability.

The present work introduced discrete dipole approximation (DDA) in combination with electron energy loss spectroscopy (EELS) to simulate and characterize physicochemical and electromagnetic features of metal-nanoparticle (MNP)-2DTMD heterostructures that contribute to enhanced catalytic activity. Heterostructures of 2DTMD and range of noble MNP were self-assembled via electrochemical reduction. Nanometer- and femtosecond-resolved EELS was used to simulate and measure low-energy MNP plasmon modes, plasmon damping and electric near fields at heterointerfaces. Results of DDA simulation and EELS characterization were compared with optical analysis by transmission ultraviolet-visible (TUV-vis) spectroscopy and catalytic reduction potential measured by cyclic voltammography. Effects of optical irradiation and resonant plasmon induction of MNP-2DTMD heterostructures on catalytic activity were quantitatively measured for the first time.

Transmission electron microscopy and x-ray photoelectron spectroscopy verified direct reduction of MNP onto 2DTMD to formi metal-sulfur bonds. Comparison of EELS and electron band structure revealed the relative influence of plasmon damping and associated direct electron transfer at the MNP-2DTMD heterointerface on catalytic activity. DDA was used to quantitate the contribution from plasmon and exciton modes to catalytic activity. The effects of frequency- and intensity-dependent irradiation on onset potential and current density were quantitatively evaluated. This quantitative comparison of simulation, optoelectronic characterization and experimental catalysis - the first reported to our knowledge - supported classification of catalytic potential of a range of MNP-2DTMD heterostructure. This enables rational design and development of the composition, geometry, and electromagnetic environment of MNP-2DTMD heterostructures to optimize their catalytic activity in a variety of chemical, biological, energy and water systems.