Nanoscale Precision Design of Metal Catalysts Using Plasmonic Nanoreactors

The utilization of highly energetic charges (“hot-electrons/holes”) generated by the non-radiative decay of plasmons in metal nanostructures is an exciting emerging topic. Hot electrons have already been suggested as an... [ view full abstract ]

The utilization of highly energetic charges (“hot-electrons/holes”) generated by the non-radiative decay of plasmons in metal nanostructures is an exciting emerging topic. Hot electrons have already been suggested as an explanation for increased kinetics and improved selectivity of illuminated metal nanoparticle catalysts. However, tracking the local generation and transfer of these hot electrons, their energy distribution and their relation to the underlying nanoparticle structure has been challenging. Here we use ultra-thin monocrystalline gold nanotriangles as a model system to study hot electron generation and activity in photoreduction reactions. 

A uniform illumination source is used for the excitation of the nanotriangles on a glass/ITO substrate, at their surface plasmon resonance, in presence of an aqueous solution of chloroplatinic acid. Scanning Electron Microscope images revealed local reduction of chloroplatinic acid to platinum nanoparticles only on the gold nanotriangles and only under optical illumination. An applied potential is used to tune the reaction kinetics, which allows for mapping out the hot electron distribution. By controlling the illumination polarization and wavelength, the spatial distribution of Pt nanoparticle deposition could be controlled. Optical simulations were conducted for different polarizations so as to study the electric field distribution around the plasmonic nanostructures. The results were compared with the experimental platinum formation sites on the gold nanotriangles and a nice match between them and the simulated location of the optical field “hot spots” was observed. Furthermore, a thin electron acceptor layer is found to increase the deposition kinetics, presumably by increasing the lifetime of hot-electrons.

Our approach provides fundamental insights into hot-electron reactions and opens up a new synthetic pathway for hierarchical nanostructures with both simple synthesis and high spatial control. Such highly controlled nanostructures could find applications in single-molecule spectroscopy, photoelectrochemical water splitting and CO₂ reduction.