  Harnessing non-equilibrium hot carriers from plasmonic metal nanostructures
constitutes a vibrant research field. It promises to enable control of activity
and selectivity of photochemical reactions, especially for solar fuel
generation. However, a comprehensive understanding of the interplay of
plasmonic hot carrier-driven processes in metal/semiconducting heterostructures
has remained elusive. In this work, we reveal the complex interdependence
between plasmon excitation, hot carrier generation, transport and interfacial
collection in plasmonic photocatalytic devices, uniquely determining the charge
injection efficiencies at the solid/solid and solid/liquid interfaces.
Interestingly, by measuring the internal quantum efficiency of ultrathin (14 to
33 nm) single-crystalline plasmonic gold (Au) nanoantenna arrays on titanium
dioxide substrates, we find that the performance of the device is governed by
hot hole collection at the metal/electrolyte interface. In particular, by
combining a solid- and liquid-state experimental approach with ab initio
simulations, we show a more efficient collection of high-energy d-band holes
traveling in [111] orientation, resulting in a stronger oxidation reaction at
the {111} surfaces of the nanoantenna. These results thus establish new
guidelines for the design and optimization of plasmonic photocatalytic systems
and optoelectronic devices.
