  Exploring nonequilibrium hot carriers from plasmonic metal nanostructures is
a dynamic field in optoelectronics, driving photochemical reactions such as
solar fuel generation. The hot carrier injection mechanism and the reaction
rate are highly impacted by the metal/molecule interaction. However,
determining the primary type of the reaction and thus the injection mechanism
of the hot carriers has remained elusive. In this work, we reveal an electron
injection mechanism deviating from a purely outersphere process for the
reduction of ferricyanide redox molecule in a gold/p-type gallium nitride
(Au/p- GaN) photocathode system. Combining our experimental approach with ab
initio simulations, we discover that the efficient inner-sphere transfer of
low-energy electrons leads to a continuous enhancement in the photocathode
device performance in the interband regime. These findings provide important
mechanistic insights, showing our methodology as a powerful tool for analyzing
and engineering hot-carrier-driven processes in plasmonic photocatalytic
systems and optoelectronic devices.
