Design Guidelines for Enhanced Activity of Water Splitting Photoelectrodes with Plasmonic Nanoparticles

Plasmonic effects have been considered as a promising way of bringing the performances of metal oxide water splitting photoelectrodes closer to their theoretical limit. Optimizing the contribution of plasmonic effects is far more complex than material selection and needs to include, in particular, morphological aspects. In this work, we establish practical design guidelines for enhancing the performances of metal oxide photoanodes with plasmonic nanoparticles. A previously reported theoretical method modeling the contribution of optical nanostructures is used to calculate the photoelectrochemical performances (photocurrent, external quantum efficiency) and experimentally validated on fabricated devices. New insights on the contribution of plasmonic nanoparticles are found. Specifically, the performances are strongly influenced by the illumination direction, the active material morphology, and the size and position of the plasmonic scatterers. The light intensity distribution is studied to understand how plasmonic nanoparticles are modifying the light absorption in the active material. It is revealed that near-field hot-spots, exponentially decreasing with the distance to the scatterers, can beneficially impact the performances only for pure nanoparticles whereas interference effects are contributing even when the nanoparticles are covered with a protective shell (e.g., SiO₂).