Engineering hematite/plasmonic nanoparticle interfaces for efficient photoelectrochemical water splitting

Surface plasmon resonance (SPR) of metallic nanoparticles has become an attractive strategy for increasing the efficiency of solar water splitting. However, the metal/semiconductor junction may introduce unwanted interfaces or surface species that reduce the SPR effect as well as compromising efficient charge transport. The processes of separation, transport, and transfer of charges in metal-based plasmonic photoelectrodes are highly sensitive to the nature of the coupling between metal/semiconductor/electrolyte and a comprehensive understanding of these interfaces is still lacking. In this work, we proposed the construction of hematite photoanodes modified with gold nanoparticles (AuNPs) and aluminum oxide with different arrangements, whose optimized coupling between the interfaces led to enhanced photoelectrochemical (PEC) performance. Using a combination of finite-difference time-domain (FDTD) simulations, well-established materials synthesis and x-ray spectroscopy, electron microscopy, and PEC characterization techniques, selected architecture design strategies are evaluated. The experimental results reveal that the direct contact between semiconductors and metals coated by the dielectric leads to an improvement in localized electric field at the interface upon the formation of hot electrons, boosting the generation and separation efficiencies of electron-hole pairs. The main role of the dielectric coating, which led to an ineffective surface state passivation, is to prevent the photooxidation of AuNPs. FDTD calculations are employed to investigate the spatial distribution of the electric-field intensity around the AuNPs deposited onto the hematite surfaces and to corroborate the local field enhancement effect. The outcome of this combined experimental-theoretical study reveals that engineering plasmonic interfaces is a powerful tool to design efficient photoanodes for plasmon-driven PEC water splitting.