Coupling surface plasmon resonance of gold nanoparticles with slow-photon-effect of TiO2 photonic crystals for synergistically enhanced photoelectrochemical water splitting

The slow photon effect of a photonic crystal (PC) is a promising characteristic for tuning light-matter interactions through material structure designing. A TiO2 bi-layer structure photoanode was constructed by fabricating a TiO2 PC layer through a template-assisted sol-gel process on a TiO2 nanorod array (NR) layer. Gold nanoparticles (Au NPs) with an average size of about 10 nm were deposited in situ into the TiO2 bi-layer structure. The extended photoelectrochemical (PEC) water splitting activity in visible light was ascribed to the energetic hot electrons and holes that were generated in the Au NPs through the excitation and decay of surface plasmons. By alternating the characteristic pore size of the TiO2 PC layer, the slow photon region at the red edge of the photonic band gap could be purposely tuned to overlap with the strong localized surface plasmon resonance (SPR) region of Au NPs. The matching slow photon effect of TiO2 PC (with a characteristic pore size of 250 nm) intensified the SPR responses (central at 536 nm) of Au NPs. Consequently, more hot electrons were generated in the Au NPs and injected into the conduction band of TiO2, resulting in improved PEC water splitting efficiency in the visible light region. Under simulated sunlight illumination, the photoconversion efficiency of the well matching Au/TiO2 photoanode approached 0.71%, which is one of the highest values ever reported in Au/TiO2 PEC systems. The work reported here provides support for designing coupling plasmonic nanostructures with PC-based materials to synergistically enhance PEC water splitting efficiency.