Synergistic Enhancement of the Photoelectrochemical Performance of TiO₂ Nanorod Arrays through Embedded Plasmon and Surface Carbon Nitride Co-sensitization

We report a unique photoanode architecture involving TiO2, g-C3N4, and AuNPs wherein a synergistic enhancement of the photoelectrochemical (PEC) performance was obtained with photocurrent densities as high as 3 mA cm–2 under AM1.5G 1 sun illumination. The PEC performance was highly stable and reproducible, and a photoresponse was obtained down to a photon energy of 2.4 eV, close to the interband damping threshold of Au. The photocurrent enhancement was maximized when the Au plasmon band strongly overlapped the g-C3N4 emission band. Our photoanode architecture, which involved AuNPs buried under TiO2 and a plasmon-induced resonance energy transfer-like interaction between g-C3N4 quantum dots (CNQDs) and AuNPs, solved four major problems associated with plasmonic photoelectrocatalysis─it reduced recombination by limiting eliminating direct electrolyte access to AuNPs, it facilitated electron extraction through single-crystal TiO2 nanorod percolation pathways, it facilitated hole extraction through a defective TiO2 seed layer or canopy, and it expanded the range of visible light harvesting by pumping the Au surface plasmons from CNQDs through exciton-to-plasmon resonant energy transfer.