Exploring the modulation mechanism of the LSPR effect of Cu periodic nanosphere arrays to promote the performance of TiO2 photoelectrodes

Abstract

Based on the previous exploration of the localized surface plasmon resonance (LSPR) effect of isolated Cu nanospheres to enhance the photoelectrochemical performance of TiO₂ photoelectrodes, this work further arranged Cu nanospheres into periodic nanosphere arrays (PNAs). The enhancement mechanism of the photoelectrochemical performance caused by the related factors of PNAs (including the type and size of the periodic cell, deposition location, and the presence of Cu₂O covering) was systematically analyzed by finite-difference time-domain simulation. We demonstrate that the deposition location of Cu PNAs is the most critical determinant, followed by the size of the periodic cell (i.e. the gap between Cu nanospheres): when a Cu PNA is immersed in a TiO₂ photoelectrode to a certain depth, the coupling effect between Cu nanospheres is the most effective; when the gap is less than 50 nm, the multiple scattering effect results in a significant enhancement of light absorption in the range of 380–590 nm. Due to the different coupling effect and charge transfer mechanism, hexagonal Cu PNAs easily excite higher-order LSPR modes, resulting in prominent enhancement of the local interfacial electric field; square Cu PNAs are more likely to excite the low-order LSPR modes, resulting in only limited enhancement of the local interfacial electric field. The presence of Cu₂O covering of Cu PNAs shields the coupling effect, resulting in the weakening or even disappearing of the above enhancement functions. These findings provide reference research cases and theoretical data for the further development and optimal design of Cu/TiO₂ composite photoelectrodes.