Plasmon-Induced Hot Electron Amplification and Effective Charge Separation by Au Nanoparticles Sandwiched between Copper Titanium Phosphate Nanosheets and Improved Carbon Dioxide Conversion to Methane

Designing the catalysts to achieve the best performance is no exception in carbon dioxide (CO2) solar fuel conversion. Herein, we designed a CuTiP/Au/CuTiP catalyst, wherein gold (Au) nanoparticles were stably sandwiched between two copper titanium phosphate nanosheets (CuTiP). The catalyst was focused on the strong localized surface plasmonic resonance (LSPR) on the Au nanoparticles which led to the amplification of hot electrons between CuTiP nanosheets and the effective charge separation. The electrostatic force microscopy for CuTiP/Au provided the images of electrons that moved into the interface between the Au nanoparticle and CuTiP sheet as the voltage increases from 0 to 5.0 V. There was no product selectivity for the CO2 conversion reaction on the CuTiP nanosheet, but the selectivity into methane (CH4) was significantly increased by anchoring Au nanoparticles. This was attributed to the effective charge separation on three phased surfaces formed between CuTiP, Au, and CuTiP, which led to excellent photocatalytic performance on CuTiP/Au/CuTiP. The density functional theory was used to support the proposed mechanism. The intensity-modulated photovoltage spectroscopy demonstrated that the recombination time between electrons and holes is remarkably slow on CuTiP/Au/CuTiP. Consequently, the designed catalyst in this study exhibited a CO2 conversion performance at least 10 folds higher than those of previous catalysts in the gas-phase reactions, and deactivation of the catalyst was not found even after five recycling tests.