Plasmonic Metal Mediated Charge Transfer in Stacked Core–Shell Semiconductor Heterojunction for Significantly Enhanced CO2 Photoreduction

Construction of core-shell semiconductor heterojunctions and plasmonic metal/semiconductor heterostructures represents two promising routes to improved light harvesting and promoted charge separation, but their photocatalytic activities are respectively limited by sluggish consumption of charge carriers confined in the cores, and contradictory migration directions of plasmon-induced hot electrons and semiconductor-generated electrons. Herein, a semiconductor/metal/semiconductor stacked core-shell design is demonstrated to overcome these limitations and significantly boost the photoactivity in CO2 reduction. In this smart design, sandwiched Au serves as a "stone", which "kills two birds" by inducing localized surface plasmon resonance for hot electron generation and mediating unidirectional transmission of conduction band electrons and hot electrons from TiO2 core to MoS2 shell. Meanwhile, upward band bending of TiO2 drives core-to-shell migration of holes through TiO2 -MoS2 interface. The co-existence of TiO2 → Au → MoS2 electron flow and TiO2 → MoS2 hole flow contributes to spatial charge separation on different locations of MoS2 outer layer for overall redox reactions. Additionally, reduction potential of photoelectrons participating in the CO2 reduction is elaborately adjusted by tuning the thickness of MoS2 shell, and thus the product selectivity is delicately regulated. This work provides fresh hints for rationally controlling the charge transfer pathways toward high-efficiency CO2 photoreduction.