Steering the Pathway of Plasmon‐Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer

Photoelectrochemical (PEC) conversion of CO2 in an aqueous medium into high‐energy fuels is a creative strategy for storing solar energy and closing the anthropogenic carbon cycle. However, the rational design of catalytic architectures to selectively and efficiently produce a target product such as CO has remained a grand challenge. Herein, an efficient and selective Si photocathode for CO production is reported by utilizing a TiO2 interlayer to bridge the Au nanoparticles and n+p‐Si. The TiO2 interlayer can not only effectively protect and passivate Si surface, but can also exhibit outstanding synergies with Au nanoparticles to greatly promote CO2 reduction kinetics for CO production through stabilizing the key reaction intermediates. Specifically, the TiO2 layer and Au nanoparticles work concertedly to enhance the separation of localized surface plasmon resonance generated hot carriers, contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during PEC CO2 reduction. The optimized Au/TiO2/n+p‐Si photocathode exhibits a Faradaic efficiency of 86% and a partial current density of −5.52 mA cm−2 at −0.8 VRHE for CO production, which represent state‐of‐the‐art performance in this field. Such a plasmon‐enhanced strategy may pave the way for the development of high‐performance PEC photocathodes for energy‐efficient CO2 utilization. The TiO2 interlayer bridging n+p‐Si and Au nanoparticles greatly boosts the photoelectrochemical (PEC) activity and selectivity of Si photocathode for CO production, which can be attributed to the reduced carrier recombination at the Au/n+p‐Si interface, enhanced capacity for the CO2 adsorption and activation, and effective utilization of the hot electrons generated in Au nanoparticles in PEC CO2 reduction.