Facet Engineering in Au Nanoparticles Buried in P-Si Photocathodes for Enhanced Photoelectrochemical CO2 Reduction

Converting CO2 into carbon-based fuels via the photoelectrochemical (PEC) approach is considered as an one-stone-two-birds strategy for alleviating the greenhouse effect and energy crisis. Here, we report a novel two-step strategy to integrate uniform Au NPs with controllable Au(111)/Au(200) boundaries on p-Si photocathodes for efficient and selective PEC CO2 conversion to CO. Theoretical calculations suggest that the Au(111)/Au(200) boundaries significantly reduce the energy barrier for forming the *COOH intermediate during CO2 reduction. Moreover, we discover that embedding the Au NPs into Si surface can not only further improve the PEC activity and selectivity but also significantly boost the operational stability of Si photocathodes, because of the ameliorated interfacial contact between the Au NPs and Si substrate. Eventually, the optimized Au/p-Si photocathode demonstrates a great CO selectivity of 82.2 % and an impressive operational stability of over one week, which offers critical insights into the design of photocathodes for solar fuel production.