Porous Carbon Nanorods\nEncapsulating Bismuth Nanoparticles\nPromote p‑Si Nanowire Array for Photoelectrocatalytic CO<sub>2</sub> Reduction to Formate

Photoelectrocatalytic reduction of carbon dioxide to\nhigh value-added\nchemicals is one of the effective means to reduce greenhouse gas emissions\nand alleviate the energy crisis. In this study, porous carbon nanorods\nencapsulating bismuth (Bi) nanoparticles were synthesized using a\nmetal–organic framework (MOF)-assisted spatial confinement\nand high-temperature carbonization strategy and then modified on silicon\nnanowires to construct a Si–Bi@Cx composite photocathode. The\npresence of the plasmonic metal Bi enhances the light absorption and\nimproves the selectivity of carbon dioxide reduction products as reactive\nsubstances. At −0.9 V vs RHE, the Si–Bi@C800 photocathode\nachieves a faradaic efficiency for formic acid (FE<sub>HCOOH</sub>) of up to 91.23%, with a production rate of 88.5 μmol·h<sup>–1</sup>·cm<sup>–2</sup>. Further experimental\nanalysis and in situ infrared spectroscopy results showed that the\nporous carbon nanorods with strong hydrophobicity not only reduce\nthe contact between the electrode and water and inhibit the occurrence\nof the hydrogen evolution reaction but also accelerate the mass transfer\nof CO<sub>2</sub> molecules and increase the local CO<sub>2</sub> concentration.\nSimultaneously, Bi nanoparticles promote the formation of the *OCHO\nintermediate and realize the efficient conversion of CO<sub>2</sub> to formic acid. This study lays a foundation for constructing active\nsites on silicon-based semiconductors.