Porous Carbon Nanorods Encapsulating Bismuth Nanoparticles Promote p-Si Nanowire Array for Photoelectrocatalytic CO2 Reduction to Formate

Abstract

Photoelectrocatalytic reduction of carbon dioxide to high value-added chemicals is one of the effective means to reduce greenhouse gas emissions and alleviate the energy crisis. In this study, porous carbon nanorods encapsulating bismuth (Bi) nanoparticles were synthesized using a metal–organic framework (MOF)-assisted spatial confinement and high-temperature carbonization strategy and then modified on silicon nanowires to construct a Si–Bi@Cx composite photocathode. The presence of the plasmonic metal Bi enhances the light absorption and improves the selectivity of carbon dioxide reduction products as reactive substances. At −0.9 V vs RHE, the Si–Bi@C800 photocathode achieves a faradaic efficiency for formic acid (FE_HCOOH) of up to 91.23%, with a production rate of 88.5 μmol·h^–1·cm^–2. Further experimental analysis and in situ infrared spectroscopy results showed that the porous carbon nanorods with strong hydrophobicity not only reduce the contact between the electrode and water and inhibit the occurrence of the hydrogen evolution reaction but also accelerate the mass transfer of CO₂ molecules and increase the local CO₂ concentration. Simultaneously, Bi nanoparticles promote the formation of the *OCHO intermediate and realize the efficient conversion of CO₂ to formic acid. This study lays a foundation for constructing active sites on silicon-based semiconductors.