Bi–Sn Co-Catalyst-Modified p-Si Nanowire Array Photocathodes for Photoelectrocatalytic CO2 Reduction to Formate

Co-catalyst modification has been studied as a strategy to enhance silicon nanowires' (SiNWs') photoelectrocatalytic performance for CO2 reduction since their high light absorption efficiency and unique radial structure facilitate electron transport. However, their limited activity and poor selectivity toward CO2 reduction remain a challenge. Herein, we report the fabrication of core–shell structured, non-noble metal Bi and Sn co-catalyst-loaded SiNW photoelectrodes for CO2 reduction to formate. Microscopic morphology results revealed that Bi co-catalysts were deposited as nanoparticles and Sn co-catalysts as thin films on Bi and Si surfaces. Notably, Bi–Sn/SiNW photocathodes showed enhanced formate yield and selectivity compared to electrodes modified with only Bi or Sn. Specifically, at −1.02 V vs reversible hydrogen electrodes, the Faraday efficiency of formate reached 88.67% and the product rate was 80.07 μmol h–1 cm–2. Further experimental analysis and computational results demonstrated that the reasonable band structure formed by Si and the two co-catalysts Bi and Sn improved migration of photogenerated electrons, thus promoting CO2 reduction reaction toward formate with high efficiency and selectivity. This work lays the foundation for composite photocathodes with multiple co-catalysts for synergistic catalysis, addressing the challenges related to CO2 reduction and sustainable energy development.