A Bismuth Species-Decorated ZnO/p-Si Photocathode for High Selectivity of Formate in CO₂ Photoelectrochemical Reduction

Photoelectrochemical (PEC) reduction of CO₂ to high value-added chemicals or fuel is an effective way to remit insufficient energy supply and global warming. Herein, Bi species-modified p-n heterojunction ZnO/p-Si was synthesized by a hydrothermal method and a subsequent electrodeposition process. For the PEC CO₂ reduction reaction (CO₂RR), the obtained photocathode Bi-Bi₂O₃/ZnO/p-Si not only improves the light absorption capacity because of p-Si and plasma metal Bi, but also increases the selectivity of CO₂ reduction products because of the existence of Bi species. In particular, compared with the electrochemical CO₂RR, the faraday efficiency of formate shows a 1.8 fold increase for the optimal sample Bi-Bi₂O₃/ZnO/p-Si reaching 84.3% in the PEC CO₂RR at −0.95 V vs RHE. More importantly, the current density and product selectivity have no decay within 8 h, implying its high stability. In addition,, a high applied bias photon-to-current efficiency of 1.14% and an energy efficiency value of 56.21% were achieved for the Bi-Bi₂O₃/ZnO/p-Si photocathode at −0.95 V vs RHE, confirming its high PEC activity. A possible electron transfer mechanism for the Bi-Bi₂O₃/ZnO/p-Si photocathode is also proposed.