Dynamically Cyclic Fe²⁺/Fe³⁺ Active Sites as Electron and Proton-Feeding Centers Boosting CO₂ Photoreduction Powered by Benzyl Alcohol Oxidation

Solar-driven CO₂ photoreduction holds promise for sustainable fuel and chemical productions, but the complex proton-coupled multi-electron transfer processes and sluggish oxidation half-reaction kinetics substantially hinder its efficiency. Here, we devised a rational catalyst design to address these challenges by fabricating ferrocene carboxylic acid-functionalized Cs₃Sb₂Br₉ nanocrystals (CSB-Fc NCs), which facilitate simultaneous benzyl alcohol oxidation and CO₂ reduction reactions under visible-light irradiation. The synchronized proton-coupled electron transfer processes between the reduction and oxidation half-reactions on CSB-Fc NCs resulted in a 5-fold increase in the CO₂ reduction rate (45.56 μmol g^-1 h^-1, 97.9% CO selectivity) and a 5.8-fold enhancement in benzyl alcohol conversion (97.7% selectivity for benzaldehyde) compared to the CSB. In situ Raman and ultraviolet-visible diffuse reflectance spectra revealed that the dynamic Fe²⁺/Fe³⁺ redox loop within the Fc unit serves as the actual active site, facilitating the activation of substrate molecules. More importantly, in situ attenuated total reflection Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry spectroscopy, with isotope labeling of Deuteron-benzyl alcohol and ¹³CO₂, confirmed that proton transfer from the hydroxyl group generates reactive protons at the Fe²⁺/Fe³⁺ site, enabling efficient CO₂ photoreduction through subsequent protonation steps. This work offers a cost-effective and efficient approach for synergetic CO₂ photoreduction driven by organic synthesis, advancing solar energy utilization.