Regulating a CoO/ZnO heterojunction aerogel with a built-in electric field for enhanced CO photoreduction to solar fuels from DFT insights.

P-N-type heterojunctions have the potential to serve as highly efficient photocatalysts for CO reduction, owing to their remarkable carrier separation efficiency, high stability, and strong redox capacity. In this study, a novel P-N CoO/ZnO heterojunction aerogel photocatalyst was fabricated through a process starting with the propylene oxide ring-opening-induced gelation technique. The resulting CoO/ZnO aerogel exhibits an interconnected, hierarchical porous structure, which endows it with a particle diameter size at around several tens of nanometers and a large BET-specific surface area, thereby providing abundant exposed active sites. Under simulated solar spectral conditions, the yields of CH and CO can attain 18 μmol g h and 14.4 μmol g h, respectively, in the absence of any sacrificial agent and photosensitizer. These values are 12.0 times and 5.8 times higher than those of the pristine CoO aerogel. Based on density functional theory (DFT) calculations, the activation mechanism of CO on the catalyst surface is illustrated. This is confirmed by the elongated CO bond length of the CO molecule from 1.174 and 1.175 Å to 1.376 and 1.259 Å, respectively, after forming the CoO/ZnO heterojunction, which is further confirmed by the more negative CO adsorption energy. Further research demonstrates that the built-in electric field formed at the heterojunction interface effectively promotes the recombination of electrons in the conduction band of CoO with holes in the valence band of ZnO, significantly enhancing the carrier separation efficiency and thereby boosting the photocatalytic reduction activity of CO. This work goes beyond providing new strategies for designing efficient CO reduction photocatalysts, extending its impact to advancing the utilization of aerogel materials in the field of photocatalysis.