Hydrogen peroxide is widely used and can serve as an environmentally friendly oxidant. The traditional anthraquinone process for producing H₂O₂ has drawbacks such as high energy consumption. Artificial photosynthesis, which uses sunlight and semiconductor photocatalysts, could be promising as a more sustainable approach to producing H₂O₂. The development of efficient photocatalysts for this reaction is, thus, an interesting research target. Single-atom catalysts with sites such as Co-N₄ units can be useful for the electrochemical reduction of O₂ to H₂O₂. However, H₂O₂ photosynthesis has remained more challenging due to H₂O₂ decomposition at transition-metal sites under light irradiation.

Xiaojun Gu, Inner Mongolia University, Hohhot, China, Xiong Wen (David) Lou, City University of Hong Kong, China, and colleagues have developed a polymeric carbon nitride (CN) decorated with single-Zn sites that have tailorable local coordination environments. The team used zinc acetate to create asymmetric Zn-N₃O, providing a CN/Zn-OAc catalyst that shows significantly improved photocatalytic H₂O₂ production activity under visible light irradiation compared with the common Zn-N₄ moiety. The catalyst was prepared by mixing tubular polymeric CN with Zn(OAc)₂·2H₂O in ethanol at 80 °C, followed by annealing at 400 °C under an argon atmosphere.

According to the researchers, the asymmetric N/O coordination environment modulates the electronic structure of the Zn centers, facilitating O₂ adsorption and the formation of the key intermediate *OOH. In addition, the Zn-N₃O unit is inert to H₂O₂ decomposition under dark and light conditions. Overall, the work provides a simple approach to creating single-atom active sites with well-defined asymmetric configurations.

• Single Zn Atoms with Acetate‐Anion‐Enabled Asymmetric Coordination for Efficient H₂O₂ Photosynthesis,
  Yunxiang Li, Yan Guo, Guilan Fan, Deyan Luan, Xiaojun Gu, Xiong-Wen (David) Lou,
  Angew. Chem. Int. Ed. 2023.
  https://doi.org/10.1002/anie.202317572