The photoelectrochemical reduction of CO₂ to form fuels could help to reduce global warming. Compared to possible gaseous products, liquids such as methanol are easier to store and transport. However, methanol production involves six-proton-coupled six-electron-transfer processes, which makes this reaction kinetically sluggish. This means it is difficult to selectively produce methanol by CO₂ reduction. It is especially challenging in aqueous electrolytes, where proton reduction (i.e., hydrogen production) is a highly competitive reaction.

Jinlong Gong, Tianjin University, China, and colleagues have developed a cathode for the increased photoelectrochemical production of methanol. The team created a well-defined Cu/Cu₂O interface by introducing metallic Cu nanoparticles onto Cu₂O films via electron-beam evaporation. The Cu/Cu₂O interfaces (pictured) greatly enhance the binding of surface‐adsorbed hydrogen atoms (H*) and reduce the binding of CO*. This provides balanced amounts of H* and CO* intermediates for methanol production.

In a photoelectrochemical cell with a TiO₂ model photoanode, a Cu/Cu₂O dark cathode has a Faradaic efficiency of up to 53.6 % for methanol production. According to the researchers, this approach provides a method for high‐efficiency, low‐cost, and stable methanol generation.

• Tuning Cu/Cu₂O Interfaces for the Reduction of Carbon Dioxide to Methanol in Aqueous Solutions,
  Xiaoxia Chang, Tuo Wang, Zhi-Jian Zhao, Piaoping Yang, Jeffrey Greeley, Rentao Mu, Gong Zhang, Zhongmiao Gong, Zhibin Luo, Jun Chen, Yi Cui, Geoffrey A. Ozin, Jinlong Gong,
  Angew. Chem. Int. Ed. 2018.
  https://doi.org/10.1002/anie.201805256