Small and salty CO ₂ reduction scheme: Most artificial photosynthesis approaches focus on making hydrogen. Modifying CO ₂ , as plants and microbes do, is more chemically complex. Asadi et al. report that fashioning WSe ₂ and related electrochemical catalysts into nanometer-scale flakes greatly improves their activity for the reduction of CO ₂ to CO. An ionic liquid reaction medium further enhances efficiency. An artificial leaf with WSe ₂ reduced CO ₂ on one side while a cobalt catalyst oxidized water on the other side. Science , this issue p. 467

Electrochemical reduction of carbon dioxide has been recognized as an efficient way to convert carbon dioxide to energy-rich products. Noble metals (for example, gold and silver) have been demonstrated to reduce carbon dioxide at moderate rates and low overpotentials. Nevertheless, the development of inexpensive systems with an efficient carbon dioxide reduction capability remains a challenge. Here we identify molybdenum disulphide as a promising cost-effective substitute for noble metal catalysts. We uncover that molybdenum disulphide shows superior carbon dioxide reduction performance compared with the noble metals with a high current density and low overpotential (54 mV) in an ionic liquid. Scanning transmission electron microscopy analysis and first principle modelling reveal that the molybdenum-terminated edges of molybdenum disulphide are mainly responsible for its catalytic performance due to their metallic character and a high d-electron density. This is further experimentally supported by the carbon dioxide reduction performance of vertically aligned molybdenum disulphide.