Electrochemical reduction of carbon dioxide on flat metallic cathodes

The most important methods for the electrochemical reduction of carbon dioxide on flat metallic cathodes have been systematically summarized using a novel classification approach. In contrast to the usual classification systems that were based solely on the products of electrolysis, the electroreduction procedures have been grouped according to both the nature of the cathode (sp or d group metal electrodes) and the solvent used for the supporting electrolyte (aqueous or nonaqueous solutions). The new classification system allows the identity of the electroreduction product to be better related to the nature of the metallic electrode and the supporting electrolyte. Similar reduction products are formed by each of the four possible combinations of electrodes and supporting electrolytes (sp group metals in aqueous and nonaqueous electrolytes, and d group metals in aqueous and nonaqueous electrolytes, respectively). The discussion has included both synthetic aspects and mechanistic considerations. Of special interest in this review is the discussion of procedures for the selective preparation of formic acid and for the manufacturing of hydrocarbons and/or alcohols using carbon dioxide as the carbon source.