Development of catalytic systems for reduction of electrochemically inert inorganic molecules: Carbon dioxide and nitrogen

Abstract

Despite the fact that both processes are complex and kinetically slow, electrochemical approaches are generally suitable for the low-temperature conversions of carbon dioxide (to carbon-based simple organic fuels or utility chemicals) and nitrogen (typically to ammonia). Remembering that the N₂ molecule is electrochemically more inert (during reduction) than CO₂, as well as being aware that hydrogen evolution is a competitive and complicating process in aqueous media, different concepts of utilization, including nanostructuring, hybridization, alloying admixing, preconditioning, modification, or functionalization of various catalytic systems for electroreduction of CO₂ and N₂ are elucidated. Experimental conditions, including a choice of solvent and electrolyte, its acidity, as well as presence of certain cations and anions are of importance as well. In the case of N₂-reduction, low yields and possibility of contamination require rigorous procedures and careful analytical approaches. A promising approach to synthesize NH₃ involves lithium- or calcium-mediated reduction of nitrogen in organic solvents. Furthermore, similarities and differences in the reaction mechanisms and important strategies to enhance the systems’ overall activities are addressed.