Organic molecules as mediators and catalysts for photocatalytic and electrocatalytic CO sub(2) reduction

Reduction of CO sub(2) by electrochemical and photoelectrochemical methods to produce carbon-rich fuels is a heavily pursued research theme. Most of the current efforts are focused on the development of transition-metal-based catalysts. In this tutorial review, we present an overview of the development of organic molecules as mediators and catalysts for CO sub(2) reduction. Four classes of organic molecules are discussed: tetraalkylammonium salts, aromatic esters and nitriles, ionic liquids, and pyridinium derivatives. It is shown that reactions mediated or catalyzed by these organic molecules can be competitive compared to their metal-catalyzed counterparts, both in terms of product selectivity and energy efficiency.