Effects of process conditions and electrode material on reaction pathways for carbon dioxide electroreduction with particular reference to formate formation

This paper reviews the most common reaction pathways for CO2 electroreduction proposed by various workers in recent years. Each pathway involves certain intermediate compounds and certain end products and thus the pathways promoted, within a specific process, can be deduced from which of these have been detected. There are considered to be four principal pathways, each based on one of the following reactions: (1) CO(g) formation via disproportionation, (2) .CO2- radical formation, (3) COOH(ad) formation and (4) the formation of reduced COxy-(ad) species giving a range of reduced CO2 end products. This paper places particular emphasis on the formation of HCOOH. The effects of electrocatalyst and process conditions on reaction pathways is also reviewed.