CHAPTER 12: Key Intermediates in the Hydrogenation and Electrochemical Reduction of CO2
Published:02 Oct 2013
K. Jan Schouten and M. Koper, in Photoelectrochemical Water Splitting: Materials, Processes and Architectures, ed. H. Lewerenz and L. Peter, The Royal Society of Chemistry, 2013, pp. 333-358.
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Mimicking photosynthesis by (re)using carbon dioxide as a carbon feedstock for the production of hydrocarbons would enable a sustainable carbon cycle. Electrochemically, CO2 can be reduced on copper electrodes to hydrocarbons, mainly methane and ethylene, and the integration of this process in a photo-electrochemical device could be a promising way to close the carbon cycle. Understanding the mechanism of this reaction is one of the keys to open up new, sustainable routes to carbon based fuels. In this chapter we aim to obtain more insights in the key intermediates that determine the selectivity of CO2 reduction to various products, by comparing the electrochemical reduction of CO2 to the metal-catalyzed hydrogenation and reduction of CO2 both homogeneously in solution and heterogeneously in the gas phase. We distinguish four main pathways: (1) methane is formed via hydroxycarboxyl (COOH) and carbon monoxide (CO), (2) methanol is formed via formate (HCOO) and formaldehyde, (3) ethylene is formed via the coupling of CO, leading to surface enolates, and (4) CO2 is inserted into existing carbon chains, close to the way CO2 is fixed in nature.