Evidence for Formaldehyde, Formic Acid, and Acetaldehyde as Possible Intermediates during Electrochemical Carbon Dioxide Reduction at Copper

Abstract

On the other hand, when a chemical step is rate controlling, the current-voltage behavior is no longer logarithmic but i is proportional to ~ (See Table V).It is pertinent to point out here a comparison of the magnitude of Tafel slope (from an analysis of ~-i profiles) on porous electrodes and planar electrodes can be used as a diagnostic criterion for arriving at mechanistic conclusions and/or for supporting the analysis of data generated on planar electrodes.The route to generalization is sketched.

A review of the aqueous electrochemical reduction of CO2 to hydrocarbons at copper

“…Early work found that the reduction of CO at Cu leads to a similar product distribution, suggesting that CO was an intermediate in CO 2 reduction [27,21,28]. Tests starting from formate do not result in any measurable products [20,29] (though from concentrated formic acid, deposits on the electrode and trace methane have been reported [28,29]). It was also found that CO directly suppressed hydrogen evolution, while CO 2 required some charge to be passed before hydrogen evolution was suppressed.…”

Catalysts and Reaction Pathways for the Electrochemical Reduction of Carbon Dioxide

“…Early mechanistic studies found that formic acid cannot be reduced to other products, suggesting that the mechanistic pathway towards formic acid is thus separate from the hydrocarbon pathway, which must go through carbon monoxide. [30][31] On the other hand, a carbene species (*CH 2 ) on the surface, formed from *CO, It is important to note that in spite of their different features, none of the above mechanisms are able to explain three important experimental observations. The first observation was made by Hori et al, 32 namely that the formation of methane from CO shows a different pH dependence from the formation of ethylene.…”

Theoretical insight into effect of doping of transition metal M (M = Ni, Pd and Pt) on CO2 reduction pathways on Cu(111) and understanding of origin of electrocatalytic activity

“…20 Reduction products include formate, CH 4 , C 2 H 4 and other higher hydrocarbons. [23][24][25][26] Furthermore, theoretical study of CO 2 reduction on transition metals Cu, Pt, Rh, Pd, Ni, Au and Ag by Nørskov and co-authors 27 revealed the "volcano" type of the activity diagram, in which Cu has also the best catalytic activity and is located at the top of the diagram among these transition metals. Thus, experimental and theoretical studies all showed that Cu is the best known metal electrocatalyst for CO 2 reduction.…”