Acetaldehyde as an Intermediate in the Electroreduction of Carbon Monoxide to Ethanol on Oxide‐Derived Copper

Abstract

Oxide‐derived copper (OD‐Cu) electrodes exhibit unprecedented CO reduction performance towards liquid fuels, producing ethanol and acetate with >50 % Faradaic efficiency at −0.3 V (vs. RHE). By using static headspace‐gas chromatography for liquid phase analysis, we identify acetaldehyde as a minor product and key intermediate in the electroreduction of CO to ethanol on OD‐Cu electrodes. Acetaldehyde is produced with a Faradaic efficiency of ≈5 % at −0.33 V (vs. RHE). We show that acetaldehyde forms at low steady‐state concentrations, and that free acetaldehyde is difficult to detect in alkaline solutions using NMR spectroscopy, requiring alternative methods for detection and quantification. Our results represent an important step towards understanding the CO reduction mechanism on OD‐Cu electrodes.

Reactivity of Copper Electrodes towards Functional Groups and Small Molecules in the Context of CO2 Electro-Reductions

“…CO (2) electrolysis yielded a product distribution, that was surprisingly similar to the one observed with CO 2 (1) under the same conditions. Thus, CO (2) is key intermediated to most products, which also corresponds to current literature [50,52,58,61]. The most prominent difference was the absence of formate (4) as product.…”

“…As origin of acetaldehyde Bertheussen et al [52] proposed a surface HC 2 O 2 intermediate (22) towards the formation of acetaldehyde (16). Its mono-hydrogenation may yield glyoxal (20), which was also found by Kuhl et al [17].…”

“…Bertheussen et al [52] recently reported the observation of considerable quantities of acetaldehyde (16) in an authentic electrolysis experiment and demonstrated the authentic bulk electro-hydrogenation of acetaldehyde (16). We attempted to reproduce these results and also intended to demonstrate the ethene (12) from acetaldehyde (16).…”

“…Yet, there is only one limited attempt of studying the reactivity of certain model compounds [52]. The research in this area is mainly focused on ethene, ethanol and formate and there is still lack of a general scheme covering all products.…”

Performance Limits of Photoelectrochemical CO2 Reduction Based on Known Electrocatalysts and the Case for Two-Electron Reduction Products

“…The present state-of-the-art copper electrocatalyst can be tweaked to give a combined faradaic yield of C 2 -products ethylene, ethanol and ethane (likely via a common acetaldehyde intermediate 46 ) of approximately 55%. 34,47 The low selectivity of Cu and Ag electrocatalysts leave much to be desired.…”