Angewandte
Communications
Chemie
Electrochemistry
Acetaldehyde as an Intermediate in the Electroreduction of Carbon
Monoxide to Ethanol on Oxide-Derived Copper
Erlend Bertheussen, Arnau Verdaguer-Casadevall, Davide Ravasio, Joseph H. Montoya,
Daniel B. Trimarco, Claudie Roy, Sebastian Meier, Jürgen Wendland, Jens K. Nørskov,
Ifan E. L. Stephens,* and Ib Chorkendorff*
Abstract: Oxide-derived copper (OD-Cu) electrodes exhibit
unprecedented CO reduction performance towards liquid
fuels, producing ethanol and acetate with > 50% Faradaic
efficiency at À0.3 V (vs. RHE). By using static headspace-gas
chromatography for liquid phase analysis, we identify acetal-
dehyde 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 À0.33 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 spectrosco-
py, requiring alternative methods for detection and quantifica-
tion. Our results represent an important step towards under-
standing the CO reduction mechanism on OD-Cu electrodes.
that potentials of À1 V (vs. RHE), or overpotentials, h >
ꢀ 1.0 V, are needed to produce significant amounts of C2
products, that is, above 5% Faradaic efficiency with a current
density of 1 mAcmÀ2 or higher.[2–6]
A viable route forward is to split the reaction into two
sequences; reducing CO2 to CO at first, and then reducing CO
to the desired product in a second step. Since CO is a key
intermediate in the reduction of CO2 to alcohols and hydro-
carbons, CO reduction can be used as a proxy for under-
standing trends in CO2 reduction.[2,4] Several catalysts have
been reported to reduce CO2 to CO efficiently and selec-
tively,[7–11] but the second step remains a challenge owing to
multi-electron transfer involving several reaction intermedi-
ates.[12] This calls for development of new catalysts with
improved energy efficiency and selectivity for CO reduction
towards valuable compounds. Kanan and co-workers recently
achieved a breakthrough in this area; they showed that
oxidation and subsequent reduction of polycrystalline copper
yields a high surface area metallic copper electrode with
unprecedented CO electroreduction performance.[13,14]
Oxide-derived copper (OD-Cu) has a Faradaic efficiency
U
tilization of CO2 as a feedstock for producing fuels and
commodity chemicals is a highly promising technology for
reducing the anthropogenic carbon footprint. Capture of CO2
from point sources or ambient air, followed by reduction,
gives an opportunity to close the carbon cycle.[1] Electro-
chemical technology provides a means of achieving this, as
electrochemical devices can operate at ambient conditions,
with minimal capital investment, and with fast start–stop
cycles enabling coupling to intermittent energy sources. To
date, implementation of this technology is hindered by a lack
of electrocatalysts capable of converting CO2 into energy-rich
products in an efficient and selective manner. Copper is the
only pure metal that is active for CO2 reduction towards
hydrocarbons and alcohols.[2] However, high overpotentials
are needed and a variety of products are formed. Measure-
ments on planar extended surfaces of Cu electrodes showed
towards ethanol as high as 43% at À0.3 V, h ꢀ 500 mV (U0
CO/
CH3CH2OH = 0.18 V), and a total Faradaic efficiency towards CO
reduction products of 57%, with a total geometric current
density of ꢀ 0.3 mAcmÀ2.
The underlying reasons for the high performance of OD-
Cu electrodes remain unknown. Our own temperature
programmed desorption (TPD) experiments show that the
activity correlates with the presence of strong binding sites,
which in turn correlates with the presence of grain bounda-
ries.[15] Importantly, the mechanism for ethanol production
[*] E. Bertheussen, Dr. A. Verdaguer-Casadevall, D. B. Trimarco, C. Roy,
Prof. Dr. I. E. L. Stephens, Prof. Dr. I. Chorkendorff
Department of Physics, Technical University of Denmark
2800 Kgs. Lyngby (Denmark)
Prof. Dr. J. K. Nørskov
SUNCAT Center for Catalysis and Interface Science
SLAC National Accelerator Laboratory
2675 Sand Hill Road, Menlo Park, CA 94025 (USA)
E-mail: ifan@fysik.dtu.dk
Prof. Dr. I. E. L. Stephens
Department of Mechanical Engineering
Massachusetts Institute of Technology (MIT)
77 Massachusetts Avenue, Cambridge, MA 02319 (USA)
Dr. D. Ravasio, Prof. Dr. J. Wendland
Carlsberg Laboratory
Gamle Carlsberg vej 4, 1799 København V (Denmark)
Supporting information and ORCID(s) from the author(s) for this
Dr. J. H. Montoya
SUNCAT Center for Catalysis and Interface Science
Department of Chemical Engineering, Stanford University
443 Via Ortega, Stanford, CA 94305 (USA)
ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution Non-Commercial NoDerivs License, which
permits use and distribution in any medium, provided the original
work is properly cited, the use is non-commercial and no modifica-
tions or adaptations are made.
Dr. S. Meier
Department of Chemistry, Technical University of Denmark
2800 Kongens Lyngby (Denmark)
1450
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1450 –1454