Journal of the American Chemical Society
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In order to verify that the irreversible reduction pro- selectively produce CO with a higher activity than the
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cess observed on the voltammogram corresponds to the
reduction of CO2, preparative scale electrolysis was
performed under galvanostatic conditions in the pres-
ence and absence of 4a, with on-line gas sampling, see
Figure 7. Similar experiments were also performed on
compounds 1a-5a, and the results are provided in the SI,
along with full experimental details.
well-established [EMIM][BF4] co-catalyst. While the
present study serves to highlight an important interac-
tion between CO2 and the C4- and C5-protons of the
imidazolium cation, it must be emphasized that other
binding modes for the stabilization of the CO2 anion
radical can be envisioned, and their contribution is likely
to depend on the electrochemical system under investi-
gation. It is hoped that these findings will serve as a
basis for improved mechanistic understanding and lead
to the development of even more efficient co-catalysts
for this important reaction.
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ASSOCIATED CONTENT
Supporting Information. Full experimental details, syn-
thetic procedures, NMR, and XRD data are included in the
Supporting Information. This material is available free of
AUTHOR INFORMATION
Corresponding Authors
E-mail: paul.dyson@epfl.ch, michael.graetzel@epfl.ch
Figure 7. CO yields obtained with electrolyte containing
0.02M 4a (red squares, left axis) and the operating poten-
tial required to maintain 4.2 mA cm-2 current density (dark
blue triangles, right axis) over the course of 2 hours. To
facilitate comparison, the operating potential required to
maintain the same current density on a bare Ag electrode
without co-catalyst 4a is also shown (light blue triangles,
left axis).
Author Contributions
‡These authors contributed equally.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was supported by the EPFL and the Swiss Na-
tional Science Foundation. M. S. would like to thank Sie-
mens AG for financial support. Prof. Gabor Laurenczy, Dr.
Patrick Voyame, Dr. Sviatlana Siankevich, Mickael Mon-
tandon-Clerc, and Katerina Sordakis are also thanked for
helpful discussions.
On-line gas sampling at regular intervals during the
chronopotentiometry (CP) experiment showed CO as the
only gaseous product formed during the reaction, with
quantitative yields obtained for all the tested com-
pounds. As can be seen in Figure 7, the addition of 4a
results in a substantial and sustained shift to a more
positive operating potential required for maintaining the
selected current density, thus demonstrating the efficacy
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1
of the co-catalyst. Importantly, high-resolution H and
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In summary, a series of structurally related imidazoli-
um salts were prepared and evaluated as co-catalysts for
the electrochemical reduction of CO2 on a silver elec-
trode. It was found that the catalytic effect primarily
originates from the cation, and that the protons at the
C4- and C5-positions are essential for efficient catalysis.
Furthermore, our investigations led to the discovery of a
novel imidazolium-based co-catalyst, 4a, that could
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