Edge Article
Chemical Science
2.0 ꢀ 2.5 ꢀ 0.64 cm3 volume immersed in the solution) as the conditions, however, Re-DMF+ was converted to Re-OCHO via
working electrode. An Ag/AgNO3 electrode (Ag wire immersed in CO2 insertion into the electrochemically produced Re-H, and
DMF containing 0.01 M AgNO3 and 0.1 M Et4NBF4, separated formate was catalytically produced even at low concentrations
from the chamber by vycol® glass) was used as a reference of CO2.
electrode. The platinum grid was employed as a counter elec-
trode, which was divided from the cathodic chamber by
a Naon® peruorinated membrane (Naon® 324, Aldrich).
Conflicts of interest
The reference electrode was placed close to the working elec- There are no conicts to declare.
trode so as to minimize the ohmic drop. The working electrode
was washed with acetone and dried for 3 h in a vacuum, and
Acknowledgements
then electrochemically pre-reduced at ꢁ1.82 V over 3 h in DMF
solution containing only the Et4NBF4 electrolyte in the same This work was supported by JST CREST Grant Number
atmosphere as the desired reaction. The cathodic chamber was JPMJCR13L1 in “Molecular Technology”. We acknowledge Prof.
´
lled with an 84 mL portion of the complex solution. The anodic Marc Robert (Universite Paris Diderot) and Prof. Alain Der-
chamber was lled with 84 mL of the DMF–TEOA solution (5 : 1 onzier (Universite Joseph Fourier) for useful discussion.
v/v) which contained the electrolyte and tetrabutylammonium
acetate (TBAOAc) as an electron donor. Before measurement,
the cathodic chamber had been purged with the gas containing
Notes and references
a specic concentration of CO2, while the anodic chamber had
been purged with Ar over 1 h. The cathodic chamber of the
electrochemical cell was attached to the gas ow system. The
gas ow was controlled by a mass ow controller, and the
possibility of the effect of back pressure can be negligible since
the gas pressure in the upstream was only 0.2 MPa and that in
the downstream should be 1 atm, which was released to the
ambient pressure. The solution had been continuously bubbled
with Ar gas containing various concentrations of CO2 (100%,
10%, 1%, and 0%), and the headspace of the reaction space had
been continuously exchanged by the steady rate of the conveyer
gas. The gas products (CO and H2) from the reaction space in
the vented conveyer gas were detected by using a gas chro-
matograph (Agilent 490 micro-GC) equipped with a thermal
conductivity detector. HCOOH in the liquid phase was detected
by Photal CAPI-3300I capillary electrophoresis aer each reac-
tion. The amount of the produced HCOOH by the electrolysis
was calculated by subtracting the HCOOH amount produced in
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Conclusions
The electrochemical reduction of low concentration CO2 by
using Re(I) complexes as catalysts was systematically investi- 15 S. K. Mandal, D. M. Ho and M. Orchin, Organometallics,
gated. The results clearly show that the CO2 capturing ability of 1993, 12, 1714–1719.
Re-TEOA is very useful for CO formation via the reduction of low 16 Y. Arikawa, T. Nakamura, S. Ogushi, K. Eguchi and
concentration CO2, such as 1%. In the absence of TEOA, on the
K. Umakoshi, Dalton Trans., 2015, 44, 5303–5305.
other hand, the Re(I) complexes cannot reduce low concentra- 17 T. Morimoto, T. Nakajima, S. Sawa, R. Nakanishi, D. Imori
tion CO2 to CO. In the presence of a proton donor which is not and O. Ishitani, J. Am. Chem. Soc., 2013, 135, 16825–16828.
an alcohol, the Re(I) complexes cannot work as electrocatalysts 18 J. Hawecker, J.-M. Lehn and R. Ziessel, J. Chem. Soc., Chem.
for CO formation under low concentration CO2. Under these
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