Insights into Carbon Dioxide Electroreduction in Ionic Liquids: Carbon Dioxide Activation and Selectivity Tailored by Ionic Microhabitat

Article abstract of DOI:10.1002/cssc.201801373

Electroreduction of carbon dioxide (CO₂) into high value-added products is a potential solution to a reduction in CO₂ levels and its utilization. One major challenge is the lack of an efficient system that can highly selectively reduce CO₂ into desirable products with low energy consumption. Ionic liquids (ILs) have been used as electrolytes for the electroreduction of CO₂, and it has been proven that the CO₂–cation complex results in a low-energy pathway. In this work, an ionic microhabitat (IMH) has been built for CO₂ electroreduction, and a novel anion-functionalized IL, 1-butyl-3-methylimidazolium 1,2,4triazolide ([Bmim][124Triz]), has been designed as the reaction medium. The results showed that the IMH played a key role in enhancing the performance of CO₂ electroreduction, especially in dominating the product selectivity, which is recognized to be a great challenge in an electroreduction process. New insights into the role of the IMH in higher CO₂ solubility, bending linear CO₂ by forming the [124Triz]–CO₂^? adduct, and transferring activated CO₂ into the cathode surface easily were revealed. The Faradaic efficiency for formic acid is as high as 95.2 %, with a current density reaching 24.5 mA cm^?2. This work provides a promising way for the design of robust and highly efficient ILs for CO₂ electroreduction.

Full text of DOI:10.1002/cssc.201801373

Accepted Article
Title: Novel insights into CO2 electroreduction in ionic liquids: CO2
activation and selectivity tailored by ionic microhabitat
Authors: Jianpeng Feng, Shaojuan Zeng, Huizhen Liu, Jiaqi Feng,
Hongshuai Gao, Lu Bai, Haifeng Dong, Suojiang Zhang, and
Xiangping Zhang
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To be cited as: ChemSusChem 10.1002/cssc.201801373
Link to VoR: http://dx.doi.org/10.1002/cssc.201801373
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ChemSusChem
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COMMUNICATION
Novel insights into CO
2
electroreduction in ionic liquids: CO
2
activation and selectivity tailored by ionic microhabitat
Jianpeng Feng,[a,b] Shaojuan Zeng, Huizhen Liu, Jiaqi Feng,
[b]
[c]
[a,b]
Hongshuai Gao, Lu Bai, Haifeng
[b]
[b]
[
b]
[b]
[*a,b]
Dong, Suojiang Zhang, Xiangping Zhang
Abstract: Electroreduction of carbon dioxide (CO
added products is a potential solution to the CO
utilization. One major challenge is lacking of efficient system that can
highly selectively reduce CO to desirable products with low energy
consumption. Ionic liquids (ILs) have been used as electrolytes for the
electroreduction of CO , and it was proved CO -cation complex
results in a low energy pathway. In this work, we build an ionic
microhabitat (IMH) for CO electroreduction, and designed a novel
2
) into high value
accelerate the electrochemical conversion efficiently. The
-
1
2
deduction and
2
CO solubility in water is only 0.033 mol L under ambient
2
conditions (298 K, 0.1 MPa). For CO reduction in aqueous
2
solution, it is crucial to suppress the hydrogen evolution
reaction (HER), which is typically kinetically favored over
2
2
2 2 2
CO reduction reaction (CO RR). Furthermore, reducing CO
to fuel precursors (such as CO) or liquid chemicals at low
overpotential, is a significant challenge due to the incredible
2
anion-functionalized IL [Bmim][124Triz] as reaction medium. The
results showed that the IMH plays a key role in enhancing the
stable structure of CO
is demanded to restructure the linear molecule to the non-
linear [·CO
]- anion, which occurs at a very negative potential,
2
molecule. Hence, tremendous energy
2
performance of CO electroreduction, especially in dominating the
2
product selectivity which is recognized as a great challenge in an
that is, -1.9 V vs. NHE.[4]
electroreduction process. New insights into the role of IMH in higher
-
As a novel type of liquid salts, ILs consisting of cations
and anions solely exhibit excellent CO
2
solubility,[5] especially
by functionalized ILs, such as amino-,[6] acetate-,[7] azolate-,[8]
pyridine-,[9] and amino acid-based ILs.[10] Besides the reports
on the ILs for CO2 capture, ILs have also been used as
CO
adduct, and transferring the activated CO
easily, were revealed. The Faradaic efficiency for formic acid is as
2 2 2
solubility, bending the linear CO by forming [124Triz]-CO
2
to the cathode surface
-
2
high as 95.2% with current density reached 24.5 mA cm , this work
will provide a promising way for designing robust and highly efficient
ILs for CO
2
electroreduction.
electroreduction in recent years.[3d, 5e, 11]
electrolytes for CO
2
Their unique physicochemical properties, such as high
intrinsic ionic conductivity and wide electrochemical potential
2
The large amount emission of carbon dioxide (CO ) has
windows,[12] as well as high solubility of CO
for CO electro-reduction in
RR.[13] Previous report[14] on CO
an aqueous 1-ethyl-3-ethylimidazolium tetrafluoroborate
[Emim][BF ]) solution with Ag as cathode, demonstrated that
, are beneficial
2
raised serious environmental and social issues in the last
hundred years.[1] On the other hand, as one of the most
2
2
2
abundant and cheap C1 resources, converting CO to useful
(
4
chemicals with the geographical, seasonal and intermittent
the overpotential for CO formation was decreased by 600 mV.
This means that the imidazolium carboxylate complex can
energy (e.g., tied, wind, and solar) is an attractive solution to
the global warming problems and energy crisis.[2] Thus,
stabilize [·CO
consequently, inhibit their dimerization to form oxalate, and
2
]- radical anion and restrain their approaching,
plenty of works were emphasized towards the
2
electrochemical conversion of CO owing to its mild reaction
lead to
a
low energy pathway for CO
2
reduction.
reduction
conditions and easy implementation for practical
applications.[3] However, nearly all reduction systems
Subsequently, the effects and mechanism for CO
2
with the aid of conventional and functionalized ILs have been
studied extensively.[11b, 15] For instance, commercialized Pb
investigated far still face great challenges, such as high
reaction overpotential and low current density, especially the
poor product selectivity. Hence, efforts are in great need to
develop efficient reaction systems, which obtain both the fast
and Sn electrodes were used to reduce CO
HCOOH) in ILs/acetonitrile (MeCN)/H O ternary mixture
along with high current densities (i.e., 37 and 32 mA cm ),
2
into formic acid
(
2
-
2 [16]
reaction rate and high selectivity of CO
Electrolytes undertake a crucial role in CO
and a considerable amount of CO in the electrolyte will
2
electroreduction.
but these results were obtained only at very negative
potentials. Recently, a high Faradaic efficiency for HCOOH
on Ag electrode is acquired at low overpotential using
functionalized phosphonium ILs,[17] but the current density is
2
dissolution,
2
-
2
less than 1 mA cm . Additionally, previous research
indicated an ambiguous role of the anions on CO
electroreduction.[18] The reduction of CO
at low overpotential
[
a]
CAS Key Laboratory of Green Process and Engineering, Institute of
Process Engineering, Chinese Academy of Sciences, Beijing,
00190, China. xpzhang@ipe.ac.cn
2
1
2
[
[
b]
c]
College of Chemical and Engineering, University of Chinese
Academy of Science, Beijing 100049, China.
Beijing National Laboratory for Molecular Sciences, CAS Key
Laboratory of Colloid and Interface and Thermodynamics, Institute
of Chemistry, Chinese Academy of Sciences, Beijing 100190,
China.
with both high current density and Faradaic efficiency is a
longstanding challenge.
In this work, we present an efficient CO
2
electroreduction microhabitat (Figure 1) based on a novel
superbase IL 1-butyl-3-methylimidazolium 1,2,4-triazolide
Supporting information for this article is given via a link at the end of
the document.
(
[Bmim][124Triz]), and compared with other systems
[
8]
containing imidazolium ILs with different anions . The IMH
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ChemSusChem
10.1002/cssc.201801373
COMMUNICATION
provides an efficient environment for CO
2
dissolve, activation
Supplementary Figure 4), and the results are consistent with
previous reports of CV curves by using metal electrodes in
dialkylimidazolium based ILs. Only small capacitive currents
were observed in a wide potential window, and no additional
reduction features associated with the reduction of the
solvent or ILs were found in the cathodic CV range.
2
and reduction. High efficiency of CO capture and conversion
is achieved via an ionic microhabitat (IMH) in the novel IL
reaction system, which means the nanoscale aggregates
and chemical interaction in the ion of [124Triz]-CO -
a superior solubility of CO
notably, it shows that the stable CO
result in
2
2
under ambient conditions. More
2
molecule is changed to
Pb was chosen to evaluate the influence of the anion on
o
a bent form (O-C-O bond angle of 136 ) with a net negative
the catalytic activity of imidazolium-based ILs for CO
2
charge (0.546 e) in the [124Triz]-CO -
expected to be favorable for CO activation and [·CO
stabilization. In addition, the IMH provides a facile route for
the transferring of the activated CO -
to the cathode surface,
which hence improves the current density and Faradaic
efficiency of CO electroreduction. Thus, the experimental
results demonstrated that the superbase IL offers a low
ion. As a result, it is
]-
reduction to HCOOH (Figure 2). In agreement with previous
reports, the potential that results in a current density of a 0.6
2
2
2
mA cm-2 was selected as the onset potential for CO
2
reduction.[20] As shown in Figure 2, the reduction current from
2
circa -1.4 V to -1.8 V range was attributed to the reduction of
H O to H
2 2
, which is similar to a previous report.[17] The
2
cathodic feature from -1.78 V is related to the CO
2
reduction
1
energy and high selective pathway for CO
through an IMH.
2
electroconversion
to HCOOH, which was validated by H NMR quantification,
2
and we found that in the potential range of CO reduction,
the reduction of water was suppressed to a large extent.
Similar with the conventional ILs, the CV curves profiles in
CO
were observed. However, compared with the conventional
ILs, the onset potential of the CO purged aqueous of
Bmim][124Triz] solution shifted anodically from -1.97 to -
2
purged aqueous of superbase IL, no new CV peaks
2
[
+
1
.78 V (vs Ag/Ag ), which indicated that the reduction
potential of carbon species was decreased significantly, and
this positive effect of [Bmim][124Triz] on lowering the
-
overpotential was ascribed to the formation of [124Triz]-CO
ion.
2
0
2
Figure 1. Schematic representation of CO electroreduction with the assistance
of novel superbase IL [Bmim][124Triz].
1
2
3
1
2
3
The anion-functionalized superbase IL [Bmim][124Triz]
was synthesized by neutralization of 1,2,4-triazole with a
solution of 1-butyl-3-methylimidazolium hydroxide, which
was acquired by the anion-exchange method.[19] The
[
Bmim][Triz]
[Bmim][PF6]
[
[
[
Bmim][Tf N]
2
absorption experiment of CO
apparatus shown in Supplementary Scheme 1, and the mole
ratio of dissolved CO in IL [Bmim][124Triz] was plotted in
Figure S2. 0.726 mol CO per mol IL was achieved at 298 K
under ambient pressure. Previous reports indicated that the
sufficient CO in electrolytes will render the electrochemical
conversion of CO
efficient.[11a] In our work, we found that the
solubility of CO in the superbase IL is nearly 45 times higher
than that in the conventional IL 1-butyl-3-methylimidazolium
tetrafluoroborate ([Bmim][BF ]).
2
was carried out by the
Bmim][BF4]
Bmim][NO3]
44
2
-2.4
-2.2
-2.0
-1.8
-1+.6
-1.4
-1.2
-1.0
2
E (V vs Ag/Ag )
Figure 2. CV traces on Pb electrode in various CO
containing ILs in MeCN-H O (5 wt% ) solution.
2
-saturated electrolytes
2
2
2
The effect of [Bmim][124Triz] content in the electrolyte
on CO reduction was investigated by using Pb electrode,
and the CV traces were illustrated in Figure S4. The CV
results showed that the polarization curves for CO reduction
were shifted slightly to more positive potentials with the
increase of the [Bmim][124Triz] content in the MeCN-H
2
2
4
We conducted the electrolysis experiments in a typical
three-electrode system at 298 K and 0.1 MPa (See
2
2
O
2
Supplementary Figure 3). The CO reduction performance in
system, and the increased current densities were observed
as a more negative potential was applied. Furthermore, we
also investigated the effect of [Bmim][124Triz] content on
Faradaic efficiency of the reduction products on Pb electrode
ILs was examined by sweeping the applied voltage at a scan
rate of 50 mV s-1 from -1.0 V to -2.4 V versus Ag/Ag+
electrode. Firstly, the cyclic voltammetry (CV) results
2
acquired in IL solutions which were saturated with N (See
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ChemSusChem
10.1002/cssc.201801373
COMMUNICATION
a
b
at different applied potentials. In all cases, CO and H
2
were
36
30
24
18
12
6
0
HCOO
-
CO
H2
the only gas products formed on the cathode and O
2
on the
100
[Bmim][124Triz]
[Bmim][PF
[Bmim][Tf
[Bmim][BF4]
anode, and HCOOH was the only liquid product. Other
gaseous or liquid products may have been present at
6
]
8
0
0
2
N]
6
3
[Bmim][NO ]
1
concentrations below the gas chromatography (GC) and H-
40
NMR detection limit. At a low IL content, the CV results
demonstrated that the partial current density of CO increased
dramatically with the IL content rising, yet the highest current
density and Faradaic efficiency for HCOOH was obtained at
20
0
-1.6
-1.8
-2.0
E (V vs Ag/Ag )
-2.2
-2.4
[Bmim][124Triz] [Bmim][PF
6
]
[Bmim][Tf
2
N] [Bmim][BF
4
]
3
[Bmim][NO ]
+
ILs
c
d
2
the IL content of 700 mM in the MeCN-H O (5 wt%) mixture.
2
2
1
4
0
6
-
2.1 V
2
700mM / MeCN-H O (5%)
7
00mM / MeCN
28
24
20
16
12
8
Given this, the possible reason is that the intensive
electrostatic attraction between anion and cation of the IL,
which impedes the motion of the ions and slows down the
charge transfer to the reaction species. Hence, the dominant
products were switched to hydrogen in the reaction system.
-2.2 V
-2.3 V
-2.4 V
-2.1 V
-2.2 V
-2.3 V
-2.4 V
12
8
The Faradaic efficiency of the major products from CO
2
4
electroreduction was measured by different ILs as the
electrolytes, and controlled trials were carried out on Pb
0
1000
2000
3000
4000
5000
6000
7000
0
1000
2000
3000
4000
5000
6000
7000
Time (s)
Time (s)
(
Figure 3) electrode at an applied potential of -2.2 V (vs.
Figure 3. CO
Pb electrode, (b) Corresponding Faradaic efficiency for HCOOH, CO and H
ILs/MeCN-H O (5 wt%), (c) Dependence of current density over time on Pb
electrode at different applied potentials (vs Ag/Ag ) without and with water (d).
2
electroreduction performances. (a) Partial current of HCOOH on
+
Ag/Ag ) for 2 hours. Generally, high HCOOH selectivity was
obtained in most IL systems, and the Faradaic efficiencies
2
in
2
+
follow the order of [Bmim][124Triz]
methylimidazolium hexafluorophosphat ([Bmim][PF
Bmim][BF 1-butyl-3-methylimidazolium
trifluoromethanesulfonate ([Bmim][Tf N]) 1-butyl-3-
methylimidazolium nitrate ([Bmim][NO ]). Therein, we found
>
1-butyl-3-
6
])
>
[
4
]
>
The mechanism of CO
based reaction system can be described as follows in
Equation 1 ~ 8 (See Scheme 1). All species involved CO
2
reduction in [Bmim][124Triz]
2
>
3
2
that the anion plays a significant role in the observed catalytic
selectivity, and the anion without fluorine, such as
reduction were assumed to be adsorbed on the cathode
surface. The clear evidences confirmed that the imidazolium
cations as the electrode materials also play a dominant role
[
3
Bmim][NO ], yielded much lower Faradaic efficiency for
HCOOH formation, while in [Bmim][124Triz] IL system, it
exhibited the highest Faradaic efficiency of 95.2% (Figure 3b)
and the current density reached as high as 24.5 mA cm-2
electroreduction.[21] The presented scheme is
in CO
2
analogous to that proposed by Nakamura et al. according to
the theoretical calculations.[22] In the light of this reaction
(
Figure 3a). This results indicate that the anion plays an
important role in dominating the electrochemical reduction of
CO to HCOOH, and the reason may be attributed to the
interaction differences between CO and anions of ILs.
mechanism, imidazolium cations are reduced to neutral
2
radicals, which in turn transfer the electrons to CO and form
2
]- and prevent their
a complex which can stabilize [·CO
2
2
dimerization to form oxalate. However, contrast to the
conventional ILs, the overpotential of CO reduction to
To investigate the durability of [Bmim][124Triz] under
long-term bulk electrolysis conditions, the current density
was measured as a function of time with different applied
2
HCOOH is lower in [Bmim][124Triz] solution, and the positive
effect on lowering the overpotential is ascribed to the strong
+
voltages (vs. Ag/Ag ). With no water in IL/MeCN, the current
2
interaction between the anion of the IL and CO . This
densities remained relatively constant in the beginning
mentioned catalytic mechanism reveals that the formation of
carbene from the reduction of imidazolium leads to a rapid
attenuation of current density during potentiostatic
electrolysis. While, the inactive species can be reactivated
(Figure 3c). However, when the electrolysis proceeded
further, the current densities fell rapidly, probably due to the
+
[
Bmim] species were consumed in the course of the bulk
electrolysis (See Supplementary Scheme 1). Yet, when
adding water to [Bmim][124Triz]/MeCN, the catalytic activity
when adding water into the system. Furthermore, the
-
[
124Triz] anion helps to maintain a high CO
2
content in
2
of [Bmim][124Triz]/MeCN-H O (5 wt%) systems remained
electrolyte and transport CO
2
to the catalyst surface quickly,
constant during all electrolysis period (Figure 3d), indicating
that the inactive form of carbene was regenerated when a
small amount water was present. Otherwise, carbene, the
reduced species from imidazolium cation, can form an
resulting in a superior performance for CO
reduction to HCOOH.
2
electrochemical
inactive complex with CO
2
,[18a] and then the catalytic action
of imidazole ILs on CO
significantly.
2
electroreduction was deactivated
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ChemSusChem
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COMMUNICATION
Table 1. Structure parameters for various species associated with the
reduction of CO
level.
2
, calculated using the B3LYP/6-31++G (d,p) theoretical
species
CO
2
ΔE(kJ/m
ol)[b]
<O-C-
O(deg.)[b]
172
Solubility[a]
~0.1[5e]
[
NO
BF
Tf
PF
3
]-···CO
2
-37.14
-28.98
-29.23
-24.79
-206.5
-274.1
[
4
]-···CO
2
0.0161[5e]
0.0168[5e]
0.0308[5e]
0.726
174
-
[
2
N] ···CO
2
176
[
6
]-···CO
2
175
-
[
124Triz] ···CO
2
136
-
[
124Triz] ···HCOOH
—
126
[a]
The absorption was carried out at 298 K and 0.1 MPa in aqueous
solution of ILs (mol CO
per mol IL). [b] These values represent a gas-
2
phase calculation using the B3LYP/6-31++G(d,p) basis set with no
solvation model.
Furthermore, Natural Population analysis (NPA) was carried
out to ascertain the change of charge distribution in the related
-
species. For isolated [124Triz] anion, the N3 atom of triazole ring
which presents the largest negative charge (See Supplementary
Table 2) provides a chemical binding site with CO , therefore
2
resulting in a charge distribution change of the total electron
-
density of [124Triz]-CO
2
ion (See Supplementary Figure 9). The
-
negative charge value of [124Triz] decreases from -1 e to -0.454
e, while the net charge of neutral CO
2
molecule turns to -0.546 e.
-
In this vein, we portrayed that the [124Triz]-CO
above provides a low energy pathway for CO
Although it has been proved that the imidazolium cation on
the electrode surface plays a key role in CO reduction at a low
2
anion proposed
2
electroreduction.
2
Scheme 1. The possible pathways for CO conversion into HCOOH with the
2
help of [Bmim][124Triz].
energy pathway. However, we found that the aforementioned CV
curves in Figure 2 illustrates a notable enhancement of catalytic
2
activity for CO electroreduction in [Bmim][124Triz], and the
Additionally, Quantum Chemical calculations were performed
to evaluate the interaction between the anions and CO (Table 1),
increase of current density at low overpotential may be ascribe to
-
2
the high CO2 solubility and the stabilization of [·CO ] in the
2
and the lowest energy structures of the intermediates were shown
superbase IL. Electrochemical impedance spectroscopy (EIS)
can provide useful information about the properties of bulk
electrolytes and the electrode interfaces. Hence, a Nyquist plot
was obtained by running the experiment at an open circuit
in Figure S9-S13. A strong interaction with a high ΔE value (-
-
2
06.5 kJ/mol) between [124Triz] and CO
2
is found, and the N···C
bond length of 1.56 Å is approximate to that in the triazole ring of
the anion (1.36 Å) (See supplementary Figure 9), resulting in a
potential
(Figure
4c).
A
simple
equivalent
circuit
predictable bent CO
2
molecular with O-C-O bond angle of 136o.
(LR)R(C(R(Q(RW)))) was then used to fit the acquired data of
[Bmim][124Triz] (See supplementary Figure 7), and the charge
The calculation results indicate a rehybridization of CO
to nearly sp character, and bond angle change to percentage π
2
is from sp
2
-2
transfer resistance (R ) was 41.8 Ω cm , which was much lower
ct
-2
-2
character of a hybridized orbital based on the Pauling correlation.
than that in the conventional ILs (80.2 Ω cm , 120.4 Ω cm , 454.7
Ω cm-2 and 802.8 Ω cm ). This means that the electron transfer
to the electrode surface in [Bmim][124Triz] is more facile, which
can enhance the current density.[23] Additionally, previous works
presumed that the monolayer formed by ILs on the electrode
surface plays a key role in CO2 reduction and inhibiting H2
formation on the cathode surface, and we found that the
-
-2
In addition, the Gaussian calculation results for [124Triz]-CO
2
complex species suggested that the CO
is 75% sp hybridized, retaining 25% of its sp character only. The
2
molecule in the complex
2
carbon hybridization of CO
2
in the complex is close to that in
HCOOH, which will possibly facilitate the formation of HCOOH.
f
resistance of the absorbed film on the cathode surface (R) was
-2
only 0.7 Ω cm , it suggested that the reaction species can be
easily transferred through the IL monolayer. These results provide
sufficient supports to the excellent performance of CO
electroreduction in the superbase IL.
2
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ChemSusChem
10.1002/cssc.201801373
COMMUNICATION
higher current density and Faradaic efficiency in potential static
electrolysis, this subsequently result in a low energy and efficient
pathway for CO
develop more ILs to enhance this reaction and open a potential
way for CO utilization and the construction of a carbon neutral
2
reduction. Our new finding will stimulate to
2
energy system.
Experimental Section
Materials
Experimental Details Materials and syntheses. [Bmim][124Triz] was
[
24]
synthesized by a reported method using a two step synthesis: Firstly,
Bmim][OH] was synthesized by an anion exchange resin from [Bmim][Cl]
[
(
(
purity>99%). A column was packed with 600 mL ion exchange resin
Amberlite IRN-78, OH-form, from Sigma-Aldrich), and the resin was
washed with absolute ethanol to wet it sufficiently and remove any air from
the resin. 30 g of [Bmim][Cl] was mixed with 500 mL of ethanol and the
mixed solution was poured into the column and flowed through the resin
with one drop per 5~6 seconds. After ion exchange process, halide content
of the mixture was below the detectable limit by AgNO
[
3
testing, and the
Bmim][OH] in its ethanol mixture was measured by 1H-NMR. With a 1:1
2
Figure 4. The role of IL [Bmim][124Triz] in CO capture, activation and reduction.
mol ratio, the desired amount of 124Triz was added into the solution and
reacted with [Bmim][OH] at least 12 hours under ambient conditions and
(a) Dissolution of CO
2
in [Bmim][124Triz], (b) The formation of chemical bond
between CO and the anion of the superbase IL, (c) Nyquist plots for a Pb
2
electrode in various electrolytes, (d) The activation and reaction of CO
electrode surface with the aid of [Bmim][124Triz].
2
at the
stirred.
methylimidazolium chloride ([Bmim][Cl]), [Bmim][BF
6 2
Bmim][NO ], purity>98%, [Bmim][PF ], purity>99%, and [Bmim][Tf N],
Conventional
imidazolium
ionic
liquids,
1-butyl-3-
4
], purity>99%,
[
3
purity>99% in this study were purchased from Linzhou Keneng Tech Co.,
Ltd. All used ILs were purified and dried in vacuum oven at 333.15 K for
Further computationally results were carried out to validate
the underlying mechanism of the superbase IL, as shown in
48 hours at least, the water content of the ILs was measured using a
Metrohm 787 KF Titrino Karl Fischer and was found to be < 100 ppm, and
finally obtained dry and pure ILs. Gasses used for absorption and
Figure 4. it can be seen that the C2H···CO
Bmim]···CO ···[124Triz] (2.30 Å) is much shorter than that in the
conventional ILs ([Bmim][PF ] (3.15 Å), [Bmim][BF ] (2.93 Å),
Bmim][Tf N] (3.08 Å) and [Bmim][NO (3.29 Å)) (See
supplementary Figure S9-S13). This means the interaction
between CO and the superbase IL is much stronger than that
between the CO and the conventional ILs. Therefore, compared
with the conventional ILs, during the potential static electrolysis,
the fast transportation feasibility of activated CO to the cathode
surface in [Bmim][124Triz] medium caused by the anion most
likely to account for the higher Faradaic efficiency of CO
reduction products. Based on the above analysis and previous
2
bond length in
[
2
electrochemistry reaction including H
from Beiwen and used as delivered.
2 2 2
, N , CO and CO were purchased
6
4
[
2
3
]
Pb (purity>99.99%) electrode was purchased from Tianjin Aida
Hensheng Technology Development Co. Ltd. Before each electrocatalysis
test, the Pb electrode was polished with #800, #2000 and #5000
sandpaper sequentially, followed by washing with ethanol and acetone in
an ultrasonic bath for 5 minutes, and finally rinsed with hyperpure water
2
2
2
2
and then dried in N atmosphere.
2
2
CO absorption experiments
reports, the novel reduction pathway of CO
IMH is proposed and verified.
2
with the help of the
The CO
2
absorption solubility in the ILs was measured by a typical
weighing method at room temperature and pressure[9] (See
In summary, we put forward a novel insight for highly
selective CO electrochemical reaction by building an ionic
microhabitat and revealed the underlying mechanism of the
advanced performance. We proved that the ionic microhabitat of
Supplementary Figure 1). CO was dried by calcium chloride before went
through a glass container with an inner diameter of 8 mm, the glass
container was immersed in water bath to maintain the system
temperature, the flow rate of CO
of CO absorbed in the ILs was obtained at intervals by an electronic
2
2
a
-
1
2
was 20 mL min . The real-time amount
2
the IL plays a key role in CO
studied ILs, the superbase IL reaction system with [124Triz] anion
2
capture and conversion. Among the
-
balance (METTLER TOLEDO PL403) with an accuracy of 0.1 mg.
exhibits an exceptionally high Faradaic efficiency for CO
electroreduction to HCOOH (95.2%) on Pb electrode at
appreciable current density (24.5 mA cm ). The H-bond between
2
Electrochemical experiment setup and electrolysis measurements
-2
An electrochemical workstation (CHI 660E, Shanghai CH instruments Co.,
China) was used for electrochemical experiments. Electrolysis
measurements were carried out at room temperature (298 K) using a
commonly used H-type cell (Figure S3), the cathode and anode
compartments were separated by a proton exchange membrane (Alfa
Nafion@117). The diameters of the cathode chamber and anode chamber
were both 30 mm, and the volume of each chamber were about 40 mL. In
CO
CO
2
and anion, and the chemical interaction between C atom of
and N3 atom of the [124Triz] anion makes a great change of
-
2
configuration and electronic distribution of CO
means that the anion can efficiently activate CO
·CO
easily transferred to the electrode surface, therefore leading to the
2
molecule, which
2
and stabilize the
[
2
]- intermediate. Furthermore, the activated CO
2
can be
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ChemSusChem
10.1002/cssc.201801373
COMMUNICATION
2 4
a typical experiment, IL containing solution and H SO aqueous solution
Keywords: CO
2
reduction • ionic microhabit • electrolysis
(
0.1 M) were used as cathodic and anodic electrolytes, respectively. The
amount of electrolyte used was 30 mL in all the experiments. Before
measurement, CO was bubbled through the catholyte for 30 min under a
steady follow of 30 mL min . Cyclic voltammograms (CVs) were recorded
at working electrode in ILs/MeCN-H O mixture solution system, Pb as the
conversion • superbase ionic liquids • formic acid
2
-
1
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2
H and HCOOH are shown in
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
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Jianpeng Feng,[a,b] Shaojuan Zeng,[b]
Huizhen Liu,[c] Jiaqi Feng,[a,b] Hongshuai
Gao,[b] Lu Bai,[b] Haifeng Dong,[b]
Suojiang Zhang,[b] Xiangping Zhang,[*a,b]
Page No. – Page No.
Novel insights into CO
2
electroreduction in ionic liquids: CO
activation and selectivity tailored by
ionic microhabitat
2
We built an ionic microhabitat (IMH) for CO
IL [Bmim][124Triz]. The anion plays a critical role in improving the selectivity and
lowering the overpotential of CO complex,
electroreduction by the [124Triz]-CO -
and high selective reduction product, HCOOH was obtained. The method developed
in this study opens a potential way for CO utilization.
2
electroreduction by using a superbase
2
2
2
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