Design of a Cu(I)/C-doped boron nitride electrocatalyst for efficient conversion of CO2 into acetic acid

Article abstract of DOI:10.1039/c7gc00503b

Electrocatalytic CO₂ reduction to C₂ products is a promising technique when compared with the traditionally complicated and energy intensive routes in the industrial process. As an important bulk chemical, it is highly desirable for acetic acid to be produced via a sustainable method. In this work, we prepared N-based Cu(I)/C-doped boron nitride (BN-C) composites for electrocatalytic reduction of CO₂ to acetic acid. It was found that the Faradaic efficiency of acetic acid could reach as high as 80.3% with a current density of 13.9 mA cm^-2 when 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF₄)-LiI-water solution was used as the electrolyte, which was about 4 times higher than the best value reported in the literature. Detailed studies further indicated that the Cu complex, BN-C, and the electrolyte have an excellent synergistic effect for producing acetic acid. In particular, as a promoter, LiI played a key role in C-C coupling to form acetic acid in the electrocatalytic process. Our study shows a promising way to produce C₂ products via electrochemical reduction of CO₂ by the combination of composite electrodes and electrolytes with a promoter.

Full text of DOI:10.1039/c7gc00503b

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Design of Cu (I)/C-doped boron nitride electrocatalyst for efficient
conversion of CO2 into acetic acid
Xiaofu Sun,a,b Qinggong Zhu,a Xinchen Kang,a,b Huizhen Liu,a,b Qingli Qian,a Jun Ma,a Zhaofu Zhang,a
Guanying Yang,a and Buxing Han*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Electrocatalytic CO2 reduction to C2 products is a promising technique when compared with the traditionally complicated
and energy intensive routes in the industrial process. As an important bulk chemical, acetic acid is highly desirable for
producing via sustainable method. In this work, we prepared N-based Cu (I)/C-doped boron nitride (BN-C) composites for
electrocatalytic reduction of CO2 to acetic acid. It was found that the Faradaic efficiency of acetic acid could reach as high
as 80.3 % with a current density of 13.9 mA cm-2 when 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4)-LiI-
water solution was used as the electrolyte, which was about 4 times higher than the best value reported in the literature.
Detailed study further indicated that Cu complex, BN-C, and the electrolyte have excellent synergistic effect for producing
acetic acid. Especially, as a promoter, LiI played a key role for the C-C coupling to form acetic acid in the electrocatalytic
process. Our study shows a promising way for producing C2 product via electrochemical reduction of CO2 by combination
of composite electrodes and electrolytes with a promoter.
www.rsc.org/
efforts have been devoted to tuning the composition and
structure of Cu-based materials with the aim of optimizing the
C2 selectivity. Cu nanotube and Cu2O films exhibited high
selectivity for transforming CO2 to ethylene. 12-14 Ethanol and
ethane were also formed on Cu2O films. 12,14 Bouwmanet al.
reported that a dinuclear Cu (I) complex could be used as a
Introduction
The demand of fossil resource is increasing for energy and
1,2
chemicals.
However, fossil resource is not renewable and
the reserve is limited. CO2 is nontoxic, cheap and abundant
carbon resource. Developing efficient methods for the
catalyst for the reductive coupling of CO2 to oxalate upon
15
conversion of CO2 to value-added chemical products are of
3-6
technological and societal importance.
electrochemical reduction.
Lee et al. demonstrated a Cl-
In the past two
induced bi-phasic Cu2O-Cu catalyst for the formation of C3-C4
compounds. 16 Mechanism of Cu-catalyzed reduction of CO2 to
C2+ products has also been studied. 10,17,18 It was also reported
that N-based organometallic catalysts could enhance the
efficiency of electrochemical reduction CO2 by reducing the
overpotential and increasing the product selectively. 8 N-doped
materials or N-containing ligands have higher overpotential for
hydrogen evolution which may inhibit H2O reduction, and thus
enhancing the selectivity to desired product.8,9 Besides, they
have excellent chemical stability to keep high active in long-
term operation. 19-21 In addition, N species, especially pyridinic
and pyridonic/pyrrolic N, can act as electrochemically active
decades, electrocatalytic CO2 reduction has attracted
increasing attention because the required electricity may be
obtained from renewable energy sources, such as wind, wave
and solar. 7-9 In most cases, the products from electrochemical
reduction processes can be tuned by varying reaction
conditions at ambient temperature and pressure. Exploration
of efficient and selective catalysts and electrolytes are crucial
for electrocatalytic CO2 reduction.8 Particularly, converting CO2
to C2 products is much more attractive because synthesis of C2
products is more complicated and energy intensive in the
current industrial processes.10,11 However, the mild
electrocatalytic reduction of CO2 to C2 products is challenging
because C-C coupling is very difficult in electrocatalytic
reduction.
·- 22,23
species for the adsorption of CO2 and CO2 .
Boron nitride (BN) has been found to be composed of
alternating B and N atoms in a honeycomb arrangement
consisting of sp2-bonded 2D layers, which has a similar
structural lattice as that of the C atoms of graphene. 24 Their
unique properties, such as high thermal conductivity,
mechanical properties and high resistance to oxidation, make
them very promising in many potential applications, especially
in optoelectronic nanodevices, electro-/photo-catalysts,
functional composites, etc. 24 Recent investigations indicated
that BNs had the ability to produce CO2 chemisorption once an
Cu-based materials were found to be the most promising
electrocatalysts for converting CO2 to C2+ products. 12-18 Many
a.Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid and
Interface and Thermodynamics, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, P.R.China, E-mail: hanbx@iccas.ac.cn
b.University of Chinese Academy of Sciences, Beijing 100049, P.R.China
Electronic Supplementary Information (ESI) available: [Details of the experimental
procedures and other figures and tables]. See DOI: 10.1039/x0xx00000x
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extra electron is injected into the material. 25-27 CO2 reduction the BN-Cx with different glucose contents are shown in the ESI
based on BN-like materials may be possible. (Figs. S2-S6), which indicate that the BN-Cx nanosheets had
Acetic acid is an important petrochemical that is currently similar structures to that of BN-C30. Cu 1 and Cu 2 supported
synthesized in an energy-intensive process using methane or on BN-Cx were synthesized. The catalysts were suspended in
coal as the feedstocks.28,29 Efficient synthesis of acetic acid via acetone with Nafion D-521 dispersion (5 wt%) to form a
electrocatalytic CO2 reduction is very attractive, but is homogeneous ink assisted by ultrasound and spread onto the
challenging. Also, LiI is a common promoter in organic carbon paper (CP) surface to obtain the working electrodes.
reaction.29 The proper ion size and stronger Lewis acidity of Li+
as well as the strong nucleophilicity of I- would facilitate the C-
C bond formation. Therefore, the combination of BN-like
materials support, N-based Cu (I) catalysts, and electrolytes
with a promoter (LiI) may be an effective way to solve the
challenging problem.
In this work, we synthesized Cu (I) complex/BN-Cx
composites, in which Cu (I) complex was supported on C-
doped BN. The materials were used as electrocatalyst for CO2
reduction to acetic acid. It was discovered that the Faradaic
efficiency of acetic acid could reach 80.3 % at a current density
of 13.9 mA cm-2 when [Emim]BF4-LiI-water solution was used
as the electrolyte, which presents the best result reported up
to date.
Results and discussion
Electronic supplementary information (ESI) provides details
regarding catalyst synthesis. Scheme S1 shows molecular
structures of the ligands and Cu complexes.30-32 For clarity, Cu
1
and Cu 2 refer to complexes with the ligands of N,N,N’,N’-
tetra(2-pyridyl)-2,6-pyridinediamine (Tppda) and N,N,N’,N’-
tetra(2-pyridyl)-biphenyl-4,4’-diamine (Tpbpa), respectively.
BN-Cx refers to C-doped BN support, where x is the weight
percentage of glucose (C precursor) of the boron oxide (B
precursor) used in the BN-Cx synthesis.
Fig. 1 A) SEM image of BN-C30. Inset of A shows the thickness of the
BN-C30 (scale bar, 50 nm). B) HR-TEM image of BN-C30. C) Elemental
mappings of BN-C30 (scale bar, 10 nm). D) XPS spectrum of B 1s orbit
of BN-C30. E) Powder XRD pattern of BN-C30. F) 13C solid-state NMR
Fig. 1, S1-S6 and Tables S1-S2 show the structure
characterization of the BN-Cx. Fig. 1A depicts thescanning
electron microscopy (SEM) image of BN-C30. The material has
the sheet structure with a size thickness of about 60 nm. High-
resolution transmission electron microscopy (HR-TEM) image
(Fig. 1B) confirms that an interlayer crystal lattice spacing of
0.33 nm exists in the nanosheet. Elemental distribution
mappings (Fig. 1C) further show uniform distribution of B, N
and C in the materials, indicating homogeneity of the C-doped
BN ternary materials. X-ray photoelectron spectroscopy (XPS)
spectra (Fig. 1D and Fig. S1) show the chemical nature of the
BN-C30, including the peaks belonging to B1s (B-N: 190.4 eV; B-
C: 190.0 eV; B-O: 192.2 eV), N1s (N-B: 397.7 eV; N-C: 399.2
eV), and C1s (C-C: 283.9 eV; C-N: 285.5 eV; C-B: 283.0 eV). 33
We can also found that the C content of BN-Cx increased with
increasing glucose amount gradually (Table S2). These provide
direct evidence that the incorporation of C into BN. Fig. 1E
shows the X-ray diffraction (XRD) pattern of the BN-C30. Two
characteristic peaks at 26.4o and 42.2o can be attributed to the
(002) and (100) planes of graphitic structure of BN,
respectively. 34 13C resonance appears around 125 ppm in the
13C solid-state NMR spectrum (Fig. 1F), which corresponds to
sp2C atoms with an electron density very similar to reduced
graphene oxide/graphite.33 The detailed characterizations of
spectrum of BN-C30
.
The performance of the as-prepared electrodes for
electrocatalytic CO2 reduction was first examined in CO2 or N2
saturated [Emim]BF4 aqueous solution with 25 mol%
[Emim]BF4 in the presence of 0.01 M LiI by linear sweep
voltammetry (LSV). As shown in Fig. S7, obvious reduction
peaks are observed for both Cu 1/BN-C30 and Cu 2/BN-C30
electrodes. The much higher current density of the CO2-
saturated system than the N2-saturated system indicates the
reduction of CO2.
Based on the above results, controlled potential electrolysis
of CO2 was performed at different applied potentials between
-1.7 V and -2.4 V vs Ag/Ag+ in CO2 saturated [Emim]BF4
aqueous solution with 25 mol% [Emim]BF4 containing 0.01 M
LiI to test the catalytic activity of the synthesized catalysts, and
a typical H-type cell was used.23 Under the reported reaction
conditions, acetic acid, formic acid and methanol were the
liquid products detected by NMR spectroscopy, and H2 was the
only gaseous product determined by gas chromatography (GC).
The Faradaic efficiency was calculated from moles of each
product and total number of electrons and the details can be
seen in the ESI.9,12
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Fig. 2A and 2B show the current density and Faradaic electrolysis) and virgin electrodes (before used) by repeating 5
efficiency for each product over Cu 1/BN-C30 and Cu 2/BN-C30 times, and percentages of the complex recovered from the
electrodes at different applied potentials. CO2 reduction used electrode and virgin electrode were 75.8 ± 1.6% and 76.7
occurred with the increasing applied potential, and formic acid ± 2.0%, respectively. The values were the same in the
and methanol were produced at low potentials, and acetic acid experimental error range. There were mainly two reasons for
was generated at higher potentials. The highest Faradaic that 25% could not be recovered from the electrodes. First, it
efficiency of acetic acid occurred at -2.2 V vs Ag/Ag+ and the is impossible to remove all complex from CP due to the
performance of Cu 1/BN-C30 electrode was much better than adsorption; second, only about 0.12 mg complex was used for
Cu 2/BN-C30 electrode. If we change the potential with respect each electrode, and thus little loss covers large percentage.
to reversible hydrogen electrode (RHE), the potential was Besides, after electrolysis the electrolyte was characterized
about -1.3 V vs RHE. The Faradaic efficiency of acetic acid NMR method, and the spectrum was the same as that of the
could reach 80.3 % over Cu 1/BN-C30 electrode with a current original electrolyte. The excellent long-term stability of the
density of 13.9 mA cm-2, which is about 4 times higher than electrode during electrolysis (Fig S10), the emission spectra of
the best result reported to date at the similar Faradaic the complex before and after electrolysis (Fig S11), the results
efficiency (Table S3). The competitive hydrogen evolution of recovery experiments for the complex from the electrodes,
reaction (HER) became much higher above -2.2 V vs Ag/Ag+, and the NMR characterization of the electrolyte before and
leading to the decreasing of Faradaic efficiency of acetic acid. after electrolysis all showed that the complex in the electrode
We conducted the blank experiment at -2.2 V vs Ag/Ag+, in and the electrolyte were stable during the electrolysis. For
which N2 was used to replace CO2. The current density was comparison, the aqueous solutions of some other typical
nearly zero (Fig. S7). 1H NMR spectra (Fig. S8) showed that supporting electrolytes were also used, but their performances
there was no liquid product, indicating that the CO2 was the were not as good as [Emim]BF4 (Table S4).
carbon source for the product. To further verify that the liquid
The role of BN-Cx support in the electrolysis was also
product was derived from CO2 reduction, isotope-labeled investigated. Very little amount of acetic acid was formed
13CO2 was used to study the reaction over Cu 1/BN-C30 when Cu 1/C and Cu 2/C as electrodes (Fig. S12). When BN-Cx
electrode at -2.2 V vs Ag/Ag+. 1H NMR spectra (Fig. S9A-9C) was used separately, the main product was formic acid (Fig.
indicated that only 13C signal was observed for the product, S13). There was no CO2 reduction product when bulk BN was
demonstrating that the acetic acid was derived from CO2 used. Obviously, synergistic effect existed between Cu
rather than other organic chemicals in the reaction system. complexes and BN-Cx in promoting CO2 reduction to acetic acid.
The splitting of H peaks of formic acid, methanol and acetic We also combined Cu 1 and Cu 2 with other BN-Cx, and BN-C30
acid by the 13C atom with relatively large coupling constants gave the best results (Fig. S14-S16).
can be observed. They are not the single peaks. They
distributes on both sides of the chemical shift of H-
12C symmetrically. To further confirm that the acetic acid was
derived from CO2, we also characterized the product by 13C
NMR，and the results are given in the ESI (Fig. S9D). The
results showed that no C signal attributed to acetic acid, formic
acid and methanol can be found when 12CO2 was used as the
feedstock, but strong C signal can be seen as 13CO2 was used.
Thus, the blank experiment using N2 (no product), as well as 1H
NMR and 13C NMR characterizations of the product using 12CO2
and 13CO2 all showed that the product was only derived from
CO2.
The electrode stability was also tested with an electrolysis
time of 5 h (Fig. S10), and the current density did not change
obviously with time. We tried to dissolve Cu 1/BN-C30 after
electrolysis of into dichloromethane with the aid of ultrasound.
Both the ligand Tppda and Cu
1
complex exhibit
Fig. 2 Current density and Faradaic efficiency of the products at
different applied potentials over (A) Cu 1/BN-C30 and (B) Cu 2/BN-
C30 electrodes in aqueous solution of 25 mol% [Emim]BF4 and 75
mol% water in the presence of 0.01 M LiI at 1 atm CO2 and room
temperature with 5 h electrolysis. Curve (a) is the current density;
curves (b)-(e) are Faradaic efficiency of b) acetic acid, c) methanol, d)
formic acid, and e) H2. Current density and Faradaic efficiency of
photoluminescence in the solid state. The emission spectra of
them are shown in Fig. S11. The individual ligand exhibits
strong emission band in the 350-475 nm region (λmax = 401 nm)
upon excitation with λmax = 276 nm. It is due to the π→π*
transition.31 After the ligand coordinates to Cu1+, a significant
red shift of the emission peak (λmax = 526 nm) can be observed.
The emission bands of Cu 1 complex before and after
electrolysis were the same, indicating that Cu 1 was stable acetic acid at applied potential of -2.2 V vs Ag/Ag+ with (C) different
during the CO2 reduction. We did parallel experiments to
recover the complex from the used electrodes (after
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water mole fractions and (D) different kinds of promoters (a: 5 mM;
b: 10 mM; c: 20 mM; d: 30 mM).
We investigated the effect the water mole fraction in the
electrolyte on the electrochemical reaction using Cu 1/BN-C30
electrode (Fig. 2C). The current density and Faradaic efficiency
of acetic acid were highest when the electrolyte contained 25
mol% [Emim]BF4 and 75 mol% water. Both current density and
Faradaic efficiency of acetic acid increased dramatically with
increasing water concentration at the beginning, but
decreased after water mole fraction exceeded 75 mol%. IL can
Fig. 3 A) Tafel plot for acetic acid production over Cu 1/BN-C30
electrode in [Emim]BF4 aqueous solution with 25 mol% [Emim]BF4
and 75 mol% water, in the presence of 0.01 M LiI. B) IR spectra of
the electrolyte phase in above system at different electrolysis times
and -2.2 V vs Ag/Ag+.
play a catalytic role on the stabilization of radical species such
·- 35
as CO2
and the addition of water can affect the electrolysis
in two opposite ways.23 The viscosity of [Emim]BF4 decreases
with the addition of water, which enhances the conductivity.
On the other hand, the number of ionic species in the
electrolyte decreases with increasing IL concentration. The
attained highest rate can be also attributed to the high
concentration of H+ in the electrolyte (Table S5). It has been
demonstrated that the adsorbed CO (COads), CHO (CHOads) and
Fig. 3B presents the electrolysis time-dependent infrared (IR)
spectra for CO2 reduction over Cu 1/BN-C30 electrode in
[Emim]BF4 aqueous solution with 25 mol% [Emim]BF4 and 75
mol% water, in the presence of 0.01 M LiI at -2.2 V vs Ag/Ag+.
The signal of the original CO2-saturated electrolyte was used as
the background, and no peak can be observed from IR spectra
before electrolysis started. After electrolysis started, the
formation of COO- can be verified from the peaks at 1639 (a)
and 1331 cm-1 (d).11,41 The intensity increased with the
increasing electrolysis time. The peak at 1576 cm-1 (b) was
attributed to the acetic acid dimer.41 They indicate the
formation of acetic acid along with theappearance of CH3 peak
at 1466 cm-1 (c). In addition, the bands related to C−H and C−O
areobserved at 1172 (e) and 1061 cm−1 (f), respectively.
CH3O (CH3Oads
) for protonation and the C-C path for
dimerization are strongly pH-dependent over Cu-based
electrode, which may be attributable to reduce the free energy
barrier of these processes.36 Meanwhile, low pH can depress
the HER and enhance the Faradaic efficiency of CO2
reduction.36
The effect of inorganic salt LiI was also important for
producing acetic acid. It was found that no acetic acid was
formed without LiI (Fig. S17). When other inorganic salts in Fig.
2D were utilized, the Faradaic efficiency of acetic acid was
poor. LiI was the best promoter in catalytic CO2 reduction to
acetic acid. The proper ion size and stronger Lewis acidity of
Li+may be favorable to producing acetic acid.37 Moreover, the
strong nucleophilicity of I- can facilitate the formation of C-C
bond in CO2 reduction to acetic acid.29
The high performance of Cu 1/BN-C30 electrode for CO2
reduction to acetic acidis probably related to the synergistic
effect between Cu complexes and BN-C30. It is worth noting
that BN-C30 can generate large amounts of formic acid and
bulk BN has no CO2 reduction product. N-doped graphitic
·- 19,23
carbon materials can adsorb CO2 and stabilize CO2 .
N can
induce some defect sites and polarize the adjacent C atoms.19
The resulted positively charged C atoms and defects can
We determined the electrokinetic data in order to studythe
mechanism of CO2 reduction to acetic acid. The equilibrium
potential for acetic acid generation was -1.68 V vs Ag/Ag+,
which was obtained from extrapolation method38,39 using the
current densities for acetic acid at different potentials (Fig.
S18). Therefore, the overpotential for acetic acid can be easily
calculated, and was 0.52 V for this process at -2.2 V vs Ag/Ag+
with the current density of 13.9 mA·cm-2, which was very low
for acetic acid production. Tafel plots in Fig. 3A show the
variation of overpotential versus the partial current density for
acetic acid production over Cu 1/BN-C30 electrode. The plot is
linear in the overpotential rangefrom 0.12 to 0.30 V with a
slope of 102.7 mV dec-1 for Cu 1/BN-C30 electrode, indicating
·-
facilitate the formation of CO2 . On the other hand, Cu (I)-
·-
based materials are able to bind CO2 and COads intermediate
strongly for the further conversion to multi-carbon products.12-
14 Fig.S19 compares the performance of Cu 1/BN-C30 electrode
with CuI/BN-C30 electrode, Tppda ligand/BN-C30 electrode and
CuI+Tppda ligand (physical mixture of CuI and Tppda
ligand)/BN-C30 electrode. It can be found that no acetic acid
can be obtained over CuI/BN-C30 electrode and Tppda
ligand/BN-C30 electrode. A very little amount of acetic acid can
be obtained over CuI+Tppda ligand/BN-C30 electrode.So the
coupling effect of Cu (I) center and N-based ligand in the
complex Cu 1 can help the bonding of COads. It favors the
further reduction of CO to methanol and C-C coupling for the
acetic acid formation in the present of LiI. This pathway is also
supported by the fact that acetic acid was not formed without
LiI (Fig. S17). As mentioned above, the potential has significant
impact on the selectivity of CO2 reduction. For C-C coupling,
two C-based adsorbates must be adjacent to one another and
relatively favourable reaction energetics may be needed. In
the meantime, the proton and electron transfer becomes
·-
that single electron transfer to CO2 to form adsorbed CO2
intermediate is a pre-equilibrium prior to a rate-determining
step for our system.40 The main product is acetic acid rather
than formic acid, suggesting that the C-C coupling is faster
·-
than the protonation of CO2
.
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easier at more negative potentials. Therefore, the high activity coupling in the presence of LiI. This study opens a way for
of Cu 1/BN-C30 electrode for CO2 reduction to acetic acid can highly efficient CO2 reduction to C2+ products by combination
be attributed to the synergistic effect among the C-doped BN, of composite catalysts and suitable electrolytes with promoter.
Cu metal center, N-based ligand, and the electrolyte.
On the basis of all the results above, we proposed a
Acknowledgements
plausible mechanism for electrocatalytic CO2 reduction to
acetic acid (Fig. 4). First, CO2 is adsorbed on the surface of
·-
The authors thank the National Natural Science Foundation of
electrode and reduced to CO2 in the present of [Emim]BF4,
China (21133009, 21533011, 21403253) and Chinese Academy
which may be due to that the complex [Emim-CO2]+ formed
of Sciences (QYZDY-SSW-SLH013).
through the hydrogen bond between CO2 and [Emim]+.42,43 It
can reduce the reaction barrier forelectron transfer to CO2.35,44
Then, the formation of COads and the protonation of CO2·- may
occur simultaneously, and the former is the main procedure.
Notes and references
1
J. Klankermayer, S. Wesselbaum, K. Beydoun and W. Leitner,
Angew. Chem. Int. Ed., 2016, 55, 7296.
COads can be transformed into CHOads via capturing a pair of
electron and proton, followed by the protonation of CHOads
,
2
E. M. Nichols, J. J. Gallagher, C. Liu, Y. Su, J. Resasco, Y. Yu, Y.
Sun, P. Yang, M. C. Y. Chang and C. J. Chang, Proc. Natl. Acad.
Sci. U. S. A., 2015, 112, 11461.
which formed CH3Oads via accepting another two electrons.
The downstream step is the conversion of CH3Oads to
methanol, which was detected in the product. Subsequently,
with the promotion of Lewis acidic cation Li+, CH3I may form on
the surface of electrode by the reaction of methanol and I-. It
can be captured by the Cu species (Cu*) to form CH3Cu*I,
which is a basic step in organic synthesis and has been well
3
4
5
M. He, Y. Sun and B. Han, Angew. Chem. Int. Ed., 2013, 52,
9620.
M. Aresta, A. Dibenedetto and A. Angelini, Chem. Rev., 2014,
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M. Cui, Q. Qian, Z. He, Z. Zhang, J. Ma, T. Wu, G. Yang and B.
Han, Chem. Sci., 2016,
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43, 631.
7, 5200.
6
7
8
·-
proven.29,37 As the process of CO2 formation via single
electron transfer to CO2 is fast, CH3Cu*I can combine with
·-
another CO2 and generate CH3COOCu*I. Finally, CH2COOCu*I
9
C. E. Tornow, M. R. Thorson, S. Ma, A. A. Gewirth and P. J. A.
Kenis, J. Am. Chem. Soc., 2012, 134, 19520.
is protonated, resulting in the production of acetic acid. The
by-products, LiOH and HI generated in situ neutralized
spontaneously to form LiI and H2O. All these catalytic species
can be regenerated for the next process. Discussion of more
detailed mechanism is very interesting, but is very difficult at
present, which needs to be studied further.
10 F. Calle-Vallejo and M. T. M. Koper, Angew. Chem. Int. Ed.,
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Cu (I) complex/BN-Cx composites exhibited high performance for electrochemical
reduction of CO2 to acetic acid in [Emim]BF4-LiI-water electrolyte.