Selective electrochemical reduction of carbon dioxide to ethanolviaa relay catalytic platform

Article abstract of DOI:10.1039/d0sc01133a

Efficient electroreduction of carbon dioxide (CO₂) to ethanol is of great importance, but remains a challenge because it involves the transfer of multiple proton-electron pairs and carbon-carbon coupling. Herein, we report a CoO-anchored N-doped carbon material composed of mesoporous carbon (MC) and carbon nanotubes (CNT) as a catalyst for CO₂electroreduction. The faradaic efficiencies of ethanol and current density reached 60.1% and 5.1 mA cm^?2, respectively. Moreover, the selectivity for ethanol products was extremely high among the products produced from CO₂. A proposed mechanism is discussed in which the MC-CNT/Co catalyst provides a relay catalytic platform, where CoO catalyzes the formation of CO* intermediates which spill over to MC-CNT for carbon-carbon coupling to form ethanol. The high selectivity for ethanol is attributed mainly to the highly selective carbon-carbon coupling active sites on MC-CNT.

Full text of DOI:10.1039/d0sc01133a

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Selective electrochemical reduction of carbon dioxide to ethanol
by relay catalytic platform†
Juan Du,a,b Shaopeng Li,a,b Shulin Liu,a,b Yu Xin,a,b Bingfeng Chen,a Huizhen Liu,*a,b Buxing Hana,b
Received 00th January 20xx,
Accepted 00th January 20xx
Efficient electroreduction of carbon dioxide (CO2) to ethanol is of great importance, but this remains a challenge because it
involves transfer of multiple proton-electrons and carbon-carbon coupling. Herein, we report a CoO-anchored N-doped
carbon material composed of mesoporous carbon (MC) and carbon nanotube (CNT) as a catalyst for CO2 electroreduction.
The faradaic efficiency of ethanol and current density reached 60.1% and 5.1 mA cm−2 respectively. Moreover, the selectivity
of ethanol products was extremely high among the products produced from CO2. A proposed mechanism was discussed that
the MC-CNT/Co catalyst provided a relay catalytic platform, where CoO catalyze the formation of CO* intermediates which
spill over to MC-CNT for carbon-carbon coupling to form ethanol. The high selectivity of ethanol was attributed mainly to
the highly selective carbon-carbon coupling active site on MC-CNT.
DOI: 10.1039/x0xx00000x
FE of 24% for ethanol production.10 On bimetallic Ag/Cu
electrocatalysts, ethanol could be formed with FE of 41%.11 The
hierarchically structured Cu dendrites electrodes with
Introduction
The excessive use of fossil fuels and deforestation result in
continuous increase of carbon dioxide (CO2) concentration in
the atmosphere and ocean, which is a crucial issue for human
beings.1 The efficient conversion of CO2 to fuels and high-value
added chemicals can promote the development of the cyclic
utilization of carbon resource and the reduction of CO2
superhydrophobic surface attained a 56% FE for ethylene and
17% for ethanol production.12 An ethanol FE of 41% on
porphyrin-based Fe/Cu was reported and the ratio of ethanol to
ethylene is 1.0 under the optimized operation conditions.13
Copper-nitrogen-doped carbon materials achieved aqueous
CO2 electroreduction to ethanol at a FE of 55% under optimized
conditions.14 On copper-cuprous oxide electrodes, ethanol and
acetic acid could be produced, while the main product is acetic
acid.15
In addition to the Cu-based electrocatalysts, Ag-, Fe- and carbon
materials-based catalysts have also been reported for the
electroreduction of CO2 to ethanol. The Ag-anchored N-doped
graphene/carbon foam could efficiently catalyze the conversion
of CO2 to ethanol with FE of 82.1-85.2%, but the current density
was only 0.35 mA cm−2.16 Fe2P2S6 nanosheet was used as an
efficient electrocatalyst for highly selective electroreduction of
CO2 to methanol and ethanol, with 23.1% FE of ethanol.17 Ru(II)
polypyridyl carbene complex immobilized on an N-doped
porous carbon displayed 27.5% FE of ethanol with very low
current density.18 Carbon materials electrodes could catalyze
the conversion of CO2 to ethanol with high selectivity while the
current density was very low. For example, 77% FE of ethanol
3
emission.2, Electrocatalytic reduction of CO2 is a promising
route due to its mild operation conditions (ambient pressure
and temperature) and modular reaction systems, which can be
easily controlled by adjusting electrochemical parameters and
make them facile for scale-up applications.4-6 Ethanol is a widely
used intermediate in chemical synthesis and a liquid fuel with a
high energy density (26.8 MJ/kg).7 Direct electroreduction of
CO2 to ethanol is of great importance. However, it is challenging
because the process involves not only the transfer of multiple
proton-electrons but also carbon-carbon coupling with high
overpotential.
Cu is documented to be a key component for multicarbon
chemical production. Unfortunately, most Cu based electrodes
is more favorable for ethylene over ethanol. On plasma
activated Cu nanocube electrocatalysts, the faradaic efficiency
(FE) of ethylene and ethanol were 45% and 22%, respectively.8
Electrodeposited
electroreduction performance with FE of 60% for ethylene and
25% for ethanol.9 Oxide-derived Cu/carbon catalyst exhibited
CuAg
alloy
films
showed
good
was obtained on
a nitrogen-doped ordered cylindrical
mesoporous carbon with current density of < 1 mA cm-2.
Moreover, the selectivity of ethanol among the products
produced from CO2 is nearly 100%.19 Further study shows that
medium micropores embedded in the channel walls of
nitrogen-doped ordered mesoporous carbon could promote
ethanol production from CO2 electroreduction, and the FE for
ethanol reached 78%.20
a. Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid
and Interface and Thermodynamics, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, P.R. China. E-mail: liuhz@iccas.ac.cn
b. School of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, P.R. China.
†Electronic
DOI:10.1039/x0xx00000x
Supplementary
Information
(ESI)
available.
See
Literature survey shows that the electrocatalysts that has been
reported exhibit high current density and low selectivity for
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ethanol or high selectivity with low current density. It is obvious 24 h, respectively. Finally, the solid products were obtained by
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DOI: 10.1039/D0SC01133A
that more efforts should be made to develop highly efficient filteration. Afterwards, the material was washed with deionized
electrocatalysts for the electroreduction of CO2 to ethanol. CO water and air-dried overnight. The P123 was removed by
is an important intermediate for the generation of C2+ products calcining in air at 550 oC for 5 h.
from CO2 electroreduction. It has been reported that high-
concentration CO could generate on the doping metal sites and Preparation of MS with amino-functional composites (MS-NH2).
spill over to the Cu sites for carbon-carbon coupling before 1 g of as-made MS was dispersed in 30 mL of toluene by
further reduction to C2+ products on Cu-based bimetallic ultrasonication, and then dropped 2 mL of aminopropyl-
electrodes. Rich local CO intermediates can effectively promote methoxysilane (APTMS). The mixture was refluxed at 80 oC with
the next carbon-carbon coupling process in CO2 continuous stirring for 24 h. The resulting functionalized MS
electroreduction. Moreover, the highly selective carbon-carbon composites were recovered by filteration followed by washing
coupling active site on
a
catalyst are crucial for the with toluene several times and then dried at 60oC under vacuum
electroreduction of CO2 to ethanol with high selectivity.
for 12 h. The products obtained are denoted as MS-NH2.
Cobalt-based materials can be used as catalysts for
electroreduction of CO2 to CO. On semiconducting Co3O4 Synthesis of MC-CNT/Co and MC-CNT. To obtain the MC-
nanofibers, CO could be formed with FE of 65%.21 Cobalt CNT/Co, the 2-methylimidazole was used as carbon precursor.
phthalocyanine (CoPc) molecules anchored on carbon In a typical process, Co2+/MS composite template and powder
nanotubes exhibit 95% FE for CO production.22 Inspired by the of 2-methylimidazole were mixed to place in quartz boat inside
high selectivity of carbon materials for CO2 electroreduction to the quartz tube. Ar was introduced as protective and carrier gas.
ethanol and good performance of cobalt-based materials for Then the furnace was heated to 700 °C at a rate of 5 °C min-1
CO2 electroreduction to CO, in this work, we designed a catalyst and kept at the temperature for 3 h to obtain Co/MS/carbon
MC-CNT/Co, in which CoO was anchored in N-doped carbon composite. After removing of silica by 10 wt.% NaOH aqueous
material composed of mesoporous carbon (MC) and carbon solution, the MC-CNT/Co was obtained. Moreover, MC-CNT
nanotube (CNT), for CO2 electroreduction, which provided a could be obtained by etching metal particles in MC-CNT/Co with
relay catalytic platform, where CoO catalyze the formation of hydrochloric acid solution (2 M) for 72 h.
*CO intermediates that spill over to MC-CNT for carbon-carbon
coupling to ethanol. The selectivity of ethanol and acetaldehyde Materials Characterization
could reach nearly 100% among the CO2 electroreduction
The morphologies of those electrodes were characterized on a
products at -0.2 to -0.45 V and a FE of 60.1 % was achieved for
S4800 scanning electron microscope (SEM) and JEOL-2100F
ethanol under low overpotential (-0.32 V vs RHE) with the
transmission electron microscope (TEM) operated at 200 kV.
current density of 5.1 mA cm−2. The Co species, ordered
Powder X-ray diffraction (XRD) patterns were performed on the
X-ray diffractometer (Model D/MAX2500, Rigaka) with Cu-Kα
radiation. X-ray photoelectron spectroscopy (XPS) analysis was
mesoporous structure and CNT had excellent synergistic effect
for promoting CO2 electroreduction to ethanol.
conducted on the Thermo Scientific ESCA Lab 250Xi using 200
W monochromatic Al Kα radiation. The content of Co in the
catalysts was determined by inductively coupled plasma optical
Experimental
Reagents
emission spectroscopy (ICP-OES, Vista-MPX). The N2
adsorption/desorption isotherms were determined using a
Micromeritics TriStar 3020 instrument at -196 °C. The Brunauer-
Emmett-Teller (BET) method was employed to calculate the
specific surface area, while the Barrett-Joyner-Halenda (BJH)
method was applied to analyze the pore size distribution using
the adsorption branch of isotherm. The FTIR spectra were
collected at a resolution of 4 cm-1 on a Bruker Vector 27
spectrophotomfeter in the 400-4000 cm-1 region. The IR spectra
of samples were measured by the conventional KBr pellet
Toray Carbon Paper (CP, TGP-H-60, 19×19 cm), Nafion D-521
dispersion (5 % w/w in water and 1-propanol, ≥ 0.92 meg/g
exchange capacity) and Nafion N-117 membrane (0.180 mm
thick, ≥ 0.90 meg/g exchange capacity) were purchased from
Alfa Aesar China. 3-(Aminopropyl)trimethoxysilane (APTMS), 2-
Methylimidazole (purity>98%), Tetraethyl orthosilicate (TEOS)
(purity>99%), Cobalt nitrate hexahydrate (Co(NO3)2) was
purchased from Beijing Innochem Company, Pluronic P123
(average Mn ~ 5800) was obtained from Sigma. Hydrochloric
acid, Sodium hydroxide, Toluene (purity>99%) was provided by
Beijing Chemical Company.
method. Thermogravimetric analysis (Pyris
1 TGA) was
performed under Ar flow from 20 to 800 °C at a heating rate of
10 °C min-1.
Synthesis of the electrode materials
Electrochemical measurements
Preparation of mesoporous silica (MS). The MS was prepared
according to the work reported previously.23 Typically, 4.0 g of
Pluronic P123 was dissolved in 50 mL of water and stirred for 5
h at room temperature. The mixture was added to 120 mL of 2
M hydrochloric acid solution and stirred for 2 h, and then TEOS
(8.5 g) was added. The solution was aged at 35oC and 100oC for
The electrochemical workstation (CHI 660E, Shanghai CH
Instruments Co., China) was used for all CO2 reduction
experiments. Typically, a 10 mg sample and 20 μL of Nafion
solution (5 wt%) were dispersed in 1 mL of deuterium
acetonitrile by sonicating for 30 min to form a homogeneous
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ink. Then, the dispersion was loaded onto a carbon paper with We can obtain the Qtatal from the chronoamperogram and the
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DOI: 10.1039/D0SC01133A
1
cm × 1 cm. For CO2 reduction experiments, cyclic total number of electrons by measuring,
voltammograms (CV) measurements were performed in a H-
type cell using 0.5 M KHCO3 (60 mL, pH = 7.8) as electrolyte with
a typical three-electrode setup, which contained working
electrode, a platinum gauze auxiliary electrode, and an Ag/AgCl
reference electrode. All the measured potentials in this work
are cited with respect to the RHE using the following
conversion: ERHE (V) = EAg/AgCl (V) + 0.197 V + (0.059 V × pH).
Before electrolysis, the electrolyte was purged with Ar or CO2
gas for at least 30 min. The CV measurement in gas-saturated
electrolyte was conducted at a sweep rate of 5 mV s-1 in the
potential between -0.6 V and -1.4 V (vs. Ag/AgCl). Constant
magnetic stirring was kept in the process. The electrolysis
experiments were conducted at 25 oC in a typical H-type cell. It
consisted of a cathode, an anode (platinum gauze auxiliary
electrode) and an Ag/AgCl reference electrode. In the
experiments, the cathode and anode compartments were
separated by a Nafion-117 proton exchange membrane. KHCO3
aqueous solution (0.5 M) was used as anodic electrolyte. Then,
potentiostatic electrochemical reduction of CO2 was carried out
with CO2 bubbling (5 mL min-1). The reduction of acetaldehyde
was also performed over MC-CNT/Co electrode at -0.32 V (vs
RHE) in 0.5 M KHCO3 electrolysis solution with 0.05 M
acetaldehyde. The electrolysis experiment was conducted at 25
oC in a H-type cell with Nafion-117 proton exchange membrane
Ntotal = Qtotal / e
The Faradaic efficiency (FE) of liquid product is:
FE = N / Ntotal × 100%
Results and discussion
(a)
(c)
(b)
2 μm
(d)
50 nm
(e)
1
and lasted 2h. The liquid products were analyzed by H NMR
(Bruker Avance III 400 HD spectrometer) in Acetonitrile-d3 with
dimethyl sulfoxide (DMSO) as an internal standard. The gaseous
product was collected using a gas bag and analyzed by gas
chromatography (GC, HP 4890D), which was equipped with a
TCD detector using helium as the internal standard. Each data
point is an average of the measurements collected from at least
three separate NMR or GC analysises. Each prepared catalyst
was used only once for CO2 reduction at a chosen potential.
0.25 nm
0.34 nm
pore
0.34 nm
5 nm
5 nm
C
(f)
(g)
N
Calculations of Faradaic efficiencies of gaseous and liquid
products:
Gaseous products:
FE = moles of products per second/theoretical moles equivalent
per second
Co
O
Based on the GC peak areas and calibration curves, the V % of
H2 can be obtained. The amount of moles of H2 (or CO) per
second could be calculated from the flow rate of the gas and the
V % of H2. The theoretical moles per second were obtained from
current density.
500 nm
500 nm
Fig. 1. Schematic illustration of the synthesis process (a), SEM
(b), TEM (c and f) images, high-resolution TEM (d and e) and the
corresponding elemental mapping of C, O, Co and N elements
(g) of the MC-CNT/Co.
liquid products:
In NMR spectra, DMSO was used as the internal standard, and
the relative peak area of CH3CH2OH can be calculated.
The number of electrons required to produce liquid product
during the entire CO2 electro-reduction reaction is:
Ordered MS was prepared using TEOS as the precursor and
P123 as the template. Amino groups were grafted to the MS
using APTMS as amination reagent, which was proved by the N-
H vibration peaks at 1560 cm-1 and 3120 cm-1 in the FTIR spectra
(Fig. S1). The mesoporous structure of MS was kept after amino
N = C × V × NA × ne
(V: the volume of catholyte; NA: Avogadro constant; n: transfer
electron number)
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0
-3
-6
-9
groups grafting (Fig. S2).24-26 The MC-CNT/Co was synthesized
by three steps as shown in Fig. 1a. First, the cobalt species was
adsorbed onto the MS to obtain Co2+/MS owing to the
electrostatic force between amino and cobalt ion. Second, MC-
CNT/Co/MS was obtained by thermal treatment of a mixture
composed of Co2+/MS composite and powder of 2-
methylimidazole under Ar atmosphere, in which 2-
methylimidazole was used as carbon and nitrogen precursor.
Subsequently, MC-CNT/Co/MS was treated by 10 wt.% NaOH
aqueous solution to remove silica resulting in MC-CNT/Co. SEM
and TEM images showed that the MC-CNT/Co had a 3D network
structure formed by CNT connected to rod-like mesoporous
carbon (Fig. 1b and 1f). As shown in Fig. 1d and 1e, the graphene
layers with lattice distance of 0.34 nm could be clearly seen. It
has been reported that Co could catalyze the formation of
CNT.27 Ordered mesoporous structure observed from TEM
images of MC-CNT/Co displayed that the pores of MS template
were replicated (Fig. 1c). Additionally, cobalt nanoparticles
(diameter: 3 ～ 5 nm) were also detected, and their lattice
spacing was 0.25 nm, which is assigned to CoO (111) (Fig. 1d).28,
(a)
(b)
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DOI: 10.1039/D0SC01133A
0
-10
-20
-12
-15
CO2
AR
0
5000
10000
15000
20000
-0.6
-0.4
-0.2
0.0
Potential (V vs RHE)
Times (s)
(c)
CH3CHO
CO
CH3CH2OH
H2
CH3CH2OH
100
80
60
40
20
0
-0.2
-0.3
-0.4
-0.5
29
Potential (V vs.RHE)
The content of cobalt in MC-CNT/Co was 13.20 wt%, which
was analyzed by inductively coupled plasma optical emission
spectroscopy (ICP-OES). The corresponding elemental mapping
reveals its elemental distribution, which shows the uniform N,
Co distribution in the carbon framework (Fig. 1g).
Fig. 3. Cyclic voltammograms curves in the potential range from
0 V to -0.7 V (vs. RHE) at a sweep rate of 5 mV s-1 in 0.5 M Ar-
saturated and CO2-saturated 0.5 M KHCO3 on MC-CNT/Co
electrodes (a); Total current density versus time in 0.5 M KHCO3
under a CO2 atmosphere on electrodes at -0.32 V (vs. RHE) (b)
and FE for ethanol, aldehyde, carbon monoxide and hydrogen
production obtained from the electrochemical reduction of CO2
for 6 h on MC-CNT/Co electrode at -0.2 to -0.6 V (vs. RHE) (c).
Fig. 2a shows the XRD patterns of the MC-CNT/Co. The broad
diffraction peaks around 23.3o and 26.0o correspond to the
amorphous and graphitized carbon respectively. Three peaks at
36.8o, 43.1o and 63.4o are indexed to the CoO(111), CoO(200)
and CoO(220) (CoO-75-0418).30, 31 As depicted in Fig. 2b, the
MC-CNT/Co exhibited type IV adsorption-desorption isotherm
and type H3 hysteresis loops, showing the existence of the
mesopores. The specific surface area calculated using the BET
method was 303 m2 g-1. The BJH method was used to calculate
pore-size distribution from the adsorption branch of the
nitrogen isotherm and the average pore size was 4.4 nm (Fig.
2c).
The electronic states of different elements in MC-CNT/Co were
investigated by XPS. As shown in Fig. S4, Co, N, C and O elements
were observed. The high resolution Co 2p3/2 XPS spectrum of
MC-CNT/Co (Fig. 2d) can be deconvoluted into three set peaks
at 780.6 eV, 779.3 eV and satellite at 785.5 eV, which are
attributed to Co(II)Nx and Co(II)O. 32-34 The O1s signal (Fig. S5a)
was deconvoluted into three oxygen configurations, including
carboxyl oxygen (532 eV), hydroxyl oxygen (534 eV) in
amorphous hydrogenated carbon and Co-O (529 ev).33
Deconvolution of the N 1s peak (Fig. S5b) revealed two peaks
that can be assigned to pyridinic-N (398.5 eV) and pyrrolic-N
(400.0 eV), respectively.34
(b)
(a)
20
Amorphous carbon
CoO-111
CoO-200
15
10
5
Graphitized carbon
CoO-220
JCPDS 75-0418
The CV tests over MC-CNT/Co were performed in Ar-saturated
and CO2-saturated 0.5 M KHCO3 electrode aqueous solution (pH
7.8) respectively. In this work, the applied potential is
referencing to the reversible hydrogen electrode (RHE) and the
current density is calculated by geometric surface area. As
shown in Fig. 3a, an obvious reduction peak can be observed at
ca. -0.3 V (vs RHE) in a CO2-saturated electrolyte, which shows
the reduction of CO2. Controlled-potential CO2 electrolysis
experiments were performed in 0.5 M KHCO3 aqueous
electrolyte solution using a typical H type cell. The onset
potential of MC-CNT/Co was as low as −0.25 V (vs RHE), which
is more positive than that of many other carbon-based
10
20
30
40
50
60
70
80
0.0
0.2
0.4
0.6
0.8
1.0
2 Theta (degree)
P/P0
(c) 0.5
(d)
0.4
Co(II)Nx
CoO
0.3
0.2
Shake up
0
10
20
30
40
50
795
790
785
780
775
770
Pore Size (nm)
Binding Energy (eV)
Fig. 2. XRD patterns (a), N2 adsorption and desorption curves (b),
pore size distribution (c) and XPS spectrum of Co2p (d) of the
MC-CNT/Co.
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electrodes.19, 35-38 More importantly, ethanol and acetaldehyde densities could facilitate the formation of ethanol which is
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19,20
DOI: 10.1039/D0SC01133A
(trace) were the only liquid products detected by NMR consistent with the results reported in the literature.
spectroscopy. H2 was the only gaseous product in the range of - Furthermore, because of the excellent conductivity of CNT, the
0.20 to -0.45 V (vs RHE), showing that the selectivity of C2 liquid current density was measured to be 3.2 mA cm−2, which is
products from CO2 is 100% on the MC-CNT/Co catalyst. The higher than the reported carbon electrode. Recent studies have
current density and FE for ethanol and acetaldehyde were 5.1 also proved the vital role of CNT in facilitating the
mA cm−2 and 70.7% (60.1% for ethanol and 10.0% for electrocatalytic reduction of CO2.19, 35, 41, 42 These experimental
acetaldehyde), respectively (Fig. 3b and c). Except for ethanol, results suggest that MC-CNT/Co creates a relay catalytic
a small amount of CO was detected at -0.48 V and -0.52 V platform that CoOx and MC-CNT cooperate very well to catalyze
(versus RHE), which is a very important intermediate for C2 the formation of C2 products via CO.
products as the reported results.39 MC-CNT/Co exhibited higher Electrochemical impedance spectroscopy (EIS) was performed
FE for ethanol than Cu-based catalysts and higher current at −0.56 V vs. RHE in CO2 saturated 0.5 M KHCO3 solution to
density than carbon material-based electrodes. In addition, the measure the charge transfer resistance (Rct) for MC-CNT/Co
MC-CNT/Co catalyst showed long-term stability in the and MC-CNT. As shown in Fig. S14, the Rct value of MC-CNT/Co
electrolysis, which was known from the fact that both current was as low as 0.28 ohm, lower than that of MC-CNT (0.47 ohm),
density and FE did not change considerably with electrolysis implying that electrons could be more easily transported on
time in 20 h at -0.32 V (vs RHE), as shown in Fig. S6.
MC-CNT/Co.
From the product distribution shown in Fig. 3c, we deduce that
acetaldehyde was the possible intermediate to form ethanol.
and it can be confirmed by the electroreduction of
acetaldehyde. The reduction of acetaldehyde was performed
over MC-CNT/Co at -0.32 V (vs RHE) in 0.5 M KHCO3 electrolysis
solution (Fig. S7). It can be found that ethanol was produced
with 50% conversion and 98% FE.
To confirm that the product was derived from CO2 reduction,
the blank experiments using Ar to replace CO2 in the electrolysis
at -0.3 V vs. RHE (Fig. S8) were conducted and no product was
formed after electrolysis 6 h. The reaction in Isotope−labeled
13CO2 and 12CO2 saturated 0.5 M KHCO3 electrolyte solution at -
0.32 V vs RHE was also studied over MC-CNT/Co. The product
1
1
was analyzed by H NMR after electrolysis 1 h. From H NMR
spectra in Supplementary Fig. S9, we can only see the H signal
of 13CH3 group on the ethanol, which splits into two peaks by
the coupling with 13C atom. The results indicate that carbon
atoms in the product were from CO2 rather than other C-based Scheme 1. Proposed mechanism for the electrochemical
chemicals in the reaction system.18, 40
reduction of CO2 to ethanol on the MC-CNT/Co electrode.
To unveil the reasons behind the good performance of MC-
CNT/Co, MC-CNT and pure CoOx as reference samples for
electroreduction of CO2 were checked. MC-CNT was prepared
by etching CoO in MC-CNT/Co with hydrochloric acid solution (2 According to the experimental data and the results have been
43, 44
M) for 72 h, and characterized by TEM, XRD and XPS. Fig. S10 reported,35,
the possible mechanistic pathway for the
shows CNT and mesopores structure of MC-CNT, and no electrocatalytic production of ethanol over MC-CNT/Co was
detectable Co or CoO nano-particles or subnano-clusters were proposed and shown in Scheme 1. One-electron transfers to
observed. Moreover, no signals of Co or CoO were detected in CO2 molecule to form intermediate CO2*- anion radical.
XRD and XPS spectrum (Fig. S11). These results indicate that Co Subsequently, the obtained CO2*- reacts with proton-electron
or CoO was removed by HCl. The pure CoOx sample also pair and forms CO* intermediates, which is mainly attributed to
prepared by annealing Co(NO3)2 under Ar atmosphere (Fig. the CoO species. CO* is the key intermediates for the
S12). CO2 electrolysis measurements were performed in CO2- dimerization35 and it spill over to MC-CNT for carbon-carbon
saturated 0.5 M KHCO3 electrolyte solution using CoOx or MC- coupling to form *COCHO or *COCO intermediates. Pyrrole-N
CNT as the catalysts and the electrolysis process was carried out and pyridinic-N in MC-CNT/Co and its mesoporous structure are
at the range of -0.20 to -0.6 V (vs RHE) for 2 h. On CoOx both favorable for stabilizing CO* intermediates and promoting
electrode, CO was detected with a maximum FE of 5.6% at -0.46 the carbon-carbon coupling reaction to ethanol.19,20
V (vs RHE), which is an important intermediate during CO2 Furthermore, CoO species and MC-CNT are intimate in MC-
electroreduction to C2 products (Fig. S13). On MC-CNT CNT/Co because it is synthesized by one-pot pyrolysis, which is
electrode, CO and ethanol as result of carbon-carbon coupling benefit for the spillover of CO* intermediates to MC-CNT.
were produced with FE of 0.98% and 48.1% at -0.46 V (vs RHE),
respectively. The pyridinic-N and pyrrolic-N with high electron
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ARTICLE
Journal Name
Voznyy, D. Sinton and E. H. Sargent, J. Am. Chem. Soc.,
Conclusions
View Article Online
2019, 141, 8584-8591.
DOI: 10.1039/D0SC01133A
In summary, the MC-CNT/Co catalyst designed in this work
shows excellent performance for CO2 electroreduction to
ethanol. The FE of ethanol could reach 60.1% at −0.32 V versus
the reversible hydrogen electrode. The ordered mesoporous
structure and CoO particles cooperate very well to promote the
reaction. CoO catalyze the formation of CO* intermediates that
spill over to MC-CNT for carbon-carbon coupling to ethanol.
Pyrrole-N and pyridinic-N in MC-CNT/Co and its mesoporous
structure are both favorable for stabilizing CO* intermediates
and promoting the carbon-carbon coupling reaction. The high
selectivity of ethanol was attributed mainly to the highly
selective carbon-carbon coupling active site on MC-CNT. We
believe that relay catalytical platform strategy can also be used
for designing highly efficient catalysts for electroreduction CO2
to C2+ products.
12.
13.
D. Wakerley, S. Lamaison, F. Ozanam, N. Menguy, D.
Mercier, P. Marcus, M. Fontecave and V. Mougel, Nature
materials, 2019, 18, 1222–1227.
F. Li, Y. C. Li, Z. Wang, J. Li, D.-H. Nam, Y. Lum, M. Luo, X.
Wang, A. Ozden, S.-F. Hung, B. Chen, Y. Wang, J. Wicks, Y.
Xu, Y. Li, C. M. Gabardo, C.-T. Dinh, Y. Wang, T.-T. Zhuang,
D. Sinton and E. H. Sargent, Nature Catal., 2020, 3, 75–82.
D. Karapinar, N. T. Huan, N. R. Sahraie, J. Li, D. Wakerley, N.
Touati, S. Zanna, D. Taverna, L. H. G. Tizei, A. Zitolo, F.
Jaouen, V. Mougel and M. Fontecave, Angew. Chem. Int.
Ed., 2019, 58, 15098 – 15103.
Q. Zhu, X. Sun, D. Yang, J. Ma, X. Kang, L. Zheng, J. Zhang,
Z. Wu and B. Han, Nat. Commun., 2019, 10, 3851.
K. Lv, Y. Fan, Y. Zhu, Y. Yuan, J. Wang, Y. Zhu and Q. Zhang,
J. Mater. Chem. A, 2018, 6, 5025-5031.
L. Ji, L. Chang, Y. Zhang, S. Mou, T. Wang, Y. Luo, Z. Wang
and X. Sun, ACS Catal., 2019, 9, 9721−9725.
Y. Liu, X. Fan, A. Nayak, Y. Wang, B. Shan, X. Quan and T. J.
Meyer, PNAS, 2019, 116, 26353-26358.
Y. Song, W. Chen, C. Zhao, S. Li, W. Wei and Y. Sun, Angew.
Chem. In. Ed., 2017, 56, 10840-10844.
Y. Song, S. Wang, W. Chen, S. Li, G. Feng, W. Wei and Y.
Sun, ChemSusChem, 2020, 13, 293 – 297.
A. Aljabour, H. Coskun, D. A. Apaydin, F. Ozel, A. Hassel, P.
Stadler, N. S. Sariciftci and M. Kus, Appl. Catal., 2018, 229
163–170.
X. Zhang, Z. Wu, X. Zhang, L. Li, Y. Li, H. Xu, X. Li, X. Yu, Z.
Zhang, Y. Liang and H. Wang, Nat. Commun., 2017, 8,
14675.
A. Chen, Y. Yu, R. Wang, Y. Yu, W. Zang, P. Tang and D. Ma,
Nanoscale, 2015, 7, 14686-14690.
S. H. Huang and D. H. Chen, J. Hazard. Mater., 2009, 163,
174-179.
S. Wang, K. Wang, C. Dai, H. Shi and J. Li, Chem. Eng. J.,
2015, 262, 897-903.
L. You, F. Yuan and F. Ma, J. Phys. Chem. A, 2015, 89, 2298-
2303.
Z. Li, M. Shao, Q. Yang, Y. Tang, M. Wei, D. G. Evans and X.
Duan, Nano Energy, 2017, 37, 98-107.
K. M. Nam, J. H. Shim, D.-W. Han, H. S. Kwon, Y.-M. Kang,
Y. Li, H. Song, W. S. Seo and J. T. Park, Mater. Chem., 2010,
22, 4446-4454.
14.
15.
16.
17.
18.
19.
20.
21.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was financially supported by the National Key
Research
and
Development
Program
of
China
22.
(2017YFA0403003, 2017YFA0403101), National Natural Science
Foundation of China (21871277, 21603235 and 21403248),
Beijing Municipal Science
&
Technology Commission
23.
24.
25.
26.
27.
28.
(Z191100007219009), and Chinese Academy of Sciences
(QYZDY-SSW-SLH013).
Notes and references
1.
2.
3.
4.
X. Duan, J. Xu, Z. Wei, J. Ma, S. Guo, S. Wang, H. Liu and S.
Dou, Adv. Mater., 2017, 29, 1701784.
A. Vasileff, X. Zhi, C. Xu, L. Ge, Y. Jiao, Y. Zheng and S.-Z.
Qiao, ACS Catal., 2019, 9, 9411-9417.
L. Lin, H. Li, C. Yan, H. Li, R. Si, M. Li, J. Xiao, G. Wang and X.
Bao, Adv. Mater., 2019, 31, 1903470.
H. Yang, Y. w. Hu, J. j. Chen, M. S. Balogun, P. p. Fang, S.
Zhang, J. Chen and Y. Tong, Adv. Energy Mater., 2019, 9,
1901396.
29.
30.
F. D. Wu and Y. Wang, J. Mater. Chem., 2011, 21, 6636.
Jiaxin Zhao, Zhongcai Shao and H. Zhang, Mater. Manuf.
Processes, 2020, 35, 195-201.
F. Wu, S. Zhang, B. Xi, Z. Feng, D. Sun, X. Ma, J. Zhang, J.
Feng and S. Xiong, Adv. Energy Mater., 2018, 8, 1703242.
W. Hu, Q. Wang, S. Wu and Y. Huang, J. Mater. Chem. A,
2016, 4, 16920-16927.
H.-C. Huang, I. Shown, S.-T. Chang, H.-C. Hsu, H.-Y. Du, M.-
C. Kuo, K.-T. Wong, S.-F. Wang, C.-H. Wang, L.-C. Chen and
K.-H. Chen, Adv. Funct. Mater., 2012, 22, 3500-3508.
H. Wang, X. Bo, A. Wang and L. Guo, Electrochem.
Commun., 2013, 36, 75-79.
K. Lv, Y. Fan, Y. Zhu, Y. Yuan, J. Wang, Y. Zhu and Q. Zhang,
J. Mater. Chem. A, 2018, 6, 5025-5031.
5.
D. Gao, I. Sinev, F. Scholten, R. M. Arán-Ais, N. J. Divins, K.
Kvashnina, J. Timoshenko and B. R. Cuenya, Angew. Chem.
Int. Ed., 2019, 18, 17047-17053.
31.
32.
33.
6.
7.
8.
9.
H. Cui, Y. Guo, L. Guo, L. Wang, Z. Zhou and Z. Peng, J.
Mater. Chem. A, 2018, 6, 18782-18793.
H. Pramanik and S. Basu, The Canadian Journal of Chemical
Engineering, 2008, 85, 781-785.
D. Gao, I. Zegkinoglou, N. J. Divins, F. Scholten, I. Sinev, P.
Grosse and B. R. Cuenya, ACS Nano, 2017, 11, 4825-4831.
T. T. H. Hoang, S. Verma, S. Ma, T. T. Fister, J. Timoshenko,
A. I. Frenkel, P. J. A. Kenis and A. A. Gewirth, J. Am. Chem.
Soc., 2018, 140, 5791-5797.
34.
35.
36.
37.
N. Sreekanth, M. A. Nazrulla, T. V. Vineesh, K. Sailaja and K.
L. Phani, Chem. Commun., 2015, 51, 16061-16064.
J. Wu, S. Ma, J. Sun, J. I. Gold, C. Tiwary, B. Kim, L. Zhu, N.
10.
11.
K. Zhao, Y. Liu, X. Quan, S. Chen and H. Yu, ACS Appl. Mater.
Interfaces, 2017, 9, 5302−5311.
Y. C. Li, Z. Wang, T. Yuan, D.-H. Nam, M. Luo, J. Wicks, B.
Chen, J. Li, F. Li, F. P. G. d. Arquer, Y. Wang, C.-T. Dinh, O.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Chopra, I. N. Odeh, R. Vajtai, A. Z. Yu, R. Luo, J. Lou, G. Ding,
View Article Online
P. J. Kenis and P. M. Ajayan, Nat. Commun., 2016, 7, 13869.
H. Wang, Y. Chen, X. Hou, C. Ma and T. Tan, Green Chem.,
2016, 18, 3250-3256.
E. Bertheussen, A. Verdaguer-Casadevall, D. Ravasio, J. H.
Montoya, D. B. Trimarco, C. Roy, S. Meier, J. Wendland, J.
K. Norskov, I. E. Stephens and I. Chorkendorff, Angew.
Chem. Int. Ed., 2016, 55, 1450-1454.
DOI: 10.1039/D0SC01133A
38.
39.
40.
41.
W. M. Brooks, L. N. Moxon, J. Field, M. G. Irving and D. M.
Doddrell, Biochem. Biophys. Res. Commun., 1985, 128,
107-112.
Y. Liu, Y. Zhang, K. Cheng, X. Quan, X. Fan, Y. Su, S. Chen, H.
Zhao, Y. Zhang, H. Yu and M. R. Hoffmann, Angew. Chem.
Int. Ed., 2017, 56, 15607-15611.
42.
43.
Y. Liu, S. Chen, X. Quan and H. Yu, J. Am. Chem. Soc., 2015,
137, 11631-11636.
J. Shen, R. Kortlever, R. Kas, Y. Y. Birdja, O. Diaz-Morales, Y.
Kwon, I. Ledezma-Yanez, K. J. Schouten, G. Mul and M. T.
Koper, Nat. Commun., 2015, 6, 8177.
44.
I. Ledezma-Yanez, E. P. Gallent, M. T. M. Koper and F. Calle-
Vallejo, Catal. Today, 2016, 262, 90-94.
This journal is © The Royal Society of Chemistry 20xx
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Chemical Science
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DOI: 10.1039/D0SC01133A
Table of Contents:
The relay catalytic catalyst is very efficient and selective for CO2 electroreduction to
ethanol through platform.