Rethinking Co(CO3)0.5(OH)·0.11H2O: A new property for highly selective electrochemical reduction of carbon dioxide to methanol in aqueous solution

Article abstract of DOI:10.1039/c7gc03744a

Co(CO₃)_0.5(OH)·0.11H₂O is usually acknowledged and used as a precursor to synthesize other nanomaterials. However, some important properties of Co(CO₃)_0.5(OH)·0.11H₂O have not been discovered yet. Herein, we report an important new property of hollow urchin-like Co(CO₃)_0.5(OH)·0.11H₂O for highly selective electrochemical reduction of carbon dioxide to methanol in NaHCO₃ aqueous solution at -0.98 V versus saturated calomel electrode (SCE) with Faradaic efficiency of up to 97.0% under ambient conditions, which is superior to most of the electrocatalysts reported to date. Finally, this low-cost electrocatalyst shows great potential in CO₂ conversion industry for practical application in the future.

Full text of DOI:10.1039/c7gc03744a

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Huang, Q. Hu,
X. Guo, Q. Zeng and L. Wang, Green Chem., 2018, DOI: 10.1039/C7GC03744A.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Page 1 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03744A
Green Chemistry
COMMUNICATION
Rethinking Co(CO ) (OH)·0.11H O: New property for highly
3
0.5
2
selective electrochemical reduction of carbon dioxide to methanol
in aqueous solution
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Jianzhi Huang, Qiong Hu, Xinrong Guo, Qiang Zeng and Lishi Wang*
www.rsc.org/
Co(CO
3
)
0.5(OH)·0.11H
2
O was usually acknowledged and used as a now, high selectivity, high faradaic efficiency and low
precursor to synthesize other nanomaterials. However, some overpotential of methanol formation by electroreduction of
important properties of Co(CO 0.5(OH)·0.11H O have not been carbon dioxide has rarely been reported, due to six electrons
discovered yet. Herein we report an important new property of participation is difficult to take place in aqueous solution, a
hollow urchin-like Co(CO 0.5(OH)·0.11H O for highly selective more negative potential is required for the formation of
electrochemical reduction of carbon dioxide to methanol in methanol.
NaHCO aqueous solution at –0.98 V versus saturated calomel product selectivity, high faradaic efficiency and low
electrode (SCE) with faradic efficiency up to 97.0% under ambient overpotential is highly desirable. In Rybchenko’s work,
conditions, superior to most of electrocatalysts reported to date. pyridine-catalyzed CO electrochemical reduction to methanol
was explored on platinum electrodes at high CO pressure (5.5
MPa), with faradaic yield of up to 10%, however, it needs
high CO pressure, and also needs noble metal platinum
electrodes, all limit its practical use. Quan and co-workers
synthesized oxide-derived Cu/carbon catalyst for
electroreduction of CO to alcohols, exhibited the faradaic
efficiency of 43.2% and 28.0% for methanol and ethanol at
3
)
2
3
)
2
1
9,20
Therefore, a low-cost electrocatalyst with good
3
2
Finally, this low-cost electrocatalyst shows great potential in CO
conversion industry for practical application in the future.
2
2
2
1
2
Currently, the conversion of carbon dioxide to carbon-
containing fuels and chemical products has become research
frontier and interesting issue, which can effective reduce the
2
1
,2
carbon dioxide content and solve the energy crisis. And the
conversion methods of carbon dioxide to useful products
1
6
−
0.94 V (vs. SCE) respectively, however, the product
3
include photochemical, thermochemical, biochemical and
4
5
selectivity is low. In Zhang’s work, RuO /TiO2 nanotubes
2
6
−8
electrochemical methods.
Because of the renewable and
composite modified Pt electrode obtained 60.5% faradaic
2
2
clean energy of electricity source and high efficiency of
electroreduction, electrochemical reduction of carbon dioxide
has become an outstanding pathway toward zero
efficiency for methanol at a potential of –0.8 V (vs. SCE),
however, this faradaic efficiency was still not enough. In
Bocarsly’s work, p-GaP semiconductor electrode with
a
9
,10
emissions.
a convenient method to produce a series of reduced products,
such as CO, CH , HCOOH, CH OH, C H OH and CH COOH, since
Moreover, electroreduction of carbon dioxide is
homogeneous pyridinium ion catalyst was used for selective
conversion of CO to methanol with light energy, yield faradaic
2
-
2 23
4
3
2
5
3
efficiency near 100% with current density of 0.20 mA cm ,
but it requires light and uses a complicated catalyst system.
As a non-noble metal, cobalt and its oxides show
prominent and promising in CO2 electrocatalytic reduction
electroreduction process is composed of multiple electron-
1,12
1
and proton-transfer steps.
more desirable among these reduced products, due to its high
Alcohols such as methanol are
1
3,14
2
4,25
energy density, easy storage and transportation.
However,
recently, especially in Xie’s works,
the partially oxidized Co
so far, CO2 reduction has been performed in various
electrocatalysts, but the major products for most
4-atom-thick layers attain the highest faradaic efficiency for
formate production of 90.1% at –0.85 V (vs. SCE) in 0.1 M
1
electrocatalysts are still CO and HCOOH. Although CO can
,2
2
4
2
Na SO solution; the oxygen vacancy-rich Co O4 single-unit-
2 4 3
be reduced to CH OH in thermodynamics at the potential of
3
cell layers obtain ca. 85% formate selectivity at –0.87 V (vs.
2
1
5−19
5
0.02 V (versus reversible hydrogen electrode (RHE)).
Up to
SCE) in 0.1
M
KHCO3 aqueous solution.
Till now,
Co(CO3)0.5(OH)·0.11H O was usually acknowledged and used as
2
2
5
a precursor to synthesize other nanomaterials, such as Co O
3
4
2
6
and CoP.
However, some important electrochemical
properties of Co(CO3)0.5(OH)·0.11H O have not been
2
discovered yet, the reason may be due to the high
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1

Green Chemistry
Page 2 of 7
View Article Online
DOI: 10.1039/C7GC03744A
COMMUNICATION
Green Chemistry
3 4
performance for CoP and Co O respectively used as hydrogen Scheme 1 Schematic of the synthesis of hollow urchin-like
2
evolution catalyst and supercapacitor, resulting the neglect Co(CO
6
27
3
)
0.5(OH)·0.11H
2
O
and its application in CO
2
of electrocatalytic activity of Co(CO )0.5(OH)·0.11H O itself, electrochemical reduction.
3
2
which showed promising in electrochemical reduction of CO
2
to methanol. It is worth mentioning that in latest report,
2
8
The obtained electrocatalyst was first characterized by X-
ray diffraction (XRD), as depicted in Fig. 1A, nice resolved
another common Zn
good photocatalytic reduction activity of CO
under light irradiation. In this work, we report a new discovery and 65.4° in XRD pattern can be well indexed to the diffraction
of hollow urchin-like Co(CO 0.5(OH)·0.11H for highly from (020), (001), (111), (220), (121), (300), (221), (040), (301),
selective electrochemical reduction of carbon dioxide to (231), (050), (340), (060), (142), (412), (450) and (023) planes
methanol in aqueous solution, which can realize high of Co(CO 0.5(OH)·0.11H O respectively (JCPDS No. 48-0083),
selectivity that CO directionally electrochemical reduce to which proves the high purity and good crystallinity of
5
(OH)
6
(CO
3
)
2
has been proven that exhibits diffraction peaks at 17.1°, 20.3°, 24.4°, 26.6°, 28.4°, 30.4°,
2
to CO and CH 33.7°, 35.0°, 36.4°, 39.3°, 44.3°, 46.8°, 53.7°, 56.0°, 59.3°, 61.9°
4
3
)
2
O
3
)
2
2
methanol at –0.98 V (vs. SCE) with relative low overpotential Co(CO3)0.5(OH)·0.11H O. Then, X-ray photoelectron spectra
2
of 360 mV in 0.1 M NaHCO aqueous solution under ambient (XPS) measurements were carried out to further investigate
3
conditions, with faradic efficiency of 97.0%, superior to most the composition and determine the surface electronic state of
of electrocatalysts reported to date. Notably, the onset Co(CO3)0.5(OH)·0.11H O. Only Co, C and O elements can be
2
potential for methanol formation is ca. −0.88 V (vs. SCE), observed in survey XPS spectrum in Fig. 1B, which also
corresponding to 260 mV of overpotential, which is a relative confirmed the formation of pure Co(CO3)0.5(OH)·0.11H O.
2
low overpotential reported to date for the reduction of CO to Moreover, the high-resolution Co 2p spectrum exhibits two
2
methanol. Therefore, the Co(CO3)0.5(OH)·0.11H O shows great prominent peaks at 797.2 and 781.4 eV, corresponding to the
2
2
9
potential in sustainable energy industry in the future.
Co 2p1/2 and Co 2p3/2 spin–orbit peaks
of
Schematic of the synthesis of hollow urchin-like Co(CO3)0.5(OH)·0.11H O (Fig. 1C). More importantly, two
2
Co(CO3)0.5(OH)·0.11H O through facile hydrothermal method distinct peaks were clearly displayed in high-resolution O 1s
2
2
5
and its application in CO2 electrochemical reduction was core level spectrum in Fig. 1D, according to previous report,
shown in Scheme 1. 62.5 mg cobalt(III) acetylacetonate was one peak at 529.8 eV was deemed as the lattice oxygen, while
added into a solution of 12.5 mL dimethylformamide, 2.5 mL another peak located at 531.4 eV was ascribed to the oxygen
H2O and 0.625 mL n-butylamine. After vigorous stirring for 15 atoms in the vicinity of an oxygen vacancy. Moreover, in Xie’s
min, the mixture was transferred into
a 25-mL Teflon work, these oxygen vacancies have been well studied and
2
autoclave, heated at 220 °C for 3 h. Finally, the autoclave was proved that can enhance CO2 electroreduction activity.
5
cooled down to room temperature, and the product was Therefore, all the above results proved the successful synthesis
collected by centrifuging the mixture (washed with of high purity and good crystallinity of Co(CO3)0.5(OH)·0.11H O
2
cyclohexane and absolute ethanol), then dried in vacuum. The with distinct oxygen vacancy concentrations.
working electrode was fabricated through loading sample
suspension onto the glassy carbon electrode. Firstly, 5 mg
electrocatalyst was dispersed in 5 mL water and sonicated for
-
1
1
5 min to form a 1 mg mL homogeneous suspension. Then, 5
μL of the well dispersed catalyst suspension was loaded onto
the pre-polished 3 mm glassy carbon electrode. After drying
under infrared lamp, 10 μL of 0.445 wt% Nafion solution (1 mL
5
wt% Nafion solution + 5 mL H O + 5 mL absolute ethanol)
2
was dropped onto the surface of the catalyst layer to form a
thin protective film, and then dried under infrared lamp.
Finally, the well-prepared electrode was used for the CO2
electrochemical reduction.
Fig. 1 (A) XRD pattern, (B) survey XPS spectrum, (C) high
resolution Co 2p XPS spectrum and (D) high resolution O 1s
3 2
XPS spectrum of hollow urchin-like Co(CO )0.5(OH)·0.11H O.
2
| J. Name., 2013, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx

Page 3 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03744A
Green Chemistry
COMMUNICATION
Moreover,
the
obtained
Co(CO
3
)
0.5(OH)·0.11H
2
O
3 2 2
Co(CO )0.5(OH)—0.11H O electrocatalyst was applied for CO
electrocatalyst was further studied by scanning electron electroreduction. As depicted in Fig. 3A, linear sweep voltammetry
test was first respectively performed in CO or N saturated 0.1 M
NaHCO aqueous solution. A significant reduction peak was
observed for hollow urchinꢀlike Co(CO 0.5(OH)—0.11H O electrode
in CO ꢀsaturated 0.1 M NaHCO aqueous solution (pH=6.7), while
no reduction peak appears under N atmosphere, demonstrating
that CO can be electrochemically reduced on hollow urchinꢀlike
Co(CO 0.5(OH)—0.11H O electrode. This obvious reduction peak
under CO atmosphere can reveal the electroreduction of CO
which was also observed for other metal oxide catalysts such as
partially oxidized Co, Co and oxideꢀderived Cu in some
can be reduced to CH OH in
thermodynamics at the potential of 0.02 V (vs. RHE), based on
microscope (SEM) and transmission electron microscopy
TEM). Fig. 2A and 2B depict SEM images at low and high
magnification of the obtained Co(CO 0.5(OH)·0.11H
electrocatalyst with urchin-like morphology in a uniform size of
μm. Interestingly, hollow structure was clearly observed in
urchin-like Co(CO 0.5(OH)·0.11H at low and high
magnification TEM images in Fig. 2C and 2D, a thick shell of
00 nm with many nanowires inside and outside on its surface
2
2
3
(
3
)
2
3
)
2
O
2
3
2
2
2
3
)
2
O
3
)
2
2
2
,
3
construct the urchin, which significant increased the BET
surface area of electrocatalyst and may provide more
catalytically surface-active sites for CO2 reduction. The BET
3
O
4
1
6,24,25
previous reports.
CO
2
3
surface area of hollow urchin-like Co(CO ) (OH)·0.11H O following equation: E(vs. SCE) = E(vs. RHE) − 0.059 × pH −
3
0.5
2
2
15−19
electrocatalyst is 52 m /g. Moreover, the hollow urchin-like 0.241 (V),
2 3
in this system, CO can be reduced to CH OH at
structure of the electrocatalyst was further investigated by the potential of −0.62 V (vs. SCE) in aqueous solution (pH=6.7).
STEM image and its corresponding EDS elemental mapping of Notably, in Fig. 3A, the onset potential for methanol formation is
ca. −0.88 V (vs. SCE), corresponding to an overpotential of 260
mV, which is a relative low overpotential reported to date for the
Co and O elements in Fig. 2E−2H, Co and O elements mainly
exists in the shell of the urchin, which also confirmed the
hollow structure. Therefore, the unique hollow urchin-like
reduction to
of
CO
2
methanol.
Hollow
urchinꢀlike
Co(CO 0.5(OH)—0.11H O electrode generates a biggest current
3
)
2
ꢀ2
structure
and
abundant
oxygen
vacancy
of
density of 0.59 mA cm at −0.98 V (vs. SCE), corresponding to an
overpotential of 360 mV. Moreover, constantꢀpotential electrolysis
Co(CO3)0.5(OH)·0.11H O made it become
2
a
promising
electrocatalyst in CO electroreduction.
2
was applied at −0.98 V (vs. SCE) for 10 h in 0.1 M NaHCO
aqueous solution with CO
qualitative and quantified analyzed by
3
2
flow, and the liquid products were
1
13
H
and
C
nuclear
magnetic resonance (NMR). As shown in Fig. 3B and 3C,
significant peaks at 3.32 ppm and 49.1 ppm were respectively
1
13
observed at HꢀNMR (Fig. 3B) and CꢀNMR spectra (Fig. 3C),
attributed to methanol (DMSO is used as an internal standard at
1
HꢀNMR spectra for quantification of methanol). Moreover, no
other liquid products were observed, the results revealed that
hollow urchinꢀlike Co(CO
excellent selectivity for electroreduction of CO
ambient conditions. CO molecules were directionally converted to
methanol with high selectivity, and attained 97.0% faradic
efficiency (2.0% faradic efficiency of H and 0.7% of CO were
detected by GC). To the best of our knowledge, without injecting
external H to hydrogenation, without solar light irradiation, without
3
)
0.5(OH)—0.11H
2
O electrocatalyst exhibits
2
to methanol under
2
2
2
high pressure or high temperature, such high faradaic efficiency
has never been reported to date. The hollow urchinꢀlike structure
of electrocatalyst minimized the diffusion resistance for mass
transfer, contributing to the efficient transfer of CO
2
and diffusion
16
of the methanol product,
electrocatalyst also enhance CO
Moreover, in order to better confirm the advantage of hollow
urchinꢀlike structure of the electrocatalyst, reference
electrocatalytic material was being compared. We have prepared
solid flowerꢀlike Co(CO 0.5(OH)—0.11H O, its SEM image, TEM
and the oxygen vacancies in
25
2
electroreduction activity.
a
3
)
2
image, XRD pattern, linear sweep voltammogram and faradaic
efficiency were shown in Fig. S1 (Electronic Supplementary
Fig. 2 (A) Low and (B) high magnification SEM images, (C) low
Information).
Co(CO 0.5(OH)—0.11H
observed at linear sweep voltammogram of hollow urchinꢀlike
Co(CO 0.5(OH)—0.11H O. In addition, the methanol faradaic
efficiency of hollow urchinꢀlike Co(CO 0.5(OH)—0.11H O (97.0%)
was much higher than solid flowerꢀlike Co(CO 0.5(OH)—0.11H
49.5%). These results showed that hollow urchinꢀlike structure of
the catalyst can improve the catalytic reduction activity of CO . In
Compared
with
solid
flowerꢀlike
and (D) high magnification TEM images of hollow urchin-like
3
)
2
O, much stronger CO
2
reduction peak was
Co(CO
mapping of (F) Co and (G) O, (H) EDS line mapping profile of
hollow urchin-like Co(CO 0.5(OH)·0.11H O along the direction
marked by the yellow lines in (E).
3 2
)0.5(OH)·0.11H O. (E) STEM image, EDS elemental
3
)
2
3
)
2
3
)
2
3
)
2
O
(
With the unique hollow urchinꢀlike structure and abundant
oxygen vacancy determined above, hollow urchinꢀlike
2
contrast with the formate product obtained from partially oxidized
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3

Green Chemistry
Page 4 of 7
View Article Online
DOI: 10.1039/C7GC03744A
COMMUNICATION
Green Chemistry
2
4
Co 4ꢀatomꢀthick layers catalyst or oxygen vacancyꢀrich Co
3
O
4
catalyst suspension was chosen as the best catalyst loading in
the this work. Notwithstanding the high faradaic efficiency to methanol,
urchinꢀlike both actual current density and methanol production rate are very
2
5
singleꢀunitꢀcell layers
electroreduction product
Co(CO 0.5(OH)—0.11H
we have synthesized Co sphere (Fig. S2) and hollow urchinꢀlike can be observed. The faradic efficiency for producing methanol,
Co (Fig. S3), the electrochemical tests were performed in the carbon monoxide and hydrogen at various electrolysis potentials
same conditions. Compared with the onset potential of the CO
electroreduction on hollow urchinꢀlike Co(CO 0.5(OH)—0.11H
−0.88 (vs. SCE)), the onset potential of the CO
electroreduction on hollow urchinꢀlike Co was observed at of CO. However, with the electrolysis potential shifted to more
more negative value (−1.00 V (vs. SCE)). The results showed the negative value, the faradaic efficiency for methanol production
catalyst
in Xie’s
works,
of
hollow
3
)
2
O electrocatalyst was methanol. Moreover, low. Thus, nearly no variation of the pH during time on reaction
3
O
4
2
was shown in Fig. 3E, the faradic efficiency for methanol
increases initially (−0.88 to −0.98 V (vs. SCE)), reaching the
3
)
2
O
(
V
2
2
maximum of 97.0% at −0.98 V (vs. SCE) with 2.0% of H and 0.7%
3
O
4
only liquid product for Co sphere and hollow urchinꢀlike Co
3
O
4
decreases due to the increase in hydrogen evolution reaction
(HER) and carbon monoxide formation, which compete with
24,25
was formic acid, according with the results of previous reports.
However, the hollow urchinꢀlike Co(CO 0.5(OH)—0.11H
applied for CO electroreduction in this work, the only liquid Moreover, CO
product was methanol. The valence of cobalt atom for these different electrolysis times was also investigated in Fig. 3F, where
materials: Co(0), Co (+8/3), Co(CO 0.5(OH)—0.11H O(+2). We the amount of methanol product increased with the increase of
assumed that the valence of cobalt atom may determine the liquid electrolysis time. Compared with other reported catalysts in Table
product. The valance of 0 and +8/3 may favour the formation of S1, the hollow urchinꢀlike Co(CO 0.5(OH)—0.11H O electrocatalyst
3
)
2
O was first electroreduction of CO
2
to methanol under these conditions.
2
2
reduction electrolysis at −0.98 V (vs. SCE) for
3
O
4
3
)
2
3
)
2
formic acid, but +2 may favour the formation of methanol. As one shows superior faradaic efficiency for methanol production with
of the best metals to obtain methanol, Cu electrode (3 mm in relative low overpotential.
3
0
2
diameter) was also applied for CO electrochemical reduction,
the electrochemical test was performed in the same condition.
The result showed the Cu electrode can obtain the liquid product
of methanol same as hollow urchinꢀlike Co(CO
Fig. S4). The effect of bare glassy carbon electrode substrate
can be neglected, which showed inert for electrocatalytic CO
3 2
)0.5(OH)—0.11H O
(
2
reduction in linear sweep voltammogram, and no signal of
1
methanol can be detected at HꢀNMR spectra (Fig. S5). In
addition, the effect of Nafion film can be neglected, there was not
obvious CO reduction behaviour of bare glassy carbon electrode
2
with Nafion film in its linear sweep voltammogram, and no
methanol product can be detected (Fig. S6). In order to further
verify methanol derived from CO
experiment was performed
Co(CO 0.5(OH)—0.11H O electrocatalyst in N
NaHCO
methanol was detected at HꢀNMR spectra in Fig. S7, confirmed
that methanol was synthesized from CO electroreduction.
The performance of the hollow urchinꢀlike
Co(CO 0.5(OH)—0.11H O electrocatalyst for electrocatalytic CO
2
electroreduction, control
on
hollow
urchinꢀlike
3
)
2
2
ꢀsaturated 0.1 M
3
aqueous solution at −0.98 V (vs. SCE) for 10 h, no
1
2
3
)
2
2
reduction under various potentials was further investigated by
constantꢀpotential electrolysis. Fig. 3D and Fig. S8A respectively
present average production rates for methanol normalized by
catalyst loading and available reaction area under various
electrolysis potentials, which obtained from the data of
2
electroreduction of CO for 10 h. The production rates of methanol
increased with the increasing of applied potential from −0.88 to
−
0.98 V (vs. SCE), and respectively attained maximum production
ꢀ1
ꢀ1
ꢀ2
ꢀ1
rates of 145.0 mmol g
h
and 3.30 ꢁmol cm
h methanol at
−
0.98 V (vs. SCE). Production rates of methanol almost keep
constant with the increasing of electrolysis potential from −0.98 to Fig. 3 (A) Linear sweep voltammograms of hollow urchin-like
1.10 V (vs. SCE). However, the production rate for methanol Co(CO 0.5(OH)·0.11H O in CO -saturated (red line) and N
normalized by charge (Fig. S8B) increased with the increasing of saturated (black line) 0.1 M NaHCO aqueous solution (scan
−
3
)
2
2
2
-
3
−
1
1
13
applied potential from −0.88 to −0.98 V (vs. SCE), and attained rate of 20 mV s ). (B) H-NMR and (C) C-NMR spectra of the
ꢀ
1
ꢀ1
maximum production rate of 0.168 ꢁmol C
V (vs. SCE), then declined with the increasing of electrolysis
potential from −0.98 to −1.10 (vs. SCE). Linear sweep
voltammograms of different catalyst loadings were shown in Fig.
S9, the biggest CO reduction peak was observed at 5 ꢁL of 1 mg
mL hollow urchinꢀlike Co(CO 0.5(OH)—0.11H O. Thus, ꢁL
h methanol at −0.98
electrolyte after CO
2
reduction electrolysis at −0.98 V (vs. SCE)
0.5(OH)·0.11H O.
for 10 h at the hollow urchin-like Co(CO
3
)
2
V
1
DMSO is used as an internal standard at H-NMR spectra for
quantification of methanol. (D) Production rate of methanol
normalized by catalyst loading and (E) Faradaic efficiency
2
ꢀ1
3
)
2
5
4
| J. Name., 2013, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx

Page 5 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03744A
Green Chemistry
COMMUNICATION
obtained from electrochemical reduction of CO
2
for 10 h at
1
different applied electrolysis potentials. (F) H-NMR spectra of
the electrolytes after CO
2
reduction electrolysis at −0.98 V (vs.
SCE) for different electrolysis times.
During 10 h electrolysis at −0.98 V (vs. SCE) in 0.1 M
NaHCO
Co(CO
3
aqueous solution with CO
0.5(OH)—0.11H O electrocatalyst showed negligible decay
2
flow, the hollow urchinꢀlike
3
)
2
−2
in current density (0.60 mA cm ) while maintaining a methanol
faradaic efficiency of 97.0% (Fig. S10A), indicating a stable
electroreduction process catalyzed by the hollow urchinꢀlike
3 2
Co(CO )0.5(OH)—0.11H O electrocatalyst. After 10 h electrolysis
test, the electrocatalyst was characterized by XRD, SEM and TEM.
As shown in Fig. S10B, S10C and S10D, XRD pattern of
electrocatalyst after test was also well indexed to the diffraction
peaks of Co(CO
3 2
)0.5(OH)—0.11H O (JCPDS No. 48ꢀ0083), and the
hollow urchinꢀlike structure of electrocatalyst was also preserved,
3 2
which proves the stability of Co(CO )0.5(OH)—0.11H O
electrocatalyst.
Finally, we further investigated the hollow urchinꢀlike
Co(CO 0.5(OH)—0.11H O electrocatalyst for CO electroreduction
3
)
2
2
in various aqueous solutions, linear sweep voltammetry test and
constantꢀpotential electrolysis were respectively performed in
CO
.1 M NaNO
2
ꢀsaturated 0.1 M NaCl (pH=3.9), 0.1 M Na
2 4
SO (pH=4.3) and
0
3
(pH=4.1) aqueous solutions. In Fig. 4A, a biggest
−2
current density of 0.72 mA cm at −1.08 V (vs. SCE) was
observed in NaCl aqueous solution, and the onset potential for
Fig. 4 Linear sweep voltammograms of hollow urchin-like
CO
density of 0.22 mA cm at −1.15 V (vs. SCE) and onset potential
at −0.88 V (vs. SCE) were observed in Na SO aqueous solution
in Fig. 4B. In Fig. 4C, a biggest current density of 0.69 mA cm at
0.95 V (vs. SCE) and onset potential at −0.80 V (vs. SCE) were
2
electroreduction was –0.87 V (vs. SCE). A maximum current
Co(CO ) (OH)·0.11H O in CO -saturated (A) 0.1 M NaCl, (B)
2
−2
3 0.5
2
0
.1 M Na SO and (C) 0.1 M NaNO aqueous solution (scan rate
2 4 3
2
4
−
1
of 20 mV s ). (D) H-NMR spectra of 0.1 M various electrolytes
1
−2
after CO reduction electrolysis for 10 h. (E) Faradaic efficiency
2
−
1
of methanol obtained from electrochemical reduction of CO2
for 10 h in 0.1 M various electrolytes.
observed in NaNO
3
aqueous solution. Moreover, HꢀNMR spectra
constantꢀpotential electrolysis at
of various electrolytes after CO
2
their reduction peak potentials were shown in Fig. 4D, only
methanol product can be observed without any other liquid
products. And the faradaic efficiency for methanol in NaCl,
Conclusions
Na
2
SO
4
and NaNO
3
aqueous solutions were 94.1%, 84.3%,
can
In summary, an important new property of hollow urchin-like
92.5% respectively (Fig. 4E). These results showed that CO
2
Co(CO
reduction of carbon dioxide to methanol in aqueous solution
was reported in this work. CO directionally electrochemical
reduce to methanol at –0.98 V (vs. SCE) with faradic efficiency
of 97.0% in 0.1 M NaHCO aqueous solution under ambient
3 2
)0.5(OH)·0.11H O for highly selective electrochemical
be selective electrochemical reduced to methanol with high
faradic efficiency in various aqueous solutions at hollow urchinꢀ
like Co(CO )0.5(OH)—0.11H O electrocatalyst, indicating the effects
3 2
from various electrolyte anions to such high selectivity were
negligible. Based on previous experimental studies as well as
density functional theory (DFT) calculations,
electroreduction process of CO to CH OH is composed of
multiple electronꢀ and protonꢀtransfer steps. Possible high
2
3
16,31−33
conditions, with relative low overpotential of 360 mV, superior
to most of electrocatalysts reported to date. Moreover, the
onset potential for methanol formation is ca. −0.88 V (vs. SCE),
the
2
3
selectivity reaction mechanism for electrochemical reduction of corresponding to 260 mV of overpotential, which is a relative
CO
electrocatalyst in aqueous solution was proposed in Fig. S11. The methanol.
structural formula of Co(CO 0.5(OH)—0.11H
S11, the reaction centre site was Co atom. CO
adsorbed on the catalyst surface, and then was activated by an
2
to CH
3
OH on hollow urchinꢀlike Co(CO
3
)
0.5(OH)—0.11H
2
O
low overpotential reported to date for the reduction of CO
2
to
The hollow urchin-like structure
2
O was shown in Fig. Co(CO3)0.5(OH)·0.11H O facilitates the transfer and reduction
2
of
3
)
2
was first
of CO
and diffusion of the methanol product, the oxygen
electroreduction
2
vacancies in electrocatalyst also enhance CO
2
−
electron to form the intermediate CO
CꢀCo bond. Subsequently, the obtained CO
proton−electron pair and forms the *COOH intermediate. The
2
* anion radical, linked by a
activity. Finally, this low-cost electrocatalyst was successfully
applied in various aqueous solutions for electroreduction of
−
2
*
reacts with a
2
CO to methanol with high faradic efficiency, which will great
*
*
CH
COOH further reacts with another proton−electron pair to form
CO. Then, the *CO was further reduced to CH OH. Finally, the
OH product was desorbed from the catalyst surface.
benefit the development of sustainable energy economy.
3
3
Conflicts of interest
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5

Green Chemistry
Page 6 of 7
View Article Online
DOI: 10.1039/C7GC03744A
COMMUNICATION
Green Chemistry
There are no conflicts to declare.
26 H. Yang, Y. Zhang, F. Hu and Q. Wang, Nano Lett., 2015, 15
616–7620.
,
7
7 Y. Wang, A. Pan, Q. Zhu, Z. Nie, Y. Zhang, Y. Tang, S. Liang
and G. Cao, J. Power Sources, 2014, 272, 107–112.
2
2
2
3
3
3
3
Acknowledgements
8 C. Xin, M. Hu, K. Wang and X. Wang, Langmuir, 2017, 33
667–6676.
9 Y. F. Zhao, B. Sun, X. D. Huang, H. Liu ; D. W. Su, K. N. Sun and
G. X. Wang, J. Mater. Chem. A, 2015, , 5402–5408.
0 C. Genovese, C. Ampelli, S. Perathoner and G. Centi, Green
Chem., 2017, 19, 2406–2415.
1 X. Nie, M. R. Esopi, M. J. Janik and A. Asthagiri, Angew.
Chem. Int. Ed., 2013, 52, 2459–2462.
2 L. Zhang, Z. J. Zhao and J. L. Gong, Angew. Chem. Int. Ed.,
,
This work was financially supported by the National Natural
Science Foundation of China (Grant Nos. 21475046, 21427809,
6
21645004).
3
Notes and references
1
2
3
J. Qiao, Y. Liu, F. Hong and J. Zhang, Chem. Soc. Rev., 2014,
, 631–675.
A. J. Martín, G. O. Larrazábal and J. Pérez-Ramírez, Green
Chem., 2015, 17, 5114–5130.
X. Jiao, Z. Chen, X. Li, Y. Sun, S. Gao, W. Yan, C. Wang, Q.
43
2
017, 56, 11326–11353.
3 K. J. P. Schouten, Y. Kwon, C. J. M. van der Ham, Z. Qin and
M. T. M. Koper, Chem. Sci., 2011, , 1902–1909.
2
Zhang, Y. Lin, Y. Luo and Y. Xie, J. Am. Chem. Soc., 2017, 139
586–7594.
S. Kattel, P. Liu and J. G. Chen, J. Am. Chem. Soc., 2017, 139
739–9754.
C. Liu, B. C. Colón, Z. Marika, P. A. Silver and D. G. Nocera,
Science, 2016, 352, 1210–1213.
S. Zhang, P. Kang and T. J. Meyer, J. Am. Chem. Soc., 2014,
,
7
4
5
6
7
8
9
1
,
9
1
36, 1734–1737.
Y. Liu, S. Chen, X. Quan and H. Yu, J. Am. Chem. Soc., 2015,
37, 11631–11636.
1
Y. Song, W. Chen, C. Zhao, S. Li, W. Wei and Y. Sun, Angew.
Chem. Int. Ed., 2017, 56, 10840–10844.
G. Centi, E. A. Quadrelli and S. Perathoner, Energy Environ.
Sci., 2013, 6, 1711–1731.
0 D. R. Kauffman, J. Thakkar, R. Siva, C. Matranga, P. R.
Ohodnicki, C. Zeng and R. Jin, ACS Appl. Mater. Interfaces,
2
015, 7, 15626–15632.
1 R. J. Lim, M. Xie, M. A. Sk, J. M. Lee, A. Fisher, X. Wang and K.
H. Lim, Catal. Today, 2014, 233, 169–180.
2 E. E. Benson, C. P. Kubiak, A. J. Sathrum and J. M. Smieja,
Chem. Soc. Rev., 2009, 38, 89–99.
1
1
1
1
1
3 I. Ganesh, Renewable Sustainable Energy Rev., 2014, 31
21–257.
4 X. Jiang, N. Koizumi, X. Guo and C. Song, Appl. Catal., B,
015, 170–171, 173–185.
,
2
2
5 O. A. Baturina, Q. Lu, M. A. Padilla, L. Xin, W. Li, A. Serov, K.
Artyushkova, P. Atanassov, F. Xu, A. Epshteyn, T. Brintlinger,
M. Schuette and G. E. Collins, ACS Catal., 2014,
695.
6 K. Zhao, Y. Liu, X. Quan, S. Chen and H. Yu, ACS Appl. Mater.
Interfaces, 2017, , 5302–5311.
7 K. P. Kuhl, E. R. Cave, D. N. Abram and T. F. Jaramillo, Energy
Environ. Sci., 2012, , 7050–7059.
8 M. Le, M. Ren, Z. Zhang, P. T. Sprunger, R. L. Kurtz and J. C.
Flake, J. Electrochem. Soc., 2011, 158, E45–E49.
9 J. H. Q. Lee, S. J. L. Lauw and R. D. Webster, Electrochem.
Commun., 2016, 64, 69–73.
0 Y. X. Pan, Y. You, S. Xin, Y. Li, G. Fu, Z. Cui, Y. L. Men, F. F. Cao,
4, 3682–
3
1
1
1
1
2
9
5
S. H. Yu and J. B. Goodenough, J. Am. Chem. Soc., 2017, 139
123–4129.
1 S. I. Rybchenko, D. Touhami, J. D. Wadhawan and S. K.
Haywood, ChemSusChem, 2016, , 1660–1669.
2 J. Qu, X. Zhang, Y. Wang and C. Xie, Electrochim. Acta, 2005,
, 3576–3580.
3 E. E. Barton, D. M. Rampulla and A. B. Bocarsly, J. Am. Chem.
Soc., 2008, 130, 6342–6344.
4 S. Gao, Y. Lin, X. Jiao, Y. Sun, Q. Luo, W. Zhang, D. Li, J. Yang
and Y. Xie, Nature, 2016, 529, 68–71.
5 S. Gao, Z. Sun, W. Liu, X. Jiao, X. Zu, Q. Hu, Y. Sun, T. Yao, W.
,
4
2
2
2
2
2
9
5
0
Zhang, S. Wei and Y. Xie, Nat. Commun., 2017,
4511.
8, 14503–
1
6
| J. Name., 2013, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx

Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03744A
1
69x128mm (96 x 96 DPI)