Controlled synthesis of a Bi2O3-CuO catalyst for selective electrochemical reduction of CO2 to formate

Article abstract of DOI:10.1039/c8nj05205k

The electro-reduction of CO₂ to produce energy sources has been considered as a visionary pathway with the help of renewable electricity, which can achieve carbon neutrality and mitigate global warming. Nevertheless, developing a high selectivity, good activity and superior stability catalyst is a big challenge. Here, Bi₂O₃-CuO(x) bimetallic oxide catalysts were synthesized by a facile coordination-precipitation method with concisely controlled atomic ratios (Cu/Bi). They exhibit a remarkable performance for sufficient reduction of CO₂ to formate, achieving a maximum faradaic efficiency of 89.3% at a potential of ?1.4 V vs. SCE. The catalysts are shown to be robust during 10 h of uninterrupted electrolysis. The notable catalytic activity suggests that controlling the Cu/Bi molar ratio is a key factor in developing special micro-structure Bi₂O₃-CuO(x) catalysts for electrochemical reduction of CO₂ to formate in aqueous systems.

Full text of DOI:10.1039/c8nj05205k

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Du, C. Dai, Y.
Qiu, Y. He, C. Tao, Q. Zhang and R. L. Liu, New J. Chem., 2019, DOI: 10.1039/C8NJ05205K.
This is an Accepted Manuscript, which has been through the
Volume 40 Number
1 January 2016 Pages 1–846
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
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 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Please do not adjust margins
Page 1 of 8
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C8NJ05205K
Journal Name
5
6
7
8
9
ARTICLE
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Controlled synthesis of Bi2O3-CuO catalyst for selective
electrochemical reduction of CO2 to formate
formReceived 00th January 20xx,
Accepted 00th January 20xx
Chaoneng Daia, Yue Qiua,b, Yu Hea, Qiang Zhanga, Renlong Liua, Jun Dua*, Changyuan
Taoa*
DOI: 10.1039/x0xx00000x
www.rsc.org/
a. College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331. b.
Chongqing Academy of Metrology and Quality Inspection, Chongqing, 401123. P.R.China
The electro-reduction of CO2 to produce energy sources has been considered as a visionary pathway with the help of
renewable electricity, which can achieve carbon neutral and mitigate global warming. Nevertheless, developing a
high selectivity, good activity and superior stability catalyst is a big challenge to achieve this goal. Here, the Bi2O3-
CuO(x) bimetallic oxide catalysts were synthesized by facile coordination-precipitation method with concisely
controlled atomic ratios (Cu/Bi). It exhibits a remarkable performance for sufficient reduction of CO2 to formate,
achieving a maximum faradaic efficiency of 89.3% at the potential of -1.4 V vs.SCE. The catalyst is shown to be robust
during 10 h of uninterrupted electrolysis. The notable catalytic activity suggests that controlling the molar ratio of
Cu/Bi is a key in developing a special micro-structure Bi2O3-CuO(x) catalysts for electrochemical reduction of CO2 to
formate
in
aqueous
system.
9. Direct formic acid fuel cells 10, and more currently, direct formate
fuel cells11, have been investigated in the literature owing to the
demonstrated significant benefits for methanol fuel cells including
lower crossover and higher open circuit voltage. Currently, many
researchers have been devoted to the ERC to formate, the most
popular used electrocatalysts are Sn12, 13, Hg14, Pb15 and Bi16-18 etc,
which featured by positive free energy of hydrogen adsorption and
low affinities for CO adsorption. The regulated catalyst
morphologies were proved to be an effective way for enhancing
catalytic activity. In our previous research, di-halogen assembled
bismuth oxyhalide (BiOX0.5Y0.5, X, Y=Cl, Br, I) catalyst, which
possessed nanoflower structure, and HCl etched Bi2O3 nanorods
catalyst achieved considerable electrocatalytic activities and
durabilities, but the applied overpotential was proved to be slightly
1 Introduction
The overgrowth of CO2 in the atmosphere is considered to be a
major effect contributor to climate change, namely, global
warming1. In order to alleviate the greenhouse effect and achieve
carbon-neutral, the CO2 conversion and utilization have been
attracting significant attention and many solutions have been
3
applied to tackle this problem (eg, Photocatalysis2,
,
Electrocatalysis4-6, and Biocatalysis7, 8). While, electroreduction of
CO2 (ERC) appears to be promising for CO2 conversion which is
ascribed to mild operating condition, low-cost proton source from
H2O, simple device and easy to scale-up for commercial production
in the future.
Formic acid, or formate salts may be a considerable hydrogen
storage medium and its storage capacity was 580 times higher than
H2 in the same volume of gas at ambient temperature and pressure
higher 19, 20
.
To improve the Bi-based catalyst performance, Sun et al21
designed the bimetallic Bi-Mo chalcogenide (BMC) ERC to methanol
with 1-butyl-3-methylimidazolium tetrafluoroborate in MeCN as the
* College of Chemistry and Chemical Engineering, Chongqing University, 55
South road, University City, Chongqing 401331, P.R.China.
E-mail: dujune@cqu.edu.cn (J.Du), taocy@cqu.edu.cn (CY. Tao)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 2 of 8
ARTICLE
Journal Name
1
2
3
4
5
6
7
8
9
electrolyte, and the Faradaic efficiency (FE) and current density (CD) mixture was transferred to an evaporating dish in a VwieawteArrticbleaOthnlinaet
DOI: 10.1039/C8NJ05205K
60 ℃ to form aerogel, followed by the calcination in a muffle
reached 71.2% and 12.1 mA.cm-2 respectively, which was superior
22
to single Bi-based catalyst. Lv et al
conducted the nanoscale
furnace at 500 ℃ for 5 h. The as-prepared catalysts were named
bismuth particles on copper foil with electrodeposition strategy to
obtain electrocatalyst for ERC to formate, approaching low
potential (0.69 V) and a high FE (91.3%) .
Bi2O3-CuO (x) for short, x represented the Cu/Bi molar ratio, which
ranges from 0 to 1.25.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.2 Catalyst Characterization
It has been reported that the Cu or CuO-based catalyst
showed good performance for ERC at relatively lower overpotential,
while the stability and selectivity are poor 23-25. So it is an efficient
The morphologies and Energy-dispersive X-ray spectroscopy (EDS)
of Bi2O3-CuO (x) catalysts were described by a scanning electron
microscope (SEM, JEOL JSM-7800F). EDS was analyzed on a region
of 40 × 40μm2 of each sample. X-ray diffraction (XRD) patterns were
collected on a diffractometer (Rigaku D/max-3C) by Cu Kα radiation
source (λ = 0.154 nm) under 40 kV, 30 mA and scanning rate of 10°
min−1. AFM (Digital Instruments MFP-3D-BIO, USA) topographical
measurement was performed in contact tapping mode with a
NanoScope IIIa controller and equipped with a J-type scanner (max
scan size of 90 90 15 um). Field Emission Transmission electron
microscopy (FE TEM, talos, F200S G2) was equipped with a thermo
fisher system, and the accelerating voltage was 200 KV. The X-ray
photoelectron spectroscopy (XPS) was performed on a Kratos AXIS
Ultra DLD (Thermo ESCAlab250) spectrometer under ultra-high
vacuum, with monochromatic 1486.6 eV Al Kα X-ray source at
power of 450 W (30 mA, 15 kV). The binding energies in each XPS
spectrum was calibrated on the basis of C 1s peak (284.8 eV).
way to introduce CuO to another high stability and selectivity metal
26,
oxides. Fan et al
27found that SnO2-CuO composite catalysts
showed obvious distinct ERC activity by tuning the molar ratios of
Sn/Cu. When the molar ratios of SnO2 to CuO increased to 1.0, the
activity of the composite SnO2(50%)-CuO(50%) catalyst reaches a
maximum with the onset potential of -0.75 V vs. SHE, and maximum
CD of -24 mA cm-2 at -1.25 V vs. SHE. In addition, compared with
CuO or SnO2 alone, the stability of SnO2 (50%)-CuO (50%) composite
catalyst was greatly improved. However, the prepared catalyst still
needed higher overpotential for ERC and it remained unclear why
the catalytic properties of bimetallic oxides are better than those of
single metal oxide in this paper.
Here, we report the preparation of Bi2O3-CuO(x) bimetallic
oxides via
a coordination-precipitation strategy. The uniform
distribution of Bi2O3-CuO(x) was synthesized by concisely controlled
the molar ratio of Cu /Bi. The electrochemical measurements were
used to evaluate the electrocatalytic activity and selectivity for
Bi2O3-CuO(x) catalysts for ERC to formate reaction. The effects of
Cu/Bi ratios, as well as the catalyst loading amount (LA) on
electrode were investigated correlating with the catalytic
performances. Based on the analysis, a plausible reason for
composition dependent activity of ERC at the Bi2O3-CuO(x)
bimetallic oxide catalyst was proposed and a great potential for ERC
of commercial in the future was provided.
2.3 Electrochemical reduction of CO2
After dispersing catalyst powder into isopropanol solvent of 5 wt%
Nafion solution, the working electrode was fabricated by drop-
casting 5 ul catalyst ink onto glassy carbon electrode of 0.07 cm2
geometric areas, which was denoted as Bi2O3-CuO(x)/GCE.
Saturated calomel electrode (SCE) and platinum sheet were used as
the reference electrode and counter electrode, respectively.
Electrochemical measurements were executed on a CHI-660E
electrochemistry workstation.
A cation exchange membrane
2 Experimental Section
2.1 Catalyst synthesis
(Nafion 212), In order to prevent cathode products from being
oxidized, was used in homemade airtight two-compartment
electrochemical cell. The electroreduction experiments were
conducted in 0.5 M KHCO3 solution with saturated CO2 (298 K, pH
7.6). The Bi2O3-CuO/GCE was firstly cycled between 0 to -1.8 V vs.
SCE , with a scan rate of 100 mV s-1, then the electroreduction
Bi2O3-CuO catalyst with designed ratios was prepared as follows:
calculated molar ratio of Bi(NO3)3•5H2O and Cu(NO3)2•3H2O were
dissolved in 100 ml 0.1 M EDTA solution under stirring, then the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 8
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
1
2
3
4
behavior was recorded by Liner sweep voltammetric (LSV) from -0.8 While, when the molar ratio of Cu/Bi continues increasing to 1.0,
View Article Online
DOI: 10.1039/C8NJ05205K
to -1.8 V vs. SCE (100 mVs-1). The faradaic efficiency and the catalyst the macroporous structure disappears, and finally all of the pore
5
6
7
8
stability were evaluated via chronoamperometry method in CO2 structure disappear when its ratio reaches to 1.25. Based on the
saturated 0.5 M KHCO3 solution at room temperature. The liquid analyze of TEM images (Fig S 2), Bi2O3-CuO (0.75) catalyst shows
products were used presaturation method of water suppression by more lattice interlaced stripes, this indicates the strong interaction
1H nuclear magnetic resonance spectroscopy (NMR, Agilent 600 for Bi2O3-CuO (0.75) catalyst. From the results mentioned above, it
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
DD2).
was found that increasing the molar ratio of Cu/Bi in an appropriate
range can significantly increase the size of the pore structure and
promote the uniform distribution of pore structure on the surface.
However, excessive Cu will make the structure of the catalyst
surface become dense, and the pore structure will disappear.
3 Results and discussion
3.1 Catalyst Characterizations
The XRD patterns of Bi2O3-CuO(x) revealed the monoclinic structure
of Bi2O3 (JCPDF No. 41-1449) at 27.4°, 28° and 33.2° , corresponding
to (120), (012) and (200) planes (Fig.1) . As CuO is introduced, the
distinct diffraction peaks reflecting the (002) and (111) planes of
monoclinic CuO appear at 35.4 and 38.7°, respectively (JCPDF No.
In order to fairly analysis the surface compositions of the
Bi2O3-CuO(x) catalysts, the EDS technology (Fig. 2) and XPS
measurement (Fig.3) were used. The results showed that the
primary Bi, and minority of C, O and Si were observed on Bi2O3
catalyst (Fig. 2a). While, it confirmed the presence of Cu on Bi2O3-
CuO(x) catalysts (Fig. 2b-f), and the element ratios of Cu/Bi (0.26,
0.46, 0.78, 0.94, and 1.20) were confirmed by EDS, which were
consistent with the proportion of precursors added. This indicated
that the molar ratio of Cu/Bi can be concisely controlled too. From
XPS results, Bi2O3-CuO(x) catalysts displayed two distinct binding
energy peaks at 158.7 and 164.2 eV, which were corresponding to
Bi3+4f7/2 and Bi3+4f5/2, respectively17 . Moreover, the influence of
Cu/Bi molar ratios on the chemical shifts of Bi4f and Cu2p was
investigated. It was found that as the molar ratio of Cu to Bi
increases from 0.25 to 1.25, the binding energy of Bi 4f5/2 and Bi
4f7/2 shifts to the lower field direction (Fig. 3a), while the binding
energy of Cu 2p1/2 and Cu 2p3/2 shifts to the high field direction
(Fig. 3b). This may be due to chemical shift of the band peak in XPS
spectra, which is closely related to the charge, electronegativity,
and oxidation state of the atom28. Therefore, when Bi is combined
with Cu of lower valence (+2) and electronegativity (Cu：1.36，Bi
： 2.02), it would induce electron density transfer from Cu to Bi
orbital, which resulted in Bi outer-layer electron density increase,
thereby reduced the shielding effect of the inner layer of electrons,
and eventually led to lower inner binding energy. The induced
effect of the Bi will aggravate the electronic delocalization of Cu,
resulting in an increase in the binding energy of Cu. Furthermore, it
is noteworthy that the Bi 4f peaks were slightly shifted toward a
lower binding energy for CuO-Bi2O3(x) samples, which could be
related to the changes of Bi electronic structures. Because of the
48-1548).
A new diffraction peak of Bi2O3-CuO(x) composite
catalysts appears at 20.9°, which belongs to the (200) crystal plane
of the tetragonal CuBi2O4.
Fig 1. The XRD spectra and SEM images of Bi2O3-CuO(x) catalysts (x= 0 (a), 0.25
(b), 0.5 (c), 0.75 (d), 1. 0 (e), 1.25 (f)).
The microscopic morphology of the Bi2O3 shows a block
structure with protruding staggered stripes on surface (Fig. 1a).
When CuO is introduced into Bi2O3, the stripe structure is gradually
thinning to disappear and the porous structure is formed on
surface. As the Cu/Bi molar ratio increases from 0.25 to 0.75, the
average size of the macroporous structure increases from 0.4 μm to
1.5 μm, accompanying an amount of small pores exists around the
large pore (Fig. 1b-c). Moreover, the structure of surface is more
evenly distributed, and whether it is before or after ERC, the surface
with Cu/Bi (0.75) is flattest and the particle size is the smallest
compared with other molar ratios of Cu/Bi (Fig. S1, Table. S1).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 4 of 8
ARTICLE
Journal Name
1
2
3
4
difference in electron valence states of Bi and Cu, a free electron and most of them are approximately 4.37 nm (Fig. S3 a). While, with
View Article Online
DOI: 10.1039/C8NJ05205K
will be ejected into the electron clouds of CuO when a Bi atom is the doping amount of CuO increase, the memorable pore diameter
5
6
7
8
interstitially incorporated into the CuO lattice sites, resulting in CuO gradually increases, and the number of pores in the range from 20
crystal overall charge surplus. In order to maintain the charge to 100 nm are increase too. When the molar ratio of Cu/Bi increases
stability of the crystal, Bi will absorb the outer electrons of the to 0.75, the most probable pore diameter increases to 9.45 nm. As
surrounding Cu atoms, which will increase the density of the outer continue increasing the amount of CuO, the most probable pore
electron cloud of the Bi, and reduce the shielding effect on the diameter starts to gradually decrease, and considerable pores also
inner electrons, causing decrease in the self-electron binding energy decreases significantly. The results mentioned above indicate that
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
and shift to low field. Simultaneously, as Cu is induced by Bi, the
density of outer electron cloud decreases, while the electron
delocalization exhibited more intensity, and eventually caused the
Cu electron binding energy shifts to a high field.
SBET
Pore volume
(cm3 g-1) b
0.0256
Pore diameter
(nm) c
4.37
Samples
(m2 g-1)a
1.7820
Bi2O3
Bi
Bi2O3-CuO(0.25) 4.3356
Bi2O3-CuO(0.5) 8.0349
Bi2O3-CuO(0.75) 24.5681
Bi2O3-CuO(1.0) 15.3368
Bi2O3-CuO(1.25) 8.8587
0.0307
5.57
Bi
(a)
(b)
Cu/Bi=0.11
0.0535
7.71
O
C
Si
O
Cu
Si
C
Bi
Bi
0.1162
9.45
Bi
Bi
(d)
(c)
Cu/Bi=0.28
Cu/Bi=0.33
0.0821
3.87
O
Cu
OCu
C
C
Si
Si
Bi
Bi
Cu
Cu
0.0714
3.29
Bi
Bi
(f)
(e)
Cu/Bi=0.43
Cu/Bi=0.67
conductive mesoporous were formed in Bi2O3-CuO(x) catalysts,
which can provide suitable activity sites with absorption of reactant
molecules and further promote catalytic reactions.
Cu
O
Cu
O
C
Si
Si
Bi
Bi
C
Cu
Cu
2
4
6
8
0
2
4
6
8
10
0
Binding energy/Kev
Table 1 BET surface areas and pore volumes of Bi2O3-CuO(x) catalysts (x=0,
0.25, 0.5, 0.75, 1.0, 1.25)
Fig 2. EDS spectra of Bi2O3-CuO(x) catalysts (x=0, 0.25, 0.5, 0.75, 1.0, 1.25) :(
a)=0, (b)=0.25, (c)=0.5, (d)=0.75, (e)=1.0, (f)=1.25.
a BET Specific surface area
b BJH desorption pore volume
c The most pore diameter
(b)
Cu2p3/2
(a)
Cu2p1/2
satellite
Bi4f7/2
Bi4f5/2
satellite
(f)
(e)
(d)
(c)
(b)
(f)
(e)
(d)
(c)
The texture structural parameters of Bi2O3-CuO(x) catalysts
were indicated (table 1). The specific surface area and pore volume
are poor for Bi2O3. While, compared with Bi2O3 to Bi2O3-CuO(x), the
specific surface area remarkably increases from 1.7820 to 24.5681
m2 g-1 by modified with CuO. Which indicates that the composite of
Bi2O3-CuO (0.75) bimetal-oxides has richer surface pore structure
and higher specific surface area. In general, as the specific surface
area increases, more active sites can be provided in catalytic
reaction, and can obtain higher catalytic activity. Furthermore,
when obtained greater pore volume, the pore structure of the
catalyst material may be richer, which is more favourable for the
(b)
(a)
(a)
965 960 955 950 945 940 935 930 925
Binding Energy / eV
168 166 164 162 160 158 156
Binding Energy / eV
Fig 3. XPS spectra of Bi2O3-CuO(x) catalysts (x=0, 0.25, 0.5, 0.75, 1.0, 1.25): (a) Bi
4f, (b) Cu 2p.
The Bi2O3-CuO(x) catalysts specific surface areas and porosities
are measured by specific surface area instrument. The N2
adsorption–desorption isotherms (Fig. S3) of Bi2O3-CuO(x) catalysts
are attributing to the type IV nitrogen isotherm with a H3-type
hysteresis loop in the middle and high specific pressure ranges 29, 30
.
The pore sizes of Bi2O3 catalyst are mostly in the range of 2–20 nm,
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 8
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
1
2
3
4
5
6
7
8
9
adsorption and desorption of substances, and facilitates the
View Article Online
DOI: 10.1039/C8NJ05205K
catalytic reaction execution 31. Therefore, combined with LSV test
results(Fig 4), it is obviously concluded that the discrepancy of
catalytic activity of Bi2O3-CuO(x) is consistent with the change of
specific surface area and pore volume, and indicates that the
performance of Bi2O3-CuO(x) ERC depends on the internal structure
and specific surface area of the catalyst.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3.2 Electrochemical reduction of CO2
The electrochemical performance of ERC on Bi2O3-CuO(x)
catalysts was performed on 0.5 M KHCO3 aqueous solution. The
precursor Bi2O3-CuO(x) was reduced electrochemically before ERC
experiment. The LSV test was performed on different molar ratio of
Bi2O3-CuO(x) (Fig. 4). It was found that with the increase of Cu/Bi in
Fig 4. LSV curves and electrochemical active surface area of Bi2O3-CuO(x) catalysts
(x=0, 0.25, 0.5, 0.75, 1.0, 1.25) with different molar ratio in 0.5 M KHCO3 solution.
The energy barrier for charge transfer on the electrode
surface was measured by electrochemical impedance spectroscopy
(EIS). The resistance value over Bi2O3 catalyst is 396 ohms (Fig. 5),
which is obviously higher than those of other Bi2O3-CuO(x)
composite catalysts, meaning that the doping of CuO improves the
electron transfer rate on the surface of the electrode32. In addition,
as the amount of CuO increasing, the impedance values decrease
gradually. When the molar ratio of Cu/Bi is 0.75, the impedance
value is the smallest, which is 98 ohms. But the resistance values
starts to increase when the amount of Cu/Bi ratio excesses 0.75,
indicating that excessive CuO is unfavourable for electron transport,
and consequently suppresses the ERC reaction. Namely, the
reaction rate of Bi2O3-CuO (0.75) electrode surface can be
enhanced, which is superior to other molar ratios of Bi2O3-CuO(x).
molar ratio from
0 to 1.25, the Bi2O3-CuO(x) catalysts
electrocatalytic reduction of CO2 catalytic performance exhibits
volcanic relationships. Bi2O3 catalyst has inferior electrocatalytic
performance of ERC in this catalytic system, which may be related
to the lower EAS of the Bi2O3 catalyst (1.93 cm-2 mg-1) (Fig. S4).
When CuO was doped into the Bi2O3 catalyst, the onset potential of
the LSV curve showed a significant positive shift compared with
Bi2O3, and the current density had a significant increase too,
indicating that the combination of Bi2O3 and CuO effectively
improved the performance of ERC. With the molar ratio of Cu/Bi
arrives at 0.75, the current density and catalytic performance of
Bi2O3-CuO (0.75) catalyst reach to the top of volcanic curves, which
is 4.7 times higher than that for Bi2O3, and the onset potential
positively shifts 160 mV. From the trend of the EAS of each catalyst
(Table S2), the ratios of Cu/Bi in the Bi2O3-CuO(x) composite
catalysts have a great effect on increasing the active area of the
electrode surface. A suitable Cu/Bi molar ratio is more favourable to
promote electrocatalytic reactions for increasing the surface area
and active sites of the catalyst.
400
300
200
Bi2O3
100
Bi2O3 -CuO(0.25)
Bi2O3 -CuO(0.5)
Bi2O3 -CuO(0.75)
Bi2O3 -CuO(1.0)
0
Bi2O3 -CuO(1.25)
0
200
400
600
800 1000 1200
Z' / ohm
Fig 5. Electrochemical impedance spectra of Bi2O3-CuO(x) catalysts (x=0, 0.25, 0.5,
0.75, 1.0, 1.25) in 0.5 M KHCO3 solution.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 6 of 8
ARTICLE
Journal Name
1
2
3
4
Subsequently, to explore the effects of catalyst LA to ERC Bi2O3-CuO(x) catalysts with CO2 saturated 0.5 M KHCO3 solution,
View Article Online
DOI: 10.1039/C8NJ05205K
performance, the catalyst of Bi2O3-CuO (0.75) was conducted at and the relationships of Bi2O3-CuO(x) catalysts and electrolysis
5
6
7
8
different LA. It was found that the LA of the Bi2O3-CuO (0.75) has potential were investigated by quantified liquid products (Fig.7). For
made a great effect on the onset potential and current density of Bi2O3 electrode, the formation of formate was detected in -1.35 V,
the LSV curve (Fig. 6). As the catalyst LA is lower than 0.25 mg cm-2, and the formate efficiency achieved 3.3%. As applied potential
causing the catalytic performance and current density decrease, the increased, the Faradaic efficiency of formate increased gradually,
current density, onset potential and electrochemical active surface reaching 42.2% at -1.5 V. For Bi2O3-CuO(x) catalyst, the onset
areas(EAS)13, 33 are 6.0 mA cm-2 at -1.6 V vs. SCE (the following same potential for formate formation shifted to lower as the Cu/Bi molar
as it), -1.38 V and 2.12 cm-2 mg-1 (Table. S3), respectively. With the ratios increased, accompanied with faradaic efficiency for formate
LA increased from 0.25 mg cm-2 to 1.0 mg cm-2, the current density increased significantly. For example, as Bi/Cu ratio increased from
of ERC by Bi2O3-CuO (0.75) increases obviously, and the onset 0.25 to 0.75, the formate was detected from -1.35 V (FE = 5.8%) to -
potential gradually shifts to positive. When it arrives at 1.0 mg cm-2, 1.25 V, indicating 100 mV decrease of overpotential, and the Bi2O3-
The current density reaches to -16.1 mA cm-2 at -1.6 V and the CuO (0.75) catalyst achieved the highest faradic efficiency of 89.3%
onset potential decreases to -1.17 V. Compared with the LA of 0.25 at -1.4 V. While, LSV and EIS results manifested, the faradic
mg cm-2, the onset potential shifts to positively 210 mV and EAS efficiency of ERC to formate was composited dependent of Bi2O3-
increases 2.6 times (5.61 cm-2 mg-1) (Fig. S5). While, as Bi2O3-CuO CuO(x) and which was a crucial factor when considered the
(0.75) LA continues increasing to 1.25 mg cm-2, the electrocatalytic performance of catalyst too. The results may be due to when the Cu
activity slightly decreases, and the EAS significantly declines, which content is too high, causing a higher density of adsorbed CO*,
was attributed to the catalyst agglomeration and consequently the leading lower density of adsorbed protons. Therefore, the
catalytic active sites reducing, these would be not conducive to gas performance of the Bi2O3-CuO(x) at higher Cu concentration was
adsorption on the catalyst surface. Therefore, it is concluded that limited may be due to the low density of adsorbed protons at the
catalytic activity for ERC highly relies on LA and the optimum LA of Bi2O3-CuO(x) catalysts surface34. In addition, the suitable Cu/Bi
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Bi2O3-CuO(x) composite catalyst is 1.0 mg cm-2.
molar ratio can improve the morphology and inner structure of the
catalyst, and then the pore structure and specific surface area were
enriching and increasing, respectively. (Fig 4d).
100
Bi2O3
Bi2O3 -CuO(0.25)
Bi2O3 -CuO(0.5)
80
Bi2O3 -CuO(0.75)
Bi2O3 -CuO(1.0)
Bi2O3 -CuO(1.25)
60
40
20
0
Fig 6. LSV curves of Bi2O3-CuO (0.75) catalyst with different loading amount in 0.5
-1.50 -1.45 -1.40 -1.35 -1.30 -1.25
Potential / V vs. SCE
M KHCO3 solution.
3.3 Selective production of formate
Fig. 7 FEs for formate production over Bi2O3-CuO(x) catalysts (x=0, 0.25, 0.5, 0.75,
1.0, 1.25) at various potentials.
From the results of LSV on Bi2O3-CuO (0.75), we applied the
electrolysis at potential range from −1.25 to −1.55 V for 3 h on
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
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
1
2
3
4
5
6
7
8
9
To explore the kinetics and possible mechanistic for ERC on
View Article Online
DOI: 10.1039/C8NJ05205K
Bi2O3-CuO(x) catalysts, the Tafel curve were measured by step
potential electrolysis, which combined with liquid product of
formate performances. The Tafel slopes for formate (Fig. 8) on
Bi2O3, Bi2O3-CuO(0.5), Bi2O3-CuO(0.75), Bi2O3-CuO(1.0) and Bi2O3-
CuO(1.25) catalysts were 136, 129, 111,100,107 and 105 mV/dec,
respectively. On the one hand, we can find that the Tafel slope
value of Bi2O3-CuO(0.75) is smallest in all ratios Cu/Bi catalysts ,
which benefits for practical application because it can lower the
energy barrier of rate-limiting activation and make the catalytic
activity increase remarkably35. On the other hand, the Tafel slopes
of all of catalysts are close to the value of 118 mV/dec, and we can
infer that ERC mechanism on these catalysts carried on an initial
rate determining step, which is one electron transferred to form a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
.−
surface-absorbed CO2 species on interface of electrode and
electrolyte 36. The excellent FE of formate in Bi2O3-CuO(0.75)
•−
catalyst indicated that suitable molar ratio of Cu/Bi can make CO2
intermediate generation more estasily, and the hydrogen evolution
reaction was suppressed 5, 37. In addition, it has been informed that
Fig 9. Partial current density and FE for formate over Bi2O3-CuO(x) catalysts in
0.5 M KHCO3 solution for 10 h over, x=0 (a), 0.25(b), 0.5(c), 0.75(d), 1.0(e), 1.25(f)
at -1.4 V.
•−
because the weakly adsorbed/stabilized of intermediate CO2
formed to catalyst’s surface, large overpotential was needed during
this process 36, 38
.
3.4 Stability of catalysts
0.72
0.70
0.68
0.66
0.64
0.62
The stability of the Bi2O3-CuO(x) catalysts was evaluated by
constant potential electrolysis at −1.4 V for 10 h (Fig. 9). Specially,
the EF for formate on Bi2O3-CuO(0.75) maintained at ∼90% (Fig. 9d)
with the average current density of 9.1 mA cm−1, and it maintained
desirable stabilities during 10 h electrolysis. Furthermore, as the
molar ratio of Cu/ Bi increased, the Bi2O3-CuO(x) catalysts stability
(FE and current density) remained basically unchanged during 10 h
electrolysis at −1.4 V (Fig 9, Fig S6). The results demonstrated that
the Bi2O3-CuO(x) catalysts possessed notable stability for ERC to
formate under these reaction systems.
(e)
(a)
(d)
(f)
(b)
(a) Bi2O3
(b) Bi2O3 -CuO(0.25)
(c) Bi2O3 -CuO(0.5)
(d) Bi2O3 -CuO(0.75)
(e) Bi2O3 -CuO(1.0)
(f) Bi2O3 -CuO(1.25)
(c)
0.60
-0.4 -0.2
0.0
0.2
0.4
0.6
-2
0.8
log ( j
formate
/ mA cm )
Fig. 8 Tafel plots for formate over Bi2O3-CuO(x) (x=0 (a), 0.25(b), 0.5(c), 0.75(d),
4 Conclusions
1.0(e), 1.25(f)) catalysts in 0.5 M KHCO3 solution.
In summary, we applied a simple method to synthesize
morphology-controlled Bi2O3-CuO(x) catalysts through
coordination-precipitation, and investigated their application
as electrocatalysts for ERC. The Bi2O3-CuO(x) samples exhibit
composition dependent activities towards ERC. Among all the
as-prepared catalysts, Bi2O3-CuO (0.75) is an efficient
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 8 of 8
ARTICLE
Journal Name
1
2
3
4
5
6
7
8
9
electrocatalysts with the highest activity and Faradaic
efficiency for ERC in 0.5 KHCO3 solution at room
13. S. Zhang, P. Kang and T. J. Meyer, J Am Chem Soc, V2ie0w14Ar,ti1cl3e6O,nline
1734-1737.
DOI: 10.1039/C8NJ05205K
M
14. C. Liu, T. R. Cundari and A. K. Wilson, Journal of Physical
Chemistry C, 2012, 116, 5681-5688.
15. F. Köleli, T. Atilan, N. Palamut, A. M. Gizir, R. Aydin and C. H.
Hamann, Journal of Applied Electrochemistry, 2003, 33, 447-450.
16. E. Bertin, S. Garbarino, C. Roy, S. Kazemi and D. Guay, Journal of
CO2 Utilization, 2017, 19, 276-283.
temperature. With this novel Bi2O3-CuO (0.75)/GCE as
electrode, CO2 could electrochemically reduce to formate
selectively and efficiently. FE of formate can achieve 89.3% at
apply potential −1.4 V, which is much higher than that on Bi2O3
powder (11.3%). Furthermore, during 10 h electrolysis, Bi2O3-
CuO (0.75) catalyst is still rigorous for CO2 reduction. From the
mentioned in experimental analysis, a reasonable mechanism
of ERC at the Bi2O3-CuO(x) bimetallic oxide catalyst was
proposed and composition dependent activity of the Bi2O3-
CuO(x) was observed. This work highlights the importance of
compositional effect morphology, further impacting on their
catalytic activities of bimetallic oxide catalyst and provides a
useful strategy for designing efficient catalysts for ERC in the
future.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
17. J. Medina-Ramos, J. L. DiMeglio and J. Rosenthal, J Am Chem
Soc, 2014, 136, 8361-8367.
18. H. Zhang, Y. Ma, F. Quan, J. Huang, F. Jia and L. Zhang,
Electrochemistry Communications, 2014, 46, 63-66.
19. Y. Qiu, J. Du, C. Dai, W. Dong and C. Tao, Journal of The
Electrochemical Society, 2018, 165, H594-H600.
20. Y. Qiu, J. Du, W. Dong, C. Dai and C. Tao, Journal of CO2
Utilization, 2017, 20, 328-335.
21. X. Sun, Q. Zhu, X. Kang, H. Liu, Q. Qian, Z. Zhang and B. Han,
Angew Chem Int Ed Engl, 2016, 55, 6771-6775.
22. W. Lv, J. Zhou, J. Bei, R. Zhang, L. Wang, Q. Xu and W. Wang,
Applied Surface Science, 2017, 393, 191-196.
23. J. Lee and Y. Tak, Electrochimica Acta, 2002, 46, 3015-3022.
24. D. Raciti, K. J. Livi and C. Wang, Nano Lett, 2015, 15, 6829-6835.
25. D. Chi, H. Yang, Y. Du, T. Lv, G. Sui, H. Wang and J. Lu, RSC Adv.,
2014, 4, 37329-37332.
26. C. Ma, W. Sun, X. Cha, M. Fan, Y. Zhang, C. Ma, W. Sun, X. Cha,
M. Fan and Y. Zhang, Gongneng Cailiao/journal of Functional
Materials, 2017, 48, 04090-04095.
27. M. Fan, C. Ma, T. Lei, J. Jung, D. Guay and J. Qiao, Catalysis
Today, 2017, DOI: 10.1016/j.cattod.2017.09.018.
28. R. Kötz, 1990.
29. M. Baerns, Springer, 2004, 2004, 8.
30. M. A. Kebede, M. E. Varner, N. K. Scharko, R. B. Gerber and J. D.
Raff, J Am Chem Soc, 2013, 135, 8606-8615.
31. B. Liu, J. Du, X. Lv, Y. Qiu and C. Tao, Catalysis Science &
Technology, 2015, 5, 1241-1250.
32. T. Su, H. Tian, Z. Qin and H. Ji, Applied Catalysis B:
Environmental, 2017, 202, 364-373.
33. J. L. DiMeglio and J. Rosenthal, J Am Chem Soc, 2013, 135, 8798-
8801.
34. X. Guo, Y. Zhang, C. Deng, X. Li, Y. Xue, Y. M. Yan and K. Sun,
Chem Commun (Camb), 2015, 51, 1345-1348.
35. F. Lei, W. Liu, Y. Sun, J. Xu, K. Liu, L. Liang, T. Yao, B. Pan, S. Wei
and Y. Xie, Nat Commun, 2016, 7, 12697.
Conflicts of interest
There are no conflicts to declare.
Notes and references
1. C. Costentin, M. Robert and J. M. Saveant, Chem Soc Rev, 2013,
42, 2423-2436.
2. X. Chang, T. Wang, P. Zhang, Y. Wei, J. Zhao and J. Gong, Angew
Chem Int Ed Engl, 2016, 55, 8840-8845.
3. K. K. Sakimoto, A. B. Wong and P. Yang, Science, 2016, 351, 74.
4. P. Kang, C. Cheng, Z. Chen, C. K. Schauer, T. J. Meyer and M.
Brookhart, Journal of the American Chemical Society, 2012, 134,
5500-5503.
5. H. Wang, Z. Han, L. Zhang, C. Cui, X. Zhu, X. Liu, J. Han and Q. Ge,
Journal of CO2 Utilization, 2016, 15, 41-49.
6. A. Klinkova, P. De Luna, E. H. Sargent, E. Kumacheva and P. V.
Cherepanov, Journal of Materials Chemistry A, 2017, 5, 11582-
11585.
7. J. Annie Modestra, B. Navaneeth and S. Venkata Mohan, Journal
of CO2 Utilization, 2015, 10, 78-87.
8. S. Schlager, A. Dibenedetto, M. Aresta, D. H. Apaydin, L. M.
Dumitru, H. Neugebauer and N. S. Sariciftci, Energy Technol
(Weinh), 2017, 5, 812-821.
9. A. S. Agarwal, Y. Zhai, D. Hill and N. Sridhar, Chemsuschem, 2011,
4, 1301.
10. X. Yu and P. G. Pickup, Journal of Power Sources, 2008, 182,
124-132.
11. J. Jiang and A. Wieckowski, Electrochemistry Communications,
2012, 18, 41-43.
12. P. Bumroongsakulsawat and G. H. Kelsall, Electrochimica Acta,
2014, 141, 216-225.
36. Y. Chen and M. W. Kanan, J Am Chem Soc, 2012, 134, 1986-
1989.
37. T. Hatsukade, K. P. Kuhl, E. R. Cave, D. N. Abram and T. F.
Jaramillo, Phys Chem Chem Phys, 2014, 16, 13814-13819.
38. M. Gattrell, N. Gupta and A. Co, Journal of Electroanalytical
Chemistry, 2006, 594, 1-19.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins