Interface-induced controllable synthesis of Cu2O nanocubes for electroreduction CO2 to C2H4

Article abstract of DOI:10.1016/j.electacta.2019.03.146

Electroreduction CO₂ to high value-added chemicals is a promising way to mitigate the greenhouse effect while storing the renewable electricity in chemicals. As an important chemical, C₂H₄ is a desirable product of CO₂ reduction but limited by lacking of efficient and durable catalysts. Herein, we proposed an interface-induced method to prepare Cu₂O nanocubes with controllable morphology and size. Due to the imidazolyl groups connected to the surface of ionic liquid functionalized graphite sheets (ILGS), Cu₂O nanocubes were induced to grow on ILGS to obtain Cu₂O/ILGS composites, where the size of Cu₂O can be controlled by adjusting the concentration of Cu²⁺. Interestingly, as the concentration of Cu²⁺ increases from 12.5 mmol/L to 100 mmol/L, the size of Cu₂O nanocubes decreases from 456 nm to 72 nm. As catalyst for CO₂ electroreduction in 0.1 M KHCO₃ aqueous solution, Cu₂O/ILGS-100 (synthesized under 100 mmol/L CuCl₂) behaves the best catalysis performance with a high faradic efficiency of C₂H₄ (31.1%) and long durability at ?1.15 V (vs. reversible hydrogen electrode).

Full text of DOI:10.1016/j.electacta.2019.03.146

Accepted Manuscript
Interface-induced controllable synthesis of Cu O nanocubes for electroreduction CO
2
2
to C H
2 4
Wenhang Wang, Hui Ning, Zhongxue Yang, Zhaoxuan Feng, Jialin Wang, Xiaoshan
Wang, Qinhu Mao, Wenting Wu, Qingshan Zhao, Han Hu, Yan Song, Mingbo Wu
PII:
S0013-4686(19)30569-9
https://doi.org/10.1016/j.electacta.2019.03.146
EA 33862
DOI:
Reference:
To appear in: Electrochimica Acta
Received Date: 29 November 2018
Revised Date: 12 March 2019
Accepted Date: 20 March 2019
Please cite this article as: W. Wang, H. Ning, Z. Yang, Z. Feng, J. Wang, X. Wang, Q. Mao, W.
Wu, Q. Zhao, H. Hu, Y. Song, M. Wu, Interface-induced controllable synthesis of Cu O nanocubes
2
for electroreduction CO to C H , Electrochimica Acta (2019), doi: https://doi.org/10.1016/
2
2 4
j.electacta.2019.03.146.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Interface-induced controllable synthesis of Cu2O nanocubes
for electroreduction CO2 to C2H4
Wenhang Wanga, Hui Ning a,*, Zhongxue Yanga, Zhaoxuan Fenga, Jialin Wanga, Xiaoshan Wanga,
Qinhu Maoa, Wenting Wua, Qingshan Zhaoa, Han Hua, Yan Songb, Mingbo Wua,*
aState Key Laboratory of Heavy Oil Processing, Institute of New Energy, College of Chemical
Engineering, China University of Petroleum (East China), Qingdao 266580, China
bCAS Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of
Sciences, Taiyuan 030001, China
*Corresponding author. Email: wumb@upc.edu.cn (M.B. Wu); ninghui@upc.edu.cn (H. Ning);
Tel.: +86-532-86983452.
1

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Abstract
Electroreduction CO2 to high value-added chemicals is a promising way to mitigate the
greenhouse effect while storing the renewable electricity in chemicals. As an important chemical,
C2H4 is a desirable product of CO2 reduction but limited by lacking of efficient and durable
catalysts. Herein, we proposed an interface-induced method to prepare Cu2O nanocubes with
controllable morphology and size. Due to the imidazolyl groups connected to the surface of ionic
liquid functionalized graphite sheets (ILGS), Cu2O nanocubes were induced to grow on ILGS to
obtain Cu2O/ILGS composites, where the size of Cu2O can be controlled by adjusting the
concentration of Cu2+. Interestingly, as the concentration of Cu2+ increases from 12.5 mmol/L to
100 mmol/L, the size of Cu2O nanocubes decreases from 456 nm to 72 nm. As catalyst for CO2
electroreduction in 0.1 M KHCO3 aqueous solution, Cu2O/ILGS-100 (synthesized under 100
mmol/L CuCl2) behaves the best catalysis performance with a high faradic efficiency of C2H4
(31.1%) and long durability at -1.15 V (vs. reversible hydrogen electrode).
Key wordsꢀ
CO2 electroreduction; graphite sheets; ionic liquid; ethylene; cuprous oxide
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1. Introduction
Electroreduction of carbon dioxide (CO2RR) to high value-added chemicals offers an
opportunity for alleviating the greenhouse effect and storing the renewable electricity in chemicals
[1-4]. Recent progresses in electroreduction of CO2 mainly focus on the production of gaseous
carbon products, such as carbon monoxide (CO) [5, 6] methane (CH4) [7, 8] and ethylene (C2H4)[9, 10]
of which C2H4 is of significant value but limited by lacking of efficient and durable catalysts [11]
,
.
Among all the screened materials, copper-based materials have shown the best performance
for electrocatalytic CO2 to hydrocarbons, especially for C2H4 [12-15]. Recently, Cu2O is found to
have high selectivity to C2H4 in electrocatalytic CO2RR, whose performance is closely related to
its morphology and size [16-20]. Recent research has proved that the surface of Cu2O is reduced to
Cu0 with O vacancies during the CO2RR [21], which is greatly affected by the applied potentials
and currents [22]. The high C2H4 selectivity brought by Cu2O catalysts is more likely due to a high
density of grain boundaries with plenty of unsaturated coordinated copper atom with suitable
atomic spacing. Liu et al. [23] proposed a metal embedded in oxidized matrix model with quantum
mechanics methods to explain the activity and selectivity of Cu2O in electrocatalytic CO2RR,
indicating that the Cu2O matrix plays the key role in maintaining the high performance of oxide
derived Cu0.
As a result, construction of Cu2O crystals with suitable morphology and size to exposure
plenty of unsaturated coordinating Cu atoms are crucial to improving the activity and selectivity of
Cu2O for electrocatalytic CO2RR to C2H4. Unfortunately, the synthesis of well-defined and highly
dispersed Cu2O nanocrystals is still a great challenge. Huang et al. prepared Cu2O nanocubes by
controlling the aggregation of Cu2O seed particles and surface reconstruction method via sodium
dodecyl sulfate as capping surfactant [24]. Yeo et al. reported copper(I) oxide films electrodeposited
from an electrolyte of 0.3 mol/L CuSO4, 3.2 mol/L NaOH and 2.3 mol/L Lactic acid in water at
various electrochemical potentials [25]. Wang et al. prepared Cu2O hollow spheres by adjusting the
concentration of CTAB in water under 60 °C [26]. These reported methods usually need trivial
steps and massive energy consumption, bulk organic solvents or mass surfactants, which are
environmentally unfriendly. Therefore, it is of great significance to invent an economic method for
controllable synthesis of Cu2O nanocrystals with high catalytic performance for C2H4 production
from CO2RR.
The interface-induced method is an outstanding strategy for controllable preparation of metal
materials [27]. Carbon materials generally possess excellent chemical and thermal stabilities, good
electrical conductivity [28], and flexible designability, making them promising candidates as
supports to synthesize metal based composites based on interface-induced method [29, 30]. Pan et al.
developed a facile interface-induced Zn(II)-ligand-fragment co-assembly strategy to in situ
fabricate boronate-based MOF membrane on hydrophobic porous carbon substrate for specific
molecular recognition and separation. A catechol-containing medicinal natural flavone luteolin
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was found to be efficiently and selectively recognized on the MOF composite in water-containing
solution due to the phenylboronic acid groups and carbon substrate [31]. Ren et al. employed the
graphene oxide (GO) support to template Cu2O nanocrystals resulting in well-dispersed Cu2O
nanocrystals that show much promise in photo and chemo-catalytic applications, where GO play
roles as the template and a surfactant to achieve dispersed Cu2O crystals [32]. These preliminary
works motivate us to investigate the interface-induced method with carbon materials for
controllable synthesis of Cu2O nanocubes as high efficient catalyst for ethylene production from
CO2RR.
Herein, the ionic liquid functionalized graphite sheets (ILGS) were prepared by
electro-exfoliation method according to our previous works [33], which was dispersed into aqueous
solution to construct ILGS-water interface. Under the interface effects of ILGS on Cu2+, a series of
well-defined Cu2O nanocubes were in situ fabricated on the surface of ILGS, in which the
morphology and size of Cu2O were completely different with those without ILGS. The
as-prepared Cu2O/ILGS showed significant enhancement of catalytic performance for ethylene
formation in CO2RR.
2. Experiment
2.1 Materials
1-octyl-3-methylimidazolium chloride (OmimCl, 99.0%) was supplied from the Centre of
Green Chemistry and Catalysis, LICP, CAS, P. R. China. Copper chloride dihydrate (99.0%),
sodium hydroxide (96.0%), potassium hydrogen carbonate (99.5%), ethanol anhydrous (99.7%)
and L-ascorbic acid (99.99%) are provided by Sinopharm Chemical Reagent Co., Ltd., P. R. China.
Nafion N-117 membranes (0.180 mm thick, ≥0.90 meqꢀg−1 exchange capacity) were purchased
from Alfa Aesar China Co., Ltd. High purity graphite rod (ø = 3 mm) was provided by Beijing
Crystal Dragon Carbon Technology Co., Ltd., P. R. China. All the reagents are used as received
without further treatments. The water was purified by a Millipore system in all experiments.
2.2 Synthesis of Cu2O/ILGS
Cu2O/ILGSs were prepared using a simple wet chemical approach. Firstly, ILGS was
synthesized according to our previous work [33]. Then, 40 mg ILGS is added into 40 mL water to
obtained a well-dispersed suspension under ultrasonic for 30 min at room temperature, denoted as
solution A. After that, 12 mL of 12.5 mmol/L CuCl2 aqueous solution was mixed with solution A
and stirred vigorously for 1 hour, flowing by adding 20 mL of 0.1 mol/L NaOH slowly under
stirring to obtain solution B. Subsequently, 50 mL of 6 mmol/L L-ascorbic acid is added to
solution B and stirred for 2 hours at room temperature. At last, the precipitate was filtered and
washed with water and ethanol thoroughly before drying under vacuum at 60 °C for 6 hours to
obtain a brown power, denoted as Cu2O/ILGS-12.5. Cu2O/ILGS-25, Cu2O/ILGS-50, and
Cu2O/ILGS-100 were prepared with the same procedure except that the concentration of CuCl2 is
25, 50 and 100 mmol/L, respectively. The yields of synthesis method, the nominal and real amount
of Cu2O obtained with the method were listed in Table S1.
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As control experiments, pristine Cu2O-12.5, Cu2O-25, Cu2O-50 and Cu2O-100 were also
prepared with the same procedure without adding ILGS in solution A, where the number after the
Cu2O represented the concentration of Cu2+ (mmol/L).
2.3 Materials Characterization
The morphologies of materials were characterized by scanning electron microscopy (SEM,
Hitachi S-4800, Japan). The crystal property and phase composition of all as-prepared materials
were investigated by X-ray diffraction (X’Pert PRO MPD, Holland) with Cu Kα radiation at 40
kV and 40 mA with Cu Kα radiation (λ=1.5406Å). The surface elemental compositions were
recorded by X-ray photoelectron spectroscopy (XPS, Thermo Scientific Escalab 250XI, America)
with Al Kα radiation. UV-Vis absorption spectra were measured by a UV-Vis spectrophotometer
(UV-2700, SHIMADZU). Thermogravimetric analysis (TGA) was carried on a Shimadzu
TA-60Ws thermal analyser (Japan) in air at a ramp rate of 10 °C min-1.
2.4 CO2RR and product analysis
The CO2RR was carried out in an H-type electrolytic cell with two compartments, where the
anode and cathode were separated by a Nafion 117 proton exchange membrane. A Pt plate (1×1
cm2) and Ag/AgCl electrode (KCl saturated) were used as counter and reference electrode,
respectively. Both compartments were filled with 30 mL of 0.1 M KHCO3 as electrolyte. All the
working potentials were referred to the reversible hydrogen electrode (RHE). The pH value of the
CO2 saturated electrolyte is 6.8. All the electrochemical measurements were performed using an
electrochemical workstation (CHI 760, Shanghai CH Instruments Co., P. R. China).
The working electrode was fabricated by drop-casting 100 µL of catalyst ink onto a L-type
glassy-carbon (GC, ø = 10 mm) and dried with N2. Before ink deposition, the GC electrode was
polished and sonicated in ethanol. The catalyst inks were prepared by dispersing 5.0 mg materials
in 10 µL of 5% Nafion solution and 500 µL of ethanol anhydrous.
Before testing, the electrolyte in cathode side was saturated with N2 for 30 min to exclude air.
Then high purity CO2 (99.999%) was bubbled into the electrolyte for another 30 min. During the
electrochemical measurements, the CO2 gas flow was controlled at 20 mL/min. The gas-phase
products generated during CO2 electrolysis at each fixed potential were collected and
quantitatively analyzed by gas chromatograph (BFRL-3420A ꢁChina), which was online
connected with the head space of the cathodic side of the H-type cell. The gas products were
injected to GC using a ten-port valve system with high purity Ar (99.999%) as carrier gas. The GC
system was equipped with two columns associating with two detectors. The thermal conductivity
detector (TCD) was installed to detect hydrogen and carbon monoxide while the flame ionization
detector (FID) was fabricated to detect hydrocarbons. The liquid product was tested with Nash's
colorimetric method by UV-Vis spectrophotometer [35]. The faradaic efficiency of all products was
calculated according to the methods reported by Yeo et al [25]
.
3. Results and Discussion
The typical preparation procedure is schematically illustrated in Scheme 1. The XRD patterns
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(Fig. 1) and XPS spectra (Fig. 2) indicate that Cu2O nanocrystals are successfully synthesized and
in-situ supported on the ILGS. As shown in Fig. 1, the wider diffraction peak at 26.43° is ascribed
to the (002) peak of ILGS due to the increased amorphousness and defects after exfoliation of
graphite. Other diffraction peaks can be exactly indexed to Cu2O (JCPDS No.78-2076) at 29.58°
(110), 36.44° (111), 42.33° (200), 52.49° (211), 61.40° (220), and 73.56° (311), respectively. No
other characteristic peaks exit in the XRD patterns, indicating Cu2O was successfully synthesized
and in-situ supported on ILGS.
It can be seen from the XPS spectra (Fig. 2a) that all Cu2O/ILGSs are consist of C, N, O and
Cu. In Fig. 2b, the peaks at 399.57 eV and 401.06 eV indicate that nitrogen in ILGS is derived
from the cations of 1-octyl-3-methylimidazolium chloride, which is used as electrolyte for
graphite electro-exfoliation [36]. In Fig. 2c, the characteristic peaks at 932.1 eV and 952.0 eV are
corresponding to Cu2p3/2 and Cu2p1/2, respectively. The specific valence of Cu+ and Cu0 was
further investigated by Cu LMM Auger spectra (Fig. 2d), the kinetic energy around 916.9 eV
confirms the purity of Cu2O without Cu0 exiting [37]
.
SEM images revealed that all the Cu2O nanocrystals present cubic morphology with
obviously different size distributions, as shown in Fig. 3 and Fig. S1. To be specific, obvious
cavities on the surface of Cu2O nanocubes was found in Cu2O/ILGS-12.5 due to incomplete
growing, which is beneficial for the exposure of unsaturated coordinate Cu atoms. The size
distribution of Cu2O nanocubes supported on ILGS showed an abnormal rule in comparison with
pristine Cu2O. As shown in Fig.S2 and Table S2, with the concentration of Cu2+ increases from
12.5 mmol/L to 100 mmol/L, the average side length of Cu2O in Cu2O/ILGSs decreases from 456
nm to 72 nm, while the average side length of pristine Cu2O increases from 113 nm to 228 nm,
indicating the ILGS can inhibit the growth and aggregation of Cu2O crystals under high
concentration of Cu2+.
The catalytic performances of Cu2O/ILGSs for CO2 electroreduction to C2H4 were
investigated with CO2-saturated 0.1 M KHCO3 solution as electrolyte in an H-type cell under
series potentials. The faradic efficiency of C2H4 and other gas products were depicted in Fig. 4.
For all Cu2O/ILGSs, the optimum values of faradaic efficiency for C2H4 are at -1.15 V (vs. RHE).
Cu2O/ILGS-100 shows a maximum faradaic efficiency (FE) of 31.1% for C2H4 products. As
shown in Fig. S3, formate as the only liquid product was detected with a combined FE of ca. 100%
with gas products for Cu2O/ILGS-100.
In our previous work, ILGS has been proved to have no catalytic activity for electroreduction
of CO2 while Cu2O is the main active sites. For pristine Cu2O (Fig. 4e), along with the average
size of Cu2O increasing from 113 nm to 228 nm, the FEC2H4 declines from 17.5% to 13.8%.
Similar trends can also be found for Cu2O/ILGS-25, Cu2O/ILGS-50 and Cu2O/ILGS-100.
Reasonably, the highest FEC2H4 (31.1 %) was obtained over Cu2O/ILGS-100 due to the smallest
size of Cu2O nanocubes (72 nm). Specially, the FE of C2H4 on Cu2O/ILGS-12.5 is 25.5%, which
is close to Cu2O/ILGS-25 (25.0%), though the size of Cu2O in Cu2O/ILGS-12.5 is much larger
than that in Cu2O/ILGS-25. This special phenomenon is corresponding to the special morphology
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of Cu2O with obviously cavities on the crystal surface (Fig. 3a), which may arise from the
interface-induced effects of ILGS associating with the low concentration of Cu2+. These
concavities increase the density of grain boundaries of Cu2O nanocubes with more unsaturated
copper atoms exposed, which is conducive to enhancing the selectivity of C2H4 [38]. Among all the
materials as made, the Cu2O nanocubes in Cu2O/ILGS-100 have the largest loading of 77.6 wt%
(Fig. S4, Table S3) and the smallest size of 72 nm, indicating this is a facile method for rapid
synthesis of smaller Cu2O nanocubes using high concentrations of Cu2+ for industrial applications.
It is worth noting the mass activity of Cu2O towards ethylene formation is meaningful for
evaluating the real catalytic activity of copper. Under the optimum potential -1.15V (vs. RHE), the
formation rate of ethylene on unit mass of Cu2O was calculated, as shown in Fig. S5. Not
surprisingly, Cu2O/ILGS-12.5 presents the best performance due to its lowest loading of Cu2O
with obvious concavities, flowing by Cu2O/ILGS-25 and Cu2O/ILGS-50. Interestingly,
Cu2O/ILGS-100 exits a relative high yield of C2H4, much better than Cu2O/ILGS-50 and
Cu2O/ILGS-25, with the highest Cu2O loading. With further to explain this phenomenon, the BET
surface area of different materials as-made was calculated according to N2 adsorption-desorption
isotherms. As depicted in Fig. S6, the BET surface area of Cu2O/ILGS-12.5, Cu2O/ILGS-25,
Cu2O/ILGS-50 and Cu2O/ILGS-100 is 5.90, 5.23, 6.07, and 6.30 m2 g-1, respectively, which is
closely related to the size and morphology of Cu2O nanoparticles. Cu2O/ILGS-100 has the largest
specific surface area due to its smallest size of Cu2O crystals. However, Cu2O/ILGS-12.5 has a
larger specific surface area than Cu2O/ILGS-25, even though the latter has a much smaller size of
Cu2O. This is consistent with the special morphology of Cu2O crystals in Cu2O/ILGS-12.5, which
have obvious surface cavities (Fig. 3a). As revealed by the linear sweep voltammetry (LSV) curve
in Fig. S7a, Cu2O/ILGS-100 achieved the highest total current density from -0.85 V to -1.3 V (vs.
RHE). According to the mass content of Cu supported on ILGS, the mass-specific current density
of all the catalysts was tested and normalized by 1.0 mg copper, as shown in Fig. S7b. It is found
that Cu2O/ILGS-100 still has the largest current density under the measured potentials, indicating
that ILGS as supports facilitate the utilization of Cu atom as catalyst for CO2 electroreduction.
In the end, the stabilities of Cu2O/ILGS-100 and Cu2O/ILGS-12.5 were selected as
representative samples to investigated the durability of Cu2O under -1.15 V (vs. RHE), as depicted
in Fig. 4f and Fig. S8, respectively. Despite the great difference of Cu2O nanocubes in size and
morphology, both Cu2O/ILGS-100 and Cu2O/ILGS-12.5 showed better durability than the
corresponding pristine Cu2O, indicating the interface-induced method is preferable to synthesize
Cu2O materials with higher selectivity and better durability for electrocatalytic reduction of CO2
towards C2H4. We further explored the morphology and state of Cu2O after CO2 electroreduction.
Taking Cu2O/ILGS-100 for example, the edge of Cu2O nanocubes is blurred (Fig. S9), indicating
the morphology of Cu2O is not stable during the CO2 electroreduction [39]. As shown in Fig. S10,
the Cu 2p XPS showed that Cu+ or Cu0 exists in Cu2O/ILGS-100 and no Cu2+ peaks were
observed. With further analyzed form the Auger Cu LMM line (Fig. S11), it is concluded that only
minimal Cu+ was reduced to Cu0 under the applied negative potential and Cu+ is still the main
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active species in Cu2O/ILGS-100, which play the key role in selectively catalytic CO2RR to
ethylene [19]
.
4. Conclusions
In summary, an interface-induced method was developed to synthesize Cu2O nanocubes with
controllable morphology and size. Due to the nanostructured surface functionalities of ILGS,
Cu2O nanocubes with smaller size and high loading amount on ILGS were prepared. As the
concentration of Cu2+ decreases from 100 mmol/L to12.5 mmol/L , the size of Cu2O on ILGS
increases from 72 nm to 456 nm, while the size of pristine Cu2O without ILGS as supports
decreases from 228 nm to 113 nm. This abnormal phenomenon was ascribed to the interface
effects of ILGS: (1) The Cu2O nucleus is preferable to generate on the surface of ILGS rather than
in the bulk solution due to the absorption effect of ILGS to Cu2+; (2) The nanostructures of ILGS
can fix the position of Cu2O crystals and inhibit their aggregation. Under the optimal potential for
C2H4 formation (-1.15 V vs. RHE), all Cu2O/ILGSs show higher selectivity towards C2H4 than the
corresponding pristine Cu2O prepared with the same concentration of Cu2+, of which
Cu2O/ILGS-100 exhibits the highest faradic efficiency of ethylene (31.1%). The high performance
of Cu2O/ILGS-100 is attributed to its larger electrochemically active surface area than
Cu2O/ILGS-50, Cu2O/ILGS-12.5 and Cu2O/ILGS-25. It is worth noting that Cu2O nanocubes in
Cu2O/ILGS-100 present the smallest size of 72 nm and the highest loading amount of 77.6 wt%,
indicating this interface-induced method has a great potential in scaling up synthesis of small size
of Cu2O with high concentrations of Cu2+. This work not only paves the way for scale preparation
of well-defined Cu2O nanocubes as efficient catalyst for green synthesis of ethylene from CO2RR,
but also enlightens a facile way to control the morphology and size of metal oxides for various
electrochemical applications.
Acknowledgements
This work is financially supported by the National Natural Science Foundation of China (Nos.
21808242, 51572296); the Natural Science Foundation of Shandong Province (ZR2018BB070),
the Financial Support from Taishan Scholar Project.
References
[1] M. He, Y. Sun, B. Han, Green carbon science: scientific basis for integrating carbon resource
processing, utilization, and recycling, Angew. Chem. Int. Ed. 52 (2013) 9620-9633.
[2] X. Chang, T. Wang, J. Gong, CO2 photo-reduction: insights into CO2 activation and reaction
on surfaces of photocatalysts, Energy Environ. Sci. 9 (2016) 2177-2196.
[3] Y. Wang, J. Liu, Y. Wang, A.M. Al-Enizi, G. Zheng, Tuning of CO2 Reduction Selectivity on
Metal Electrocatalysts, Small, 13 (2017) 1701809.
[4] A. Vasileff, C. Xu, Y. Jiao, Y. Zheng, S.-Z. Qiao, Surface and Interface Engineering in
Copper-Based Bimetallic Materials for Selective CO2 Electroreduction, Chem, 4 (2018)
8

ACCEPTED MANUSCRIPT
1809-1831.
[5] F. Li, M. Xue, G. P. Knowles, L. Chen, D. R. MacFarlane, J. Zhang, Porous nitrogen-doped
carbon derived from biomass for electrocatalytic reduction of CO2 to CO, Electrochim. Acta
245 (2017) 561-568.
[6] L. Jin, B. Liu, P. Wang, H. Yao, L.A. Achola, P. Kerns, A. Lopes, Y. Yang, J. Ho, A. Moewes, Y.
Pei, J. He, Ultrasmall Au nanocatalysts supported on nitrided carbon for electrocatalytic CO2
reduction: the role of the carbon support in high selectivity, Nanoscale 10 (2018)
14678-14686.
[7] X. Liu, H. Yang, J. He, H. Liu, L. Song, L. Li, J. Luo, Highly Active, Durable Ultrathin MoTe2
Layers for the Electroreduction of CO2 to CH4, Small 14 (2018) 1704049.
[8] X. Sun, X. Kang, Q. Zhu, J. Ma, G. Yang, Z. Liu, B. Han, Very highly efficient reduction of
CO2 to CH4 using metal-free N-doped carbon electrodes, Chem. Sci. 7 (2016) 2883-2887.
[9] A. Loiudice, P. Lobaccaro, E. A. Kamali, T. Thao,B. H. Huang, J. W. Ager, R. Buonsanti,
Tailoring Copper Nanocrystals towards C2 Products in Electrochemical CO2 Reduction,
Angew. Chem. Int. Ed. 128 (2016) 5883-5886.
[10] D. Wu, C. Dong, D. Wu, J. Fu, H. Liu, S. Hu, Z. Jiang, S.-Z. Qiao, X.-W. Du, Cuprous ions
embedded in ceria lattice for selective and stable electrochemical reduction of carbon dioxide
to ethylene, J. Mater. Chem. A 6 (2018) 9373-9377.
[11] F. S. Roberts, K. P. Kuhl, A. Nilsson, High Selectivity for Ethylene from Carbon Dioxide
Reduction over Copper Nanocube Electrocatalysts, Angew. Chem. Int. Ed. 54 (2015)
5179-5182.
[12] H. Xie, T. Wang, J. Liang, Q. Li, S. Sun, Cu-based nanocatalysts for electrochemical
reduction of CO2, Nano Today 21 (2018) 41-54.
[13] Y. Hori, K. Kikuchi, S. Suzuki, Production of CO and CH4 in electrochemical reduction of
CO2 at metal electrodes in aqueous hydrogen carbonate solution, Chem. Lett. 14 (1985)
1695-1698.
[14] Y. Jiao, Y. Zheng, P. Chen, M. Jaroniec, S. Qiao, Molecular scaffolding strategy with
synergistic active centers to facilitate electrocatalytic CO2 reduction to hydrocarbon/alcohol, J.
Am. Chem. Soc. 139 (2017) 18093-18100.
[15] C.F.C. Lim, D.A. Harrington, A.T. Marshall, Effects of mass transfer on the electrocatalytic
CO2 reduction on Cu, Electrochim. Acta 238 (2017) 56-67.
[16] C. W. Lee, K. D. Yang, D. H. Nam, J. H. Jang, N. H. Cho, S. W. Im, K. T. Nam, Defining a
materials database for the design of copper binary alloy catalysts for electrochemical CO2
conversion, Adv. Mater. 30 (2018) 1704717.
[17] P. D. Luna, R. Quintero-Bermudez, C. Dinh, M. B. Ross, O. S. Bushuyev, P. Todorović, T.
Regier, S. O. Kelley, P. Yang, E. H. Sargent, Catalyst electro-redeposition controls
morphology and oxidation state for selective carbon dioxide reduction, Nat. Catal. 1 (2018)
103-110.
[18] Y. Chen, C. W. Li, M. W. Kanan, Aqueous CO2 reduction at very low overpotential on
oxide-derived Au nanoparticles, J. Am. Chem. Soc. 134 (2012) 19969-19972.
[19] C. Chen, X. Sun, L. Lu, D. Yang, J. Ma, Q. Zhu, Q. Qian, B. Han, Efficient electroreduction
of CO2 to C2 products over B-doped oxide-derived copper, Green Chem. 20 (2018)
4579-4583.
[20] A. Eilert, F. Cavalca, F. S. Roberts, J. Osterwalder, C. Liu, M. Favaro, E.J. Crumlin, H.
9

ACCEPTED MANUSCRIPT
Ogasawara, D. Friebel, L. G. Pettersson, A. Nilsson, Subsurface oxygen in oxide-derived
copper electrocatalysts for carbon dioxide reduction, J. Phys. Chem. Lett. 8 (2017) 285-290.
[21] Y. Lum, J. W. Ager, Stability of residual oxides in oxide-derived copper catalysts for
electrochemical CO2 reduction investigated with 18O labeling, Angew. Chem. Int. Ed. 57
(2018) 551-554.
[22] D. Ren, J. Fong, B. S. Yeo, The effects of currents and potentials on the selectivities of copper
toward carbon dioxide electroreduction, Nat. Commun. 9 (2018) 925.
[23] D. Kim, C. S. Kley, Y. Li, P. Yang, Copper nanoparticle ensembles for selective
electroreduction of CO2 to C2-C3 products, PNAS 114 (2017) 10560-10565.
[24] C. H. Kuo, C. H. Chen, M. H. Huang, Seed-Mediated Synthesis of Monodispersed Cu2O
Nanocubes with Five Different Size Ranges from 40 to 420 nm, Adv. Funct. Mater. 17 (2007)
3773-3780.
[25] D. Ren, Y. Deng, A. D. Handoko, C. S. Chen, S. Malkhandi, B. S. Yeo, Selective
electrochemical reduction of carbon dioxide to ethylene and ethanol on copper(i) oxide
catalysts, ACS Catal 5 (2015) 2814-2821.
[26] H. Xu, W. Wang, Template synthesis of multishelled Cu2O hollow spheres with a
single-crystalline shell wall, Angew. Chem. Int. Ed. 46 (2007) 1489-1492.
[27] Z. Zuo, Y. Wen, S. Zhang, Interface-induced nucleation and growth: a new route for
fabricating ordered silver nanohole arrays, Nanoscale 10 (2018) 14039-14046.
[28] M. Ding, F. Du, B. Liu, Z. Y. Leong, L. Guo, F. Chen, A. Baji, H. Y. Yang, Rod-like
nitrogen-doped carbon hollow shells for enhanced capacitive deionization, FlatChem, 7 (2018)
10-17.
[29] J. Yuan, W. Zhi, L. Liu, M. Yang, H. Wang, J. Lu, Electrochemical reduction of CO2 at
metal-free N-functionalized graphene oxide electrodes, Electrochim. Acta 282 (2018)
694-701.
[30] L. Qu, Y. Liu, J. Baek, L. Dai, Nitrogen-doped graphene as efficient metal-free electrocatalyst
for oxygen reduction in fuel cells, ACS nano 4 (2010) 1321-1326.
[31] S. Liu, S. Shinde, J. Pan, Y. Ma, Y. Yan, G. Pan, Interface-induced growth of boronate-based
metal-organic framework membrane on porous carbon substrate for aqueous phase molecular
recognition, Chem. Eng. J 324 (2017) 216-227.
[32] C. Hong, X. Jin, J. Totleben, J. Lohrman, E. Harak, B. Subramaniam, R. V. Chaudharib, S.
Ren, Graphene oxide stabilized Cu2O for shape selective nanocatalysis, J. Mater. Chem. A 2
(2014) 7147-7151.
[33] H. Ning, W. Wang, Q. Mao, S. Zheng, Z. Yang, Q. Zhao, M. Wu, Catalytic electroreduction
of CO2 to C2H4 using Cu2O supported on 1-Octyl-3-methylimidazole functionalized graphite
sheets, Acta Phys. -Chim. Sin. 34 (2018) 938-944.
[34] T. T. Zhuang, Z. Q. Liang, A. Seifitokaldani, Y. Li, P. D. Luna, T. Burdyny, F. Che, F. Meng, Y.
Min, R. Quintero-Bermudez, C. T. Dinh, Y. Pang, M. Zhong, B. Zhang, J. Li, P. N. Chen, X. L.
Zheng, H. Liang, W. N. Ge, B. J. Ye, D. Sinton, S. H. Yu, E. H. Sargent, Steering post-C-C
coupling selectivity enables high efficiency electroreduction of carbon dioxide to multi-carbon
alcohols, Nature Catal. 1 (2018) 421-428.
[35] J. Hong, W. Zhang, J. Ren, R. Xu, Photocatalytic reduction of CO2: a brief review on product
analysis and systematic methods, Anal. Methods 5 (2013) 1086.
[36] N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, One-step ionic-liquid-assisted
10

ACCEPTED MANUSCRIPT
electrochemical synthesis of ionic-liquid-functionalized graphene sheets directly from graphite,
Adv. Funct. Mater. 18 (2008) 1518-1525.
[37] S. Y. Lee, H. Jung, N. K. Kim, H. S. Oh, B. K. Min, Y. J. Hwang, Mixed copper states in
anodized Cu electrocatalyst for stable and selective ethylene production from CO2 Reduction,
J. Am. Chem. Soc. 140 (2018) 8681-8689.
[38] Y. Huo, X. Peng, X. Liu, H. Li, J. Luo, High selectivity toward C2H4 production over Cu
particles supported by butterfly-wing-derived carbon frameworks, ACS Appl. Mater.
Interfaces 10 (2018) 12618-12625.
[39] P. Grosse, D. Gao, F. Scholten, I. Sinev, H. Mistry, B. Roldan Cuenya, Dynamic Changes in
the Structure, Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2
Electroreduction: Size and Support Effects, Angew. Chem. Int. Ed. 57 (2018) 6192-6197.
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Scheme. 1 Illustration for preparation of Cu2O/ILGS.

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Fig. 1 XRD patterns of Cu2O/ILGSs.

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Fig. 2 (a) XPS spectra of Cu2O/ILGSs, (b) High-resolution N1s spectra of Cu2O/ILGS-12.5, (c)
High-resolution Cu2p spectra of Cu2O/ILGSs, (d) Cu LMM Auger spectra of Cu2O/ILGSs.

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Fig. 3 SEM images of (a) Cu2O/ILGS-12.5, (b) Cu2O/ILGS-25, (c) Cu2O/ILGS-50, (d) Cu2O/ILGS-100.

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Fig. 4 Faradaic efficiencies of gas products from CO2RR on (a) Cu2O/ILGS-12.5, (b) Cu2O/ILGS-25, (c)
Cu2O/ILGS-50, (d) Cu2O/ILGS-100. (e) Comparison of FEC2H4 on Cu2O/ILGSs and Cu2Os at -1.15 V (vs. RHE).
The insets illustrate the morphology and size of Cu2O. (f) Stability test of Cu2O/ILGS-100 and Cu2O-100 at -1.15
V (vs. RHE).