Size-Dependent Activity and Selectivity of Atomic-Level Copper Nanoclusters during CO/CO2 Electroreduction

Article abstract of DOI:10.1002/anie.202011836

As a favorite descriptor, the size effect of Cu-based catalysts has been regularly utilized for activity and selectivity regulation toward CO₂/CO electroreduction reactions (CO₂/CORR). However, little progress has been made in regulating the size of Cu nanoclusters at the atomic level. Herein, the size-gradient Cu catalysts from single atoms (SAs) to subnanometric clusters (SCs, 0.5–1 nm) to nanoclusters (NCs, 1–1.5 nm) on graphdiyne matrix are readily prepared via an acetylenic-bond-directed site-trapping approach. Electrocatalytic measurements show a significant size effect in both the activity and selectivity toward CO₂/CORR. Increasing the size of Cu nanoclusters will improve catalytic activity and selectivity toward C₂₊ productions in CORR. A high C₂₊ conversion rate of 312 mA cm^?2 with the Faradaic efficiency of 91.2 % are achieved at ?1.0 V versus reversible hydrogen electrode (RHE) over Cu NCs. The activity/selectivity-size relations provide a clear understanding of mechanisms in the CO₂/CORR at the atomic level.

Full text of DOI:10.1002/anie.202011836

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
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International Edition
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Accepted Article
Title: Size-dependent activity and selectivity of atomic-level Cu
nanoclusters during CO/CO2 electroreduction
Authors: Weifeng Rong, Haiyuan Zou, Wenjie Zang, Shibo Xi, Shuting
Wei, Baihua Long, Junhui Hu, Yongfei Ji, and Lele Duan
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202011836
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10.1002/anie.202011836
Angewandte Chemie International Edition
RESEARCH ARTICLE
Size-dependent activity and selectivity of atomic-level Cu
nanoclusters during CO/CO2 electroreduction
Weifeng Rong,[a,b]† Haiyuan Zou,[a,c]† Wenjie Zang,[d] Shibo Xi,[e] Shuting Wei,[a] Baihua Long,[a] Junhui
Hu,[a] Yongfei Ji[f] and Lele Duan*[a]
[a]
Dr. W. Rong, H. Zou, Dr. S. Wei, Dr. B. Long, J. Hu, Prof. Dr. L. Duan
Department of Chemistry and Shenzhen Grubbs institute
Southern University of Science and Technology (SUSTech)
Shenzhen, Guangdong 518055, P. R. China
E-mail: duanll@sustech.edu.cn
[b]
[c]
[d]
[e]
[f]
Dr. W. Rong
School of Chemistry and Materials Science
University of Science and Technology of China
Hefei, Anhui 230026, P. R. China
H. Zou
School of Chemistry and Chemical Engineering
Harbin Institute of Technology
Harbin, Heilongjiang 150001, P. R. China
W. Zang,
Department of Materials Science and Engineering, Faculty of Engineering
National University of Singapore
117574, Singapore
S. Xi
Institute of Chemical and Engineering Sciences, Agency for Science
Technology and Research (A*STAR)
1 Pesek Road, Jurong Island 627833, Singapore
Prof. Dr. Y. Ji
School of Chemistry and Chemical Engineering
Guangzhou University
Guangzhou, Guangdong 510006, P. R. China
†These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.
Abstract: As a favourite descriptor, the size effect of Cu-based
catalysts has been regularly utilized for activity and selectivity
regulation toward CO2/CO electroreduction reactions (CO2/CORR).
However, little progress has been made in regulating the size of Cu
nanoclusters at the atomic level. Here, the size-gradient Cu catalysts
from single atoms (SAs) to subnanometric clusters (SCs, 0.5−1 nm)
to nanoclusters (NCs, 1−1.5 nm) on graphdiyne matrix are readily
the selectivity and geometric activity.[2] The size effects on the
reactivity of electrocatalysts have been extensively investigated.
For example, Reske et al. demonstrated that a dramatic
increase in the catalytic activity and selectivity for H2 and CO
was observed with decreasing Cu particle size in the 2−15 nm
mean size range for CO2RR.[3] A recent study of CO2RR
indicated that small copper nanoparticles (25 nm) led to a high
ethylene production with a remarkable high FE (92.8%).[4]
Emphasis on size-controlled Cu particles comes down to several
reasons: (1) decreasing the size leads to the enhanced surface-
to-volume ratio and thus improves the metal atoms utilization;
prepared via
a creative acetylenic-bond-directed site-trapping
approach. Electrocatalytic measurements show a significant size
effect in both the activity and selectivity toward CO2/CORR.
Increasing the size of Cu nanoclusters will improve catalytic activity
and selectivity toward C2+ productions in CORR.
A
high C2+
(2) as the size of a particle decreases, the increasing
conversion rate of 312 mA cm−2 with the Faradaic efficiency of
91.2% are achieved at –1.0 V vs. reversible hydrogen electrode
(RHE) over Cu NCs. The presented activity/selectivity-size relations
provide a clear understanding of mechanisms in the CO2/CORR at
the atomic level.
undercoordinated sites lead to perturbed electronic structure and
oftentimes increased reactivity;[5] (3) varying size can influence
the binding strength of the different reaction intermediates, and
thus affect the final product selectivity.[6]
Inspired by these potential advantages, we attempt to explore
the size effect of Cu nanoclusters (Cu NCs) in CO2/CORR
aiming at improving the electrocatalytic activity and boosting the
C−C coupling reactions to form C2+ products. Compared to Cu
NPs, the size effects of Cu NCs are less often examined due to
the difficulty of their preparation. Yet the study on Cu NCs can
Introduction
CO2/CORR has trigged significant attention to realize the
decarbonization roadmap using excess renewable electricity. To
date, Cu-based catalysts have shown great promise for
electrochemical reduction of CO2/CO to synthesize high-value
multicarbon (C2+) products owing to the moderate binding
strength of intermediate evolutions, although oftentimes
suffering from the low activity and selectivity.[1] Nanostructuring
of bulky Cu has also been widely applied in attempts to improve
provide
a clear picture of well-defined local coordination
environments of active sites, in favor of discovering the catalytic
mechanism of CO2 activation or CO dimerization at an atomic
level.[7] Recently, a series of structural models of Cu NCs have
been evaluated by computational calculations to shed light on
the size effect for the CO2RR.[8] Nevertheless, the experimental
investigations are still lacking,[9] and the relevant mechanisms
remain elusive, leaving the size effect unexplored.
1
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RESEARCH ARTICLE
To prevent the Cu NCs from agglomeration into NPs, a Results and Discussion
suitable supporting material is required to efficiently stabilize
small Cu NCs through strong metal-support interactions and
meanwhile to maximum the undercoordinated active sites.
Moreover, the supporting materials greatly contribute to the
catalytic activity of the metal catalysts when particle size is
smaller than 6 nm.[10] Graphdiyne (GDY), first prepared by the Li
group in 2010,[11] can provide anchoring sites for immobilizing
the metal atoms due to its rich triple bonds with strong electron-
donating ability.[12] In particular its uniformly distributed 18 C
hexagonal pores not only confine active sites locally[13] but also
make the electrocatalytic performance in high durability under
reaction conditions.[14] These combined properties enable GDY
to be a proper support to control the size of Cu active sites.
However, to the best of our knowledge, no GDY-supported Cu
NCs have been documented due to the lack of impactful
synthetic strategies to prevent agglomeration of NCs to NPs
under high loading.
In this study, a family of size-controlled Cu catalysts from
single atoms (SAs) to subnanometric clusters (SCs, 0.5−1 nm)
to nanoclusters (NCs, 1−1.5 nm) confined on GDY were
synthesized via a general acetylenic-bond-directed site-trapping
approach. In CO2/CORR experiments, the product distribution
strongly depends on the size of NCs. Typically, the catalyst with
smaller NCs is less active and less selective for CO in favor of
H2 toward CO2RR. For CORR, the increasing size allows for
tuning of the C2+/C1 ratio from 0.35 to 398.5 at –1.0 V vs. RHE
and a decrease in CH4 FE from 51.3% to 0.2%. Under the
optimized conditions, we achieved an C2+ partial current density
of 312 mA cm−2 (1.0 M KOH, –1.0 V vs. RHE) and a FE of
93.9% (1.0 M KOH, –0.8 V vs. RHE) over Cu NCs. Moreover,
the long-term stability of Cu NCs during electrolysis, realized by
the strong coordination and confinement from GDY support, is
also highlighted here. Cu catalysts presented here provide a
unique opportunity to understand the mechanism of CO2/CORR
and their study is the first exploration of size effects of atomic-
level Cu NCs.
Diverse preparation technics for Cu NCs and SAs have
emerged.[15] These methods usually involve multistep
procedures. More importantly, they cannot effectively prevent
aggregation of the low coordinated Cu atoms during high-
temperature calcination at increasing atom concentration. We
introduce herein an acetylenic-bond-directed site-trapping
method to synthesize GDY-supported Cu NCs and SAs in-situ.
The formation of macromolecular GDY support and the
anchoring of metal atoms concurred to ensure their compatibility
throughout
the
reaction
process
(Scheme
1).
Hexakis[(trimethylsilyl)ethynyl]benzene (A) is deprotected by
nBu4NF; the resulting anionic intermediate B reacts with cuprous
iodide (CuI) to afford the corresponding unstable copper (I)-σ-
alkynyl complex C, which subsequently undergoes redox
reaction via a π-alkyne binuclear species D to simultaneously
generate Cu0 and GDY at elevated temperatures. These Cu0
atoms are prone to be trapped kinetically and tethered within the
pores formed by three butadiyne linkages (–C≡C–C≡C–)
between the benzene rings of GDY ascribing for the
nanoconfinement effect and strong metal-support interactions.
However, Cu atoms tend to gather into the corresponding bulk
phase thermodynamically.[16] Consequently, the balance of
combined actions leads to the formation of Cu NCs or/and SAs
under the varied amount of cuprous precursor (Figure S1,
Supporting Information). We prepared three GDY-supported Cu
catalysts (two different sized NC catalysts, one SA catalyst as a
reference). Inductively coupled plasma atomic emission
spectrometry
measurement
showed
the
Cu
doping
concentration of 45.2 wt %, 6.0 wt % and 1.5 wt % respectively
on GDY, denoted as Cu45.2/GDY (NCs), Cu6.0/GDY (SCs) and
Cu1.5/GDY (SAs). It is noteworthy that Cu45.2/GDY is the highest
loading nanocluster catalyst reported thus far.
Scheme 1. Schematic illustration for the synthesis of Cu/GDY.
2
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Figure 1. a–d) HAADF-STEM images of Cu1.5/GDY (SAs). e–h) HAADF-STEM images of Cu6.0/GDY (SCs). i–l) HAADF-STEM images of Cu45.2/GDY (NCs). a, c,
e, g, i, k) HAADF-STEM images at low magnification. b, d, f, h, j, l) Corresponding enlargement of the marked regions in a, c, e, g, i, k), respectively.
Atomic-resolution high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) reveals that
the size of bright spots increases with gradually increasing Cu
loading ranging from a single atomic to a subnanometric to a
nanometric level (Figure 1). As shown in Figures 1a–d, the
numerous individual Cu atoms can be clearly observed for
Cu1.5/GDY. A mixture of Cu SCs (0.5–1 nm) and SAs are well
dispersed on the GDY surface for Cu6.0/GDY (Figures 1e–h). Cu
NCs (1–1.5 nm) are evidently well-distributed throughout GDY
framework for the highest loading (Figures 1i–l). X-ray diffraction
(XRD) patterns (Figure S2) of three as-prepared catalysts show
a typically sole broad peak for each Cu/GDY,[13d] reflecting the
predominant carbon support.[17] The nature of carbonaceous
materials of Cu/GDY is further authenticated by Raman
spectroscopy (Figure S3). The distinct G band (1576–1588
cm−1) and D band (1386–1394 cm−1) represent the aromatic and
disordered carbon respectively.[11] The slight hypsochromic shift
for the G bands on Cu/GDY reveals the charge transfer from Cu
to GDY.[13d] The decreasing intensity ratio of D and G bands for
Cu/GDY at increasing loading conditions indicates a gradually
diminished amount of defects in Cu/GDY,[18] which should be
ascribed to the nearly perfect reaction of the copper precursor
with aryne monomer. Furthermore, the obvious peaks at 2170.6
cm–1 and 1974.8 cm–1 for Cu45.2/GDY confirm the formation of
conjugated diyne linkers (–C≡C–C≡C–). X-ray photoelectron
spectroscopy (XPS) in Figure 2a shows identical peaks at ca.
932.7 eV for Cu 2p3/2, which is situated between Cu0 (932.4 eV)
and Cu2+ (934.6 eV),[19] suggesting the ionic Cuδ+ (0 < δ < 2)
nature of copper. The peak centered at 915.9 eV in Cu LMM
Auger spectrum (Figure S5b) further demonstrates the richness
of Cuδ+ in Cu/GDY. The C 1s orbital that can be deconvoluted
into four subpeaks are assigned to the C−C (sp2), C−C (sp),
C−O, and C=O (Figure S4b–e), respectively. The area ratios of
sp peak and sp2 peak are close to 2, indicating the well-
maintained GDY skeleton.
X-ray absorption spectroscopy (XAS) was further introduced
to investigate the chemical nature and structure of Cu species at
the atomic scale. Figure 2b shows the Cu k-edge XANES
spectra of Cu foil, CuI and Cu/GDY. The near-edge features of
Cu/GDY are in between of those of Cu foil and CuI, indicating
that the Cu species are partially positively charged (Cuδ+, 0 < δ <
1) due to the charge redistribution between Cu0 and GDY,[13a] in
agreement with XPS analysis. Fourier-transformed k3-weighted
extended X-ray absorption fine structure (EXAFS) in R space
showed only one notable peak at 1.47 Å from the first
coordination shell of Cu–C bond for Cu/GDY (Figure 2c), very
close to that of the nanodiamond-graphene supported Cu SACs
(1.5 Å).[19b] Cu45.2/GDY and Cu6.0/GDY respectively display an
additional minor peak at 2.3 Å and 2.2 Å, ascribed to Cu–Cu
scattering, confirming the formation of Cun clusters. By contrast,
3
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RESEARCH ARTICLE
no obvious peaks at 2.2–2.3 Å for Cu1.5/GDY evidenced that Cu
atoms are atomically dispersed, in accordance with the HAADF-
STEM observations.
(Figure 3b), substantial loss of the CH4 selectivity is observed
along with the enhanced FE of C2 compounds. The relative ratio
of C2+/C1 is hiked from 0.35 to 2.72 at the same potential. Similar
trends can further be seen for NCs (Cu45.2/GDY) (Figure 3c).
Interestingly, CH4 is almost completely eliminated except at
more negative potentials[2c]. In sharp contrast, C2+ compounds
are constituting about 80% out of the total products generated,
whilst hydrogen evolution is hovering around the lowest level at
a wide potential window in comparison with the other two
catalysts. C2H4 and n-PrOH productions are respectively
increasing up to the maximum FEs of 40.4% and 12.8% under
appropriate potentials (Figure S14). Our results have
demonstrated a clear size dependence of activity and selectivity
toward CORR over Cu nanocluster catalysts below 2 nm for the
first time.
Figure 2. Structural characterizations of Catalysts. a) The narrow scan XPS
spectra for Cu 2p of Cu/GDY. b) Cu k-edge X-ray absorption near-edge
structure (XANES). c) FT k3–weighted extended X-ray absorption fine
structure (EXAFS) spectra of Cu/GDY and the reference Cu foil.
As is known to all, highly alkaline electrolyte greatly lowers the
overpotential of formation of C2+ product and boosts a high rate
of electrolysis.[20] The higher electrolyte concentration (1.0 M
KOH) was also employed to avoid mass transport limitation as
well as to examine the influence of pH over the Cu NCs
(Cu45.2/GDY) for CORR (Figure 3e and S23). Overall, the total
FEs at every potential are close to 100%, revealing that the
electrolysis proceeds better than that in 0.1 M KOH. Both the C2+
partial current density and FE increase with increasing the KOH
concentration. The hydrogen evolution reaction (HER) is further
suppressed. The C2+ FE reaches up to 93.9% at –0.8 V vs. RHE
and the highest conversion rate rises to 312 mA cm−2 at −1.0 V
vs. RHE. This represents the Cu nanoclusters with the highest
catalytic activity and C2+ selectivity to date for CORR. The FE of
acetate is significantly improved in higher alkaline electrolyte,
which is attributed to the suppression of H2 and n-PrOH,
indicating a high pH environment could reduce the absorption of
H* and make it difficult for C–C coupling of C2 intermediate for
The CO electrocatalytic performance of Cu/GDY and GDY
was investigated using a three-compartment flow electrolyser
(Figure S8). Initially, the electrocatalytic performances of
Cu/GDY and GDY were examined in 0.1 M KOH solution. The
results are summarized in Figure 3. Cu/GDY showed good
catalytic activities for CORR and high total FEs spanning a very
wide potential window (Figure S9). The products detected in
significant quantities are methane (CH4), ethanol, acetate,
ethylene (C2H4), n-propanol (n-PrOH) as well as H2 (Figure S16,
S20–S22). A drastic rise of the C2+ FEs at the expense of
methane is observed with the increasing size of Cu NCs. Cu
SAs (Cu1.5/GDY) shows a remarkable FE (57.3%) of C1 (CH4) as
a major product at −1.0 V vs. RHE (Figure 3a) vs. the FE (20%)
for C2, with a C2+/C1 ratio of 0.35 (Figure 3d) and no n-PrOH is
observed. When the small SCs are emerging (Cu6.0/GDY)
propanol
production
with
CO.[6]
Figure 3. CO electroreduction performance of Cu/GDY. a–c) Total current density and cumulative FEs vs. applied potential in 0.1 M KOH. d) C2+/C1 ratios of
different catalysts at –1.0 V vs. RHE. e) Total current density and cumulative FEs vs. applied potential in 1.0 M KOH. f) Stability test of Cu45.2/GDY with gas
products measured every 10000 s in 1.0 M KOH at –0.8 V vs. RHE.
4
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Long-term electrolysis was performed at a stationary −0.8 V
vs. RHE for over 22 h to test the stability of Cu45.2/GDY in 1.0 M
KOH electrolyte (Figure 3f). The total current densities fluctuate
within 210–150 mA cm–2 over the electrolysis course, which is
caused by bubble accumulation in the liquid catholyte
chamber.[21] The slight changes in FEs of H2 (6.6%−14%) and
C2H4 (37.5%−32%) imply the decrease in C2+ selectivity due to
flooding issues through the GDL into the CO gas chamber
during the long-term high-rate electrolysis.[2c, 21-22] XRD, XPS and
HADDF-STEM characterization of Cu45.2/GDY samples after
CORR were immediately carried out to examine if dynamic
changes happened. The selfsame spectra (Figure S5, S6 and
S7) reveal the robustness of Cu nanocluster catalysts during the
CORR process in comparison with the as-prepared.
Figure 4. Free energy surfaces for CO coupling reactions on Cu SAs
(Cu1.5/GDY) and the correspondingly optimized structures of the intermediates.
To better elucidate the nature and stability of as-prepared
Cu/GDY with different sizes of NCs, we also examined catalytic
performance for CO2 reduction as a contrast in a CO2-saturated
0.5 M KHCO3 (pH 7.2) during 1 h electrolysis (Figure S17).
Different from CORR, only three electroreduction products in
substantial quantities (H2, CO, formate) are detected at a wide
potential window, C2H4 is found in a small quantity (FE < 3%)
only if large overpotential is applied over Cu45.2/GDY. The
catalytic activity and selectivity are found to strongly vary as a
function of the cluster size. As shown in Figure S17a, all three
Cu/GDY catalysts show high activity and selectivity toward H2 in
comparison with that in CORR, reflecting that the weaker
binding of CO2 than CO to Cu metal cannot effectively retard
HER.[23] For SAs, H2 is a major product with a dominant FE at
−1.0 V vs. RHE. As the size of Cu NCs increases, the activity
and selectivity for CO are enhanced, while H2 production is
obviously suppressed. The influence of potentials on the product
distribution is plotted using Cu45.2/GDY in Figure S17b. A FECO
of 61.2% is achieved at −1.1 V vs. RHE while ethylene is in
minute quantity even at larger potential. The exclusive C1
products further indicate that the active sites were preserved
under electrochemical reaction conditions and no reconstruction
happened, in accordance with the observations in long-term
electrolysis for CORR. Because all the restructuring behaviors of
documented Cu catalysts, irrespective of the initial size of the
active sites, will surely lead to the substantial conversion of CO2
to C2+ and/or CH4.[24] Such excellent stability for CO2/CORR
originates from the confinement environment from the hole
enclosed by six triple bonds and the strong metal-support
interaction from orbital overlaps[13a] and electron transfer[13b,14]
between Cu and C atoms. The structural property of 2D material,
for example, a sandwich-like GDY-NCs-GDY structure, may play
an essential role in stabilizing the NCs. So a suitable supporting
material is indispensable to stabilize the geometric structure and
electronic properties of active centers during electrolysis.[25]
In order to consolidate the stability of catalysts further, the
catalytic performance of Cu45.2/GDY after long-term (>22 h)
CORR was evaluated toward CO2RR (Figure S19). The switch
to the CO2 feed was operated immediately in situ after CORR.
No obvious enhancement for C2H4 is observed compared to the
as-prepared one, indicating that the catalyst remains intact even
after long-term electrolysis. Our control experiments dispose of
concerns that CO-induced surface restructuring into
nanoparticles leads to the high C2+ selectivity toward CORR.[26]
We herein have attempted to rationalize the size effect on
CO2/CO electroreduction based on both our experimental
observations and documented theoretical investigations. As the
size of NCs decreases (to SAs), the great population of low
coordinated single-sites result in stronger chemisorption of H* vs.
CO2 as compared to bulk Cu.[3,6,27] This is the reason that the
competing HER reaction is apparently enhanced as the size of
Cu NCs decreased. But their weak binding of CO* prevents
subsequent deep reduction or coupling.[17,28] Therefore, only C1
compounds and H2 were obtained over Cu/GDY in CO2RR. As
for CORR, Back et al. concluded that single catalytic center of
SAs facilitates the protonation of CO* to CHO* due to strong
chemisorption of H*, multiple hydrogenation steps then take
place on CHO*, leading to the formation of CH2O*, CH3O* and
ultimately CH4.[29] The C−C coupling pathway between two C1
species into one C2 product is thermodynamically adverse due
to the site competition. As is shown in Figure 4, the coupling of
the two CO molecules to form OCCO* is uphill by 1.57 eV with a
barrier of 1.62 eV. Since the adsorption of the second CO is also
endothermic, the effective barrier from CO* to OCCO* is 1.68 eV.
The absorption of the third CO is absolutely inhibited on Cu SAs.
Accordingly, SAs shows the predominant C1 selectivity during
CORR. Large NCs are consisting of more undercoordinated Cu
atoms and higher areal density at each cluster compared to SAs,
which is beneficial for lowering free energy for C−C coupling,[29c]
allowing the reabsorption and dimerization of the CO or CO-
derived intermediates spilling over to C2+ compounds.[30] We
demonstrate that cluster’s size is of significant importance to
CO2/CORR. In view of little research on Cu NCs for CO2/CORR,
further studies might be necessary.
Conclusion
In summary, we synthesized a family of size-controlled Cu
catalysts from single atoms to subnanometric clusters (0.5−1
nm) to nanoclusters (1−1.5 nm) on graphdiyne matrix via a
creative acetylenic-bond-directed site-trapping approach. A clear
correlation between the size of NCs in an atomic level and the
catalytic performance could be inferred. For CO2RR, larger
nanocluster catalyst is more active and selective for CO over H2.
For CORR, increasing the size of NCs will dramatically improve
catalytic activity and selectivity for C2+ productions. The
nanoclusters catalyst (1−1.5 nm) with the highest metal loading
up to 45.2 wt %, represents the first GDY-supported
nanoclusters to access high C2+ activity and selectivity toward
5
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RESEARCH ARTICLE
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Experimental Section
Materials: THF was freshly distilled from sodium
benzophenone ketyl under Ar and stored over sodium. Cuprous
iodide (CuI) and Tetrabutylammonium fluoride (TBAF, 1.0 M in
THF) were purchased from Sigma Aldrich. The water used was
purified with a Millipore system (typically 18.2 MΩ cm resistivity).
Gas diffusion layers (GDL) were purchased from Fuel Cell Store
with Sigracet 29 BC model. IrO2-coating titanium sheet as the
counter electrode was purchased from Baoji Zhiming Special
Metal Co., LTD. Hexakis[(trimethylsilyl)ethynyl]benzene and
GDY were synthesized according to the reported methods.[11]
Synthesis of catalysts Cu/GDY: The catalysts were
synthesized under a dry and oxygen-free argon atmosphere by
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using
the
Schlenk
technique.
To
a
solution
of
hexakis[(trimethylsilyl)ethynyl]benzene (43.6 mg, 0.066 mmol) in
dry THF (15 ml) was added dropwise 0.4 mL of TBAF (1.0 M in
o
THF, 0.4 mmol) and stirred at –78 C for 30 min. The solution
was transferred to a suspension of cuprous iodide (75 mg for
Cu45.2/GDY; 3.3 mg for Cu6.0/GDY; 0.8 mg for Cu1.5/GDY) in THF.
The mixture was allowed to warm to room temperature with a
violent stirring and then heated at 60 oC for 7 days. The
precipitate was separated by centrifugation, washed by acetone,
ethanol and water, and dried in vacuum overnight to yield the
corresponding catalysts as brown to black powders.
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This work is supported by the National Natural Science
Foundation of China (21771098, 21903016), the Science and
Technology Innovation Commission of Shenzhen Municipality
(JCYJ20170817111548026), Shenzhen Clean Energy Research
Institute (No. CERI-KY-2019-003) and the Shenzhen Nobel
Prize Scientists Laboratory Project (C17783101) and
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Keywords: size effect • CO2/CO electroreduction • Cu
nanoclusters • single atoms • graphdiyne
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7
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RESEARCH ARTICLE
Entry for the Table of Contents
The size-controlled Cu catalysts from single atoms to subnanometric clusters (0.5−1 nm) to nanoclusters (1−1.5 nm) on graphdiyne
matrix are readily prepared via a creative acetylenic-bond-directed site-trapping approach. A clear size dependence of activity and
selectivity toward CO/CO2RR over these atomic-level catalysts has been demonstrated for the first time.
8
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