Synergistic surface modification of Cu with schiff-base networks for high selectivity and durability in CO_2-to-C_2H_4 electroreduction

Domain: biology
Published: 2026-03-14
Editorial outcome: major_revision

Abstract
The electrocatalytic CO reduction reaction (e-CO RR) on Cu-based catalysts has been extensively studied;
2 2
however, achieving high selectivity for C products and long-term durability remains challenging. Here,
2+
we introduce a straightforward approach that enhances both C H selectivity and catalyst durability by
2 4
incorporating a nitrogen-rich Schiff-base Network (SNW), leveraging a synergistic interaction between Cu
and SNW. Notably, Cu cubes with SNW, predominantly exposing theS Cu(200) facet, achieve a Faradaic
Efficiency (FE) of 71.2% for C
2
H
4
at a current density of 265 mA cmS -2, which not only exceeds tetrahedral
and spherical Cu with or without SNW, but also ranks competitively among state‑of‑the‑art Cu-based
E
catalysts reported to date. Theoretical calculations suggest that the presence of SNW on Cu facilitates the
R
*CO-*CHO coupling and/or the C H desorption, thereby enhancing C H formation. Furthermore, the
2 4 2 4
Cu(200)-SNW surface exhibits optimized Gibbs free enePrgies for the reaction steps compared to bare Cu
and other SNW-modified Cu surfaces, which rationaliz es the experimental observations. In situ electron
N
microscopy further suggests that SNW confers durability by stabilizing Cu facets and preventing corrosion
and dissolution under reaction conditions. I

Introduction
Global industrialization has led to a substantial release of CO into the atmosphere, significantly
2
contributing to global climate change 1, 2, 3. This situation has sparked increasing interest in strategies aimed
at reducing CO emissions alongside efforts to convert CO into valuable chemicals. However, the robust
2 2
C=O bonds in CO , with a bond dissociation energy of 750 kJ mol-1, pose a considerable challenge to its
2
conversion 4. The e-CO RR, particularly in aqueous media for enhanced environmental compatibility, has
2
emerged as a promising technique for CO conversion. While diverse metal catalysts, including Au 5, Ag 6,
2
Ru 7, and Cu 8, have beenA explored for e-CO RR, Cu-based catalysts hold particular promise. Their capacity
2
to produce multi-carbon (e.g., C ) products, coupled with cost-effectiveness, positions them as leading
2+
candidates for scalable implementation.

Despite these strengths, Cu-based catalysts face significant challenges in achieving high selectivity for C
2+
products, a critical factor limiting their industrial viability, which is hindered by the inherent complexity of
C−C coupling and the competition from the hydrogen evolution reaction (HER) 9, 10, 11, 12. As C−C coupling
relies on the dimerization of *CO intermediates 1, enhancing C selectivity demands the stabilization of
2+
*CO intermediates and promotion of their dimerization 13. This requires tailored engineering of surface
structures and electronic states. Recent advances, such as surface facet control 14, 15, heteroatom doping 16,
defect engineering 9, and modifications to size and morphology 17, have enabled Cu catalysts to achieve >
70% FE for C products at industrially relevant current densities (>300 mA cm-2) 9, 13.
2+

Beyond selectivity, Cu-based catalysts encounter operational stability issues, especially under high
overpotentials for generating C products, due to catalyst reconstruction, fragmentation, and dissolution 18,
2+
19, 20. These dynamic behaviors can significantly degrade catalytic performance, further constraining their
industrial applicability. Consequently, the development of novel Cu-based catalysts that simultaneously
deliver both high C selectivity and durability is paramount. Such advancements are essential to unlock
2+
the full potential of e-CO RR, enabling sustainable chemical production by integrating CO valorization
2 2
with renewable energy sources 21, 22. Note that, engineering challenges like mass transport limitations at
industrial current densities, product separation, and compatibility issues with existing gas diffusion
electrodes also hinder the commercial use of Cu-based catalysts in e-CO RR 4, which, however, are not the
2
primary focus of this research.

In this study, we synthesized three distinct shapes of Cu nanoparticles (NPs): cubes (Cu ), spheres (Cu ),
cub sph
and tetrahedra (Cu ), and subsequently mixed these NPs with SNW, a nitrogen-rich organic network
tet
material, to create three Cu -SNW catalysts with Cu NPs intimately surrounded by SNW, for the e-
nps
CO RR. Given the high adsorption capacity of SNW for CO 23 (confirmed herein, Figure S1), its
2 2
integration is expected to enhance CO enrichment around active sites, accelerating its conversion to CO
2
intermediates and potentially improving C selectivity in the e-CO RR. Our results demonstrated that the
2+ 2
Cu-SNW catalysts exhibit enhanced selectivity for C H , with the top-performing catalyst (Cu -SNW)
2 4 cub
achieving an FE of 71.2 ± 2.0% at a current density of 265 mA cm-2, surpassing most reported Cu-
C2H4
based catalysts. Moreover, Cu-SNW catalysts demonstrated higher durability compared to bare Cu .
nps
Especially, the Cu -SNW catalyst maintained high C H selectivity (71.2%-61.3%) at 265 mA cm-2 during
cub 2 4
a 24-hour durability test. We systematically investigated the origins of enhanced catalytic selectivity and
durability, as well as the reaction mechanism through a combination of electron microscopy, X-ray
diffraction (XRD), X-ray photoemission spectroscopy (XPS), in situ infrared absorption spectroscopy
(IRAS), and density functional theory (DFT) calculations.

Results
Synthesis and structural and chemical characterizations

Cu NPs (Cu ) of three distinct shapes, namely, Cu , Cu , and Cu , were synthesized via a colloid-
nps cub sph tet
chemistry-based method, as illustrated in Figure 1a. After surface modification with SNW, the obtained
samples were labeled as Cu -SNW, Cu -SNW, and Cu -SNW (Figure 1a). Electron microscopy was
cub sph tet
employed to analyze the morphology and structure of the prepared samples. Both scanning electron
microscopy (SEM) (Figure S2) and transmission electron microscopy (TEM) confirmed the successful
synthesis of well-defined Cu , Cu , and Cu , exhibiting cubic, spherical, and tetrahedral shapes with
cub sph tet
average diameters of 48.3 nm, 65.4 nm, and 46.0 nm, respectively (Figures 1b, c, f, g, j, k and S3). Selected-
area electron diffraction (SAED) analysis confirmed that the Cu of different shapes are primarily metallic,
nps
with a minor presence of Cu O (insets of Figures 1c, g, and k). The detected Cu O likely resulted from
2 2
surface oxidation during exposure to air in the TEM sample preparation process. High-resolution TEM
(HRTEM) images revealed that Cu and Cu were enclosed by (200) and (111) facets, respectively, while
cub tet
Cu exhibited no preferential surface terminations (Figures 1d, h, and l) (Figures S4-S5). After the addition
sph
of SNW, annular dark-field STEM (ADF-STEM) and secondary electron STEM (SE-STEM) images of
identical locations (Figures 1e, i, and m, and Figures S6a-c, S7a-c, andS S8a-c), along with supplementary
HRTEM images, confirmed an intimate contact between Cu and SNW, as well as a partially buried state
nps S
of Cu . Furthermore, energy-dispersive X-ray (EDX) mapping and electron energy-loss spectroscopy
nps
E
(EELS) demonstrated the presence of C and N surrounding the Cu, reaffirming the close contact between
Cu and SNW (Figures 1e, i, and m, and Figures S6d-g, S7d-g,R S8d-g, and S9-S11). Additionally, solid-state
nuclear magnetic resonance (13C CP/TOSS) analysis idenPtified four characteristic carbon peaks, which are
in good agreement with previous findings confirming th e presence of SNW (Figure S12) 23.

XRD was employed to further examine the phase composition and surface terminations of the prepared
samples. Figures 2a and 2b show the XRD patterns of Cu , Cu , and Cu , in their pristine and SNW-
cub sph tet
modified forms. All samples show diffraction peaks corresponding to Cu metal with an fcc structure. The
Cu O phase was absent in the XRD measurements due to its minimal presence on Cu surfaces. Each type
2 nps
of Cu displayed diffraction peaks at identical positions, indicating that the SNW decoration process did
nps
not alter the structure of the Cu . However, noticeable variations in the relative intensity of diffraction
nps
peaks were observed among the samples. Cu and Cu -SNW exhibited a Cu(111):Cu(200) intensity ratio
sph sph
of 1:0.45, consistent with standard powder diffraction data 24, 25. In contrast, Cu and Cu (and their
cub tet
respective SNW-modified counterparts) exhibited markedly different ratios of 1:2.3 and 1:0.2, respectively.
These results suggest that Cu (or Cu -SNW) exhibits no preferential facet termination, whereas Cu
sph sph cub
and Cu (their respective SNW-modified counterparts) are predominantly terminated by (200) and (111)
tet
planes, respectively, corroborating the HRTEM observations. XPS was utilized to evaluate the surface
chemical state of the catalysts (Figures 2c-e). Survey spectra of Cu and Cu -SNW are presented in
nps nps
Figures S13a and S14a. The detection of the N 1s peak in Cu -SNW confirms the presence of SNW. The
nps
relative shift of the N1s peak to the lower binding energies (by 0.3-0.4 eV) compared to that in pure SNW
indicates electron enrichment of N sites in the Cu -SNW, likely due to surface charge transfer from Cu to
nps
SNW. Analysis of Cu 2p and Cu LMM Auger spectra reveals the coexistence of Cu(I) and Cu(0) species in
both the pristine Cu and those decorated with SNW, corroborating the detection of O 1s (Figures S13 and
nps
S14) and aligning with the SAED results (Figures 2d and S13-S14) 26, 27. Notably, the Cu -SNW samples
nps
exhibited a noticeable shift of the Cu 2p peak to higher binding energies (by 0.9-1.2 eV) compared to the
bare Cu, indicating a lower electron density around Cu (Figures 2c and 2e) 28, 29, 30. This finding supports
the observed shift to lower binding energies in the N 1s peak of Cu-SNW samples compared to bare SNW.
The charge transfer and redistribution indicate strong interactions between Cu and SNW, which could
influence the overall catalytic performance, as will be shown and discussed in the following sections.
Finally, the hydrophobicity/hydrophilicity of bare Cu NPs and SNW-modified ones was investigated. Our
results show that all tested catalysts had contact angles grePater than 90°, indicating their hydrophobic nature
31. Compared to pure Cu catalysts, the Cu-SNW cata lysts showed increased contact angles (by 2-3°),
indicating improved hydrophobicity (see Figure S15). This enhanced hydrophobicity can reduce the contact
of electrolytes with active sites, thereby suppressing cathodic corrosion and enhancing catalyst stability 32.
It can also limit H⁺/H O access to active sitEes, thereby decreasing HER activity while directing electrons
2
toward CO reduction 33.
2

E-CO RR performance

Next, we evaluated the catalytic performance of Cu and Cu -SNW in the e-CO RR. Electrochemical
nps nps 2
tests were conducted in a 1 M KOH solution, using a geometric electrode area of 1 cm2 in a T2-type flow
cell (Figures 3a and S16). The optimal catalyst loading (0.5 mg cm-2) and the ratio of Cu to SNW (40
nps
mg:10 mg) were determined from optimization experiments (as detailed in Figures S17 and S18, along with
the relevant discussion) and used for all subsequent tests. All the reported potentials are referenced to the
reversible hydrogen electrode (RHE) and corrected for iR drop. Before initiating the electrochemical tests,
an activation process was conducted using cyclic voltammetry to enhance activity and ensure a relatively
stable state for the subsequent measurements 7, 17. Linear sweep voltammetry (LSV) demonstrated that Cu
cub
exhibited a higher current density than the other two Cu types in both Ar and CO environments (Figures
2
3b and S19). Furthermore, it is clearly shown that the incorporation of SNW increased the current density
in all samples, with Cu presenting the most significant improvement. Notably, Cu -SNW showed the
tet cub
highest current densities across different potentials among all samples. Electrochemical impedance
spectroscopy (EIS) analysis aligned with the trend seen in the LSV results, with Cu -SNW exhibiting the
cub
lowest resistance, which indicates the fastest charge transfer kinetics (Figure 3c and Table S1).

The FE of various products at different potentials (Figures 3d-f) was then investigated. Our results showed
that Cu has the highest yield of C H as the primary product among pure Cu catalysts, suggesting that the
cub 2 4
Cu (200) plane favors C H formation, in line with previous research 14, 15. In contrast, Cu and Cu
2 4 sph tet
predominantly produced CO. Notably, surface modification with SNW significantly enhanced the C H
2 4
yield. Specifically, the FE of C H (FE ) increased by 2.0 times, 5.5 times, and 5.2 times for Cu -SNW,
2 4 C2H4 cub
Cu -SNW, and Cu -SNW, respectively (Figure 3g). This enhancement occurred at the expense of C
sph tet 1
products, while no significant effect on the selectivity of C products was observed (Figures S20-S23),
3
implying enhanced C−C coupling in the presence of SNW. Additionally, the SNW’s inclusion was found
to decrease the sensitivity of FE to potential (see Table S2), as evidenced by the reduced coefficient of
C2H4
variation, indicating enhanced stability of the active structures/sites for C H formation in the Cu -SNW
2 4 nps
catalysts. It is important to note that pure SNW primarily produced H (Figure S24), suggesting that the
2
enhanced performance in the e-CO RR resulted not from SNW but from a synergistic effect between Cu
2
and SNW.

Finally, we assessed the catalytic durability of Cu , Cu , and Cu , along with their SNW-modified
cub sph tet
counterparts at a fixed potential with an initial current density of 100 mA cm-2 (Figure S25). Potentiostatic
tests showed that the current density of Cu
nps
-SNW remained stable andS was notably better than that of the
unmodified Cu (which decayed with a rate of 3.6 mA cm-2 h-1, 14.2 mA cm-2 h-1 and 3.4 mA cm-2 h-1 for
nps S
Cu , Cu , and Cu ), indicating that the SNW modification substantially improved the stability of the
cub sph tet
E
catalysts. To further explore the potential of Cu-SNW catalysts, we conducted a durability test on the Cu -
cub
SNW at a higher current density of 265 mA cm-2. Our resRults indicated that while the current density
remained stable, high C H selectivity, ranging from 71P.2% to 61.3%, was sustained over the 24-hour
2 4
testing period (Figure 3h).

In situ EC-STEM and IL-TEM observations

The remarkable decay in current density observed for Cu (see Figure S25) indicated instability and
nps
possible structural degradation. To investigate the structural changes of Cu during e-CO RR, we
nps 2
employed in situ electrochemical STEM (EC-STEM), a powerful emerging technique for monitoring the
dynamic changes of electrocatalysts under operating conditions (Figure S26) 34, 35, 36, 37. As illustrated in
Figure 4a, the in situ EC cell consists of a bottom chip with three screen-printed electrodes, a Pt working
electrode (WE), a Pt counter electrode (CE), and a Pt reference electrode (RE)-and a top chip, sealed with
a rubber O-ring (Figure S27). The cell was filled with CO -saturated 0.1 M KHCO solution, and the sample
2 3
was deposited on the WE. Additional details of the experimental setup are available in the Supplementary
Information. Sequential STEM images of bare Cu cubes captured under -0.79 V vs. RHE are presented in
Figures 4b-e, 4f, and S28. It was observed that the Cu cubes experienced heavy corrosion, beginning at the
corner sites and progressively spreading across the entire particle. While some cubes completely dissolved,
most underwent corrosive reshaping, transforming into ill-defined shapes during the observation period.
The projected areas of Cu cubes and their changes with time are plotted in Figure S29. Similar structural
changes were observed at -0.4 V vs. RHE, though at slower corrosion rates (Figure S30), likely due to the
lower applied potential. To assess the effect of electron beam irradiation on these transformations, we
observed the system before and after applying potentials without beam exposure. Similar phenomena
appeared in both cases (Figure S31), indicating that electron beam irradiation is not the main cause. In
contrast, in situ EC-STEM observations of the Cu -SNW at -0.4 V and -0.79 V showed only minor
cub
changes at the NP corners over the same duration (Figures S32-S34, 4g-j, 4k, and S35). These comparative
observations highlight that SNW modification can substantially enhance the structural stability of Cu ,
nps
thereby prolonging their catalytic durability in e-CO RR (Figures 4f and k).
2

Since the in situ EC-STEM experiments were conducted under static conditions and involved an insufficient
number of observable Cu participating in the reaction, the validity of the aforementioned observations
nps
could be challenged. To assess the corrosion behavior of Cu under more practical conditions, we carried
nps
out identical location TEM (IL-TEM) on Cu and Cu -SNW in CO -saturated 0.1 M KHCO 38, 39. It is
nps nps 2 3
important to note that, due to stability issues with the carbon film on the gold finder grid used in the IL-
TEM study, specifically, its tendency to break down at high potentials,S we limited the applied potential (-
0.4 V vs. RHE) to preserve the structural integrity of the carbon support film (as shown in Figure S43a6 )
S *
40, 41. Further details regarding the experimental setup and parameters are provided in Figure S36 and the
E
Methods section. Figure S37 shows IL-TEM images of Cu before and after being subjected to a reducing
nps
potential. It is clear that all forms of Cu particles experiencedR surface corrosion, qualitatively mirroring the
observations made at low potential (-0.4 V vs. RHE) durPing in situ EC-STEM experiments (Figure S30).
These observations suggest that Cu corrosion is a gen eral phenomenon under e-CO
2
RR, regardless of
particle shapes (Figures S38-S40). In contrast, morpNhological changes in Cu -SNW are less pronounced
nps
(Figures S41-S43), consistent with in situ EC-STEM observations. Ex situ TEM (Figure S44) confirmed
I
the findings of both in situ EC-STEM and IL-T EM studies. These results clearly demonstrate the role of
E
SNW in enhancing the resistance of Cu to corrosion, thereby improving the durability of catalytic
performance. Additionally, the used Cu L and Cu -SNW catalysts were examined by XRD (Figure S45).
nps nps
For the used Cu catalyst, the intensCity ratio of Cu(111) to Cu(200) significantly decreased from (1:2.3)
cub
to (1:0.9), indicating a reduced dominance of the Cu(200) facet (Figures 2a and S45). Similarly, the Cu(111)
I
facet of the used Cu catalyst beTcame less dominant, with the intensity ratio increasing from 1:0.2 to 1:0.35
tet
(Figures 2a and S45). HoweRver, both the used Cu
cub
-SNW and Cu
tet
-SNW catalysts retained the dominance
of the Cu(200) and Cu(111) facets, though to a lesser extent (see Figure S45 for more details), reaffirming
A
the improved stability after SNW modification. We propose that the close contact between Cu and SNW
creates a protective layer that shields the Cu surface from corrosion and dissolution, thus improving its
stability. Furthermore, the enhanced stability could also be associated with the electronic interactions
between Cu and SNW 29, 30. These arguments will be elaborated upon in the sections on theoretical
simulations and discussions in more detail.

Reaction intermediates and pathways

In situ infrared reflection absorption spectroscopy (IRAS) experiments were performed to elucidate the
reaction pathway for CO electroreduction to C H (Figures 5 and S46). All spectra are presented in their
2 2 4
raw form without any additional smoothing to ensur
e fidelity. Figures S47a-c compare time-resolved IRAS
data for Cu , Cu , and Cu at varied potentials. Notably, only Cu exhibited a distinct vibrational band
cub sph tet cub
at 1913 cm-1, assigned to the C-O stretching mode of bridged CO on Cu surfaces 42, 43, indicating that the
Cu(200) plane can effectively stabilize bridEged *CO. Such stabilization could promote C−C coupling by
maintaining sufficient *CO surface coverage for bimolecular reactions 44, 45, 46, explaining the higher FE
L C2H4
observed for Cu in e-CO RR in this study. The absence of detectable *CO on Cu and Cu implies
cub 2 C sph tet
significantly weaker *CO adsorption or low surface coverage on these nanocrystals, due to the dominance
I
of facets like Cu(111) or Cu(110) that exhibit lower *CO binding energies.

Figures 5a, 5b, and 5c show Rthe in situ IRAS results at different potentials for Cu
cub
-SNW, Cu
sph
-SNW, and
Cu -SNW, respectively. The universal detection of *CO (1911-1914 cm-1) and *CHO (1490-1493 cm-1,
tet A
bending vibration of C-H) signals across all Cu-SNW catalysts demonstrates that SNW modification
preserves *H availability and accelerates the CO hydrogenation step (CO + *H → *CHO) 43, 47. Moreover,
the *CO band was notably stronger for Cu -SNW in comparison to bare Cu (Figure S47), suggesting
nps nps
that SNW enhanced the formation and stabilization of *CO intermediates. This observation is consistent
with experimentally observed and reported high capacity for CO adsorption of SNW. Importantly, the
2
*OCCHO (1264-1268 cm-1, stretching vibration of C-O) intermediates, which are crucial for C H
2 4
production 47, were also detected. The co-presence of these key reaction intermediates, i.e., *CO, *CHO,
and *OCCHO, provides spectroscopic evidence for the *CO + *CHO→*OCCHO reaction pathway 42, 45.
A comparison of the three cases revealed that the *CO signal for Cu -SNW (Figure 5a) showed no obvious
cub
changes across various potentials (-0.6 ~ -0.9 V vs. RHE), whereas for both Cu -SNW and Cu -SNW
sph tet
(Figures 5b and 5c), the intensity of the *CO signal exhibited variations dependent on the applied potential.
The consistent *CO signal for Cu -SNW at different potentials indicates saturated bridged *CO adsorption,
cub
which is beneficial for C−C coupling 48. For Cu -SNW, the *CO signal increased progressively while the
tet
*OCCHO intensity remained nearly constant. This observation indicates that C−C coupling is not favored
for Cu -SNW. In the case of Cu -SNW, correlated intensity changes between *CO and *OCCHO were
tet sph
observed, indicating relatively efficient C−C coupling. However, the water signal diminished at
increasingly negative potentials, which may lead to insufficient proton supply for further hydrogenation.
This could explain the observed decrease in selectivity towards C H at more negative potentials (see Figure
2 4
3e). The reduced water signal might be associated with a high H production rate (bubble formation) of this
2
catalyst (Figure S24), which impedes mass transfer at the electrode surface.

Theoretical simulations

Finally, to elucidate the origins of differences in C H selectivity and to further understand the role of SNW
2 4
in enhancing catalytic performance, we constructed structural models of Cu(111), Cu(200), Cu(111)-SNW,
and Cu (200)-SNW (Figures 6 and S48-S56) and performed DFT calculations. It is important to emphasize
that these calculations employed simplified, idealized models under static conditions, which may not fully
capture the complexity of the actual electrochemical interfaces. Therefore, the following discussion focuses
on identifying general trends and plausible explanations that are complementary to the experimental
observations. Our results revealed that the decoration of SNW on Cu induces charge transfer and
redistribution. Specifically, charge transfer from Cu(200) to SNW led to charge accumulation at the N sites
of SNW, as illustrated by the charge density difference plots in Figures 6a, 6b, and S57. This results in
electron deficiency at the Cu sites and enrichment at nearby N sites, which is qualitatively consistent with
the XPS observations of shifts in Cu 2p peaks to higher binding energies and shifts in N 1s peak to lower
binding energies in both the fresh and used catalysts (Figures 2c, S58, and S59). Furthermore, our
calculations showed that the CO adsorption energy at the N site was the most negative among all N sites
2 1
in SNW and Cu sites (refer to Figure S60 and relevant discussions), suggesting that the N site could be a
1
plausible active center for e-CO RR in Cu-SNW catalysts.

Subsequently, we calculated the Gibbs free energy changes (ΔG) for the reaction steps on Cu(200), Cu(111),
and their SNW-modified counterparts (see Figure 6c). Based on in situ IRAS results, which identified the
*CO+*CHO→*OCCHO pathway, and in conjunction with previous studies on C H formation over Cu
2 4
catalysts, we considered a complete reaction pathway from CO to C H , as illustrated in Figure 6c. We
2 2 4
define the largest free energy change as ΔG in the reaction pathway. Our calculations indicate that
M
Cu(200)-SNW has a ΔG of 0.32 eV for the *CO+*CHO→*OCCHO step. In comparison, for Cu(200),
M
Cu(111)-SNW, and Cu(111), the ΔG increases during the *OCCH → *O + *C H step, which is related
M 3 2 4
to the C H desorption process, with values of 0.57, 0.65, and 0.71 eV, respectively (Figure S61). Since
2 4
neither the desorption step nor the *CO−*CHO coupling step involves electron transfer, these barriers are
independent of the electrode potential. Thus, under the assumptions of our model, at high cathodic
potentials, the desorption step could act as the rate-limiting step for Cu(111), Cu(111)-SNW, and Cu(200).
On the other hand, for Cu(200)-SNW, the *CO−*CHO coupling step becomes rate-limiting, as its energy
barrier exceeds that of desorption. Note that SNW-modified surfaces show smaller ΔG values compared
M
to their bare Cu counterparts, suggesting that the presence of SNW effectively optimizes the free energies
for reactions towards C H , which is in support of the observed enhancement in selectivity. The Cu(200)-
2 4
SNW exhibits the smallest ΔG among studied surfaces, suggesting a potentially higher C H selectivity,
M 2 4
a trend that aligns with our experimental observations (Figure 3d).

We also computed the energy profiles for other possible steps in the e-CO RR, including the pathways from
2
*CHO to CO(g) and CH (g), as well as the energy associated with the *H adsorption in the competing HER
4
(Figures S62-65). Our results indicate that the ΔG for CH formation S(0.87, 0.86, 1.16, and 0.93 eV) are
M 4
consistently higher than those for C
2
H
4
(0.32, 0.57, 0.65, and 0.71 eVS) across all catalyst surfaces (Cu(200)-
SNW, Cu(200), Cu(111)-SNW, and Cu(111)), which aligns with the experimentally observed suppression
of CH production. Furthermore, for Cu(200)-SNW and Cu(200), the ΔG values for CO (0.93 and 0.76
4 M
eV) and H (0.87 and 0.80 eV) formation exceed those for C H (0.32 and 0.57 eV), indicating a higher
2 2 4
selectivity towards C H , in agreement with experimenPtal trends. In contrast, for Cu(111)-SNW and
2 4
Cu(111), the free energies for CO (0.60 and 0.33 eV) fo rmation are lower than those for both H (0.73 and
2
0.54 eV) and C H (0.65 and 0.71 eV), suggesting a thermodynamic preference for CO production, again
2 4
aligning with the experimental observation that CIO is the dominant product on these surfaces. Notably, our
calculations also show a trend where SNW mo dification increases the free energies for the formation of
CO, CH , and H across all catalyst surfaces (Figures S62-S64), in addition to its role in optimizing the
4 2
energies for C H production as described above, thereby making the pathway towards C H formation
2 4 2 4
more favorable.

Methods
Chemicals: The chemicals used in this study include Oleylamine (OAM, 80−90%), Trioctylphosphine
oxide (TOPO, 99%), and CuBr (99.99%), all sourced from Sigma-Aldrich. Melamine (99%) was obtained
from Aladdin, while Terephthalaldehyde (99%) was procured from Rhawn. Dimethyl sulfoxide (DMSO,
99.99%), Tetrahydrofuran (THF, 99.9%), Dichloromethane (DCM, 99.9%), N, N-Dimethylformamide
(DMF, 99.9%), n-Hexane (99%), Acetone (99%), Ethanol (99.9%), KOH (99.5%), and KHCO (99.99%)
3
were acquired from Sinopharm Chemical Reagent Co., Ltd. D O (99.9%) was purchased from Manalab.
2
All chemicals were utilized as received without any further purification.

Synthesis of Cu : The synthesis of copper nanoparticles with distinct shapes was adapted from the methods
cub
published in the literature18. TOPO (9.37 g) was introduced into a three-neck flask and maintained under
vacuum for 30 minutes to ensure thorough drying. Subsequently, 117 mL of OAM was added under a
nitrogen atmosphere. The mixture was heated to 110 °C under vacuum for 30 minutes before being cooled
naturally to 50 °C, followed by the addition of CuBr (0.717 g). Under a nitrogen atmosphere, the
temperature was increased to 260 °C at a rate of 10 °C min-1. The reaction proceeded at this constant
temperature for an additional hour before being cooled naturally to 9S0 °C. After centrifugation with ethanol
and n-hexane three times each, the samples were collected in seaEled glass bottles containing n-hexane and
subsequently transferred into a glove box for further analysis.

Synthesis of Cu :
TOPO (5.7975 g) and 117 mL of OAMP were added to a three-neck flask and maintained
sph
under vacuum for 30 minutes to ensure thorough dryin g. The mixture was then heated to 125 °C under
vacuum for two hours, after which it was cooled nNaturally to 50 °C. Following this CuBr (0.3873 g) and
DMF (0.5 mL) were added. The mixture was subsequently heated to 120 °C and kept at this temperature
for ten minutes. Under nitrogen conditions, the temperature was increased to 270 °C at a rate of 10 °C min-
1, and the reaction proceeded at this constantE temperature for two hours before being cooled naturally to 90
°C. After centrifugation with ethanol andL n-hexane three times each, the samples were collected in sealed
glass bottles containing n-hexane andC transferred into a glove box for further analysis.

Synthesis of Cu : OAM (45 mL) wIas introduced into a three-neck flask and maintained under vacuum for
tet
30 minutes to ensure complete drying. Subsequently, TOPO (6.9510 g) and CuBr (0.4415 g) were added
under a nitrogen atmosphereR. The mixture was then heated to 125 °C under vacuum for three hours before
it was cooled naturally toA 50 °C, followed by the addition of DMF (0.65 mL). Under nitrogen atmosphere,
the temperature was increased to 270 °C at a rate of 10 °C min-1; the reaction was conducted at 270 °C for
two hours before being cooled naturally to 90 °C. After centrifugation with ethanol and n-hexane three
times each, the samples were collected in sealed glass bottles containing n-hexane, and subsequently
transferred into a glove box for further analysis.

Synthesis of SNW: A nitrogen-rich SNW was synthesized using the method described in the literature 23.
Melamine (156.5 mg), terephthalaldehyde (250 mg), and DMSO (7.65 mL) were mixed and subjected to
ultrasonic treatment for 60 minutes. The resulting mixture was then transferred into a Teflon-lined stainless
steel high-pressure reactor, which was heated to 180 °C for 10 hours and subsequently cooled naturally to
room temperature (25 °C). The product was filtered and washed with acetone to yield a white powder.
Unreacted precursors within the product were purified using acetone at 45 °C for 6 hours, THF at 55 °C for
3 hours, and DCM at 30 °C for another 6 hours. Finally, the synthesized product was dried overnight in a
vacuum oven at 45 °C, collected, and ground for further analysis.

Synthesis of Cu -SNW / Cu -SNW / Cu -SNW: Cu (40 mg) were introduced into a three-neck flask
cub sph tet nps
containing 150 mL of n-hexane. After achieving a uniform dispersion through ultrasonic treatment for 30
minutes, SNW (10 mg) was added to the solution. The mixture was stirred for 10 hours at 69 °C before
being cooled to room temperature. The solution was subjected to centrifugation to isolate Cu -SNW.
nps
The whole experiment was conducted under a nitrogen atmosphere.

Materials characterization.
TEM and HRTEM images were recorded using FEI Talos F200×G2 transmission electron microscope
operated at 200 kV. BF-STEM, ADF-STEM, and SE-STEM were recorded from JEOL JEM F200
transmission electron microscope operated at 200 kV. EELS and EDX mappings were collected with a
Gatan 1077 module and an EDX spectrometer integrated with the JEOL JEM F200 transmission electron
microscope. SEM images were taken on a field-emission scanning electron microscope (SEM Verios G4).
In situ EC cell system and in situ holder (TLM-ST) provided by Zep Tools Technology Co., Ltd. XRD data
were collected from a Rigaku Ultima IV. XPS data were collected from a Thermo Scientific ESCALAB
250Xi. The reaction products were analyzed by gas chromatography (GC-2014C, Shimadzu) and nuclear
magnetic resonance spectroscopy (Bruker Avance III 400 HD spectrometer). The contact angles were
measured on the Powereach JC2000C contact angle system.

Electrochemical measurements.
Electrochemical measurements were performed using an electrochemical workstation (Autolab
PGSTAT302N) equipped with the FRA32M module and a flow cell (Shanghai Chuxi Industrial Co., Ltd).
The pretreated sample, platinum mesh, and Ag/AgCl served as the working electrode (WE), counter
electrode (CE), and reference electrode (RE), respectively. The catalyst ink was prepared by dispersing 0.8
mg of Cu
nps
and 0.2 mg of SNW in a mixture of 950 μL ethanol and 50 μSL of 5 wt% Nafion solution. Then,
0.5 mL of the ink was drop-cast onto a carbon paper substrate (YSL-30T) and dried at room temperature to
obtain the working electrode. For the LSV curve measurements, the scan rate was set to 2 mV s-¹. EIS of
the catalysts was carried out at an amplitude of 5 mV over a frequency range from 100 kHz to 10 mHz. All
tests were conducted in a 1 M KOH aqueous solution. The soRlution was prepared by dissolving 28.053 g of
KOH in a volumetric flask and diluting to a final volumPe of 500 mL. The pH was measured to be 14 at
room temperature. The resistance between the assembl ed anode and cathode plates (R
cell
) was measured
using a multimeter (VC890C/D) and determined to bNe 0.2 ± 0.05 Ω. The ion exchange membrane (Fumasep
FAB-PK-75) was activated by immersion in the electrolyte for more than 24 hours. All reported potentials
in the manuscript were iR-corrected using 80% compensation based on EIS. Non iR-corrected
voltammograms are shown in Figure S67 of the Supplementary Information (corresponding to Figure 3b).
The electrode potential relative to the RHLE is calculated using the following equation:
E = E + 0.197 V + 0.0591 × CpH – (R × I) × 0.8, where E and E are the applied potentials
RHE Ag/AgCl s RHE Ag/AgCl
of reversible hydrogen electrode (RHE) and Ag/AgCl, respectively. R is the solution resistance of the
I s
electrolyzer, and I is the total cuTrrent.

In situ EC-STEM measurements.
Assembly of in situ EC Acell.
A total of 2.5 µL of a 0.05 mg mL-1 Cu and Cu -SNW solution (CO -saturated 0.1 M KHCO aqueous
cub cub 2 3
solution) was deposited onto the top chip, which was subsequently capped with the bottom chip sealed with
a rubber O-ring. The bottom chip is equipped with three screen-printed electrodes: the working electrode
(WE), reference electrode (RE), and counter electrode (CE), all of which are made of Pt.

Calibration of the potentials of Pt RE.
Given that the in situ electrochemical EC cell was equipped with a Pt RE instead of the conventional
Ag/AgCl RE, we need to convert equivalently the potentials of both the Pt RE and Ag/AgCl RE in relation
to the RHE to accurately determine the potentials applied during in situ experiments. The calibration
process was conducted following the approach reported by Yang et al. 37. We performed electrochemical
cyclic voltammetry tests on polycrystalline Pt in a 0.1 M HCl electrolyte, where two pairs of peaks at -0.74
V and -0.62 V (see Figure S26) were observed, corresponding to hydrogen adsorption/desorption on the
{110} and {100} facets of Pt. Typically, the hydrogen adsorption/desorption peak for Pt{110} appears at
0.1 V vs. RHE. Using the relationship RHE + 0.0591 = SHE, established under the test conditions of 0.1 M
HCl, 25 °C, and 1 atm, we estimated that the potential of Pt RE is about 0.79 V higher than that of SHE.

In situ EC-STEM observations.
After mounting the EC cell onto the in situ holder, the holder was inserted into the TEM chamber of a FEI
Talos F200 × G2 (200 kV). The holder was connected to an electrochemical workstation (Autolab
PGSTAT302N). In situ EC-STEM observations were conducted at -0.79 V vs. RHE and -0.4 V vs. RHE,
respectively. The acquisition time for STEM images was set to 2.5 s per frame (1024×1024 pixels with a
dwell time of 3 μs per pixel) with a dose rate of ~204 e nm-2 s-1.

IL-TEM measurements.
In the IL-TEM studies, a loaded gold finder TEM grid (with coordinates) was utilized, which was
sandwiched between a PEEK-embedded glass carbon (GC) electrode (as the working electrode) and a
Teflon cap with a 2.7 mm hole (Figure S36). A graphite rod and an Ag/AgCl were employed as the counter
and reference electrodes, respectively. The electrochemical measurements were carried out in a CO -
2
saturated 1.0 M KOH electrolyte. Various potentials were applied to different samples: Cu and Cu -
nps nps
SNW at -0.40 V vs. RHE. The samples were characterized at the same locations both before and after the
e-CO RR process.
2

In situ IRAS.
In situ IRAS experiments were conducted using an FTIR Thermo Scientific Nicolet iS50 (Figure S46). The
electrochemical cell was filled with a 0.1 M KHCO electrolyte solution, which was purged with CO gas
3 2
for 60 min prior to and during the experiments. The catalysts were closely mounted on the working
electrodes, maintaining distances of about 5-50 μm from the bottom CaF window. We first acquired IRAS
2
signals at the open circuit potential (OCP) to ensure the precision and reliability of subsequent data
measurements. In situ IRAS data were then collected with a 32 s dweSll time at 5-minute intervals for various
potentials.

FE calculation.
The composition of gaseous products was monitored inP real time using an online gas chromatography
system. Each chromatographic analysis was completed within a 16-minute cycle. Electronic mass flow
controllers (Sevenstar-D07-CO ) were installed at bNoth the inlet and outlet streams of the electrochemical
2
cell to control the gas flow rate, which was maintained at 55 sccm. The liquid-phase products in the
electrolyte formed during the e-CO
2
RR was ana lyzed using NMR spectroscopy on a Bruker AVANCE III
HD system. Specifically, 0.5 mL of the electErolyte was mixed with 0.1 mL of D O and an additional 0.5 μL
2
of DMSO was included as an internaLl standard. The proton NMR spectra were recorded at room
temperature. The FE of the productsC were calculated using the following formula: FE (%) = Fnz ×100%,
Q
where Z is the number of electrons required to form product, F is the Faraday constant (96485 C/mol), n is
the total amount of product (in mol), and Q is the total charge.

DFT calculations.
DFT calculations were conducted using the projected augmented wave (PAW) method implemented in the
Vienna ab initio simulation package (VASP) 49, 50, 51, 52. The Kohn-Sham one-electron states were expanded
using a plane-wave basis set with a kinetic energy cutoff of 450 eV. The generalized gradient approximation
(GGA) with the Perdew-Burke-Ernzerhof (PBE) functional was applied to account for the nonlocal
exchange-correlation energy. A sufficiently large vacuum region of 15 Å was included in the vertical
direction to prevent interaction between periodic images, facilitating the investigation of reaction
mechanism on the surface. The Brillouin-zone integration was carried out using the Gamma point sampling
method with a 3 × 3 × 1 k-point grid 53 for geometry optimization. During geometry optimizations, atoms
were allowed to relax until the maximum force acting on each atom was smaller than 0.02 eV/Å, and the
total energy convergence criterion was set to 1 × 10-4 eV. The Gibbs free energy calculation of the reaction
intermediates in the e-CO RR was computed using the CHE method established by Nørskov and co-
2
workers 54, 55, 56. The adsorption energy (E ) of the activated molecules on electrocatalyst surface was
ads
defined as: E = E - E - E , where the E , E , and E represent the energies of the substrate
ads ad/sub ad sub ad/sub ad sub
with adsorbate species, the adsorbate species and the substrate, respectively. For each step, Gibbs free
energy change was calculated as: ΔG =ΔE + ΔZPE – TΔS, where the ΔZPE, ΔS, and T represent zero-
ads
point energy change, entropy change between the adsorbate species and the substrate, and the temperature
(set at 298.15 K), respectively. ΔZPE can be determined by additional vibrational frequency analysis.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "From the multiple experimental measurements, the authors demonstrated that the specific facets of Cu decorated nitrogen-rich Schiff-base Network exhibits the outstanding performance for CO2 reduction into C2 product (C2H4), the catalysts possess high selectivity and long-term durability. Theoretical simulations indicated that it is originated from the presence of SNW on Cu which promotes the *CO-*CHO coupling and/or the C2H4 desorption. Overall the findings are interesting and sound, it may provide the useful guidance to push the electrocatalytic reduction of CO2 a step forward. However, i have concerns about the mechanism understanding, especially the theoretical simulation part. These issues need to be reasonably addressed before considering to be published.\n1. Obviously, the reaction feedstock of present work is CO2, however the reaction starts from CO and CO-COH coupling during the theoretical simulation in Figure 6. How is the electrocatalytic performance of CO2 reduction on 200 and 111 surfaces? How is the selectivity of CO2 reduction into CO (CH4, HCOOH and so on)?\n2. the last step of the reactions should be the desorption of C2H4, it could be the determinating step. what is the desorption energy?\n3. From Figure 6 and Figs. 31 & 32, in the models of Cu@SNW, it is unclear where are the reactive sites. It seems that the reactions happen on top of SNW, what role of Cu 200 plays if it is the case?", "reviewer_2": "General comment:\nThe study presents a novel synergistic surface modification of Cu with nitrogen-rich Schiff-base Networks (SNW), demonstrating significant improvements in C₂H₄ selectivity and catalyst durability. However, the manuscript requires major revisions to be appropriate for publication in Nature Communications.\n1, P2, L33-34: The authors need to provide a specific, literature-supported discussion regarding the challenges associated with achieving high selectivity for C2+ products. The current phrasing weakens the problem statement.\n2. P2, L46-47: Avoid overgeneralization when discussing the bottlenecks for the commercial use of Cu-based catalysts. Provide specific challenges drawn from industrial practice and relevant literature. Clarify the term “sustainable chemistry” and specify the context in which it is being used.\n3. L105-111: Expand the XPS analysis by integrating a detailed discussion of Fig. S10 into the main manuscript. It is acceptable to present a contradictory observation regarding reduced electron density around Cu, as this helps identify future research gaps. Thoughtful research questions contribute to advancing knowledge. Support claims with appropriate citations.\n4. Results and Discussion: Cu-based catalysts are typically sensitive to the potential window. Clearly explain how your strategy impacts this sensitivity—whether it is reduced or amplified—based on your results.\n5. P6, L121: Have you conducted a sensitivity analysis on catalyst loading? Justify the selection of 0.5 mg·cm⁻². If this choice is inspired by the literature, provide a citation; if not, include the sensitivity analysis results.\n6. Include the product distribution categorized into C1, C2, and C3 products to present a comprehensive picture of your results.\n7. Have you performed a quantitative analysis of the observed corrosion? If so, provide the associated results.\n8. P9, L195-196: Elaborate on the results regarding the formation of a protective layer over the Cu surface upon contact with SNW. Highlight how this layer mitigates corrosion and dissolution.\n9. Fig. 5: Provide a mechanistic explanation for the disappearance, appearance, or changes in peaks for intermediates/products at specific potentials. Discuss why certain species emerge or vanish under these conditions.", "reviewer_3": "The paper by Wangjing Xie et al. reports on the synergistic surface modification of Cu with Schiff-Base Networks (SBNs) for high selectivity and durability in the CO2RR process. The high ethylene selectivity and durability have a significant impact on the field of electrochemical CO2 reduction. The authors reported high ethylene (60.7 %) product selectivity and employed IRAS to detect intermediates, explaining the reason for high C2H4 selectivity. However, the reported ethylene performance is inferior to already published results (https://doi.org/10.1021/jacs.2c13384, https://doi.org/10.1038/s41929-020-00504-x). As the authors mentioned in Line 251 (Ref. 14 and 15 in this manuscript), the Cu facet-dependent selectivity is similar to what has already been widely studied in the literature and lacks novelty.\nThe second concern is the study of durability. Although the authors achieved stabilization of the Cu facets by introducing SBN and observed this property using in-situ TEM technique, the in-depth understanding of the durability during CO2RR remains insufficient. For example, there is a lack of detailed experiments on how the change of surface properties of Cunps (e.g., hydrophobicity or hydrophilicity) upon the introduction of SNW affects durability. Tuning catalyst surface properties can have a significant impact on CO2RR performance (https://doi.org/10.1038/s41563-019-0445-x, https://doi.org/10.1038/s41467-023-39351-2). Additionally, the intrinsic studies (e.g., morphology, nitrogen species...) of SNW that contribute to maintaining the durability of Cunps during the CO2RR process have not been thoroughly investigated. Therefore, this study does not present any critical breakthroughs in the perspectives provided. As detailed below, this paper is not recommended for publication in this journal.\nComments:\n1. Line 81: Represent \"Cusph\" with the \"sph\" as a subscript.\n2. In Fig. 2d and Fig. S10, the deconvoluted line shape of Cucup appears unclear. What type of line shape was used? Additionally, in the high-resolution Cu 2p3/2 spectrum of Fig. S10, how were Cu0 and Cu1 distinguished, and what was the basis for this distinction?\n3. The authors should explain the significance of the peak shifts in the high-resolution XPS results (Cu and N) shown in Fig. 2e, c. Moreover, the statement in Lines 193-194, \"We propose that the enhanced stability is due to the electronic interaction between Cu and SNW~,\" requires further discussion.\n4. Please provide the circuit and parameters for the EIS fitting in Fig. 3c. Additionally, include error bars for the liquid products shown in Figs. 3d-f.\n5. The author should provide F.E of C2+ products over time for the stability test presented in Fig. 3h.\n6. The term \"1M KOH saturated with CO2\" is ambiguous. What is meant by this? Can CO2 be saturated in a KOH electrolyte? (See Line 120, Line 175, Figure 5, and Figure S29 captions.)\n7. The author should provide a detailed description of the IRAS in the experimental section. Was the infrared reflection absorption spectroscopy (IRAS) set up with an external reflection configuration?\n8. Please include the wavenumber assignments for the IRAS signal results in Figure 5. Are there any wavenumber shifts depending on the Cu facet?\n9. The authors should provide additional experimental results to support the claim in Line 260 regarding \"SNW's strong adsorption capacity for CO2.\"\n10. Referencing the paper (https://doi.org/10.1021/jacs.1c09508), can the authors identify the facets of the Cunps catalysts?\n11. Please provide the material characterizations, including XPS, TEM, and XRD analyses, of post-Cucubic-SNW catalysts (and Cucubic) after long-term stability test.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "1 Response to Reviewers’ Comments\n4 which are very helpful in further enhancing the quality of our work. Following these insightful\n5 suggestions and comments, we have made significant revisions to our manuscript, with the\n6 main changes highlighted in yellow. Below, we provide a point-by-point response to the\n7 reviewers’ comments. The original comments are presented in black, while our responses are\n8 in blue. We hope that the revised and significantly improved manuscript can now be accepted\n9 for publication in Nature Communications.\n14 of Cu decorated nitrogen-rich Schiff-base Network exhibits the outstanding performance for\n2 2 2 4\n16 durability. Theoretical simulations indicated that it is originated from the presence of SNW on\n2 4\n18 are interesting and sound, it may provide the useful guidance to push the electrocatalytic\n19 reduction of CO a step forward. However, i have concerns about the mechanism understanding,\n2\n20 especially the theoretical simulation part. These issues need to be reasonably addressed before\n21 considering to be published.\n23 suggestions/comments on our work.\n2\n25 starts from CO and CO-COH coupling during the theoretical simulation in Figure 6.\n27 computationally evaluated four catalyst surfaces, namely, Cu(111), Cu(111)-SNW, Cu(200),\n28 and Cu(200)-SNW. Due to the substantial computational demands associated with modeling of\n29 these systems, our initial analysis focused only on the *CO-*CHO coupling and downstream\n30 reaction steps.\n32 pathway, starting from gaseous CO through *COOH formation to *CHO intermediates, for all\n2\n33 four surfaces. As shown in Figures S53, S46, and S45, the energy barriers for the early steps\n34 (CO → *CHO) are consistently lower than those for subsequent steps (*CHO → C H ).\n2 2 4\n36 simulations provided a complete reaction pathway (CO (g) → C H (g)) across all catalysts,\n2 2 4\n37 thereby deepening our mechanistic understanding of the system.\n40 page 9, lines 269-270). Furthermore, we have included Figures S45, S46, and S53 into the\n42\n43\n2\n46\n48 during e-CO RR to *CHO. Cu, red; C, purple; N, yellow; O, green; and H, pink.\n2\n49\n50\n52 during e-CO RR to *CHO. Cu, red; C, purple; N, yellow; O, green; and H, pink.\n2\n2\n54 surfaces? How is the selectivity of CO reduction into CO (CH , HCOOH and so on)?\n2 4\n4\n56 summarized in Figure S17. Our data reveals a marked preference for CO production on both\n57 surfaces, with CO selectivity of 21~32% and 41~66% for Cu(200) and Cu(111) surfaces,\n58 respectively (Figure S17a). In contrast, the selectivity of CH and HCOOH remains consistently\n4\n59 low (<3%), as shown in Figures S17b and c. The incorporation of SNW significantly enhances\n60 the selectivity of C products while simultaneously decreasing the selectivity of C products\n2 1\n61 (Figures S18-20). The C product counts for only a small portion and shows no significant\n3\n62 changes with SNW modification.\n64 with SNW significantly enhanced the C H yield. Specifically, the Faradaic efficiency of C H\n2 4 2 4\n65 (FE ) increased by 2.0 times, 5.5 times, and 5.2 times for Cu -SNW, Cu -SNW, and Cu -\nC2H4 cub sph tet\n67 while no significant effect on the selectivity of C products was observed (Figures S17-S20),\n3\n68 implying enhanced C-C coupling in the presence of SNW. Additionally, the SNW’s inclusion\n69 was found to decrease the sensitivity of FE to potential (see Table S2), as evidenced by the\nC2H4\n70 reduced coefficient of variation, indicating enhanced stability of the active structures/sites for\n2 4 nps\n72 produced H (Figure S21), suggesting that the enhanced performance in the e-CO RR resulted\n2 2\n73 not from SNW but from a synergistic effect between Cu and SNW” (refer to page 5, lines 150-\n74 156). We have also incorporated Figure S17 into the Supplementary Information.\n75\n76\n4,\n78 potentials for Cu(200) and Cu(111).\n79\n1 2 3\n81 for Cu (left) and Cu -SNW (right).\ncub cub\n82\n1 2 3\n84 for Cu (left) and Cu -SNW (right).\nsph sph\n85\n1 2 3\n87 for Cu (left) and Cu -SNW (right).\ntet tet\n2 4\n89 determinating step. What is the desorption energy?\n91 labelled as *O + *C H to *O + C H , where the latter C H refers to the gaseous product. To\n2 4 2 4 2 4\n92 eliminate ambiguity, we have revised the final state as *O + C H (g). As shown in Figure 6c,\n2 4\n93 for Cu(111), Cu(111)/SNW, and Cu(200), the calculated desorption energies are 0.71 eV, 0.65\n94 eV, and 0.57 eV, respectively. These values represent the largest energy differences among all\n95 reaction steps in the e-CO RR pathway on these surfaces. However, for Cu(200)/SNW, the\n2\n96 desorption energy is 0.27 eV, which is smaller than the energy difference (0.32 eV) of the *CO\n97 + *CHO → *OCCHO coupling step (Figure S54). Since neither the desorption step nor the\n99 electrode potential. Thus, at high cathodic potentials, the desorption step acts as the rate-\n100 limiting step for Cu(111), Cu(111)/SNW, and Cu(200). On Cu(200)/SNW, the CO-CHO\n101 coupling step becomes rate-limiting, as its energy barrier exceeds that of desorption.\n103 “We define the largest free energy change as ΔG in the reaction pathway. Our calculations\nM\n104 indicate that Cu(200)-SNW has a ΔG of 0.32 eV for the *CO+*CHO→*OCCHO step. In\nM\n105 comparison, for Cu(200), Cu(111)-SNW, and Cu(111), the ΔG increases during the\nM\n106 *OCCH →*O+*C H step, which is related to the C H desorption process, with values of 0.57,\n3 2 4 2 4\n107 0.65, and 0.71 eV, respectively (Figure S54). Since neither the desorption step nor the CO-\n109 potential. Thus, at high cathodic potentials, the desorption step acts as the rate-limiting step for\n111 rate-limiting, as its energy barrier exceeds that of desorption. Note that SNW-modified surfaces\n112 showed smaller ΔG values compared to their bare Cu counterparts, suggesting that the\nM\n113 presence of SNW effectively optimizes the free energies for reactions towards C H , thus\n2 4\n114 enhancing its selectivity. The Cu(200)-SNW exhibited the smallest ΔG among studied\nM\n115 surfaces, suggesting the highest C H selectivity, aligning well with our experimental\n2 4\n116 observations (Figure 3d).”\n118\n2 4\n121\n2 4\n123 *O + C H on Cu(200)-SNW. The free-energy changes (ΔG) of *O + *C H to *O + C H on\n2 4 2 4 2 4\n126 are the reactive sites. It seems that the reactions happen on top of SNW, what role of Cu 200\n127 plays if it is the case?\n129 system. In our model, the N sites (particularly the N configuration shown in Figure S52) within\n1\n130 the SNW framework were considered the primary active sites for CO reduction. This\n2\n131 conclusion was supported by the negative CO adsorption energies (-0.37 eV at N vs -0.25 eV\n2 1\n132 at N , and -0.16 eV at N ). This assignment also aligned with prior studies demonstrating\n2 3\n2 2\n134 molecules and the nitrogen-containing functional groups in SNW (J. Hazard. Mater. 2018, 341,\n135 321–327).\n137 significant charge transfer from Cu to the N sites of SNW. This electron enrichment at the N\n138 sites can further enhance CO adsorption and activation, promoting subsequent C-C coupling.\n2\n140 reaction mainly occurs on the SNW layer rather than the underlying Cu in Cu-SNW catalysts.\n2 1\n142 most negative, and since the number of N sites in SNW was the highest (66.7%) (Figure S10),\n1\n143 we considered the N sites in SNW to be the active centers for e-CO RR in Cu/SNW catalysts.\n1 2\n2\n145 adsorption energy at the N site was the most negative (refer to Figure S52 and relevant\n1\n146 discussions), suggesting the N site likely served as active centers for e-CO RR in Cu-SNW\n1 2\n147 catalysts” (refer to page 9, lines 268-270).\n148\n2\n150 (200)-SNW. Cu, red; C, purple; N, yellow; O, green and H, pink.\n151\n153 spectrum of SNW.\n156 base Networks (SNW), demonstrating significant improvements in C H selectivity and catalyst\n2 4\n157 durability. However, the manuscript requires major revisions to be appropriate for publication\n158 in Nature Communications.\n160 comments, we have made major changes to our manuscript to further enhance its quality.\n162 regarding the challenges associated with achieving high selectivity for C products. The\n2+\n163 current phrasing weakens the problem statement.\n165 the challenges associated with achieving high selectivity for C products has been added to the\n2+\n166 manuscript. The text added reads as follows:\n167 “Despite these strengths, Cu-based catalysts face significant challenges in achieving high\n168 selectivity for C products, a critical factor limiting their industrial viability, which is hindered\n2+\n169 by the inherent complexity of C-C coupling and the competition from the hydrogen evolution\n170 reaction (HER). As C-C coupling relies on the dimerization of *CO intermediates, enhancing\n2+\n172 dimerization. This requires tailored engineering of surface structures and electronic states”\n173 (refer to page 1, lines 32-37).\n174 …\n175 “Beyond selectivity, Cu-based catalysts encounter operational stability issues, especially under\n176 high overpotentials for generating C products, due to catalyst reconstruction, fragmentation,\n2+\n177 and dissolution. These dynamic behaviors can significantly degrade catalytic performance,\n178 further constraining their industrial applicability” (refer to page 1, lines 40-43).\n180 commercial use of Cu-based catalysts. Provide specific challenges drawn from industrial\n181 practice and relevant literature. Clarify the term “sustainable chemistry” and specify the context\n182 in which it is being used.\n184 regarding the bottlenecks for the commercial use of Cu-based catalysts from industrial practice:\n185 “Note that, engineering challenges like mass transport limitations at industrial current densities,\n186 product separation, and compatibility issues with existing gas diffusion electrodes also hinder\n187 the commercial use of Cu-based catalysts in e-CO RR, which, however, are not the primary\n2\n188 focus of this research” (refer to page 1, lines 46-49).\n190 “Consequently, the development of novel Cu-based catalysts that simultaneously deliver both\n191 high C selectivity and exceptional durability is paramount. Such advancements are essential\n2+\n192 to unlock the full potential of e-CO RR, enabling sustainable chemical production by\n2\n193 integrating CO valorization with renewable energy sources” (refer to page 1, lines 43-46).\n194\n197 reduced electron density around Cu, as this helps identify future research gaps. Thoughtful\n198 research questions contribute to advancing knowledge. Support claims with appropriate\n199 citations.\n201 follows:\n202 “XPS was utilized to evaluate the surface chemical state of the catalysts (Figures 2c-e). Survey\n203 spectra of Cu and Cu -SNW are presented in Figures S11a and S12a. The detection of the\nnps nps\nnps\n205 the lower binding energies compared to that in pure SNW indicates that electron enrichment of\nnps\n208 the pristine Cu and those decorated with SNW, corroborating the detection of O 1s (Figures\nnps\nnps\n211 compared to the bare Cu, indicating a lower electron density around Cu (Figures 2c and 2e).\n213 samples compared to bare SNW” (refer to page 3, lines 106-112; page 4, lines 113-116).\n214\n216 window. Clearly explain how your strategy impacts this sensitivity—whether it is reduced or\n217 amplified—based on your results.\n2 4\nnps nps\nC2H4\n221 in the coefficient of variation. This phenomenon may be attributed to the enhanced stability of\n222 the active structures/sites towards C H formation in the Cu -SNW catalysts. We have\n2 4 nps\n223 included Table S2 and the relevant discussion in the revised manuscript.\n2 4\nStandard Coefficient\nPotential: ~ -0.69→ -0.86 V vs. RHE Mean\ndeviation of\nCatalysts\nvariation\nCu -SNW- 60.9% 66.1% 71.2% 65.1% 63.9% 65.4% 3.4 0.05\ncub\nFE\nC2H4\nCu -FE 25.8% 32.7% 34.9% 35.8% 35.9% 33.0% 3.8 0.11\ncub C2H4\nCu -SNW- 24.4% 35.6% 37.6% 39.2% 32.2% 33.8% 5.2 0.15\nsph\nFE\nC2H4\nCu -FE 11.5% 6.5% 8.7% 11.2% 16.2% 10.8% 3.2 0.30\nsph C2H4\nCu -SNW- 26.1% 30.8% 17.4% 26.7% 25.8% 25.4% 4.4 0.17\ntet\nFE\nC2H4\nCu -FE 16.2% 12.4% 7.9% 5.1% 19.6% 12.2% 5.3 0.43\ntet C2H4\n225\n227 the selection of 0.5 mg·cm–2. If this choice is inspired by the literature, provide a citation; if not,\n228 include the sensitivity analysis results.\n230 using Cu -SNW catalysts as a case study in our preliminary electrocatalytic tests. Given that\ncub\n231 the HER competes with e-CO RR, inhibiting HER is crucial for improving CO conversion\n2 2\n232 efficiency and enhancing the selectivity of reduction products. Therefore, we assessed the HER\n233 activity of catalysts with different loadings, as shown in Figure S15. The experimental results\n234 indicated that a catalyst loading of 0.5 mg·cm⁻2 effectively inhibited HER, demonstrating the\n235 lowest HER performance at both low (50 mA·cm⁻2) and high (450 mA·cm⁻2) current densities.\n2\n237\ncub\n240 132-133) and provided Figure S15 in the Supplementary Information.\n241\n1 2 3\n243 a comprehensive picture of your results.\n245 categorized into C , C , and C for all catalysts in the Supplementary Information. Our results\n1 2 3\n246 (Figures S17-S20) indicate that the Cu(200) surface is more favorable for the generation of C\n2\n247 products, whereas the Cu(111) surface promotes the formation of C products. The\n1\n248 incorporation of SNW significantly enhances the selectivity of C products and simultaneously\n2\n249 decreases the selectivity of C products. The C product counts for only a small portion and\n1 3\n250 shows no significant changes with SNW modification.\n2 4 2 4 C2H4\n253 2.0 times, 5.5 times, and 5.2 times for Cu -SNW, Cu -SNW, and Cu -SNW, respectively\ncub sph tet\n254 (Figure 3g). This enhancement occurred at the expense of C products, while no significant\n1\n255 effect on the selectivity of C products was observed (Figures S17-S20), implying enhanced C-\n3\n257 the sensitivity of FE to potential (see Table S2), as evidenced by the reduced coefficient of\nC2H4\n258 variation, indicating enhanced stability of the active structures/sites for C H formation in the\n2 4\nnps 2\n260 suggesting that the enhanced performance in the e-CO RR resulted not from SNW but from a\n2\n261 synergistic effect between Cu and SNW” (refer to page 5, lines 148-156).\n262\n4,\n264 potentials for Cu(200) and Cu(111).\n265\n1 2 3\n267 for Cu (left) and Cu -SNW (right).\ncub cub\n268\n1 2 3\n270 for Cu (left) and Cu -SNW (right).\nsph sph\n271\n1 2 3\n273 for Cu (left) and Cu -SNW (right).\ntet tet\n275 provide the associated results.\n277 area of Cu and Cu -SNW (Figures S26 and S32) with time, based on the in situ EC-STEM\ncub cub\n278 observations. The comparative analysis demonstrated that heavy corrosion occurred on bare\ncub cub\n280 this data in the Supplementary Information.\n281\n283 during in situ EC-STEM investigation of bare (a) Cu and (b) Cu -SNW catalysts.\ncub cub\n285 layer over the Cu surface upon contact with SNW. Highlight how this layer mitigates corrosion\n286 and dissolution.\n290 read as follows: “After the addition of SNW, annular dark-field STEM (ADF-STEM) and\n291 secondary electron STEM (SE-STEM) images of identical locations (Figures 1e, i, and m, and\nnps\n293 well as a partially buried state of Cu . EDX mapping and electron energy-loss spectroscopy\nnps\n294 (EELS) revealed the presence of C and N surrounding the Cu, reaffirming their intimate contact\n295 (Figures 1e, i, and m, and Figures S6d-g, S7d-g, S8d-g, and S9)” (refer to page 3, lines 83-88).\n299 propose that the close contact between Cu and SNW creates a protective layer that shields the\n301 enhanced stability could also be associated with the electronic interactions between Cu and\n303 discussions in more detail” (refer to page 7, lines 214-218).\n304 …\n306 the electronic interaction between Cu and SNW enhanced the stability of Cu:\n307 “Our results revealed that the decoration of SNW on Cu induces charge transfer and\n308 redistribution. Specifically, charge transfer from Cu(200) to SNW led to charge accumulation\n309 at the N sites of SNW, as illustrated by the charge density difference plots in Figures 6a, 6b,\n310 and S49. This results in electron deficiency at the Cu sites and enrichment at nearby N sites,\n311 consistent with the XPS observations of shifts in Cu 2p peaks to higher binding energies and\n312 shifts in N 1s peak to lower binding energies in both the fresh and used catalysts (Figures 2c,\n2 1\n314 site was the most negative among all N sites in SNW and Cu sites (refer to Figure S52 and\n315 relevant discussions), suggesting that the N site likely serves as an active center for e-CO RR\n1 2\n316 in Cu-SNW catalysts” (refer to page 9, lines 262-270).\n317 …\n319 observations of Cu -SNW under the same conditions show remarkably improved stability and\ncub\n320 resistance to electrochemical corrosion. This resembles chainmail catalysts, where carbon\n321 layers encapsulate transition metal catalysts. In such systems, while reactions proceed through\n322 electronic interaction on the protective layers, the encapsulation of internal active metal\n323 components effectively prevents metal dissolution or sintering (via particle coalescence or\n325 10, lines 317-318; page 10, lines 328-332).\n327 changes in peaks for intermediates/products at specific potentials. Discuss why certain species\n328 emerge or vanish under these conditions.\n330 changes in peaks for intermediates at varied potentials and their implications. See highlighted\n331 text below:\ncub sph\ntet\n334 *CHO (1490-1493 cm-1, bending vibration of C-H) signals across all Cu-SNW catalysts\n335 demonstrates that SNW modification preserves *H availability and accelerates the CO\n336 hydrogenation step (CO + *H → *CHO). Moreover, the *CO band was notably stronger for\nnps nps\n338 formation and stabilization of *CO intermediates. This observation is consistent with\n339 experimentally observed and reported high capacity for CO adsorption of SNW. Importantly,\n2\n340 the *OCCHO (1264-1268 cm-1, stretching vibration of C-O) intermediates, which are crucial\n341 for C H production, were also detected. The co-presence of these key reaction intermediates,\n2 4\n342 i.e., *CO, *CHO, and *OCCHO, provides spectroscopic evidence for the *CO +\n343 *CHO→*OCCHO reaction pathway. A comparison of the three cases revealed that the *CO\n344 signal for Cu -SNW showed no obvious changes across various potentials (~0.6-0.9 V vs.\ncub\nsph tet\n346 variations dependent on the applied potential. The consistent *CO signal for Cu -SNW at\ncub\n347 different potentials indicates saturated bridged *CO adsorption, which is beneficial for C-C\n348 coupling. For Cu -SNW, the *CO signal increased progressively while the *OCCHO intensity\ntet\n349 remained nearly constant. This observation indicates that C-C coupling is not favored for Cu -\ntet\nsph\n351 observed, indicating relatively efficient C-C coupling. However, the water signal diminished at\n352 increasingly negative potentials, which may lead to insufficient proton supply for further\n353 hydrogenation. This could explain the observed decrease in selectivity towards C H at more\n2 4\n354 negative potentials (see Figure 3e). The decreased water signal may be associated with the high\n2\n356 surface (refer to page 8, lines 242-254).\n357\ncub sph tet\n359 in CO -saturated 0.1 M KHCO electrolyte.\n2 3\n360\n2\n364 high ethylene selectivity and durability have a significant impact on the field of electrochemical\n2\n2 4\n367 reported ethylene performance is inferior to already published results\n368 (https://doi.org/10.1021/jacs.2C 3384, https://doi.org/10.1038/s41929-020-00504-x). As the\n1\n369 authors mentioned in Line 251 (Ref. 14 and 15 in this manuscript), the Cu facet-dependent\n370 selectivity is similar to what has already been widely studied in the literature and lacks novelty.\n372 the Cu facets by introducing SBN and observed this property using in-situ TEM technique, the\n373 in-depth understanding of the durability during CO RR remains insufficient. For example, there\n2\n374 is a lack of detailed experiments on how the change of surface properties of Cu (e.g.,\nnps\n375 hydrophobicity or hydrophilicity) upon the introduction of SNW affects durability. Tuning\n376 catalyst surface properties can have a significant impact on CO RR performance\n2\n377 (https://doi.org/10.1038/s41563-019-0445-x, https://doi.org/10.1038/s41467-023-39351-2). Additionally, the intrinsic studies (e.g., morphology, nitrogen species) of SNW that contribute\n378 to maintaining the durability of Cu during the CO RR process have not been thoroughly\nnps 2\n379 investigated. Therefore, this study does not present any critical breakthroughs in the\n380 perspectives provided. As detailed below, this paper is not recommended for publication in this\n381 journal.\n383 critiques provided. We acknowledge that the initially reported FE (60.7%) is below the\nC2H4\n384 leading values in the literature, and our investigation into the durability enhancement\n385 mechanisms resulting from the incorporation of SNW was insufficiently detailed. To enhance\n386 the novelty and rigor of our study, we have conducted additional experiments, performed DFT\n387 calculations, and added relevant discussions to address the concerns raised by Reviewer 3 and\n388 other reviewers. Below, we detail these improvements.\n389 1) Enhancement of FE to 71.2 ± 2.0%: In our initial submission, we prioritized achieving\nC2H4\n390 high catalyst stability under industrially relevant current densities, which represents a key\n391 challenge in this field. As a result, systematic optimization of C H selectivity was not pursued\n2 4\n392 in our preliminary study. Following Reviewer 3’s suggestion, we conducted investigations\n393 aimed at enhancing the selectivity of C H . It has been well established that maintaining gas-\n2 4\n394 liquid pressure equilibrium is fundamental for stabilizing the triple-phase boundary (TPB) at\n395 the gas diffusion electrode (GDE). Pressure imbalances can lead to operational failures such as\n396 flooding, where liquid intrusion into gas pores deprives catalysts of CO and promotes the\n2\n397 hydrogen evolution reaction (HER), and dry-out, where gas displaces the electrolyte, increases\n398 ionic resistance and accelerates degradation. In our current work, we discovered that tilting the\n399 flow cell setup from its original horizontal orientation to an angle of 45°, inspired by recent\n400 literature (Angew. Chem. Int. Ed. 2022, 61, e202111700), effectively optimizes the gas-liquid\n401 pressure balance in our system (Figure S14). Consequently, we achieved significantly higher\n2 4 C2H4\n403 stability at 71.2 ± 2.0% under a current density of 265 mA cm⁻2, as validated in Figure R2 using\n404 a 1 cm2 electrode with a CO flow rate of 55 sccm. Original GC data is provided in Figure R2.\n2\nC2H4 2 2\n408 selectivity. To emphasize this superior performance, we have included a performance\n409 comparison table (Table S3), summarizing the trade-offs between ethylene selectivity and long-\n410 term stability across recent literature, including the references mentioned by Reviewer 3. This\n411 exceptional balance is facilitated by the Schiff-Base Network (SNW) interfacial stabilization\n412 strategy, which, to the best of our knowledge, has not been reported previously.\n413\n415\n417\n2\n419\n420 2) Improved understanding of the durability for SNW-modified catalysts: We\n421 acknowledge Reviewer 3’s insightful feedback regarding the insufficiency of our initial\n422 analysis of the enhanced durability mechanisms. In our original submission, we attributed the\n423 observed stability improvement to charge transfer between Cu and SNW, as well as shielding\n424 effects due to their intimate contact. However, we recognize that our discussion on this topic\n425 lacked sufficient detail. In response to Reviewer 3’s constructive critique, we conducted\n426 additional experiments, including assessments of catalyst hydrophobicity and hydrophilicity.\n428 by experimental data and DFT calculations.\n430 exceeding 90 degrees, indicating their hydrophobic nature. In comparison to pure Cu catalysts,\n431 the Cu-SNW catalysts demonstrated slight increases in contact angle (2-3 degrees), suggesting\n432 enhanced hydrophobicity (Figure S13). This modification in hydrophobicity can reduce the\n433 contact of electrolytes with active sites, therefore suppressing cathodic corrosion and improving\n434 catalyst stability. The enhanced hydrophobicity could also limit H⁺/H O access to active sites,\n2\n435 which could lower HER activity while directing electrons towards CO reduction.\n2\n437 that SNW closely surrounds Cu particles. This structural configuration could significantly limit\n438 electrolyte contact with Cu, contributing to stability enhancement.\n441 studies indicated that Cu donates electrons to the N sites of SNW, with the N site of SNW\n1\n442 receiving the most electrons (as indicated by DFT calculations). This N site exhibits the most\n1\n443 negative CO adsorption energy among all N sites in SNW and Cu sites (Figure S52), aligning\n2\n444 with experimental observations of SNW’s high CO adsorption capacity (Figure S1).\n2\n2 1\n447 layers encapsulate active metals. In such systems, while reactions proceed through electronic\n448 interactions on the protective layers, the encapsulation of active metal components inhibits\n449 metal dissolution or sintering, thereby enhancing catalyst stability.\nC2H4\n451 leading level, and a more detailed discussion on the enhancement of catalyst durability has been\n452 provided in the revised manuscript. We hope that these important improvements will be\n453 recognized and that our revised manuscript can be published in Nature Communications. We\n454 would like to express our gratitude to Reviewer 3 for their insightful comments and suggestions,\n455 which have significantly improved our manuscript.\n456\nnps nps\n458 and (g) SNW.\n459\n2\n461\ncub sph tet\n2 3\n464\n2\n467\nsph\nsph\n470\ncub\n3/2\n475 spectra were fitted using reference spectra for Cu⁰ and Cu⁺ reported in the literature. The fitting\n476 was performed using a Non-Linear Least Squares Fitting (NLLSF) approach. (Previously, a\n477 linear least squares method had been used).\n479 employed a Voigt line shape with a Gaussian contribution of 20% and a Lorentzian contribution\n480 of 80%. This fitting was constrained based on the results of the Cu LMM analysis, which\n481 revealed the presence of both Cu⁰ and Cu⁺ and provided their relative ratios. Additionally, the\n482 peak separation (ΔBE) between the Cu⁰ 2p and Cu⁺ 2p components was constrained to the\n3/2 3/2\n483 range of 0.1–0.3 eV, consistent with literature reports. We recognize that deriving definitive\n484 chemical state information solely from Cu 2p analysis is challenging, requiring strict adherence\n485 to physical constraints during peak fitting. Therefore, to avoid potential misinterpretation, we\n486 have chosen to present the original Cu 2p spectra without deconvolution. The chemical states\n487 of Cu (Cu⁰, Cu⁺) are more reliably determined from the Cu LMM analysis.\n488\nnps nps\nnps\n491 resolution XPS standard spectra of and (e) Cu 2p for Cu(0), Cu(I), and Cu(II) reported in\n492 literature.\n493\n495 resolution XPS results (Cu and N) shown in Fig. 2e, c. Moreover, the statement in Lines 193-\n496 194, \"We propose that the enhanced stability is due to the electronic interaction between Cu\n497 and SNW~,\" requires further discussion.\n499 these comments, we have provided detailed descriptions about the peak shifts and highlighted\n500 the importance of this phenomenon. Furthermore, we have detailed how electronic interaction\n501 between Cu and SNW enhances catalyst stability:\n502 “XPS was utilized to evaluate the surface chemical state of the catalysts (Figures 2c-e). Survey\n503 spectra of Cu and Cu -SNW are presented in Figures S11a and S12a. The detection of the\nnps nps\nnps\n505 lower binding energies compared to that in pure SNW indicates that electron enrichment of N\n506 sites in the Cu -SNW, likely due to surface charge transfer from Cu to SNW. Analysis of Cu\nnps\n507 2p and Cu LMM Auger spectra reveals the coexistence of Cu(I) and Cu(0) species in both the\n508 pristine Cu and those decorated with SNW, corroborating the detection of O 1s (Figures S11\nnps\n509 and S12) and aligning with the SAED results (Figures 2d and S11-S12). Notably, the Cu -\nnps\n511 compared to the bare Cu, indicating a lower electron density around Cu (Figures 2c and 2e).\n513 samples compared to bare SNW” (refer to page 3, lines 106-112; page 4, lines 113-116).\n514\n518 propose that the close contact between Cu and SNW creates a protective layer that shields the\n520 enhanced stability could also be associated with the electronic interactions between Cu and\n522 discussions in more detail” (refer to page 7, lines 214-218).\n523 …\n525 the electronic interaction between Cu and SNW enhanced the stability of Cu:\n526 “Our results revealed that the decoration of SNW on Cu induces charge transfer and\n527 redistribution. Specifically, charge transfer from Cu(200) to SNW led to charge accumulation\n528 at the N sites of SNW, as illustrated by the charge density difference plots in Figures 6a, 6b,\n529 and S49. This resulted in electron deficiency at the Cu sites and enrichment at nearby N sites,\n530 consistent with the XPS observations of shifts in Cu 2p peaks to higher binding energies and\n531 shifts in N 1s peak to lower binding energies in both the fresh and used catalysts (Figures 2c,\n2 1\n533 site was the most negative among all N sites in SNW and Cu sites (refer to Figure S52 and\n534 relevant discussions), suggesting that the N site likely serves as an active center for e-CO RR\n1 2\n535 in Cu-SNW catalysts. The preference for the reaction at N site rather than Cu sites may\n1\n536 contribute to the enhanced stability of Cu NPs against corrosion and dissolution during e-\n2\n538 …\n540 we attribute the enhanced stability of Cu-SNW catalysts to the shielding effect of SNW, along\n541 with the electronic interaction between SNW and Cu, which stabilizes surface Cu atoms against\n542 corrosion during e-CO RR. Specifically, the shielding effect of SNW, resulting from the close\n2\n543 contact between Cu and SNW, can limit electrolyte contact with Cu, therefore hindering\n544 cathodic corrosion during the e-CO RR. Furthermore, the SNW incorporation leads to\n2\n545 improved hydrophobicity, as revealed by contact angle measurements, which could further\n546 reduce the contact of electrolytes with Cu, thereby contributing to enhanced stability. Lastly, as\n547 suggested by DFT calculations, the charge transfer from Cu to SNW renders the nearby N sites\n1\n548 of SNW more favorable for CO adsorption and reduction compared to the Cu sites.\n2\n550 such systems, while reactions proceed through electronic interaction on the protective layers,\n551 the encapsulation of internal active metal components effectively prevents metal dissolution or\n552 sintering (via particle coalescence or Ostwald ripening) under harsh reaction conditions for\n553 electrochemical processes” (refer to page 10, lines 320-332).\n555 include error bars for the liquid products shown in Figs. 3d-f.\n557 parameters for the EIS fitting in Figure 3c. Furthermore, we have added the error bars for the\n558 liquid products.\n559\nnps nps\n562\n564 data under identical testing conditions (Figure 3).\n565\n2 nps\n567 and Cu -SNW (right).\nnps\n568\n2\n570 presented in Fig. 3h.\n572 performance, specifically increased C H selectivity at higher current density by optimizing the\n2 4\n573 test conditions (see our response above for details), we performed the FE measurement at a\nC2H4\n574 higher current density in the stability test (Figure 3c). We have updated the text and included\n575 the new results in our revised manuscript and Supplementary Information.\n576\n577\n2 cub\n579 and Cu -SNW (right). (b) Faradaic efficiency of C H for Cu and Cu -SNW. (c) i-t curve\ncub 2 4 nps nps\n580 and Faradaic efficiency of C H for Cu -SNW during a durability test.\n2 4 cub\n581\n2\n2\n584 captions.)\n2\n2\n587 gas alongside a 1M KOH aqueous solution, without direct saturation contact during\n588 measurements. We have therefore removed “saturated with CO ” from the manuscript. For the\n2\n2\n590 saturated 0.1M KHCO aqueous solutions. All necessary corrections have been made in the\n3\n591 revised manuscript. We appreciate your diligence in identifying these issues.\n592\n594 section. Was the infrared reflection absorption spectroscopy (IRAS) set up with an external\n595 reflection configuration?\n597 included supplementary explanations, along with a photograph and a schematic representation\n598 of our setup (Figure S43). Furthermore, we have provided more details concerning the IRAS\n599 experiments, which are outlined as follows: “The electrochemical cell was filled with a 0.1 M\n3 2\n601 experiments. The catalysts were closely mounted on the working electrodes, maintaining\n602 distances of about 5-50 μm from the bottom CaF window. We first acquired IRAS signals at\n2\n603 the open circuit potential (OCP) to ensure the precision and reliability of subsequent data\n604 measurements. In situ IRAS data were then collected with a 32 s dwell time at 5-minute\n605 intervals for various potentials” (refer to page 13, lines 449-454).\n606\n607\n609\n611 5. Are there any wavenumber shifts depending on the Cu facet?\n613 species identified in the IRAS spectra, as shown in Figure 5 and Figure S44. Regarding the\n614 wavenumber shifts depending on the Cu facet, we have re-examined the data and found no\n615 significant wavenumber shifts related to crystal planes.\n616\ncub sph tet\n2 3\n619\ncub sph tet\n621 in CO -saturated 0.1 M KHCO electrolyte.\n2 3\n622\n2\n626 to characterize the CO adsorption capacity of SNW. As depicted in Figure S1, the test results\n2\n627 indicate that SNW possesses a CO adsorption capacity of 2.15 mmol/g at 1 atm pressure,\n2\n628 consistent with a previous report (Figure R3, J. Hazard. Mater. 2018, 341, 321–327). We have\n629 included Figure S1 in the Supplementary Information to support our claim.\n630\n2\n[FIGURE REDACTED]\n632\n2\n634 (n represents Cu content, wt%).\n636 identify the facets of the Cu catalysts?\nnps\nnps\n638 high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD)\n639 (Figures 1 and 2). HRTEM imaging of the Cu NPs solidly confirms that they are primarily\ncub\n640 terminated by (002) planes (Figure S4a and S4a*), which is reflected in their square shape\n641 (Figure 1c and S4a). Furthermore, XRD analysis of the Cu NPs revealed significantly\ncub\n642 enhanced reflections of (002) planes (Figure 2a), corroborating the predominant presence of\n643 these planes. Similarly, HRTEM imaging of Cutet NPs reveals a primary termination of (111)\n644 facets (Figures S4c, S4c*, and S5), which is consistent with their tetrahedral shape (Figures 1k,\ntet\n647 compared to Cu (1:0.2 vs 1:0.45), indicating a preferential termination of (111) facets in Cu .\nsph tet\nsph\n649 (Figure 2). Particularly, the XRD data shows relative peak intensities that resemble the standard\n650 powder diffraction pattern of Cu0. We have clarified the surface terminations in the revised\n651 manuscript by adding further discussion and experimental data. Thank you for your comment.\n652\ncub\n654\ntet\n656\nnps\n658\ncub sph tet\n660\ntet\n662\n664 analyses, of post-Cu -SNW catalysts (and Cu ) after long-term stability test.\ncub cub\n666 on the requested post-reaction Cu -SNW, but also on the post-reaction Cu , Cu , Cu ,\ncub cub sph tet\nsph tet\n668 confirms the predominance of Cu(0) with minor Cu(I) species, similar to the fresh state (Figures\n669 2, S11, and S12). Furthermore, TEM imaging of the post-reaction catalysts demonstrates that\n670 the Cu-SNW catalysts largely preserve the structural integrity of Cu NPs within the catalysts.\n672 reconstruction following electrocatalysis (Figure S41). Additionally, XRD analysis reveals that\n673 the characteristic peaks of pure Cu NPs after-catalysis align more closely with those of\n674 polycrystalline Cu(0) with an fcc structure, whereas the Cu-SNW catalysts predominantly\n675 exhibit the Cu(200) and Cu(111) reflections, indicating the persistence of these facets in Cu\ncub\n676 and Cu , respectively (Figures 2 and S42). These findings demonstrate that SNW can\ntet\n677 effectively maintain the structural stability of Cu NPs during catalytic processes. We have\n678 included all this new data into the revised manuscript and Supplementary Information.\n679\n680\nnps\n682 1s, (c) O 1s, (d) N 1s, and (e) Cu 2p, as well as (f) Cu LMM Auger spectra for Cu -SNW before\nnps\n683 electrocatalysis.\n684\nnps\nnps\n687 electrocatalysis.\n688\nnps\n690 and (d) Cu 2p, as well as (e) Cu LMM Auger spectra for Cu before electrocatalysis.\nnps\n691\n692\nnps\n694 and (d) Cu 2p, as well as (e) Cu LMM Auger spectra for Cu after electrocatalysis.\nnps\n695\ncub cub sph sph tet tet\n697 recorded before (a-f) and after (a*-f*) actual electrocatalytic CO RR.\n2\n698\nnps nps\n700\nnps nps\n702\n705 is part of the Nature Communications initiative to facilitate training in peer review and to\n706 provide appropriate recognition for Early Career Researchers who co-review manuscripts.\n708 have significantly revised the manuscript based on the insightful comments provided by you\n709 and other reviewers. Furthermore, our responses to the comments have been detailed above;\n710 please refer to our reply for further information."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Although part of the questions raised in the first round of review have been well addressed, further clarifications are still required for the mechanism understanding for publication, especially the comment 1.2 regarding the selectivity. The replies are from the perspective of experimental measurements, however the theoretical understanding from simulations are required for readers to gain more insights of the new findings.\nThe authors did supplementary calculations to examine the reaction pathway from CO2-COOH-CO-CHO as shown in Figure S53, however the reaction could go proceed to produce the intermediates like C* or HCOH*, or finally CH4; at the third step, CO* may desorb from the surface and act as the source of CO to couple with CHO. Comprehensive calculations for all the possible reaction pathways need to be done to figure out the one with the lowest energy.\nTo clarify the C2 product selectivity (rather than C1), the Gibbs free energy of further reaction from CHO* to the next step is essential, the obtained values then compare with the Gibbs free energy of CO*-CHO coupling to decide which reaction is preferred. Beside, the competing reaction HER (theoretical) is also required, and compare with CO2 reduction reaction.", "reviewer_2": "They have addressed my comments. It can be accepted.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_5": "Comments:\nIn this manuscript, Xie et al. propose the use of SNW to modify Cu catalysts for electrochemical CO₂ reduction (e-CO₂RR). The authors claim that SNW enhances both the selectivity towards C₂H₄ and the structural stability of Cu catalysts. They support their conclusions with electrochemical performance testing and comprehensive characterization. While the study addresses an important challenge and the results are potentially interesting, in its current form the evidence presented is not yet sufficient to support the conclusion. Addressing the points above would greatly enhance the manuscript’s rigor and impact.\nComment 1. In the synthesis of Cucub-SNW / Cusph-SNW / Cutet-SNW, why was 10 mg of SNW chosen? From the results (Fig. 1e, i, and m), only a small amount of SNW appears to ‘wrap’ around the Cu particles, while most of the remainder aggregates together. On the one hand, this may cover the active sites and hinder the structural analysis and interpretation; on the other hand, it could introduce competing hydrogen evolution. Please provide an explanation.\nComment 2. In Fig. S9, the edge signals could originate from overlapping SNW rather than true surface encapsulation. A line scan profile across Cu–SNW boundaries would help confirm intimate interfacial contact, find a particle at edge.\nComment 3. Also, to verify the presence of SNW, the authors should provide higher-magnification SEM images and high-resolution TEM images of Cucub-SNW, Cusph-SNW, and Cutet-SNW. This would make the structural assignments more convincing.\nComment 4. Figure 3h shows that C₂H₄ selectivity decreases from 71.2% to 61.3% over 24 hours while current density and Cu NPs structure remains stable. The underlying cause of this decline must be clarified. Is this due to SNW degradation, Cu surface reconstruction, or another factor?\nRelatedly, on page5, line 164, the authors should explicitly discuss the mechanistic origin of this selectivity drop.\nComment 5. On page7, line 213, “However, both the used Cucub-SNW and Cutet-SNW catalysts retained the dominance of the Cu(200) and Cu(111) facets”, please give the ratio number for a better comparation.\nComment 6. On Page7, lines 217–218, the authors state that “electronic interactions between Cu and SNW enhance stability.” Please clarify how these interactions specifically contribute to stabilization and use appropriate citations.\nComment 7. In-situ STEM (Fig. 4b–e; Figs. 25–28) shows rapid Cucub particle corrosion or decomposition within 36–60 s, whereas IL-TEM (Fig. S35) shows slow morphology change in 60 min. Do Cusph and Cutet also exhibit the same In-situ STEM corrosion results? If so, the authors should discuss why these two “quasi in-situ” TEM approaches yield such different results and their relevance to the real reaction (Fig.S22). Possible influences include beam effects, electrolyte environment differences, or imaging timescales. Otherwise, the results will be less convincing in supporting the conclusion."}, "author_response": "Response to Reviewers’ comments\nWe thank the reviewers for their time and valuable feedback on our revised manuscript. In response to their comments, we have conducted additional experiments and DFT calculations, included new results, and revised our manuscript accordingly. Below, we provide a detailed point-by-point response to each comment. The reviewer’s comments are in black, while our responses are in blue.\nReviewer #1 (Remarks to the Author):\nAlthough part of the questions raised in the first round of review have been well addressed, further clarifications are still required for the mechanism understanding for publication, especially the comment 1.2 regarding the selectivity. The replies are from the perspective of experimental measurements, however, the theoretical understanding from simulations are required for readers to gain more insights of the new findings.\nThe authors did supplementary calculations to examine the reaction pathway from CO2-COOH-CO-CHO as shown in Figure S53, however, the reaction could go proceed to produce the intermediates like C* or HCOH*, or finally CH4; at the third step, CO* may desorb from the surface and act as the source of CO to couple with CHO. Comprehensive calculations for all the possible reaction pathways need to be done to figure out the one with the lowest energy.\nResponse: We sincerely appreciate your valuable comments on our revised manuscript and for providing additional feedback that further strengthens our work. We have performed new DFT calculations to address the raised concerns and have made relevant revisions to both the main manuscript and the Supplementary Information. Our responses to your comments are detailed below. We hope that the revised manuscript can now be accepted in Nature Communications.\nComment 1: The authors did supplementary calculations to examine the reaction pathway from CO2-COOH-CO-CHO as shown in Figure S53, however, the reaction could go proceed to produce the intermediates like C* or HCOH*, or finally CH4; at the third step, CO* may desorb from the surface and act as the source of CO to couple with CHO. Comprehensive calculations for all the possible reaction pathways need to be done to figure out the one with the lowest energy.\nResponse: We thank Reviewer 1 for raising this important point. Following it, we have carried out new DFT calculations to systematically evaluate possible elementary steps involved in the CO reduction pathways, including those leading to C2H4 (g), CO(g), and CH4 (g), across all catalyst surfaces investigated in this study (see Figure 6c, Figure S62, and Figure S63). Our results indicate that both Cu(200) and Cu(200)-SNW favor the C2H4 (g) formation pathway with the largest free energy change (ΔGM) in their respective reaction pathway being 0.57 eV and 0.32 eV, respectively. In contrast, Cu(111) and Cu(111)-SNW preferentially follow the CO formation pathway, with ΔGM values of 0.60 eV and 0.33 eV, respectively. Importantly, all surfaces exhibit higher energy barriers for CH4 formation compared to those for C2H4 and CO, which aligns well with our experimental observations.\nTo provide a more comprehensive picture, we have now included the complete reaction pathway from CO2 (g) to C2H4 (g) in Figure 6c, along with the newly computed energy profiles for CO(g) and CH4 (g) formation on all surfaces in Figures S62 and S63. Corresponding descriptions of these results have also been incorporated into the main text, as highlighted in yellow shown below:\nWe also computed the energy profiles for other possible steps in the e-CO2RR, including the pathways from *CHO to CO(g) and CH4 (g), as well as the energy associated with the *H adsorption in the competing HER (Figures S62-65). Our results indicate that the ΔGM for CH4 production (0.87, 0.86, 1.16, and 0.93 eV) are consistently higher than those for C2H4 (0.32, 0.57, 0.65, and 0.71 eV) across all catalyst surfaces (Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111)), which aligns with the experimentally observed suppression of CH4 formation. Furthermore, for Cu(200)-SNW and Cu(200), the ΔGM values for CO (0.93 and 0.76 eV) and H2 (0.87 and 0.80 eV) formation exceed those for C2H4 (0.32 and 0.57 eV), indicating a higher selectivity towards C2H4 , in agreement with experimental trends. In contrast, for Cu(111)-SNW and Cu(111), the free energies for CO (0.60 and 0.33 eV) formation are lower than those for both H2 (0.73 and 0.54 eV) and C2H4 (0.65, and 0.71 eV), suggesting a preference for CO production, aligning with the experimental observation that CO is the dominant product on these surfaces. Notably, our calculations also reveal that SNW modification increases the free energies for the formation of CO, CH4, and H2 across all catalyst surfaces (Figures S62-S64), in addition to its role in optimizing the energies for C2H4 production as described above, thereby making the pathway towards C2H4 formation more favorable.\nFigure 6. (c) The free energy changes of the reaction steps towards the C2H4 formation on Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111).\nFigure S62. The free energy changes of the reaction steps towards the CO formation on Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111).\nFigure S63. The free energy changes of the reaction steps towards the CH4 formation on Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111).\nComment 2: To clarify the C2 product selectivity (rather than C1), the Gibbs free energy of further reaction from CHO* to the next step is essential, the obtained values then compare with the Gibbs free energy of CO*-CHO coupling to decide which reaction is preferred.\nResponse: To address this comment, we have compared the Gibbs free energy changes for the key steps following *CHO. Specifically, *CHO can either undergo coupling with *CO to form *OCCHO (leading to C2H4) or proceed via protonation to form *CH2O (toward CH4 formation). Our calculations reveal that, for Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111), the free energy changes for the *CO-*CHO → *OCCHO step are 0.32, 0.45, 0.51, and 0.60 eV, respectively, while those for the *CHO → *CH2O step are 1.16, 0.93, 0.87, and 0.86 eV, respectively.\nThese results clearly indicate that the *CO-*CHO coupling step is energetically more favorable across all catalyst surfaces. Moreover, across the entire reaction steps, the largest free energy change in the C2H4 formation pathway remains significantly lower than that required for CH4 formation, further confirming the overall suppression of CH4 production. This conclusion is fully consistent with our experimental observations.\nFor additional details, please refer to our response to Comment 1.\nComment 3: Besides, the competing reaction HER (theoretical) is also required, and compare with CO2 reduction reaction.\nResponse: Thank you for this valuable suggestion. Following your comment, we have evaluated the free energy of hydrogen adsorption (ΔGH) as a key descriptor for the competing HER, and compared it with the free energy changes for the e-CO2RR toward C2H4 (g).\nAs shown in Figure S64, the calculated ΔGH values for Cu(200), Cu(111), Cu(200)-SNW, and Cu(111)-SNW are 0.80, 0.54, 0.87, and 0.73 eV, respectively. These values are consistently higher than the corresponding ΔGM along the e-CO2RR pathway to C2H4 (g), which are 0.57, 0.71, 0.32, and 0.65 eV, respectively. This thermodynamic comparison clearly rationalizes the preferential occurrence of CO2RR over HER on these surfaces.\nThe energy profiles of *H adsorption on all catalyst surfaces investigated, along with structural models and relevant discussions, have been incorporated into the revised manuscript (Page 9, Lines 264–266; Page 10, Lines 291–293) and Supplementary Information (Figures S52-S56 and S64).\nFigure S64. The energy profiles of *H adsorption on Cu(200)-SNW, Cu(200), Cu(111)-SNW, and Cu(111).\nFigure S52. The configurations of reaction intermediates on Cu(111) for the reactions from CO2 to C2H4.\nFigure S53. The configurations of reaction intermediates on Cu(111)-SNW for the reactions from CO2 to C2H4.\nFigure S54. The configurations of reaction intermediates on Cu(200) for the reactions from CO2 to C2H4.\nFigure S55. The configurations of reaction intermediates on Cu(200)-SNW for the reactions from CO2 to C2H4.\nFigure S56. The configurations of *H adsorption on Cu(111), Cu(111)-SNW, Cu(200), and Cu(200)-SNW. Cu, red; N, yellow; C, purple; O, green; and H, pink.\nReviewer #2 (Remarks to the Author):\nComment : They have addressed my comments. It can be accepted.\nResponse: We appreciate the Reviewer’s positive evaluation of our work and the valuable suggestions provided previously.\nReviewer #4 (Remarks to the Author):\nComment: I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We thank Reviewer 4 for the time and the valuable feedback provided previously.\nReviewer #5 (Remarks to the Author):\nIn this manuscript, Xie et al. propose the use of SNW to modify Cu catalysts for electrochemical CO₂ reduction (e-CO₂RR). The authors claim that SNW enhances both the selectivity towards C₂H₄ and the structural stability of Cu catalysts. They support their conclusions with electrochemical performance testing and comprehensive characterization. While the study addresses an important challenge and the results are potentially interesting, in its current form the evidence presented is not yet sufficient to support the conclusion. Addressing the points above would greatly enhance the manuscript’s rigor and impact.\nResponse: Thank you for your insightful and constructive feedback, which has been instrumental in helping us further improve the quality of our manuscript. In response to your comments, we have carefully revised the manuscript and hope that the revised version is now suitable for publication in Nature Communications. Below, we provide detailed responses to each of your comments.\nComment 1. In the synthesis of Cucub-SNW / Cusph-SNW / Cutet-SNW, why was 10 mg of SNW chosen? From the results (Figures 1e, i, and m), only a small amount of SNW appears to ‘wrap’ around the Cu particles, while most of the remainder aggregates together. On the one hand, this may cover the active sites and hinder the structural analysis and interpretation; on the other hand, it could introduce competing hydrogen evolution. Please provide an explanation.\nResponse: We thank Reviewer 5 for these valuable comments. We have indeed conducted a series of experiments to systematically optimize the mass ratio between Cu and SNW in our nps catalysts.\nAs shown in Figure S18a–c, the Faradaic efficiency (FE) for H2 (FEH2%) of Cucub-SNW, Cusph-SNW, and Cutet-SNW catalysts prepared at different Cu-to-SNW mass ratios was evaluated.\nFor Cucub-SNW, the lowest FEH2% (13.1%) was achieved at the 40 mg:10 mg ratio, which is significantly lower than the values observed at 40 mg:40 mg (44.4%), 40 mg:20 mg (26.3%), 40 mg:5 mg (15.5%), and 40 mg:2.5 mg (23.7%). Therefore, the 40 mg:10 mg ratio was selected as the optimal formulation for Cucub-SNW to effectively suppress the competing HER.\nFor Cusph-SNW, the FEH2% values at 40 mg:5 mg (28.5%) and 40 mg:2.5 mg (28.2%) were slightly lower, yet comparable to, that at 40 mg:10 mg (33.1%), indicating that the HER activity is relatively insensitive to minor variations in SNW loading within this range. In contrast, Cutet-SNW showed a trend similar to Cucub-SNW, achieving the lowest HER activity (13.5%) at the 40 mg:10 mg ratio. This behavior may originate from the favorable synergistic interaction between the specific exposed Cu crystal facets and the SNW matrix, which effectively suppresses HER and promotes selective e-CO2RR.\nAt higher SNW contents, all three catalysts, including Cucub-SNW (44.4% at 40 mg:40 mg; 26.3% at 40 mg:20 mg), Cusph-SNW (67.2% at 40 mg:40 mg; 46.4% at 40 mg:20 mg), and Cutet-SNW (66.6% at 40 mg:40 mg; 44.9% at 40 mg:20 mg, exhibited progressively higher HER activity. This trend is consistent with the intrinsically strong HER catalytic activity of prinstine SNW, as confirmed in control experiments (see Figure S24).\nIn summary, to ensure a fair and comparable evaluation of e-CO2RR performance among the three Cu-SNW catalysts, the 40 mg:10 mg Cu-to-SNW ratio was selected as the optimal condition. We have provided the rationale to justify the choice of this ratio in the revised manuscript (page 4, lines 135–137) and the Supplementary Information (Figure S18).\nFigure S18. HER activities of (a) Cucub-SNW, (b) Cusph-SNW, and (c) Cutet-SNW with different Cu-to-SNW ratios.\nComment 2. In Figure S9, the edge signals could originate from overlapping SNW rather than true surface encapsulation. A line scan profile across Cu–SNW boundaries would help confirm intimate interfacial contact, find a particle at edge.\nResponse: Following your comment, we have conducted additional EELS line scan analysis across the Cu-SNW boundaries for all SNW-modified Cu catalysts. To minimize signal overlap, we specifically selected Cu NPs that were not fully overlapped with SNW, particularly in the scanned edge regions.\nThe results, now included as Figure S11, clearly show the presence of both C and N K-edge signals at the Cu-SNW boundaries. This observation confirms the intimate contact between the Cu NPs and the SNW. These additional data have been incorporated into the Supplementary Information to support our conclusions (page 3, lines 87–89). Thank you for this valuable comment.\nFigure S11. EELS line scan. ADF-STEM images of (a) Cucub-SNW, (c) Cusph-SNW, and (e) Cutet-SNW and corresponding EELS line scan profiles across the Cu-SNW interfaces for (b) Cucub-SNW, (d) Cusph-SNW, and (f) Cutet-SNW.\nComment 3. Also, to verify the presence of SNW, the authors should provide higher-magnification SEM images and high-resolution TEM images of Cucub-SNW, Cusph-SNW, and Cutet-SNW. This would make the structural assignments more convincing.\nResponse: We thank Reviewer 5 for this comment. We have accordingly performed additional HRTEM characterization on Cucub-SNW, Cusph-SNW, and Cutet-SNW catalysts. The obtained HRTEM images (now included as Figure S9) clearly reveal the presence of the SNW in close contact with the Cu surfaces of all three catalysts.\nThese HRTEM results, together with our EELS analysis (see Figure S11) and SEM images (see Figures 1e，i, and m), collectively provide robust and consistent evidence for the structural assignment of the SNW-modified catalysts. The relevant text in the main manuscript (page 3, lines 87–89) has been revised accordingly, and these new data have been incorporated into the revised Supplementary Information (Figure S9).\nFigure S9. Structural characterization. TEM, HRTEM images of (a, b) SNW, (c, d) Cucub-SNW, (e, f) Cusph-SNW, and (g, h) Cutet-SNW.\nComment 4. Figure 3h shows that C₂H₄ selectivity decreases from 71.2% to 61.3% over 24 hours while current density and Cu NPs structure remains stable. The underlying cause of this decline must be clarified. Is this due to SNW degradation, Cu surface reconstruction, or another factor?\nRelatedly, on page5, line 164, the authors should explicitly discuss the mechanistic origin of this selectivity drop.\nResponse: We thank Reviewer 5 for this comment.\nTEM and HRTEM analysis of the used Cucub-SNW catalyst (Figures S67) revealed that while the majority of particles retained their overall cubic morphology, a fraction underwent noticeable surface reconstruction, characterized by smoothed corners and edges. This structural evolution was further corroborated by XRD analysis (Figure S66a), which showed an increase in the relative intensity of the Cu(111) diffraction peak after the 24-hour test. The Cu(111)/Cu(200) intensity ratio increased from 0.43 to 0.64 compared to the pristine catalyst. This indicates a relative increase in the exposure of Cu(111) facets following prolonged electrolysis.\nIt is well-established, both in prior literature and confirmed in our work, that the Cu(111) surface favors the formation of C1 products (e.g., CO) (ACS Catal., 2019, 9, 5217-5222), whereas Cu(200) promotes C–C coupling toward C2H4. Consistently, our analysis showed that the decrease in C2H4 selectivity (from 71.2% to 61.3%) was accompanied by a concurrent increase in CO selectivity (from 7.9% to 15.4%), as shown in Figure S66b.\nTherefore, we attribute the gradual decline in C2H4 selectivity to the reconstruction of the Cu surface during long-term operation, which increases the proportion of Cu(111) facets and thereby enhances the competing pathway to C1 products.\nWe have provided explainations for decreased C2H4 selectity during prolonged operation in the revised manuscript (page 11, lines 339-345) and Supplementary Information (Figures S66 and S67). See below the highlighted text:\n“The severe corrosion explains the observed decrease in current density and selectivity towards C2H4. In contrast, in situ observations of Cucub-SNW under the same conditions show remarkably improved stability and resistance to electrochemical corrosion (Figures 4g-j). These findings are further corroborated by comparative ex situ XRD and TEM studies of the used Cu and Cucub-SNW (Figures S45 and S44), and are consistent with the sustained current density and only minor decline in C2H4 selectivity of the Cucub-SNW catalyst during the 24-hour stability test. Interestingly, the slight decrease in C2H4 selectivity (71.2% to 61.3%) was found to be accompanied by a concurrent increase in CO selectivity (from 7.9% to 15.4%, Figure S66). This shift in product distribution is attributed to minor surface reconstruction of Cu NPs during prolonged operation, which increased the relative population of Cu(111) facets that favor CO formation (Please refer to Figure S66 and S67 and related discussion in the Supplementary Information for more details).\nFigure S67. (a-h) TEM images of Cucub-SNW-24h.\nFigure S66. Phase composition and FE of C2H4 and C1 Products. XRD patterns of (a) Cucub-SNW at 0 h and 24 h. FE and FE for Cucub-SNW at 1 h, 12 h, and 24 h.\nComment 5. On page7, line 213, “However, both the used Cucub-SNW and Cutet-SNW catalysts retained the dominance of the Cu(200) and Cu(111) facets”, please give the ratio number for a better comparation.\nResponse: We thank Reviewer 5 for this suggestion and have labeled the XRD peaks in both the main text and the Supplementary Information (Figure S45) with ratio numbers to enhance the interpretability of the data.\nFigure 2. XRD patterns of (a) Cu and (b) Cucub-SNW.\nFigure S45. XRD patterns of (a) Cu and (b) Cucub-SNW after electrocatalysis.\nComment 6. On Page 7, lines 217–218, the authors state that “electronic interactions between Cu and SNW enhance stability.” Please clarify how these interactions specifically contribute to stabilization and use appropriate citations.\nResponse: Thank you for this valuable comment.\nWe have revised the relevant text in the main manuscript to provide a clearer and more specific explanation of how electronic interactions contribute to stability. We propose that the enhanced stability resulting from electronic interactions between Cu and SNW operates through two key mechanisms:\n1) Induced electron deficiency on Cu surface: Our XPS analysis (Figures 2c and 2e) confirms significant charge transfer from Cu to the nitrogen-rich SNW, as evidenced by the positive shift in Cu 2p binding energy. The charge transfer from Cu to SNW creates electron-rich N sites that, according to our calculations, serve as the preferred centers for CO2 adsorption and initial reduction. This effectively shifts the primary site of reactant activation from the Cu surface to the surrounding SNW network. Consequently, the Cu nanoparticles are shielded from the direct electrochemical environment that drives cathodic corrosion and dissolution.\n2) Interface stabilization via the chainmail-like effect: The electronic coupling creates an active and protective interface. DFT calculations (Figures 6a,b, and S57) suggest that the N sites in SNW, enriched with electrons from Cu, serve as favorable centers for CO adsorption and activation. This structure resembles a “chainmail” catalyst, in which the SNW not only electronically promotes the reaction but also physically shields the underlying Cu from direct electrolyte contact, thereby suppressing cathodic corrosion and dissolution.\nThe corresponding discussion has been strengthened in the revised manuscript (page 11, lines 352-355) as follows:\n“Based on our analyses, we attribute the enhanced stability of Cu-SNW catalysts to the shielding effect of SNW, along with the electronic interaction between SNW and Cu, which stabilizes surface Cu atoms against corrosion during e-CO2RR. Specifically, the shielding effect of SNW, resulting from the close contact between Cu and SNW (Figures 4g-j and S35), can limit direct contact of Cu surface to the electrolyte, therefore hindering cathodic corrosion during the e-CO2RR. Furthermore, the SNW incorporation leads to improved hydrophobicity, as confirmed by contact angle measurements (Figure S15), which could further restricts electrolyte access to the Cu surface sites, thereby contributing to enhanced operational stability. Lastly, as suggested by DFT calculations, the charge transfer from Cu to SNW makes the nearby N sites of SNW more favorable for CO adsorption and reduction compared to the Cu sites (Figure S60). Consequently, the reaction is diverted away from the Cu surface, minimizing the corrosive restructuring of Cu under operating conditions. This protective configuration resembles chainmail catalysts, where carbon layers encapsulate transition metal catalysts. In such systems, while reactions proceed through electronic interaction on the protective layers, the encapsulation of internal active metal components effectively prevents metal dissolution or sintering (via particle coalescence or Ostwald ripening) under harsh reaction conditions for electrochemical processes.”\nComment 7. In-situ STEM (Figures 4b–e; Figures 25–28) shows rapid Cucub particle corrosion or decomposition within 36–60 s, whereas IL-TEM (Figure S35) shows slow morphology change in 60 min. Do Cusph and Cutet also exhibit the same In-situ STEM corrosion results? If so, the authors should discuss why these two “quasi in-situ” TEM approaches yield such different results and their relevance to the real reaction (Figure S22). Possible influences include beam effects, electrolyte environment differences, or imaging timescales. Otherwise, the results will be less convincing in supporting the conclusion.\nResponse: We thank Reviewer 5 for this valuable comment. The main reason for the observed different morphological changes is indeed associated with the different potentials applied. The rapid corrosion in Figures 4b-e was recorded at a highly negative potential of -0.79 V vs. RHE, which drives faster electrochemical degradation. In contrast, the IL-TEM results in Figure S38 were obtained at a milder potential of -0.4 V vs. RHE. At an identical potential of -0.4 V vs. RHE, our in situ EC-STEM data (see Figure S30) indeed show a much slower rate of reconstruction for Cu NPs, qualitatively consistent with the IL-TEM observations. This confirms that the applied potential is a decisive factor. We acknowledge that this critical information was not clearly indicated in our initial submission, which may have led to confusion. We have now explicitly stated these potentials in the revised manuscript and the figure caption of Figure S38-S43 in the Supplementary Information.\nRegarding the in situ observation of corrosion of other NP shapes, due to limitations in experimental resources, we conducted the detailed in situ EC-STEM study only on Cucub as a representative case. Nevertheless, we did perform IL-TEM experiments on both Cusph and Cutet NPs. As shown in Figures S39 and S40, they exhibited similar corrosion behavior to Cucub NPs when subjected to the same potential (-0.4 V vs. RHE) in the IL-TEM setup."}, {"round": 3, "reviewer_comments": {"reviewer_5": "The authors have addressed my previous comments, and I am pleased to recommend this manuscript for publication."}, "author_response": ""}]

Decision letter