Electrochemical CO₂ reduction to value-added chemical feedstocks is of considerable interest for renewable energy storage and renewable source generation while mitigating CO₂ emissions from human activity. Copper represents an effective catalyst in reducing CO₂ to hydrocarbons or oxygenates, but it is often plagued by a low product selectivity and limited long-term stability. Here we report that copper nanowires with rich surface steps exhibit a remarkably high Faradaic efficiency for C₂H₄ that can be maintained for over 200 hours. Computational studies reveal that these steps are thermodynamically favoured compared with Cu(100) surface under the operating conditions and the stepped surface favours C₂ products by suppressing the C₁ pathway and hydrogen production

Cai, Jin

Cheng, Tao

Choi, Chungseok

Duan, Xiangfeng

Goddard, William A., III

Huang, Yu

Kwon, Soonho

Lee, Changsoo

Lee, Hyuck Mo

Pan, Xiaoqing

Tieu, Peter

Xu, Mingjie

English

Caltech Authors - Main

Articles
https://doi.org/10.1038/s41929-020-00504-x
Highly active and stable stepped Cu surface 
for enhanced electrochemical CO2 
reduction to C2H4
In the format provided by the 
authors and unedited
Supplementary information
https:/ doi. . / 1929-020- 0504-x
Supplementary Information for 
Highly active and stable stepped Cu surface for enhanced electrochemical CO2
reduction to C2H4.  
Chungseok Choi1, Soonho Kwon2, Tao Cheng2,3, Mingjie Xu4,5,6,, Peter Tieu7, Changsoo Lee1,8, 
Jin Cai1, Hyuck Mo Lee8, Xiaoqing Pan4,5,9, Xiangfeng Duan10, William A. Goddard III2*, and Yu 
Huang1*
1Department of Materials Science and Engineering, University of California, Los Angeles, Los 
Angeles, California 90095, United States, 2Department of Applied Physics and Materials 
Science, California Institute of Technology, Pasadena, California 91125, United States, 3Institute 
of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based 
Functional Materials & Devices, Joint International Research Laboratory of Carbon-Based 
Functional Materials and Devices, Soochow University, Suzhou, Jiangsu 215123, People’s 
Republic of China, 4Irvine Material Research Institute (IMRI) and 5Department of Materials 
Science and Engineering, University of California, Irvine, Irvine, California 92697, United 
States, 6Fok Ying Tung Research Institute, The Hong Kong University of Science and 
Technology, Guangzhou 511458, P. R. China, 7Department of Chemistry, University of 
California, Irvine, Irvine, California 92697, United States, 8Department of Materials Science and 
Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon, 
34141, Republic of Korea, 9Department of Physics and Astronomy, University of California, 
Irvine, Irvine, California 92697, United States, 10Department of Chemistry and Biochemistry, 
University of California, Los Angeles, Los Angeles, California 90095, United States  
*Correspondence to: yhuang@seas.ucla.edu (Y.H.), wag@caltech.edu (W.A.G.) 
This PDF file includes: 
Supplementary Figures 1 to 15 
Supplementary Tables 1 to 6 
Supplementary References
2
Supplementary Figures and Tables
Supplementary Fig. 1 ∣ (a) PXRD of Syn-CuNWs, (b) Size of Syn-CuNWs. The size was 
determined by averaging more than 100 NWs. (c) PXRD of polycrystalline Cu-foil. 
3
Supplementary Fig. 2 ∣ The highly stepped surface of A-CuNWs after the activation 
process, (a), (b) FFT on parts of A-CuNW, (c), (d) HRTEM images of the surface of A-
CuNW, (e) [n(001) x (011)] steps on the surface of A-CuNW, (f) [n(100) x (111)] on the 
surface of A-CuNW.  
4
Supplementary Fig. 3 ∣ (a) SEI of Syn-CuNWs, (b) SEI of A-CuNWs. 
5
Supplementary Fig. 4 ∣ Pb under-potential deposition (UPD) of Syn-CuNWs (black line) and 
A-CuNWs (blue line) to extract ECSA measured in N2-saturated 0.1 M HClO4 + 0.001 M 
Pb(ClO4)2 solution at room temperature. The background current (dotted lines) were 
measured in N2-saturated 0.1 M HClO4. 
6
Supplementary Fig. 5 ∣ (a, b) Nyquist plot of Syn-CuNWs (black) and A-CuNWs (blue). 
7
Supplementary Fig. 6 ∣ Redox reaction of Syn-CuNWs and A-CuNWs in 0.1 M KOH at 100 
mV/s scan rate. Cu(100) at ~0.362 V1-4, Cu(110) at 0.395 – 0.43 V1-4, Cu(111) at ~0.492 V1-
4, and A-(hkl) (high energy steps)3,4 at a negative shift from Cu(100)). 
8
Supplementary Fig. 7 ∣ OH- adsorption of CuNWs after 10 min of activation. Cu(100) at 
~0.362 V (blue color)1-4, Cu(110) at 0.395 – 0.43 V (green color)1-4.  
9
Supplementary Fig. 8 ∣ Electrochemical CO2RR performance from three independent 
measurements. (a) FEs of Cu foil, (b) FEs of Syn-CuNW catalysts, (c) FEs of A-CuNW 
catalysts. Different sizes of the shape indicate different batches of CO2RR tests. 
10
Supplementary Fig. 9 ∣ (a-d) Partial current density of Syn-CuNW and A-CuNW catalysts 
for each product. 
11
Supplementary Fig. 10 ∣ (a) Surface roughness factor (SRF) of commercial-Cu 
nanoparticles and A-CuNWs, (b) FEs for commercial-Cu nanoparticles. The SRF was 
calculated from CV of electrochemical double-layer from 152 to 202 mV by changing scan 
rates.  
12
Supplementary Fig. 11 ∣ Stability of Cu foil at -1.07 V in 0.1 M KCHO3. 
13
Supplementary Fig. 12 ∣ Stability test of A-CuNW catalysts at potential ranging from -0.98 
to -1.07 V (RHE) for 198 hours, Top axis indicates corrected potential.  
14
Supplementary Fig. 13 ∣ (a) Correlation between A-(hkl) and FEC2H4 over the long-term 
stability test (x-axis is broken at 2.1 h, 0 – 1.5 h correspond to activation period); (b) 
Correlation of both A-(hkl) and FEs with activation times at -0.99 V –  -1.00 V (RHE); (c) 
Correlation of both A-(hkl) and FEs with activation times at -1.05 V –  -1.07 V (RHE), (d) 
Correlation of A-(hkl) and FEC2H4 including data points from stability tests (indicated by solid 
red stars). 
15
Supplementary Fig. 14 ∣ (a) Low magnification SEI of A-CuNW catalysts after CO2RR for 
205 h, (b), (c) High magnification SEI of A-CuNW catalysts after CO2RR for 205 h. (d) OH
-
adsorption of CuNWs after CO2RR for 24 h, (b) after CO2RR for 50 h, (c) after CO2RR for 
205 h. Cu(100) at ~0.362 V (blue color)1-4, Cu(110) at 0.395 – 0.43 V (green color)1-4, and A-
(hkl) (high energy steps_red colour)3,4 at a negative shift from Cu(100). 
16
Supplementary Fig. 15 ∣ The H* binding energies of eight possible binding sites on 
Cu(511). Cu atoms on the step are indicated by red. 
17
Supplementary Table 1 ∣ The surface portions of OHad on each facet of all catalysts. 
Reaction Time A-(hkl) (%) Cu{100} (%) Cu{110} (%)
Before 0 67.49 32.50 
10 min 0 73.83 26.16 
30 min  17.03 62.38 20.57 
1 h 28.98 57.16 13.85 
1.5 h 41.12 39.50 19.37 
205 h 46.82 31.58 21.58 
18
Supplementary Table 2 ∣ FEs for A-CuNWs. Each point was averaged, and the standard deviation 
was calculated from three independent measurements. 
V 
(RHE) H2% CO% CH4% C2H4% Ethanol% Acetate% Formate% Total% 
-0.76 
±0.01 
74.11 
±16.37
15.56 
±11.16 0 
8.10 
±3.52 0 0 1.53 
99.32 
±4.44 
-0.94 
±0.00 
25.60 
±5.74 
4.05 
±0.98 
3.19 
±1.87 
53.62 
±1.09 0 0 1.51 
87.98 
±6.61 
-0.98 
±0.00 
28.82 
±2.33 
3.35 
±1.47 
3.18 
±4.40 
67.14 
±1.56 1.50 0 0.73 
104.75 
±0.73 
-1.00 
±0.00 
19.90 
±3.39 
3.05 
±1.11 
7.09 
±2.71 
69.79 
±1.44 2.61 1.35 0.43 
104.24 
±1.55 
-1.06 
±0.00 
16.30 
±4.16 
1.65 
±1.28 
22.22 
±3.26 
59.95 
±2.82 3.39 0 0.24 
103.77 
±6.78 
19
Supplementary Table 3 ∣ FEs for Syn-CuNWs. Each point was averaged, and the standard deviation 
was calculated from three independent measurements.  
V (RHE) H2% CO% CH4% C2H4% Total% 
-0.89±0.01 63.59±15.01 4.25±0.97 0 22.05±6.02 89.90±9.92 
-0.97±0.00 49.02±10.61 4.35±3.06 2.18±1.24 30.76±9.43 86.32±13.64 
-1.00±0.00 44.39±7.62 2.23±0.98 6.09±1.49 44.65±2.20 97.38±10.09 
-1.03±0.00 51.03±9.74 1.84±1.49 4.29±2.45 34.48±1.75 91.92±7.93 
-1.07±0.00 30.44±11.94 1.76±0.69 24.43±11.27 37.25±1.84 93.90±3.00 
20
Supplementary Table 4 ∣ FEs for Cu foil. Each point was averaged, and the standard deviation was 
calculated from three independent measurements 
V 
(RHE) H2% CO% CH4% C2H4% Ethanol% Acetate% Formate% Total% 
-0.75 
±0.01 
94.89 
±2.26 
2.04 
±2.95 0 0 0 2.08 4.79 
103.81 
±3.82 
-0.86 
±0.00 
73.87 
±3.17 
1.51 
±1.40 
0.95 
±0.62 
2.17 
±1.09 0 1.68 2.91 
83.12 
±3.73 
-0.93 
±0.00 
77.87 
±11.82
6.76 
±5.17 
2.42 
±1.22 
6.74 
±2.73 0.31 0.46 2.39 
96.96 
±8.13 
-1.04 
±0.00 
46.96 
±4.49 
4.36 
±5.59 
24.67 
±5.15 
22.80 
±4.60 0.91 0.18 0.65 
100.53 
±6.71 
-1.07 
±0.01 
35.59 
±0.62 
1.67 
±0.25 
40.97 
±2.49 
24.81 
±1.38 0.89 0.09 0.22 
104.25 
±3.03 
21
Supplementary Table 5 ∣ Summary of stability of C2H4 production in H-cell. 
Catalysts Applied 
potential 
V (RHE) 
Stable 
FEC2H4
Reported 
Duration 
(hours) 
Electrolyte CO2
Flow 
rate 
(sccm)
Source 
A-Cu NWs -0.97 – -1.07 61 – 72% 205 0.1 M KHCO3 15 
This 
work 
A-Cu NWs -0.98 – -1.07 64 – 79% 198 0.1 M KHCO3 15 
This 
work 
Cu 
Nanocube 
(250 – 300 
nm) 
- 0.95 45% 1 0.1 M KHCO3 20 (5) 
Cu 
Nanocube 
(10 – 40 nm) 
- 0.75 ~32% 10 0.1 M KHCO3 20 (6) 
Plasma 
treated Cu 
foil 
- 0.9 60% 5 0.1 M KHCO3 30 (7) 
CuZn 
nanoparticles - 1.3 ~30% 8 0.1 M KHCO3 20 (8) 
Electro-
redeposited 
Cu 
- 1.2 40 – 45% 5 0.1 M KHCO3 20 (9) 
22
Supplementary Table 6 ∣ Free energy, frequency, Zero-point energy (ZPE), Enthalpy (Cv), Entropy 
of all states in DFT calculations. 
Energy 
[eV] 
Frequency 
[cm
-1
] 
ZPE 
[eV] 
Cv 
[eV] 
TS 
[eV] 
Cu(100) 
C1 
IS -263.645 3719.04 1.606498 0.170446 0.232887 
TS -262.971 3643.092 1.473867 0.179751 0.250323 
FS -263.98 3716.55 1.731384 0.179365 0.249453 
C2 
IS -263.878 2697.653 0.630043 0.167448 0.253563 
TS -263.45 2757.024 0.613232 0.13664 0.189569 
FS -264.291 2751.579 0.674542 0.148478 0.22949 
Cu(511) 
C1 
IS -207.912 3711.546 1.435686 0.159278 0.221053 
TS -207.204 3762.022 1.348848 0.189453 0.279913 
FS -208.391 3759.418 1.583465 0.156297 0.230906 
C2 
IS -208.175 2704.296 0.641028 0.162215 0.24363 
TS -207.709 2709.244 0.617154 0.140325 0.20639 
FS -208.316 2813.459 0.680842 0.122072 0.179666 
23
Supplementary References 
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sodium hydroxide solution. J. Electroanal. Chem. 112, 387-390 (1980). 
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monoxide to acetate. Nat. Catal. 2, 423-430 (2019). 
3. Raciti, D. et al. Low-overpotential electroreduction of carbon monoxide using copper 
nanowires. ACS Catal. 7, 4467-4472 (2017). 
4. Gennero De Chialvo, M. R., Zerbino, J. O., Marchiano, S. L., & Arvia, A. J. Correlation of 
electrochemical and ellipsometric data in relation to the kinetics and mechanism of Cu2O 
electroformation in alkaline solutions. J. Appl. Electrochem. 16, 517-526 (1986). 
5. Gao, D. et al. Plasma-activated copper nanocube catalysts for efficient carbon dioxide 
electroreduction to hydrocarbons and alcohols. ACS nano 11, 4825-4831 (2017). 
6. Kim, D., Kley, C. S., Li, Y., & Yang, P. Copper nanoparticle ensembles for selective 
electroreduction of CO2 to C2–C3 products. PNAS 114, 10560-10565 (2017). 
7. Mistry, H. et al. Highly selective plasma-activated copper catalysts for carbon dioxide 
reduction to ethylene. Nat. commun. 7, 12123 (2016). 
8. Reller, C. et al. Selective electroreduction of CO2 toward ethylene on nano dendritic copper 
catalysts at high current density. Adv. Energy Mat. 7, 1602114 (2017). 
9. De Luna, P. et al. Catalyst electro-redeposition controls morphology and oxidation state for 
selective carbon dioxide reduction. Nat. Catal. 1, 103-110, (2018). 


Highly active and stable stepped Cu surface for enhanced electrochemical CO₂ reduction to C₂H₄

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Highly active and stable stepped Cu surface for enhanced electrochemical CO₂ reduction to C₂H₄

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