CO2 and CO Reduction to Liquid Fuel on Oxide-derived Copper
Transcript of CO2 and CO Reduction to Liquid Fuel on Oxide-derived Copper
Christina W. Li GCEP Research Symposium
October 15, 2014
CO2 and CO Reduction to Liquid Fuel on Oxide-derived Copper
2 CO2
O2 O2
H2O H2O
renewable energy out
renewable energy in
storage utilization
CO2 Reduction to Liquid Fuels
liquid fuel
renewable energy out
CO, HCOO–
CH3CH2OO– CH3CH2OH
2 CO2
O2 O2
H2O H2O
utilization
CO2 Reduction to Liquid Fuels
CO2 + 2 e– + 2 H+ CO + H2O
2 H2O O2 + 4 e– + 4 H+
cathode
anode
renewable energy in
E (RHE)
–1.0
–0.5
0
0.5
1.0
1.5 O2 + 4 e– + 2 H2O
CO2 + 2 e– + H2O
4 HO–
CO + 2 HO–
1.23
E0 / V
–0.11
2 e– + 2 H2O H2 + 2 HO– 0
min
imum
overpotential (η)
Selectivity: CO vs H2
Activity: current per area vs potential
Stability: activity & selectivity over time
0.01–10 mA/cm2; η = 0.1–1.0 V
% Faradaic efficiency
Key Challenges in CO2 Reduction
Studies on Polycrystalline Cu
Hori, Y. et al. Chem. Lett. 1985, 11, 1695. Hori, Y. et al. J. Chem. Soc. Faraday Trans. I 1989, 85, 2309.
Y. Hori, in Modern Aspects of Electrochemistry, vol. 42, pp. 89-189.
Energetically inefficient
Poor CO2 vs H+ reduction selectivity
Rapid deactivation
Deficiencies:
Synthesis of Oxide-derived Cu
200 nm
After electroreduction Cu annealed at 500 °C for 12 h
2 µm
Oxide-derived Cu (OD-Cu)
CO2 reduction on OD-Cu
Bulk electrolysis: –0.5 V vs RHE in 0.5 M NaHCO3/saturated CO2
Polycrystalline Cu
OD-Cu
3% HCOO–
33% HCOO–
Li, C. W. & Kanan, M. W. J. Am. Chem. Soc. 2012, 134, 7231.
Activity on OD-Cu electrodes
• 0.4–0.5 V less overpotential required for high FE CO2 reduction
• only multi-carbon products observed at high overpotential
polycrystalline Cu Oxide-derived Cu polycrystalline Cu Oxide-derived Cu
C2H4
CH4
C2H4
C2H6
Origin of Enhanced CO2 Reduction
CO Tafel Plot H2 Tafel Plot
• Normalized CO2 reduction activity for OD-Cu and polycrystalline Cu are similar • H2 suppression is responsible for high FE at low ƞ
OD-Cu
Cu NPs
Cu NPs
OD-Cu
500 nm
OD-Cu
400 nm
Cu NPs
–0.5 V, CO2/0.5 M NaHCO3
Comparison to Cu nanoparticles
CO, HCOO–
CH3CH2OO– CH3CH2OH
2 CO2
3 O2 3 O2
3 H2O 3 H2O
renewable energy
solar or wind
energy
storage utilization
CO2 Reduction to Liquid Fuels
Two-step Reduction to Liquid Fuels
Can we access these products with greater efficiency via direct CO reduction? C2H6
CH4
C2H4
E (V vs RHE)
Fara
daic
effi
cien
cy (%
)
C2H4
polycrystalline Cu Oxide-derived Cu
oxygenates oxygenates
ethanol acetate propanol
CO2 + 2 e– + 2 H+ CO + H2O E0 = –0.11 vs RHE
2 CO + 8 e– + 8 H+ CH3CH2OH + H2O E0 = +0.18
CO is the key intermediate for further reduced products
CO Reduction on OD-Cu
Bulk electrolysis: 0.1 M KOH/saturated CO (1 mM)
Li, C. W.; Ciston, J.; Kanan, M. W. Nature 2014, 508, 504.
CO Reduction on OD-Cu
• Both enhancement of CO reduction and suppression of H2 evolution are responsible for high FE at low ƞ
Surface-area normalized CO reduction and H2 evolution
Structural Characterization of OD-Cu
with Jim Ciston, NCEM
• Grain-boundaries are high-energy bulk defects • Surface energy will depend on misorientation angle
TEM Electron Diffraction: Orientation Mapping
600 nm
600 nm
with Jim Ciston, NCEM and Joe McKeown, LLNL
0 0 1 1 0 1
1 1 1
Misorientation Angle (°)
Num
ber F
ract
ion
MacKenzie Distribution (random texture)
High-density of twin boundaries in OD-Cu
Conclusions and Future Work
• CO2 reduction to liquid fuels is possible via a two-step process.
CO2 + 2 e– + 2 H+ CO + H2O
2 CO + 8 e– + 8 H+ CH3CH2OH + H2O
• Metal-oxide reduction produces unique surfaces for CO2 and CO reduction, which may be correlated to grain-boundary structures.
• Enhanced CO2 and CO reduction faradaic efficiency stems in part from suppression of H2 evolution.
Future Work
• Build structure-activity relationships for grain-boundary density and misorientation angles
• Characterize CO binding strength
• Temperature programmed desorption
• In-situ surface-enhanced Raman spectroscopy
• Synthesize materials with controlled defect and grain-boundary density
• Understanding how defect and grain-boundary structure affect catalytic activity will allow us to better design and optimize catalyts for CO2 and CO reduction
Collaborators: Dr. Jim Ciston (NCEM) Dr. Joe McKeown (LLNL) Dr. Mary Louie (JCAP) Ezra Clark (JCAP) Dr. Badri Shyam (SLAC) Dr. Mike Toney (SLAC)
Acknowledgments
Dr. Yihong Chen Xiaoquan Min Allison Yau Thomas Veltman Dr. Changhoon Lee Dr. Xiaofeng Feng Kennedy McCone George Fei
Professor Matt Kanan
Dr. Craig Gorin Eugene Beh Aanindeeta Banerjee Vivian Lau Graham Dick Dr. Tatsuhiko Yoshino
Surface Enhanced Raman: Preliminary Data
Raman Shift / cm–1
Electrochemically-Deposited Cu
Inactive
OCV
Active
Active
–0.4 V vs. RHE
Cu2O CO
–0.4 V vs. RHE
CO32–
with Mary Louie, JCAP
Activity of OD-Cu 1 and 2
Time / h j /
mA•
cm–2
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
% C
O
Time / h
j / m
A•cm
–2
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
% C
O
OD-Cu 1 OD-Cu 1, 200 °C N2
OD-Cu 2 OD-Cu 2, 200 °C N2
37% HCOO–
6% HCOO–
27% HCOO–
10% HCOO–
E vs RHE (V)
Gold Silver Palladium
% C
O P
rodu
ctio
n
Chen, Y.; Li, C. W.; Kanan, M. W. J. Am. Chem. Soc. 2012, 134, 19969. with Yihong Chen and Xiaoquan Min
Enhanced CO2 Reduction on OD-Metals
Electrodeposition of Nanocrystalline Cu
0.2 M CuSO4, 0.4 M (NH4)2SO4, 0.2 M citric acid Galvanostatic deposition, total charge passed is constant
Size (nm) Strain (%)
6 mA/cm2 31 0.46
12 mA/cm2 23 0.50
24 mA/cm2 19 0.49
6 mA/cm2
12 mA/cm2
24 mA/cm2
500 nm
500 nm
500 nm
Electrodeposition of Nanocrystalline Cu
0.2 M CuSO4, 0.4 M (NH4)2SO4, 0.2 M citric acid Galvanostatic deposition, total charge passed is constant
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
Thermal Stability
Deposition Bath: 0.2 M CuSO4, 0.4 M (NH4)2SO4, 0.2 M citric acid Galvanostatic: 24 mA/cm2, 15 m
No annealing
100 °C, 2 h, 150 sccm N2 200 °C, 2 h, 150 sccm N2
Sample % CO % HCOO– % AcO– %H2
As-dep. 29 35 2 32
100 °C 14 34 4 45
200 °C 0.2 0.8 0.3 99
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
Thermal Stability
Size (nm) Strain (%)
Annealed 200 °C 37 0.42
Annealed 100 °C 23 0.58
ECD 24 mA/cm2 19 0.49
After 12 h BE 28 0.55
ECD 24 mA 100 °C Anneal 200 °C Anneal
500 nm 500 nm 500 nm
Thermal Stability
Deposition Bath: 0.2 M CuSO4, 0.4 M (NH4)2SO4, 0.2 M citric acid Galvanostatic: 24 mA/cm2, 15 m
No annealing
200 °C, 2 h, 100 sccm N2 OD-Cu 1 pc-Cu
Sample % CO % HCOO– % AcO– %H2
As-dep. 29 35 2 32
100 °C 14 34 4 45
200 °C 0.2 0.8 0.3 99
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
Time / h
j / m
A•cm
–2
Nor
mal
ized
j H2 /
mA•
cm–2
Sample RF
As-dep. 104
200 °C 245
OD-Cu 1 160
pc-Cu 1
Cu2O NPs
Reduced
2 θ / ° 2 θ / ° 2 θ / °
<D> = 17 nm ԑ = 0.2%
<D> = 29 nm ԑ = 0.4%
<D> = 29 nm ԑ = 0.2%
Cu2O NPs
Time / h
j / m
A•cm
–2
Cu2O NPs 5 mg/cm2, drop-dried onto C-paper
BE @ –0.5 V vs. RHE 0.5 M NaHCO3
Sample % CO % HCOO– % H2
1 16 2 81
2 11 2 86
3 14 3 83
% C
O
Time / h j /
mA•
cm–2
BE @ –0.3 V vs. RHE 0.1 M KOH
Sample % AcO– % EtOH
1 24 28
2 18 22
3 21 24
Cu2O NPs: Other Exps
• Cu2O 1 • Drop-dried onto C-paper • H2 Reduction • Cu2O not fully reduced
• Cu2O NPs • Drop-dried onto C-paper • 1 M KOH
Red T Qred jtot % AcO– % EtOH jCO
80 °C 5.0 2.6 19 34 1.4
100 °C 2.2 2.1 19 40 1.3
E v. RHE jtot % AcO– % EtOH jCO
–0.2 0.62 64 13 0.48
–0.25 1.4 14 16 0.43
CO reduction pathways: Cu(100) DFT studies
Calle-Vallejo, F.; Koper, M. T. M. Angew. Chem. Int. Ed. 2013, 52, 7282.
e–,
Ethylene favored over ethanol by 0.2 eV
No ethanol observed experimentally by DEMS
CO reduction pathways: OD-Cu
Li and Kanan 2013 submitted
Tafel kinetics Selectivity in 1 M KOH
0.1 M KOH 1 mM CO
HO– e–,
Tuning OD-Cu catalytic properties
500 °C in air
OD-Cu 1 (electroreduced)
–0.5 V
Cu2O/Cu electrode 500 nm
OD-Cu 1
OD-Cu 2 (H2- reduced)
H2, 130 °C
Cu2O/Cu electrode 500 nm
OD-Cu 2
500 °C in air
400 nm
Cu NP powder
Cu NP powder electrode
glass slide
drop cast
Cu NPs
Tuning OD-Cu catalytic properties
500 nm
OD-Cu 1
500 nm
OD-Cu 2
400 nm
Cu NP powder
OD-Cu 1
Cu NP powder
GIXRD
OD-Cu 2
<D> microstrain
0.01%
0.2%
40 nm
30 nm
<0.1% 50 nm
Comparison between OD-Cu 1 & OD-Cu 2
Geometric CO reduction activity
Li and Kanan 2013 submitted
conditions: 0.1 M KOH, 1 mM CO
OD-Cu 1
Cu NP powder
OD-Cu 2
Comparison between OD-Cu 1 & OD-Cu 2
Normalized CO reduction activity
Li and Kanan 2013 submitted
conditions: 0.1 M KOH, 1 mM CO
OD-Cu 1
Cu NP powder
OD-Cu 2
22× 45×
Normalized H2O reduction activity
Cu NP powder
OD-Cu 2
OD-Cu 1
Tuning OD-Cu catalytic properties
3 CO + 12 e– + 10 H2O CH3CH2CH2OH + 12 HO–
0.1 M KOH, 1 mM CO n-PrOH
E (RHE) en
ergy
sto
red
–1.0
–0.5
0
0.5
1.0
1.5 O2 + 4 e– + 4 H+
CO2 + 4 e– + 4 H+
CO2 + 2 e– + 2 H+
CO2 + 2 e– + 2 H+
CO2 + 6 e– + 6 H+
CO2 + 8 e– + 8 H+
2 e– + 2 H+
2 H2O
CH4 + 2 H2O
CH3OH + H2O
CH2O + H2O
CO + H2O
HCO2H + H2O
H2
η
1.23
E0 / V
0.17
0.03
0
–0.07
–0.11
–0.20
Equilibrium Potentials for CO2 Reduction
Studies on Single-Crystal Cu
Hori, Y. et al. J. Mol. Cat. A 2003, 199, 39. Hori, Y. et al. J. Electroanal. Chem. 2002, 533, 135.
Norskov, J. et al. Surf. Sci. 2011, 605, 1354.
Real Surface Area
Q = CE dQ/dt = C * dE/dt I = C * (scan rate) C = (εε0/L) * A
Waszczuk, P. et al. Electrochimica Acta 1995, 40, 1717
Annealed Cu: 13.9 mF Cu: 29.3 μF Roughness factor = 476
Characterization of annealed Cu
After electroreduction Cu Annealed at 700 °C for 1 h
2 µm 1 µm 1 µm 300 nm
Electrode post-processing
• Electrode annealed at 500 °C for 1 h • Reduced at–0.5 V vs. RHE overnight • Annealed at 160 °C under vacuum for 2 h • Bulk electrolysis: – 0.5 V vs. RHE in 0.5 M NaHCO3 /sat. CO2
Annealed at 500 °C for 1h After vacuum annealing
Galvanostatic Oxide Reduction
• Electrodes annealed at 500 °C for 1 h • Reduced at indicated current density until plateau potential is
reached • Bulk electrolysis: –0.5 V vs RHE in 0.5 M NaHCO3/saturated CO2
100 µA/cm2
1 mA/cm2
10 mA/cm2
20 mA/cm2
50 mA/cm2
Electrolyte Screen
Electrolyte (0.5 M) Initial pH % CO % HCOOH % H2 jtot jCO2
NaHCO3 7.2 37.2 32.8 10.7 2.02 1.42
KHCO3 7.4 28.9 35.5 18.0 2.63 1.70
LiHCO3 7.3 25.8 35.0 18.9 2.30 1.40
LiClO4 3.7 29.8 39.0 10.5 1.75 1.20
NaClO4 3.4 26.4 29.9 18.0 1.26 0.71
KCl 4.2 26.4 10.1 33.7 1.22 0.44
LiCl 3.9 31.8 15.2 18.0 0.73 0.34
Na2SO4 4.2 11.5 23.6 37.8 1.69 0.59
NaOAc 6.1 3.8 3.0 61.0 1.70 0.12
NaH2PO4 4.2 0.18 0 70.5 5.94 0.011
• All electrodes annealed at 500 °C for 1 h • –1.13 V vs Ag/AgCl (variable E vs RHE depending on pH)
Chemical Oxidation of Cu
Conditions: 1) 0.05 M (NH4)2S2O8, 1.25 M NaOH 2) 0.1 M (NH4)2S2O8, 2.5 M NaOH 3) 0.2 M (NH4)2S2O8, 5 M NaOH
Soaked Cu foil for 3 hours Rinsed with IPA and diH2O
Crystalline CuO and Cu(OH)2
Zhang, W. et al. Inorg. Chem. 2003, 42, 5005.
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