1. Imidazolium-based Ionic Liquid – Ag Interfaces
on the CO2 Electroreduction
studied by Sum Frequency Spectroscopy
Natalia Garcia Rey and Dana D. Dlott
University of Illinois at Urbana-Champaign
International Symposium on Molecular Spectroscopy
72nd Meeting, Champaign-Urbana

2. Room Temperature Ionic liquid (RTIL) materials for the electrochemical challenges of the future
Designed RTILs for specific applications
Batteries
Aprotic
Protic
Fuel Cells
Supercapacitors
Nature Materials 8, (2009) 

3. Sum Frequency Spectroscopy to Study Electrochemical Interfaces
SFG=IR+VIS
SFG Intensity in liquid-metal interfaces has two contributions:
Metal-liquid interface: nonresonant-SFG (NR-SFG)
Molecule observed, resonant with IR : resonant-SFG (RES-SFG)
IR
VIS
SFG
Gouy-Chapman double-layer model:
Diffuse layer
Inner and outer layer
double
layer
bulk
electrolyte
electrode
CaF2 window E

4. Potential dependence SFG Intensity
IR
VIS
SFG
surface sensitive
bulk sensitive
double
layer
bulk
electrolyte
electrode
CaF2 window 
Ez integrated over the Debye Length
 potential on the interface E
<<<1
linear 
offset 
*Garcia Rey & Dlott, J. Electroanal. Chem, 2016, DOI: /j.jelechem

5. CO2electroreduction RTIL-Ag
Simplified model
SF intensity-potential dependence
Li-ion batteries
CO2electroreduction RTIL-Ag
time (s)
*Garcia Rey & Dlott, J. Electroanal. Chem, 2016, DOI: /j.jelechem

6. Water enhancement of the CO2 conversion on Ag in room temperature ionic liquids (RTIL)
RTIL: EMIM-BF4
0.3%
45%
77% 
in EMIM-BF4
- Ionic liquid mediated the CO2 electroreduction into CO at low-overpotential1,2.
- Water increases Faradaic efficiency3.
pH=6.5
pH=3.2
pH=7.6
[1] Rosen, B. A. et al., Science 2011, 334, 643, [2] A. Salehi-Khojin et al. J. Phys. Chem. C, 2013, 114, 1627, [3] Right Fig. adapted from Rosen, B. A. et al. J Electrochem. Soc. 2013, 160, H138.
*Studied concentrations

7. Water enhancement of the CO2 conversion on Ag in room temperature ionic liquids (RTIL)
0.3 mol % H2O
45 mol % H2O
77 mol % H2O
-1.33 V
-1.21 V
-0.92 V Ar Ar Ar
CO2
CO2
CO2
*Garcia Rey & Dlott, PCCP, 2017, 19, 10491

8. Water-RTIL Ag Interface:
Potential-dependent NR-SFG
0.3 mol % H2O
45 mol % H2O
77 mol % H2O
(a)
(b)
(c)
-1.3 V
-1.2 V
-0.9 V
*Garcia Rey & Dlott, PCCP, 2017, 19, 10491

9. at different water concentrations RTIL
CO adsorbed on Ag
at different water concentrations RTIL
0.3 mol% H2O
77 mol% H2O
1st cycle
2nd cycle
3rd cycle
Potential vs. Ag/AgCl(V)
C:\Users\Natalia\Documents\Data\EC-SFG\AgEMWater\160331_AgEM77CO2.pxp
IR frequency (cm-1)
*Garcia Rey & Dlott, PCCP, 2017, 19, 10491

10. Take Home Message: Water-RTIL Ag Interface
-1.33 V
-0.92 V
A structural transition of ionic liquid promotes the CO2 electroreduction, when the onset of CO2 occurs:
The CO Stark Shift doubles in magnitude.
There is a minimum of the potential- dependence NR-SFG Intensity.
At higher water concentrations:
the Stark shift is weaker: the water molecules screen the e- screening from Ag.
CO frequency increases: stronger CO bond, loosely bond to Ag.
The Potential-dependence NR-SFG shifts to lower potentials.
0.3%
77%

11. Role of Imidazolium based promoter for the CO2 electroreduction on Ag
G.P.S. Lau, M. Schreier, D. Vasilyev, R. Scopelliti, M. Grätzel, P.J. Dyson, New Insights Into the Role of Imidazolium-Based Promoters for the Electroreduction of CO2 on a Silver Electrode, Journal of the American Chemical Society 138(25) (2016)
1a. Tetrafluoborate
1b. N,N-bis(trifluoromethane)sulphonamide
1c. Trifluoromethane-sulfonate
1-methyl-2,3-dimethylimidazolium
TFSI

12. CO2 electroreduction mediated by imidazolium-based ionic liquids on Pb
EMIM-Tf2N
L. Sun, G.K. Ramesha, P.V. Kamat, J.F. Brennecke, Switching the Reaction Course of Electrochemical CO2 Reduction with Ionic Liquids, Langmuir 30(21) (2014)

13. CO2 electroreduction mediated by imidazolium-based ionic liquids
Addition of water
Anion change
Water enhances the CO2 electrochemical reduction into CO
mediated by imidazolium-based ionic liquids
Rosen, B. A. et al. J Electrochem. Soc. 2013, 160, H138.
Reference: Accelerated CO2 transport on surface of AgO nanoparticles in ionic liquid BMIMBF4
Exchange C2 imidazolium ring.
Anion change
Higher efficiency CO2 reduction
CO2 electroreduction on Pb
The protons at the C4 and C5 positions are essential for efficien catalysis
Lau et. Al. New Insights Into the Role of Imidazolium-Based Promoters for the Electroreduction of CO2 on a Silver Electrode, Journal of the American Chemical Society 138 (2016) 7820
L. Sun, G.K. Ramesha, P.V. Kamat, J.F. Brennecke, Switching the Reaction Course of Electrochemical CO2 Reduction with Ionic Liquids, Langmuir 30(21) (2014)
Cation exchange: Piridinium.
Cation tuning: Butyl chain.

14. Imidazolium based RTIL-Ag Interface
Potential-dependent NR-SFG
Anion change
Cation tuning
Cation exchange

15. Imidazolium based RTIL-Ag Interface
CO atop Stark Shift
- CO atop not seeing on the surface
Cation exchange
Cation tuning

16. Free Induction decay of CO atop on Ag at different cell potentials
FID of CO adsorbed on:
Cu, Pt (UHV) ~ 1-2 ps
0.1ML H2SO4 on Pt ~675 fs
RTIL/Ag ~250 fs

17. Take home message
The potential-dependent NR-SFG Intensity monitors the changes in the double-layer RTIL-Ag interface. Tuning the electrolyte shows different dependency on the potential.
The RTIL structural transition mediated the CO2 electroreduction. A minimum in the NR-SFG was found at the same potential where the CO2 electroreduction occurs, and where the CO Stark shift also changes and doubles.
The atop CO vibrational mode allows to monitor the changes on the interfaces by the Stark shift. The CO FID mode relaxes faster on the RTIL-Ag than other electrochemical metal interfaces.

18. Thank you all for your attention!
Acknowledgments
Prof. Dana D. Dlott
Bruno G. Nicolau
Dlott’s group
Bruno
Dana
Thank you all for your attention!
Any questions?

19. Cation exchange Cation tuning Potential vs. Ag/AgCl(V)
-0.5
-1.8
-0.5
-1.8
Potential vs. Ag/AgCl(V)
IR frequency (cm-1)
IR frequency (cm-1)