Electrochemical reduction of carbon dioxide on lead and

copper electrodes

Nastase RalucaNgassimou Abba

End products

1. Hydrocarbons:MethanePropaneEthylene

2. Oxygenated molecules:MethanolEthanolFormic acidOxalic acid

Parameters

- applied potential- buffer strength- local pH- local CO2 concentration- CO2 pressure- surface crystal structure of the electrodes

Electrochemical reduction of CO2 at Cu

• 2H+ + 2e- ↔ H2 E0=0.0V vs SHE

• 2CO2 +12H+ +12e- ↔ C2H4 + 4H2O E0= 0.079V vs SHE

• CO2 + 8H+ +8e-↔CH4 + 2H2O E0= 0.169V vs SHE

• CO2 + 2H+ +2e-↔CO + H2O E0= -0.103V vs SHE

• CO2 + H+ +2e-↔HCOO- E0= -0.225V vs SHE

Fig. 1. Voltammograms obtained in phosphate solutions with Ar: (a), CO(b), and CO2 (c) at pH 6.8, and with 0.1MKHCO3 saturated with CO2 (d)

at pH 6.8.

The CO2 reaction stepFig. 2. Partial current data. (Conditions: 0.1M KHCO3, 19C, CO2 bubbled, bulk [H+] =

1.55 · 107 M, bulk[CO2] = 3.41 · 102 M. Estimated local [H+] and [CO2] values for polarisation

measurements

Reaction pathwaysFig. 3. The main reaction pathways at the electrode surface, with

adsorbed CO blocking the majority of the surface and hydrocarbonproducts being formed by the further reduction of adsorbed CO.

Current efficiencies at different potentials

Fig. 4. Current efficiencies at different potentials (0.1M KHCO3, CO2 bubbled).

Electrochemical reduction of CO2 at Pb

Three electrode conventional cell• Voltammetric experiments were carried out in an one-compartment

conventional three electrode Pyrex cell (V=15 cm3)• Working electrode : a lead wire with a geometric surface area of

0.42cm2• Counter electrode: vitreous carbon plate• Reference electrodes: Hg/Hg2Cl2/KCl sat. (aqueous medium) and

Ag/AgCl (propylene carbonate)• Electrochemical measurements : PC controlled AutoLab PGSTAT 302

Electrochemical Interface

Electrochemical reduction of CO2 at Pb

Three electrode spectroelectrochemical cell• Designed with a CaF2 IR transparent window • Working electrode : a Pb disc of 8 mm diameter. • Counter electrode: vitreous carbon plate• Reference electrode: Hg/Hg2Cl2/KCl sat. (aqueous medium)

Ag/AgCl (propylene carbonate)• Fourier transform infrared spectrometer Bruker IFS 66v/S. • OPUS 5.5 software.• Methods: SPAIRS and chronoamperometry.• Spectra: DA = DR/R0 = (RE2 RE1)/RE1

Results and discussionAqueous mediumFig.5. Voltammograms of a Pb electrode in 0.1 MNaOH recorded at 1 mV s1. (a) In supporting electrolyte. (b) After bubbling CO2 until pH = 8.6.

Propylene carbonate Fig.6. Voltammograms of a Pb electrode in 0.2M TEAP–PrC recorded at 50mVs−1 and 25 ◦C in the absence (a) and the presence of a CO2 -saturated solution (b).

Spectroscopic study in aqueous mediumFig. 7. FTIR spectra in spectroelectrochemical cell without applied potential to a Pb electrode during CO2 bubbling in 0.5 M NaOH; DR/R = (Rti Rt=0)/Rt=0, the ‘‘reference’’ spectrum, Rt=0, was recorded at t = 0. (a) CO2 between 5 and 30 s. (b) CO2 between 40 and 90 s. (c) CO2 between 100 and 200 s.

Fig. 8. Transmission spectra of KHCO3 (a) and K2CO3 (b) diluted in KBr pellets.

Fig.9. SPAIR spectra on a Pb electrode after bubbling CO2 in 0.1 MNaOH until pH = 8.6;DR/R = (RE2 RE1)/RE1, where the ‘‘reference’’ spectrum, RE1,was taken at E = 1.8 V vs.SCE. (a) Electrode potential from 1.0 V to 1.45 V vs. SCE. (b) Electrode potential from 1.5 V to 1.8 V vs. SCE.

Reaction step

Spectroscopic study in propylene carbonateFig. 10. Reference spectra of 0.2M TEAP–PrC recorded at −2.8V vs. Ag/AgCl (a), CO2

(b), formate (c) and oxalate (d) recorded in 0.2M TEAP–PrC.

Reaction step

Conclusions

Propylene carbonate:• Better characterization • Mass transfer process• Main reaction product: oxalateAqueous medium:• Predominant species: hydrogen carbonate ions• CO2 : not absorbed at cathodic electrode potential• Exclusive organic species : formateCopper electrode:• Multiple reaction pathways• Main product: CO

References• A review of the aqueous electrochemical reduction of CO2 to

hydrocarbons at copper- M. Gatrell, N. Gupta : Journal of Electroanalytical Chemistry 594 (2006)

• FTIR spectroscopy study of the reduction of carbon dioxide on lead electrode in aqueous medium- B. Innocent, D. Pasquier, F. Ropital, F. Hahn, J.-M. Leger, K.B. Kokoh: Applied Catalysis B: Environmental 94 (2010) 219–224

• Electroreduction of carbon dioxide at a lead electrode in propylene carbonate: A spectroscopic study- B. Eneau-Innocent, D. Pasquier, F. Ropital, J.-M. Léger, K.B. Kokoh: Applied Catalysis B: Environmental 98 (2010) 65–71

Thank you!