Electrochemical reduction of Carbon Dioxide

1. Electrochemical Carbon Dioxide Reduction
Saurav Chandra Sarma

2. Future Challenges
 A recent report on the future of carbon dioxide (CO2) emission predicts that in the
coming few decades (2010–2060), ~496 gigatonnes of CO2 will be produced
because of fossil fuel combustion by existing infrastructure.
Solution to the problem
• CO2 can be artificially converted into fuel or commodity chemicals.
• The CO2 conversion methodology not only addresses the potential solution for
controlling the CO2 concentration level in the environment but also offers an
alternative approach for conversion of renewable energy to a chemical fuel or
product.
• So far, various noble metals (Ag, Au, Cu, Pt and so on) and metal complexes are
used as heterogeneous catalysts (as electrodes) for CO2 reduction. However, the
rising cost of noble metals is the main hindrance towards their large scale practical
applications

3. Attempts at CO2 reduction
M.A Scibioh and B. Vishwanathan, Proc. Indn. Natnl. Acad. Sci., 70 (A), 3, 2004

4. Electrochemical Carbon Dioxide Reduction

5. Products formed

6. Terminology and figures of merit
Current Opinion in Chemical Engineering 2013, 2:191–199
• Energetic Efficiency (EE): A measure of the overall energy utilization toward the desired
product.
• Current Density (CE): A measure of the rate of conversion.
• Faradaic Efficiency (FE): A measure of the selectivity of the process for a given product.
• Catalyst Stability
• Process Costs.

7. Product obtained using different metallic electrocatalyst
Isr. J. Chem. 2014, 54, 1451-1466
• The first step, generation of CO2
-, is critical
because it is the rate limiting step and the
coordination of this intermediate
determines if the 2e- reduction product will
be either CO or formate.
• Group 1 consists of those that do not bind
the CO2
- intermediate and cannot reduce
CO.
• Group 2 metals bind the CO2
- intermediate,
but cannot reduce CO.
• Group 3(copper) binds the CO2
-
intermediate and can reduce CO.
• There is also another group of metals that
bind hydrogen strongly, thereby excluding
CO2 reduction in aqueous media.

8. Changing/Modifying Catalysts

9. Proposed Protocol
Clean Techn Environ Policy (2015) 17:533–540

11. E (vs.RHE) = E (vs. Ag/AgCl) + 0.1988 V + 0.0591 V pH
Converting the reference scale from Ag/AgCl to RHE

13. The faradaic efficiency for the formation of
formate (f) is calculated as follows:
where 2 represents the number of electrons
required for the formation of one molecule of
formate from CO2;
n is the moles of the formate produced;
F is Faraday's constant (96485 C mol1 of
electrons);
and Q is the total charge in Coulomb passed
across the electrode during the electrolysis

17. Products obtained

18. Probable reaction pathway

20. Formation of different products
• Faradaic efficiency of CO was 21.5% at -1.73 V vs.Ag/AgCl, which was more
positive potential than those reported previously.
• Faradaic efficiency for methanol (1-2.5%) is about ten times higher compared to
previous reports that used Cu foil as the cathode catalyst (0.2 % at -1.14 V vs.RHE (so
–1.751 V vs Ag/AgCl) in 0.1 mol L-1 KHCO3).
• The catalyst may undergo a transition of CuO(shell) to Cu(I) and Cu(I) to Cu(core)
during the electrochemical reduction process, in which the generated Cu(I) can
promote the reduction of CO2.

21. Electrochemical behavior of Cu(core)/CuO(shell) catalyst
• The two oxidative peaks correspond to the oxidation of Cu to Cu(I) and Cu(I) to CuO,
respectively
• In the second scan, two reductive peaks were observed at -0.22 V and -0.62 V (III and IV
in Figure 2a), which can be attributed to the transition of CuO to Cu(I) and Cu(I) to Cu,
respectively.

22. XPS Spectra
Cu2+
Cu

23. Probable reaction mechanism

24. Other papers reported

32. More edge sites (active for CO evolution) than corner sites (active for the
competitive H2 evolution reaction) on the Au NP surface facilitates the stabilization
of the reduction intermediates, such as COOH*, and the formation of CO.

34. An important result of this study is the observation that, by controlling the size of tin oxide NPs on
carbon supports, overpotentials as low as ∼340 mV can be achieved for CO2 reduction to HCOO−,
with significant enhancements in both current density and efficiency.

36. LSVs and Faradaic Efficiencies (FE)
J. Am. Chem. Soc. 2015, 137, 5021−5027

37. Increasing Grain boundaries

38. J. Am. Chem. Soc. 2015, 137, 4606−4609

39. J. Am. Chem. Soc. 2015, 137, 4606−4609

40. J. Am. Chem. Soc. 2015, 137, 4606−4609

41. Varying particle size of Catalysts

43. • Particles of selected size are prepared by inverse micelle encapsulation.

45. Summary
• Choice of electrocatalyst with low overpotential and high current density is crucial.
• Electrolyte with high CO2 solubility must be chosen. For e.g: 1-ethyl-3-
methylimidazolium tetrafluoroborate (EMIM-BF4).
• Particle edges are more active towards CO2 than the corner sites.
• Grain boundaries are more efficient towards CO2 reduction.
• Sometimes high pressure is necessary for higher Faradaic efficiency.
• Oxide derived metallic nanoparticles are more active.
• Large electrode sizes also helps in increasing Faradaic efficiency.