Electrochemical Reduction of Carbon Dioxide

some recent studies of the electrochemical and photo-electrochemical reduction of carbon dioxide as well as some other related subjects will be reviewed and discussed. Attention is focused especially on the work done in the last ten years, to avoid duplication of previous review articles.2,4 

---

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

New Synthesis. Many attempts have been made to synthesize oxaUc acid by electrochemical reduction of carbon dioxide in either aqueous or nonaqueous electrolytes (53—57). For instance, oxaUc acid is prepared from CO2 as its Zn salt in an undivided ceU with Zn anodes and stainless steel cathodes ia acetonitrile containing (C4H2)4NC104 and current efficiency of >90% (53). Micropilot experiments and a process design were also made. 

Electrochemical reduction of carbon dioxide has found no extensive application so far, yet it is of great interest for scientists in the fields of theoretical and applied electrochemistry. To a certain extent, it is analogous to the photochemical carbon dioxide reduction, but it involves no chlorophyll and yields simpler products. In recent years some books and reviews on this topic have been published (e.g., Taniguchi, 1989 Sullivan et al., 1993 Bagotsky and Osetrova, 1995). 

Electrochemical reduction of carbon dioxide is usually conducted in aqueous or nonaqueous electrolyte solutions at cathodes made of various materials. As a result, various organic substances can form. The most common reactions are as follows ... 

Summing up, it can be said that the reaction of the electrochemical reduction of carbon dioxide will be the subject of painstaking research for a long time to come. In the future this reaction is very likely to play an important role in the electrochemical industry. 

Bagotsky, V. S., and N. Osetrova, Electrochemical reduction of carbon dioxide, Russ. J. 

Great promise exists in the use of graphitic carbons in the electrochemical synthesis of hydrogen peroxide [reaction (15.21)] and in the electrochemical reduction of carbon dioxide to various organic products. Considering the diversity in structures and surface forms of carbonaceous materials, it is difficult to formulate generalizations as to the influence of their chemical and electron structure on the kinetics and mechanism of electrochemical reactions occurring at carbon electrodes. 

Products Obtained by Electrochemical Reduction of Carbon Dioxide under High Pressure of 10 kg/cm2 Gagea... 

The direct electrochemical reduction of carbon dioxide requires very negative potentials, more negative than —2V vs. SCE. Redox catalysis, which implies the intermediacy of C02 (E° = —2.2 V vs. SCE), is accordingly rather inefficient.3 With aromatic anion radicals, catalysis is hampered in most cases by a two-electron carboxylation of the aromatic ring. Spectacular chemical catalysis is obtained with electrochemically generated iron(0) porphyrins, but the help of a synergistic effect of Bronsted and Lewis acids is required.4... 

Many attempts have been made to synthesize oxalic acid by electrochemical reduction of carbon dioxide in either aqueous or nonaqueous electrolytes. 

Tinnemans, A.H.A., Koster, T.P.M., Thewissen, D.H.M.W. and Mackor A. 1984. Tetraaza-macrocyclic cobalt(II) and nickel(II) complexes as electrontransfer agents in the photo( electro )chemical and electrochemical reduction of carbon dioxide. Recl.Trav.Chim. Pavs-Bas 103. 288-295. 

Mahmood et al. [117] studied the electrochemical reduction of carbon dioxide using gas diffusion electrodes. The reduction was performed on metal (lead, indium, and tin)-impregnated Teflon -bonded carbon gas diffusion electrodes in a sulfuric acid electrolyte over a 1 - 5 pH range. A schematic of the cell is shown in Fig. 24. The following reactions occurred ... 

A recent addition to the field of functional, catalytic ionic liquids comes in the area of carbon dioxide fixation. However, in this example, the reaction was performed under solvent free conditions and the ionic liquid was just used as a catalyst. Using [Bmim][OH], yields of up to 58% were obtained for the synthesis of disubstituted ureas from amines and carbon dioxide.By considering the electrochemical reduction of carbon dioxide discussed above, it is clear that ionic liquids could have an important role to play in the area of carbon dioxide fixation. 

Electrochemical reduction of carbon dioxide at a platinum electrode in acetonitrile-water mixtures... 

I. Taniguchi, Electrochemical and photo-electrochemical reduction of carbon dioxide, in Modem Aspect of Electrochemistry, Plenum Press, New York, 1989, p. 327, Vol. 20. 

Japanese researchers [248] have designed an apparatus for the electrochemical reduction of carbon dioxide employing ultrasound. The apparatus comprises an electrolytic cell containing C02-dissolved electrolytic solution, a porous Pt-group metal anode, a proton-conductive solid electrolyte having a porous metal cathode used as a catalyst for the electrochemical reduction of COz on one side and a second anode on the other side facing oppositely to the cathode, and an ultrasonic vibrator. C02 can be reduced effectively for a long time. 

Scheme 16.14 Electrochemical reduction of carbon dioxide (Reprinted from Ref. [119] with kind...

Amatore C, Saveant JM (1981) Mechanism and kinetic characteristics of the electrochemical reduction of carbon dioxide in media of low proton avaUabiUty. J Am Chem Soc 103 ... 

A new method of reducing carbon dioxide/bicarbonate solutions to form methanol and other reduced products is presented. The method overcomes the traditional limitations of electrochemical reduction of carbon dioxide at a cathode in that both the surface potential and concentration of reducing species can be varied independently. 

The surface states at the semiconductor electrolyte interface under illumination for the electrochemical redjgtion of carbon dioxide has been determined to be 10 cm. Surface states are induced by adsorbed ions and act as faradaic mediators for the photo-electrochemical reduction of carbon dioxide. It is shown that CO is adsorbed on platinum and adsorbed C0 is the intermediate radical. The rate determining step involves further reduction of CO to give the final products. Adsorption of NH, ions on p-GaP has been studied using FTIRRAS. At cathodic potentials adsorbed ammonium ions are reduced and the reduced ammonium radical desorbs. The structure of adsorbed ammonium is investigated. 

Electrochemical reduction of carbon dioxide provides one method of converting this plentifully available substance to useful fuels. 

The onset potential for the freshly etched p-CdTe for the photo-electrochemical reduction of carbon dioxide is -0.76V NHE. When the electrode was cycled between -0.56 to -2.24V under illumination, the onset potential for the photocurrent shifts to less cathodic potentials and remains constant at -0.66V after about c. 20 minutes. When the electrode is potentiostated at -2.0V the photocurrent remained constant for about 24 hours. These results are reproducible and consistent with the published data. Surface analysis of the etched surface of p-CdTe using XPS and SEM showed only trace amounts of carbon and oxygen. 

Ammonium ions have been shown to act as a catalyst for the photo-electrochemical reduction of carbon dioxide to carbon monoxide (36). 

Besides the well-known applications of water-soluble phosphines, e.g., in hydroformylation, water-soluble catalysts may have significant advantages for electrochemical processes in which the much lower resistance of aqueous solutions compared with that of organic solutions would improve the energy efficiency of the process. It is known that the electrochemical reduction of carbon dioxide to carbon... 

Singh, M.R. Clark, E.L. Bell, A.T. Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels. PNAS, 2015. doi 10.1073/pnas. 1519212112... 

J. P. Sauvage, J. P. Electrochemical Reduction of Carbon-Dioxide Mediated by Molecular Catalysts Coord. Chem. Rev. 1989, 93, 245. (c) Sullivan, B. P. Reduction of carbon dioxide with platinum metals electrocatalysts. A potentially important route for the future production of fuels... 

Electrosorption and Reduction of CO2. - Nowadays the electrochemical reduction of carbon dioxide to useful organic materials and fuels is an important topic with both theoretical ° and practical interest. The CO2 reduction at metal electrodes in aqueous media yields CO, HCOO, CH4, C2H4, and alcohols. The metal electrodes that show activity in CO2 reduction can be divided according to the product selectivity into the following groups ... 

Collin, J.P., and Sauvage, J.P. (1989) Electrochemical reduction of carbon dioxide mediated by molecular catalysts. Coordin. Chem. Rev., 93, 245-268. 

Development of catalyst for electrochemical reduction of carbon dioxide... 

The global warming is probably one of the most important environmental issues for this century. Every day there is new evidence of the climate change, but perhaps all this evidence is still not totally verified. However it is evident that the problem is real and the electrochemical reduction of carbon dioxide is one of the ways to solve the problem. In this chapter we discuss three families of compounds that catalyze the reduction of carbon dioxide. The general property of these macrocyclic complexes is that they reduce the overpotential required for this reaction to a more positive potential than metallic cathodes. 

---