Electrochemical reduction, carbon dioxide

A v ety of reactions are catalyzed by electrochemically generated Ni(0) (62). Electrochemical reduction of Ni(bipy)3Br2 affords a reagent that couples acid chlorides and alkyl or aryl halides to form unsymmetrical ketones (63). Symmetrical ketones are formed from alkyl halides and carbon dioxide (64). Reductive electrochemical carboxylation of terminal alkynes, enynes and diynes can be accomplished with 10% Ni(bipy)3(Bp4)2 in DMF (65-68). Terminal allies lead selectively to a-substituted acrylic acids. Electrocatalytic hydrogenation on hydrogen-active electrodes has been reviewed (69). Radical cyclizations of vinyl, alkyl and aryl radicals can be carried out by indirect electrochemical reduction with a Ni(II) complex as a mediator (70). 

Mahmood, M.N., D. Masheder, and C.J. Harty (1987). Use of gas-diffusion electrodes for high-rate electrochemical reduction of carbon dioxide. II. Reduction at metal phthalocyanine-impregnated electrodes. J. Appl. Electrochem. 17(6), 1223-1227. 

Electrochemical Fixation of Carbon Dioxide (Cathodic Reduction in the Presence of Carbon Dioxide)... 

Electrochemical Fixation of Carbon Dioxide (Cathodic Reduction in the Presence of Carbon Dioxide), Scheme 4 Synthetic Routes to NSAIDs having 2-Arylpropanoic Acid Skeletons by Electrochemical Carboxylation... 

Electrochemical Behavior of Titanium Electrochemical Investigations of the Interfacial Behavior of Proteins Electrochemical Mechanisms and the Control of Biological Growth Processes Electrochemical and Photoelectrochemical Reduction of Carbon Dioxide Electrochemical Processes at Biological Interfaces... 

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. 

Taniguchi, I. Electrochemical and Photoelectrochemical Reduction of Carbon Dioxide 20... 

The reduction of carbon dioxide is another of the basic electrochemical reactions that has been studied at modified electrodes. The reduction at Co or Ni phthalocyanine in acidic solution yields formic acid or carbon monoxide A very high selectiv-... 

Bockris O MJ, Wass JC (1989) The photoelectrocatalytic reduction of carbon dioxide. J Electrochem Soc 136 2521-2528... 

Kuwabata S, Nishida K, Tsuda R, Inoue H, Yoneyama H (1994) Photochemical reduction of carbon dioxide to methanol using ZnS microcrystaUite as a photocatalyst in the presence of methanol dehydrogenase. J Electrochem Soc 141 1498-1503... 

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 ... 

For synthetic fuels or energy-storage media to be produced electrochemically, it is necessary that the carbon dioxide reduction be conducted at potentials only slightly (not more than by 0.2 V) more negative than the corresponding equilibrium potential. To do this requires extensive research aiming at refining the catalysts and the conditions for this process. 

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. 

Taniguchi, L, Electrochemical and photoelectrochemical reduction of carbon dioxide, in Modem Aspects of Electrochemistry, J. Bockris et al., Eds., Vol. 20, Kluwer, New York, 1989, p. 327. 

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. 

Dietz and Peover examined the electrochemical reduction of cis and trans stilbene (114) in DMF containing carbon dioxide, 9>. The first electron transfer to trans-114 affords a planar radical anion (115) which then undergoes rapid reaction with carbon dioxide to produce, ultimately, 2,3-diphenylsuc-cinic acid (116) in... 

Here, 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... 

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

Halmann reported in 1978 the first example of the reduction of carbon dioxide at a p-GaP electrode in an aqueous solution (0.05 M phosphate buffer, pH 6.8).95 At -1.0 V versus SCE, the initial photocurrent under C02 was 6 mA/ cm2, decreasing to 1 mA/cm2 after 24 h, while the dark current was 0.1 mA/cm2. In contrast to the electrochemical reduction of C02 on metal electrodes, formic acid, which is a main product at metal electrodes, was further reduced to formaldehyde and methanol at an illuminated p-GaP. Analysis of the solution after photoassisted electrolysis for 18 and 90 h showed that the products were 1.2 x 10-2 and 5 x 10 2 M formic acid, 3.2 x 10 4 and 2.8 x 10-4 M formaldehyde, and 1.1 x 10-4 and 8.1xlO 4M methanol, respectively. The maximum optical conversion efficiency calculated from Eq. (23) for production of formaldehyde and methanol (assuming 100% current efficiency) was 5.6 and 3.6%, respectively, where the bias voltage against a carbon anode was -0.8 to -0.9 V and 365-nm monochromatic light was used. In a later publication,4 these values were given as ca. 1% or less, where actual current efficiencies were taken into account [Eq. (24)]. 

Electrocatalytic reduction of carbon dioxide to Q-C3 hydrocarbons with less than 0.2% electrochemical yield was reported154 at pH 7 in the presence of pyrocatechol, TiCl3, and Na2Mo04 at -1.55 V versus SCE. 

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