Carbon dioxide, reduction potentials

Fig. 5 Comparison of carbon dioxide reduction potentials observed on different electrodes together with thermodynamic potentials, E°.

Patel M. 2004. Siufactants based on renewable raw materieils carbon dioxide reduction potential and poUdes and measure for the Errropean Union. Journal of Industrial Ecology 7(3/4) 47-62. 

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. 

Semiconductor electrodes seem to be attractive and promising materials for carbon dioxide reduction to highly reduced products such as methanol and methane, in contrast to many metal electrodes at which formic acid or CO is the major reduction product. This potential utility of semiconductor materials is due to their band structure (especially the conduction band level, where multielectron transfer may be achieved)76 and chemical properties (e.g., C02 is well known to adsorb onto metal oxides and/ or noble metal-doped metal oxides to become more active states77-81). Recently, several reports dealing with C02 reduction at n-type semiconductors in the dark have appeared, as described below. 

Since noncatalyzed carbon dioxide reduction shows a large overpotential and potentials far more negative than -2.0 V versus SCE... 

Rasmussen, S.C., Richter, M.M., Yi, E., Place, H. and Brewer, KJ. (1990) Synthesis and characterization of a series of novel rhodium and iridium complexes containing polypyridyl bridging ligands Potential uses in the development of multimetal catalysts for carbon dioxide reduction. Inorg. Chem., 29, 3926—3932. 

In the case of carbon dioxide reduction, the generated conduction band electron reduces the CO2 molecule to carbon dioxide anion radical, which initiates the reduction step. The initiation step involves a large reduction potential up to -1.9V vs NHE. The carbon dioxide undergoes a... 

Products and Standard Reduction Potentials of Carbon Dioxide Reduction Reactions, at pH 6.8, Involving 2-18 Electrons Standard Reduction Potential... 

The electrons undergo the equivalent of a partial oxidation process ia a dark reaction to a positive potential of +0.4 V, and Photosystem I then raises the potential of the electrons to as high as —0.7 V. Under normal photosynthesis conditions, these electrons reduce tryphosphopyridine-nucleotide (TPN) to TPNH, which reduces carbon dioxide to organic plant material. In the biophotolysis of water, these electrons are diverted from carbon dioxide to a microbial hydrogenase for reduction of protons to hydrogen ... 

Carbon dioxide generated by the fermentation process must be removed to help maintain the pH of the solution at pH 7.6—8.0. Carbon dioxide also inhibits the activity of the bacteria. The oxidation reduction potential is kept at 100—200 mV. The ideal temperature in the reactor varies with different strains in the bacteria but generally is 25—35°C. 

Carbon dioxide as additive improves the behavior of (Li02C0CH2)2 films formed above intercalation potentials in EC/DEC-based electrolytes due to increased formation of Li 2 CO 3 [200], It is interesting to note that SO2 reduction occurs at quite high potentials, before the reduction of other electrolyte components films contain inorganic and organic lithium salts [201]. 

Atmospheric O2 has a partial pressure of 0.20 bar, and atmospheric water vapor is saturated with carbon dioxide. This dissolved CO2 forms carbonic acid, which generates a hydronium ion concentration of about 2.0 X 10 M. The Nemst equation allows calculation of the half-cell potential for the reduction of 02(g) under these... 

The reaction products often compromise a mixture of various substances. Moreover, the reduction of carbon dioxide in aqueous solutions in the cathodic potential region is always accompanied by hydrogen evolution. Hence, an important criterion that describes the reaction selectivity is the faradaic yield ri for each individual Mh organic reaction product. 

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