Fuel electrochemical reduction

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. 

H2 serves as the alternative energy source relative to fossil fuels and biomass [181] because it is clean and environmentally friendly. Hence, catalytic hydrogen generation from water under mild conditions is one of the goals for the organometallic catalysis. One of the hopeful methods is the electrochemical reduction of protons by a hydrogenase mimic. 

The electrochemical reduction of carbon monoxide also offers a route for the production of fuels from inorganic sources. For example, carbon monoxide is formed from coal in gasification... 

The photoassisted electrochemical reduction of C02 in water represents a very interesting technology that may allow the efficient use of residual or intermittent energies [6], with the concomitant conversion of large volumes of C02 into chemicals or fuels. 

As shown in Figure 18, the potential is almost proportional to the logarithm of H2 concentration diluted in air. When H2 is diluted in N2, the observed potential corresponds to the electromotive force of a H2-02 fuel cell, and in fact the EMF was as large as about 1.0 V with a theoretical slope of 30 mV/decade, as shown in the same figure. It has been shown that in the case of H2 diluted in air, the following electrode reaction, i.e., electrochemical oxidation of hydrogen (2) and electrochemical reduction of oxygen (3), are important. 

Regardless of the specific type of fuel cell, gaseous fuels (usually hydrogen) and oxidants (usually ambient air) are continuously fed to the anode and the cathode, respectively. The gas streams of the reactants do not mix, since they are separated by the electrolyte. The electrochemical combustion of hydrogen, and the electrochemical reduction of oxygen, takes place at the surface of the electrodes, the porosities of which provide an extensive area for these reactions to be catalysed, as well as to facilitate the mass transport of the reactants/products to/from the electrolyte from/to the gas phase. 

Lvov SN, Beck JR, LaBarbera MS. Electrochemical reduction of CO2 to fuels. In Muradov NZ, Veziroglu TN, editors. Carbon-neutral fuels and energy carriers. Boca Raton, FL CRC Press (Taylor Francis Group) 2012. p. 363 400. 

A porous anode and cathode are attached to each surface of the membrane, forming a membrane-electrode assembly, similar to that employed in SPE fuel cells. Electrochemical reactions (electron transfer-l-hydrogenation) occur at the interfaces between the ion exchange membrane and electrochemically active layers of electrodes. Electrochemical reductive HDH occurred at the interfaces between the ion exchange membrane and the cathode catalyst layer when an electrical current is applied between the electrodes ... 

Using Chase etal. (1998) for (AG, S) values, the increase of Carnot cycle work versus the reduction in fuel cell electrical work is now calculated for both fuel electrochemical reactions, at conditions FgTo and above. Included in brackets are (—AGWsmol 5kJmol ) ... 

The electrochemical reduction method can produce mesostmctured metals in the form of thin films. By electrodeposition of plating mixtures made from appropriate salts, mesostmctured metal films can be produced on the electrode surface with high surface areas and good mechanical and electrochemical stabihty. The ability to produce ordered mesostmctured metal films may lead to new types of electrode materials for apphcations such as batteries, fuel cells, and sensors. 

A great volume of work has been carried out on the important reaction of electrochemical reduction of O2, especially in the areas of fuel-cell development and air-cathode production for gas batteries. This field has been pioneered by Yeager (evolution reaction, it will not be treated here except... 

Hydroxamate. Hydroxamate complexes of trivalent actinides can be prepared directly in aqueous solution and other polar solvents and extracted into organic solvents, but due to the high thermodynamic stability of the corresponding tetravalent actinide complexes they are rapidly oxidized. They can also be prepared in solution via electrochemical reduction of the tetravalent complexes. These complexes have been studied for their role in separating high and low valent actinides in nuclear fuel processing schemes. ... 

The quantities of carbon stored in the form of atmospheric carbon dioxide, CO2 in the hydrosphere and carbonates in the terrestrial environment, substantially exceed those of fossil fuels. In spite of this, the industrial use of carbon dioxide as a source of chemical carbon is presently limited to preparation of urea and certain carboxylic acids as well as organic carbonates and polycarbonates. However, the situation is expected to change in the future, if effective catalytic systems allowing to activate carbon dioxide will become available. In this connection, the electrochemical reduction of CO2, requiring only an additional input of water and electrical energy, appears as an attractive possibility. 

In the present work, CO2 electrochemical reduction was examined on higji area metal electrocatalysts supported on activated carbon fibers (ACF), which contain slit-shaped pores with widths on the order of nanometers. Such electrocatalysts were used in the form of gas difiusion electrodes (GDE), which are used in the fuel-cell field. The structure of this type of electrode is shown in Figure 1. The reaction takes places at the gas phase / electrolyte (liquid phase) / electrode interface, the so-called three-phase boimdary. 

The interest in the electrochemical reduction of O2 again stems from its pivotal role in low-temperature fuel cells [137,141]. And again, by far the best catalyst for this reaction, in acid electrolytes, is platinum. 

The electrochemical reduction of platinum sails confined to the aqueous environments of lyotropic liquid-crystalline phases leads to the deposition of platinum films[262] that have a well defined long-ranged porous nanostructure and high specific surface areas. These results suggest that the use of liquid-crystalline plating solutions could be a versatile way to create mesoporous electrodes for batteries, fuel cells, electrochemical capacitors, and sensors. 

Photocurrents due to the electrochemical reduction and oxidation of H2O (H2 and O2 formation) usually occur at considerable overvoltages. Since this is an important problem for the solar production of a chemical fuel many researchers have tried to reduce the overvoltage by using a catalyst. In this case, it has to be realized again that the deposition of a metal monolayer on a semiconductor surface leads to the formation of a Schottky junction (see Section 2.2). Accordingly, the question arises whether there... 

It is a very difficult task to reduce CO2 to a useful fuel such as methanol or methane by electrochemical methods because six electrons per molecule are required for the production of methanol and as many as eight electrons for methane. Another difficulty is that high energy intermediates are involved in most steps, imposing high kinetic barriers. Hence, most electrochemical reduction experiments have yielded only formic acid as a product, according to the reaction... 

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

Oxidation of CO is also important in fuel cell applications. By combining the half reaction for the CO2/CO couple, equation (a), with electrochemical reduction of O2, fuel cells may achieve a maximum open circuit potential given by IlSlfCOj/CO) - (02/H20) = 1.34 . In practice, electrocatalysts are required to lessen the normally high kinetic overpotentials for electrodic CO oxidation. An example of a CO/O2 fuel cell which operates at the relatively low T of 80°C by employing [Rh(CO)2Br2] as the electrocatalyst and the Rh couple to mediate CO oxidation is shown below . 

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... 

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