Electrosynthesis principles

The industrial economy depends heavily on electrochemical processes. Electrochemical systems have inherent advantages such as ambient temperature operation, easily controlled reaction rates, and minimal environmental impact (qv). Electrosynthesis is used in a number of commercial processes. Batteries and fuel cells, used for the interconversion and storage of energy, are not limited by the Carnot efficiency of thermal devices. Corrosion, another electrochemical process, is estimated to cost hundreds of millions of dollars aimuaUy in the United States alone (see Corrosion and CORROSION control). Electrochemical systems can be described using the fundamental principles of thermodynamics, kinetics, and transport phenomena. 

Use of the electrosynthesis allows us to isolate, together with neutral complexes, cationic and anionic compounds [506,551,559]. The most widespread principle of electrochemical synthesis of cationic complexes is based on the anodic dissolution of a metal in an organic solvent (which frequently acts as a ligand), containing a mineral acid [551]. Such syntheses, in particular (3.239) [551,560], were carried out under dissolution of metals (Cd, Zn, In, Ti, V, Mn, Co, Cr, Fe) in CH3CN or DMSO (L), containing an equal volume of 48% solution of HBF4 ... 

Other important methods of synthesis of coordination compounds are discussed in detail [1,3,10,11,53,201,202,206,207,316,318,322,690]. In this respect, we emphasize the synthesis of metal-polymers [690,691] and preparation of complexes in the solid phase (mechano- or tribosynthesis) [10,201,202,206]. Additionally to the above-described techniques, the general methods and principles of synthesis of coordination compounds are used to obtain metal-polymers (immediate interaction of polymer ligands and metal salts, template electrosynthesis, polymer-analogous transformations). The last method consists of the polymerization of metal-monomers (metal-containing monomers) and fixation of metal complexes on the polymer... 

Suppose, however, one reversed the emphasis and made a second fuel cell principle concerning spontaneous electrosynthesis. Then one would concentrate, not on the energy produced (now the by-product), but on the substance. Obviously, one would have to choose a situation in which the spontaneously acting overall reaction in the fuel cell produced a worthwhile product. To take a very simple example, suppose one led Cl2 gas, instead of 02 to the cathode of a fuel cell and ethylene instead of hydrogen to the anode. At the cathode one would find ... 

D. Danly, D. Genders, D. Pletcher, Principles of electrochemical engineering and scale-up, Short Course at 9th International Forum on Electrosynthesis in the Chemical Industry , Clearwater Beach, 1995... 

Scientists make electrochemical measurements on chemical systems for a variety of reasons. They may be interested in obtaining thermodynamic data about a reaction. They may want to generate an unstable intermediate such as a radical ion and study its rate of decay or its spectroscopic properties. They may seek to analyze a solution for trace amounts of metal ions or organic species. In these examples, electrochemical methods are employed as tools in the study of chemical systems in just the way that spectroscopic methods are frequently applied. There are also investigations in which the electrochemical properties of the systems themselves are of primary interest, for example, in the design of a new power source or for the electrosynthesis of some product. Many electrochemical methods have been devised. Their application requires an understanding of the fundamental principles of electrode reactions and the electrical properties of electrode-solution interfaces. 

Biofilms, Electroactive, Fig. 5 Principles of the most abundant microbial bloelectrochemlcal systems (a) microbial fuel cells and (b) microbial electrosynthesis cells on the example of the H2 production. (Note Here the anodic and cathodic reactions are catalyzed by blofilms, yet as described in the text also other catalysts can be exploited)... 

CEMs such as Nation remain state-of-the-art H" ion conductors in fuel cells to this day. However, much research is being done to improve CEMs in PEMFC and DMFC. AEMs as OH ion conductors are also being investigated for alkaline hydrogen and alcohol fuel cells (see entry Fuel Cells, Principles and Thermodynamics ). Such new membranes will likely be suitable for SPE electrosynthesis in the future. 

Electrosynthesis is one of the most interesting and yet underutilized methods of preparing coordination compounds. Electrochemical reactions make use of the universal "chemical reagent" — the electron. 1 The electrosynthesis of metal complexes can, in principle, give rise to a high selectivity, because it is possible to control electrode potentials over a wide range. Electrons can be removed from, or added to, a system without the complications associated with the presence of chemical oxidants and reductants and the by-products associated with their use. However, a new set of complications in the form of electrodes and supporting electrolytes must be dealt with. 

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