Water, electrolysis mechanism

For water electrolysis, GE used Nafion for the electrolyte as well as for a separator, mechanically pressing both electrodes against the membrane. Takenaka and Torikai proposed an electroless method for the deposition of noble metals on the surface of Nafion under wet conditions based on the difPiision of reducing agent through the membrane. ... 

Paddison SJ (2003) Proton conduction mechanism at low degrees of hydration in sulfonic acid-based polymer electrolyte membranes. Ann Rev Mater Res 33 289-319 Rasten E, Hagen G, Tunold R (2003) Electrocatalysts in water electrolysis with solid polymer electrolyte. Electrochimica acta 48 3945-3952... 

BDD anodes without impurities are not electrocatalytically active because water electrolysis is characterised by the formation of OH radicals (Marselli et al. 2003), ozone (Cho et al. 2005) and hydrogen peroxide (Drogui et al. 2001). One can conclude from radical chemistry that other radicals have to be expected in the anodic reaction layer and, maybe, in the bulk. Foerster and co-workers compared active chlorine formation on Pt and BDD anodes (Foerster et al. 2002). Formation of active chlorine was explained by a mechanism involving the formation of Cl radicals (Ferro et al. 2000) ... 

Recently, Fleszar and Ploszynska [546] re-examined the kinetics of electro-oxidation of benzene and phenol at Pb02 anodes. These authors concluded that the oxidation process does follow an E.C.E.-type mechanism, there not being enough evidence to indicate direct participation of Pb02 in the oxidation of these molecules. They observed a linear dependence between oxidation rate and the rate of water electrolysis. Fleszar and Ploszynska [546] advanced the hypothesis that hydroxyl radicals formed on the anode surface caused direct hydroxylation of the benzene and phenol compounds as shown in the following scheme. In a rationalization of this mechanism, the authors invoked semiconductor-based arguments, viz. 

Ionomer membranes based on perfluorocarbon polymers became available In the late 196O s. These materials have excellent chemical resistance, thermal stability, mechanical strength and strong acid strength, A number of functionalities have been studied. Including carboxylate, sulfonate and sulfonamide, but only the first two are available as commercial materials. Ferfluorlnated lonomers have been evaluated as membranes In a variety of applications, such as water electrolysis, fuel cells, air driers, Donnan dialysis In waste metal recovery, and acid catalysts, but the primary interest in these materials is for the permselective membrane In electrochemical processes such as In the production of chlorine and caustic (58). 

Thermally prepared thin films of RUO2 and IrO2 on titanium have been tested as cathodes for use in water electrolysis cells (Kondintsev and Trasatti, 1994 Burke and Naser, 2005). The mechanism of the HER at oxide electrodes, however, should differ significantly from that studied at metal electrodes (Burke et al., 2007). 

We can also include thermal processes (such as a heat pump ), electric processes (an electrostatic machine, for instance), or chemical processes (such as a water electrolysis apparatus) in this (Fig. 2.4). However, because these kinds of processes are less familiar, we will come back to them later on in more detail. For now, we will limit ourselves to mechanical processes. 

Oickle, A. M., and H. A. Andreas. 2011. Examination of water electrolysis and oxygen rednction as self-discharge mechanisms for carbon-based, aqueous electrolyte electrochemical capacitors. Journal of Physical Chemistry C 115 4283—4288. 

The inertness of the surface raises interesting questions. The aqueous solvent window is pushed out as a result of water electrolysis being an inner-sphere mechanism. As a result, it is often stated in the literature that BDD can detect species which other electrodes cannot due to the extended solvent window. This is certainly true of outer-sphere species, but care must be taken when considering inner-sphere species. Heterogeneous ET will be retarded for many of these species on BDD, as there are no favorable adsorption sites, pushing out their electrochemical detection potential. Therefore, each species should be considered on a case-by-case basis, in combination with the effect of surface termination. For example, both oxidation [89] and reduction, in... 

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