Regenerative electrodes

Lago N, Ceballos D, Rodriguez FJ et al (2005) Long term assessment of axonal regeneration through polyimide regenerative electrodes to interface the peripheral nerve. Biomaterials 26 2021-2031. 

Development of molybdenum electrodes in the 1950s permitted the use of electrically assisted melting in regenerative furnaces (81). In the 1990s, approximately one-half of all regenerative tanks ate electrically boosted. Operating practice has shown that effective use of electricity near the back end of the furnace, where the batch is added, can reduce fossil fuel needs. This lowers surface temperature and reduces batch volatilisation. 

As the DI plant becomes exhausted, silica leakage occurs in the treated MU water and the pH falls abruptly. Furthermore, where sodium ion leakage occurs from the cation bed, it produces a regenerative effect on the anion bed, which may also lead to silica leakage. To differentiate between the two phenomena, sodium ion leakage from the cation bed should be assessed directly using selective sodium-ion electrodes, flame photometric analysis, or other appropriate test methods. 

It has been illustrated that polycrystalline materials can be operated in regenerative electrolytic solar cells yielding substantial fractions of the respectable energy conversion efficiency obtained by using single crystals. Pressure-sintered electrodes of CdSe subsequently doped with Cd vapor have presented solar conversion efficiencies approaching 3/4 of those exhibited by single-crystal CdSe electrodes in alkaline polysulfide PEC [84]. 

Assuming that no other side reactions occur at the semiconductor electrode this is a cell which operates under completely regenerative conditions. 

The photovoltaic effect is initiated by light absorption in the electrode material. This is practically important only with semiconductor electrodes, where the photogenerated, excited electrons or holes may, under certain conditions, react with electrolyte redox systems. The photoredox reaction at the illuminated semiconductor thus drives the complementary (dark) reaction at the counterelectrode, which again may (but need not) regenerate the reactant consumed at the photoelectrode. The regenerative mode of operation is, according to the IUPAC recommendation, denoted as photovoltaic cell and the second one as photoelectrolytic cell . Alternative classification and terms will be discussed below. 

A regenerative photogalvanic cell with oxidative quenching (Fig. 5.58b) is based, for example, on the Fe3+-Ru(bpy)2+ system. In contrast to the iron-thionine cell, the homogeneous photoredox process takes place near the (optically transparent) cathode. The photoexcited Ru(bpy)2+ ion reduces Fe3+ and the formed Ru(bpy)3+ and Fe2+ are converted at the opposite electrodes to the initial state. 

J. Pettersson, B. Ramsey, and D. Harrison. A review of the latest developments in electrodes for unitized regenerative polymer electrolyte fuel cells. Journal of Power Sources 157 (2006) 28-34. 

In the presence of an oxidant, e.g., chlorate or bromate ions, the electrode reaction is transposed into an adsorption coupled regenerative catalytic mechanism. Figure 2.85 depicts the dependence of the azobenzene net peak current with the concentration of the chlorate ions used as an oxidant. Different curves in Fig. 2.85 correspond to different adsorption strength of the redox couple that is controlled by the content of acetonitrile in the aqueous electrolyte. In most of the cases, parabolic curves have been obtained, in agreement with the theoretically predicted effect for the surface catalytic reaction shown in Fig. 2.81. In a medium containing 50% (v/v) acetonitrile (curve 5 in Fig. 2.85) the current dramatically increases, confirming that moderate adsorption provides the best conditions for analytical application. 

The applicability of the foregoing procednre has been tested by modeling simple reaction under semi-infinite diffusion conditions (reaction 1.1) and EC mechanism coupled to adsorption of the redox couple (reaction (2.177)) [2]. The solutions derived by the original and modified step-function method have been compared in order to evaluate the error involved by the proposed modification. As expected, the precision of the modified step-function method depends solely on the value of p, i.e., the number of time subintervals. For instance, for the complex EC mechanism, the error was less than 2% for p>20. This slight modification of the mathematical procedure has opened the gate toward modeling of very complex electrode mechanisms such as those coupled to adsorption equilibria and regenerative catalytic reactions [2] and various mechanisms in thin-film voltammetry [5-7]. 

The stability of silicon electrodes contacting an aqueous electrolyte is a severe problem in regenerative solar systems. As mentioned previously, the standard electrode potential of a silicon element is negative enough to induce an electrochemical reaction mechanism, giving rise to an insulating surface silicon oxide in the absence of complexing reactants. On the... 

Figure 17.32 Photoaction spectra obtained in presence of Cu(I)/Cu(II) electron mediators using regenerative sandwich cells equipped with gold counter electrodes. (5) Stars, (1) open circles, (4) open triangles, (2) solid triangles, (3) open squares, and (6) solid circles. Data compared with the F/I3 couple (black squares). Li+ 0.5 M was added to all copper-based electrolytes.

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