Electrode current-voltage curves

The proposed model for the so-called sodium-potassium pump should be regarded as a first tentative attempt to stimulate the well-informed specialists in that field to investigate the details, i.e., the exact form of the sodium and potassium current-voltage curves at the inner and outer membrane surfaces to demonstrate the excitability (e.g. N, S or Z shaped) connected with changes in the conductance and ion fluxes with this model. To date, the latter is explained by the theory of Hodgkin and Huxley U1) which does not take into account the possibility of solid-state conduction and the fact that a fraction of Na+ in nerves is complexed as indicated by NMR-studies 124). As shown by Iljuschenko and Mirkin 106), the stationary-state approach also considers electron transfer reactions at semiconductors like those of ionselective membranes. It is hoped that this article may facilitate the translation of concepts from the domain of electrodes in corrosion research to membrane research. 

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

Rectification effects are due to the asymmetry of a current-voltage curve of an electrode system. The asymmetry of these curves may arise from the intrinsic asymmetry of the charge transfer reaction or from the extraneous asymmetry produced by inequalities in mass... 

Several types of experimental magnesium-air cells were tested. These cells varied in their size (the working area of the air electrodes used) [10]. The current-voltage curves of an experimental Mg-air cell with two air electrodes (Sair = 80 cm2) with pyrolyzed CoTMPP catalyst and sandwich-type Mg anode (MA8M06) operating in NaCl-electrolytes with different concentrations are presented by Figure 2. 

This scanned mercury electrode technique is not a conventional measurement approach. We have compared Hg as a top electrode to other thin-film counterelectrodes, particularly platinum and aluminum, using known dielectric materials including a-SiOx, a-TaO and a-Al203 thin films. Current-voltage curves measured using mercury top electrodes are comparable to those measured using Pt or A1 top electrodes. 

Wilson RH (1977) A model for the current-voltage curve of photoexcited semiconductor electrodes. J Appl Phys 48 4292-4297... 

In parallel, Kasumov et al. [60] reported ohmic behavior of the resistance of A-DNA molecules deposited on a mica surface and stretched between rhenium-carbon electrodes (see Fig. 6). This behavior was measured at temperatures ranging from room temperature down to 1 K. Below 1 K a particularly unexpected result was observed proximity-induced superconductivity. The resistance was measured directly with a lock-in technique and no current-voltage curves were presented. This surprising proximity-induced supercon-... 

Another measurement that follows the line of the Porath et al. [14] experiment was performed by Yoo et al. [75]. In this experiment, long poly(dG)-poly(dC) and poly(dA)-poly(dT) molecules were electrostatically trapped between two planar metal electrodes that were 20 nm apart (see Fig. 11) on a Si02 surface, such that they formed a bundle that was -10 nm wide. A planar gate electrode added another dimension to this measurement. The current-voltage curves showed a clear current flow through the bundle and both temperature and gate dependencies. The resistivity for the poly(dG)-poly(dC) was calculated to be 0.025 flcm. 

Measurements on a different type of DNA-based material were reported by Rinaldi et al. [68] (see Fig. 13). In this experiment they deposited a few layers of deoxyguanosine ribbons in the gap between two planar metal electrodes, -100 nm apart. The current-voltage curves showed a gap followed by rise of the current beyond a threshold of a few volts. The curves depended strongly on the concentration of the deoxyguanosine in the solution. 

In Fig. 16 we show a current-voltage curve for >-type GaP in the presence of a dye in the dark and at illumination with light being only absorbed by the dye. We see again a saturation current, now however, in cathodic direction. The photocurrent spectrum is represented in Fig. 17. It corresponds fully with the absorption spectrum of the adsorbed dye. One sees a saturation current at a polarisation of more than 0.35 eV negative of the flat band potential. Some special features at GaP-electrodes seem to be caused by the existence of surface states with energies in the range of the band gap. It has been assumed that these surface states can... 

Fig. 12. Current/voltage curves for the cathodic reduction of oxygen at a suspension electrode in 4.5 N H2SO4 38) ------- CoTAA...

The same holds for Silflon cathodes, which with silver loadings of 0.1 g/cm2 of electrode area exhibit an active catalyst surface of no more than 0.24 m2/m2. These Silflon electrodes are produced by chemically depositing silver on PTFE particles of 0.5 to 1 fim size and working these tiny silver-covered particles into electrodes by calendaring or pressing. Figure 22 compares the current voltage curve of typical gas diffusion cathodes in alkaline electrolyte. 

It is therefore intriguing to understand what is the particular role of the platinum/electrolyte interface in the Kolbe synthesis favoring that reaction path—Eqs. (39a)-(39c)—which is thermodynamically disfavored and unlikely to occur. A closely related reaction whose kinetics are easier to investigate with conventional electrode kinetic methods is the anodically initiated addition of N3 radicals to olefins, discovered by Schafer and Alazrak (275). The consecutive reactions, which follow the initial generation of the reactive intermediate, an Na radical, are somewhat slower than that of the Kolbe radicals, so that their rate influences the shape and potential of the current voltage curves which can be evaluated in terms of reaction rates and rate laws. 

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