Polarization alternating current

Two methods are employed to obtain from these photocells output currents with large alternating current components. In Model 1 a 60-cps. alternating current polarizing voltage is applied to the cells, while Models 2 and 3 use a rotating-disk chopper... 

Fig. 5.17 a Optical transmittance spectra of the fuUy oxidized and reduced electrodes of the transparent supercapacitor device shown in Fig. 5.4b. b Transmittance variation during chronopotentiometry with alternating current polarity ( 2 mA cm for the initial 20 s and —2 mA cm for the remaining time). The red line is the potentiometric response... 

Breyer, B. and Bauer, H. H., 1963, Alternating Current Polar-graphy and Tensairwnetry, Wiley-Interscience, New York, N.Y. 

H. Gerischer [1951] Alternating-current polarization of electrodes with a potential determining step for equilibrium potential, Z physik chem., 198, 268—313. 

Haitung R, Mobius HH (1967) About alternating current polarization in platinum electrodes on oxygen ion conducting solid electrolyte (in German). Z Chem (Leipzig) 7 325... 

Figure 2.3. Alternating-current polarization impedance electrical equivalent of Figure 2.2.

Various methods have been proposed for reducing or eliminating the effects of alternating current polarization impedances (Ferris, 1959, 1963 Schwan and Ferris, 1968 Schwan, 1951, 1963). Since the impedance is a function of current density at the electrode surface, an obvious solution is the elimination of current through the probes. Unfortunately, it is impossible to do this in a two-electrode system if one is attempting to measure impedance however, it can be accomplished with a four-electrode configuration (Ferris, 1959, 1963). 

Impedance analysis overcomes polarization problems by employing alternating currents in the frequency range from 10-to 10+6Hz [39], Only in the case of sufficiently high disorder, the ionic conductiv-... 

For measurements, an ac component = / sin at with the amphmde / and angular frequency co (co = 2jt/, where/is the ac frequency) is passed through the electrode (alone or in addition to a direct current). Alternating potential (polarization) changes... 

FIGURE 7.2 Schematic of a DNA sensor based on a capacitive EIS structure. For operation, a DC (direct current) polarization voltage (VG) is applied via the reference electrode (RE) to set the working point of the EIS sensor, and a small AC (alternating current) voltage (E ) is applied to the system in order to measure the capacitance of the sensor. ssDNA - single-stranded DNA, cDNA - complementary DNA, dsDNA - double-stranded DNA. 

Conductance of a solution is a measure of its ionic composition. When potentials are applied to a pair of electrodes, electrical charge can be carried through solutions by the ions and redox processes at the electrode surfaces. Direct currents will result in concentration polarization at the electrodes and may result in a significant change in the composition of the solution if allowed to exist for a significant amount of time. Conductance measurements are therefore made using alternating currents to avoid the polarization effects and reduce the effect of redox processes if they are reversible. 

In the diode the cathode is usually a W filament which can be flashed and maintained as a reference electrode at a temperature above which adsorption occurs. The anode may be of similar construction or take the form of a metal film evaporated from an adjacent filament. Experimentally, current polarization curves are obtained, first for the clean anode surface A and then for the covered anode surface A. Alternatively, resistance-voltage characteristics are measured (SO). The potential difference comprises the applied polarization and the C.P.D. between the emitter and collector. For a given anode current j,... 

Alternating-current and frequency effects. With an AC rather than a DC voltage applied to the electrodes, the processes above reverse themselves with the period of the alternating voltage. But each process proceeds at a different rate (with a characteristic relaxation time) so that their relative contributions to energy dissipation vary with frequency. As the frequency is increased concentration-polarization can be reduced or eliminated, particularly if the electrode reaction is reversible (fast electron transfer in both directions). 

If the polarity of the current is not allowed to change too rapidly, it is possible, since oxidation and reduction occur successively at each pole, to accomplish electrolyses with alternating currents. Experiments with this end in view have been made b Drechsel.1 Dehydration is a case of simultaneous reduction and oxidation. The supposition that in living organisms carbamide is produced from ammonium carbamate by the splitting off of water prompted Drechsel to make experiments in this direction. When an aqueous solution of ammonium carbamate is electrolyzed with a current from a battery of 4-6 Grove cells, and platinum electrodes used, carbamide is obtained independently of the electrode material when alternating currents are employed. The reactions are supposed to be either... 

If the direction of current flow in the coil is reversed, so is the direction of the magnetic field. And if the current is oscillating (i.e., alternating current), the resulting linearly polarized magnetic field will oscillate (change directions) at the same frequency (Figure 3.2). 

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