Electrode DC potentials

FIGURE 2.46. Variation of the photo-injected charge with the dc electrode potential (a) and extraction of the apparent number of electron (b, c). A is the electrode dc potential and E,ilr is the threshold potential. Adapted from Figure 2 of references 51, with permission from Elsevier. 

Fig. 20.8. Differential pulse voltammograms for 2,3,4-butanethiolate (C4) and 1,5,6,7-hexanethiolate (C6) Au MPCs as a function of uniform core size, in 0.05 M Hex4NCl04/ toluene/acetonitrile (2/1 v v), at 9.5 x 10 cm Pt electrode DC potential scan 10 mV s pulse amplitude 50 mV. Concentrations...

The most cited reference electrode is the platinum-hydrogen electrode, and electrode DC potentials are often given relative to such an electrode. It is an important electrode for absolute calibration, even if it is impractical in many applications. The platinum electrode metal is submerged in a protonic electrolyte solution, and the surface is saturated with continuously supplied hydrogen gas. The reaction at the platinum surface is a hydrogen redox reaction H2 2H (aq) + 2e, of course with no direct chemical participation of the noble metal. Remember that the standard electrode potential is under the condition pH = 0 and hydrogen ion activity 1 mol/L at the reference electrode. Thus the values found in tables must be recalculated for other concentrations. Because of the reaction it is a hydrogen electrode, but it is also a platinum electrode because platinum is the electron source or sink, and perhaps a catalyst for the reaction. 

Figure 3.1.1. Audio frequency bridge modified to include working electrode dc potential control.

In electrochemical applications, these combined limitations may be severe. Figure 3.1.1 shows one of a variety of possible methods by which an imposed working-electrode dc potential can be adjusted to the desired value without influencing the detector circuit. The method shown can be used at frequencies less than the normal operating frequency limit of ac coupled amplifiers. 

FIG. 4. Schematic representation (a) of a parallel-plate, capacitively coupled RF-discharge reactor, with unequal-size electrodes. The potential distribution (b) shows the positive plasma potential Vp and the negative dc self-bias voltage... 

Figure 4. Plot of poly-I conductivity as a function of potential. A series of potential step of 20mV were employed on a sandwich electrode. Each potential was held until Faradaic current ceased, where upon a DC conductivity measurement, AE = 60MV, was taken, before proceding with the next potential. The results are for 0.05 M II electrolyte in acetonitrile vs. Ag+/Ag.

Electrophoresis. Electrophoresis, the movement of charged particles in response to an electric potential, has become very important in biochemistry and colloid chemistry. In the present study an apparatus similar to that described by Burton( M2-M5) was used. A U-tube with an inlet at the bottom and removable electrodes at the two upper ends was half filled with acetone. The a Au-acetone colloidal solution was carefully introduced from the bottom so that a sharp boundary was maintained between the clear acetone and the dark purple colloid solution. Next, platinum electrodes were placed in the top ends of the U-tube, and a DC potential applied. The movement of the boundary toward the positive pole was measured with time. Several Au-acetone colloids were studied, and electrophoretic velocities determined as 0.76-1.40 cm/h averaging 1.08 cm/h. 

DC potential was applied so that BG bacterial spores were either collected onto or repelled from the MCLW sensor surface. Figure 15.26 shows the detected number of bacterial spores on the sensor surface vs. time. At time A, a negative potential was applied to the ITO electrodes and a positive potential to the metal layer of the MCLW sensor, resulting in an increase in the number of BG bacterial spores driven to the sensor surface. At time B, the potential is reversed and a decrease in the number of BG bacterial spores on the sensor surface is observed, hence the bacterial... 

The electrodynamic balance or quadrupole began with the electric mass filter of Paul and Raether (1955), who demonstrated that a charged mass can be stably levitated by means of a quadrupole arrangement of electrodes, one of the simplest configurations being that shown in Fig. 3. An ac potential is applied to the rods in the horizontal plane, and a dc potential is applied to the upper and lower rods as in the Millikan condenser. The ac field has horizontal and vertical components that are 180° out of phase, thereby... 

Suppose that the particle is negatively charged, that + is the dc potential applied to the upper electrode, and that — Kic is applied to the lower endcap. In the absence of a charged particle, the ac and dc potentials satisfy Laplace s equation. 

The application of dual polarity DC potential, both positive and negative to the high gradient area between the electrodes successfully coalesces the majority of even the one and two micron droplets resulting in a much lower water content in the clean oil. 

The electrochemical equipment and procedures for Investigation of BLM s has been described previously In detail. (9-101 The apparatus was based on application of +25 mV DC potential across the membrane between two Ag/AgC 1 reference electrodes while monitoring Ion current with a digital electrometer. 

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