Working electrodes, shielded

Figure 19. Schematic of a shielded working electrode. The arrows illustrate the diffusion pattern below the electrode.

Figure 17.1 Schematic cross-section of the three electrodes In the flame, showing the position of the working electrode in a hole in the platinum electrode shield. Reproduced with permission from Ref [17], Copyright 2012 WILEY-VCH Verlag CmbH Co. KCaA, Weinheim.

FIG. 4—Soil sensor for electrochemical measurements, made of two reference electrodes, two working electrodes, and three counter-electrodes, all connected to their own shielded twisted pair cable. At the terminal box, they can be accessed in various combinations depending on the tests required. It also has two platinized titanium electrodes equally spaced with the reference electrodes to allow for the measurement of the average soil resistivity by the Wenner four-electrode metlrad. The two working electrodes can be designed to represent the different conditions of the structure being monitored. 

It was concluded from this and related works that suppression of the photodissolution of n-CdX anodes in aqueous systems by ions results primarily from specific adsorption of X at the electrode surface and concomitant shielding of the lattice ions from the solvent molecules, rather than from rapid annihilation of photogenerated holes. The prominent role of adsorbed species could be illustrated, by invoking thermodynamics, in the dramatic shift in CdX dissolution potentials for electrolytes containing sulfide ions. The standard potentials of the relevant reactions for CdS and CdSe, as well as of the sulfide oxidation, are compared as follows (vs. SCE) [68] ... 

In order for the ions to come closer to the electrode, work has to be done to get rid of all or part of their solvation shield. This woik is nothing other than the interaction energy of mainly primary solvent molecules with the ion. What are the parameters that determine the number of water molecules attached to the ion and how strong the attachment is ... 

A few comments are in order on the probable validity of conclusions based on this equivalent circuit to real cells. Quite simply stated, real cells that are properly designed will have the same properties as dummy cells of the same values of Rs, Ru, and Cdl. Important design features of a cell are (1) equal resistance between all points on the surface of the working electrode and the auxiliary electrode (2) low-impedance reference electrode and (3) low stray capacitance between electrodes, between leads, and to shields. Spherical symmetry is a good, but somewhat inconvenient, method of meeting the first requirement a parallel arrangement also works with planar electrodes. At the very... 

Solid electrodes in unstirred solution. The most useful solid electrodes are platinum, gold, vitreous carbon, and carbon paste. The preferred configuration for theoretical work is a flat planar surface sealed in glass with epoxy or snugly fitted into a Teflon shroud. The electrodes ordinarily are unshielded, although shielded designs have been described.94... 

In addition to the rather indirect a.c. techniques discussed above, a more direct technique for the electrical characterisation of the depletion region is available even though this is, primarily a d.c. technique, it is included here since the information is frequently highly complementary. In this technique, ohmic contacts are made to the working surface of the semiconductor electrode and then shielded from the electrolyte as shown in Fig. 36 they are then used as probes to measure the surface conductivity. Ideally,... 

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