Electrode cells recessed

Figure 10.6. Recessed-electrode cell for electrolyte impedance measurements.

Large electrodes directly into the measuring cell will disturb ionic current flow pattern, and polarization will occur on the metal surface. The electrode metal should not be in direct contact with the electrolyte, but should be recessed (Figure 7.27). The electrolyte is contained in a tube with isolating walls, and if a part of this wall is substituted by electrode metal, the current will prefer the high-conductivity path of the metal. The current lines will deviate from the path parallel to the tube walls, and in one part of the area the current will enter, in the other part it will leave. Thus the electrodes are polarized, but not by a current in the external leads. The polarization may not be uniform over the electrode surface area, and the polarization will occur according to local current direction and polarization admittance. When the metal is recessed, the current will also deviate into the electrolyte of the bridge path, but the current will not pass any metal surface, and no polarization will occur. 

It is clearly desirable that the deposit has an even thickness over the whole of the surface to be electroplated. This requires the potential to be the same at all points over the surface of the cathode and this is impossible to attain when the object to be plated has a complex shape. To some extent the evenness of the deposit can be improved by introducing auxiliary anodes (usually platinized titanium electrodes where the reaction is oxygen evolution) at various positions in the electrolyte, the objective being to increase the cathode current density at points where it would otherwise be very low, i.e. at points on the cathode furthest from the normal anodes (e.g. in holes or recesses in the object being plated). The problem with this approach, however, is that a totally new cell geometry is necessary for each new plating job and in any case its success is limited. Hence, in general, we are dependent... 

The pulse sequence with three different potentials that is usually applied for the detection of carbohydrates is shown in Figure 8.12a. However, the cleaning potential E2 being applied for 200 ms leads to an electrode recession that enlarges the cell volume as shown in Figure 8.13. This, in turn, lowers the linear speed of the liquid through the detector cell that consequently results in a decrease of the response factor for a given analyte concentration. 

Figure 8.13 Schematic representation of the electrode block of an amperometric cell, (a) New cell with a leveled gold working electrode and (b) used cell with a larger cell volume due to recession of the working electrode.

Figure 10.6 illustrates a cell for use in four-electrode measurements of electrolyte impedance. The working electrodes are platinum. The sensing electrodes are also platinum, but are platinized. They are recessed from the main cell by salt bridges. It is possible to obtain four sample sizes by changing the relative positions of the two sensing electrodes. A detailed description of this cell appears in Schwan and Ferris (1968). 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

Roy, S., Gupte, Y. Green, T.A. Flow cell design for metal deposition at recessed circular electrodes and wafers. Chem. Eng. Sci. 56 17 (2001), pp. 5025-5035. 

Goldberg IB, Bard AJ (1972) Resistive effects in thin electrochemical cells digital simulations of current and potential steps in thin layer electrochemical cells. Electroanal Chem 38 313 Ferrigno R, Brevet PF, Girault HH (1997) Finite element simulation of the chrono-amperometric response of recessed and protruding microdisc electrodes. Electrochimica Acta 42(12) 1895-1903... 

Bovine adrenal chromaffin cells were used to demonstrate a new multimicrowell array, shown in Fig. 17, with tiny indium-tin oxide semitransparent disk working electrodes at the bottoms, and with the wells suitably sized to house single cells and monitor quantal exocytosis of dopamine [91]. Disk electrodes 20 pm in diameter were recessed from the surface of an insulating film (SU-8) laminated to a microscope slide glass substrate. Polylysine modification of the ITO surfaces allowed the size-selective capture of individual cells facilitated by gravity. Poly(ethylene glycol) was used to coat the outer surfaces with a hydrophilic. 

The developed heart-on-chip (Pakazad et al., 2014) was based on a stretchable microelectrode array (Pakazad et al., 2012) (Fig. 11.27) made by a PDMS membrane with TrN electrodes (12 pm in diameter) microfabrieated on top of it. To promote the cell alignment and the adhesion to the PDMS membrane, microrecesses are patterned into the membrane, forcing the cells to lodge and to align in accordance with the recesses. 

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