Array of anodes and cathodes

Array of anodic and cathodic reaction surfaces for mathematical modeling of potentials and currents in an electrolyte... 

The electrode array consists of a series of anode and cathodes housed in wells. Figure 31.8 illustrates the array of anode and cathodes that were installed within the testing area. It can be seen that the anode well is located in the center, and the cathode wells are located in radial shape at the distance of approximately 1 m apart from the central anode well. Various types of PRB materials (i.e. ZVI, zeolite, slag, and sand) were used. The applied electrical potential difference between the electrodes was approximately 100V (i.e. voltage gradient of 1 V/cm). Two different... 

MWPC) should be used. A full discussion of the design of these is beyond the scope of this chapter, but essentially they consist of orthogonal arrays of anode and cathode wires and the readout is again by delay lines/ They are capable of fairly high count rates (2 MHz) and resolution comparable with the wire spacing ( 1 mm). As yet, a detector of this type has not been used in an electrochemical study. 

Modem cells employ arrays of anodes (Ti02 coated with a noble metal) and cathodes (mild steel) spaced 3 mm apart and carrying current at 2700Am into brine (80-100gl ) at 60-80°C. Under these conditions current efficiency can reach 93% and 1 tonne of NaC103 can be obtained from 565 kg NaCl and 4535 kWh of electricity. The off-gas H2 is also collected. 

To facilitate a demonstration of the advantages of the 3-D architecture, we quantitatively compare metrics related to performance (e.g.. areal energy capacity, active surface area) of a conventional 2-D parallel-plate design with the 3-D interdigitated array cell (Figure 3). We assume a thin-film 2-D battery that comprises a 1-cm -area anode and cathode, each 22.5-/thick electrolyte. The total volume of electrodes and separator is 5 x 10 cm (the cell housing is ignored for simplicity, but is expected to be a comparable... 

Figure 4. Square array of interdigitated anodes and cathodes.

Three-dimensional electrode arrays have been fabricated using two very different micromachining methods. One approach, named carbon MEMS or C-MEMS, is based on the pyrolysis of photoresists. The use of photoresist as the precursor material is a key consideration, since photolithography can be used to pattern these materials into appropriate structures. The second approach involves the micromachining of silicon molds that are then filled with electrode material. Construction of both anode and cathode electrode arrays has been demonstrated using these microfabrication methods. 

A second approach for fabricating electrode arrays has involved micromachining of silicon molds, which are filled with electrode material by colloidal processing methods. In contrast to G-MEMS, this fabrication approach is suitable for both anodes and cathodes, as one merely alters the composition of the powders. The process flow for electrode array fabrication is depicted in Figure 23. 

Electroremediation using electrical current is the final purification method discussed in this chapter. Here, an array of anodes are placed in the soil opposite an array of cathodes. When electric potential is apphed the following processes occur electrolysis of water in the soil, dissolution of polluting ions, migration of ions under the influence of the apphed potential field, and reduction or pH based precipitation at the cathode [68,69]. This technique, also known as electroreclamation or electrochemical soil decontamination, does not require a membrane however, improved electroremediation has been reported when ion-exchange membranes were incorporated into the system [70]. The function of the membrane is to retain OH ions produced at the cathode. Migration of these OH ions is prevented to avoid precipitation of the heavy metal ions in the sod. 

Figure 8.1. Experiment A (Warwick soil), (a) The evolution of the pH gradient between anode and cathode arrays as a function of experimental duration, (b) Cr(VI) concentration measured with 0-, 25-, and 50-cm distance from the anodes. Note that each measiu ement is the mean value of readings taken at the three depth intervals (0-5, 5-10, and 10-15 cm see Table 8.1 for individual depth interval values), (c) Cr(T) concentration measured 0-, 25-, and 50-cm distance from the anodes. Note that each measurement is the mean value of readings taken at the three depth intervals (0-5,5-10, and 10-15cm), see Table 8.1.

Figure 3 Schematic diagram of an array of PGTs with a common grid. Thickness (between anode and cathode) is approximately 0.3 pm. Each anode/cathode pad is, for example, 50 pm on a side.

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