Parallel electrode collectors

With point-plate electrospinning equipment oriented vertically, the collector plate is horizontal and the grounded parallel electrodes of interest are placed on the collector itself. However, it is also possible to collect aligned nanofibers on a parallel pair of stainless steel wires placed vertically within the gap (Chuangchote and Supaphol 2006). 

As shown in Figure 9.1a, after two separate streams including fuel and oxidant are introduced into the channel, they come into contact to create a parallel colaminar flow in the channel with a liquid-liquid interface. This interface takes action as a separator of fuel and oxidant streams. Current collectors and electrodes with appropriate catalyst layer on the surface are fabricated on channel walls where the electrochemical reactions take place. To obtain charge transport between two electrodes, both fuel and oxidant solutions should contain ionic conductivity, which is obtained by adding supportive electrolyte to both streams. The supporting electrolyte contains hydroxide or hydronium ions such as diluted solutions of potassium hydroxide or sulfruic acid. 

Cell geometry, such as tab/terminal positioning and battery configuration, strongly influence primary current distribution. The monopolar constmction is most common. Several electrodes of the same polarity may be connected in parallel to increase capacity. The current production concentrates near the tab connections unless special care is exercised in designing the current collector. Bipolar constmction, wherein the terminal or collector of one cell serves as the anode and cathode of the next cell in pile formation, leads to gready improved uniformity of current distribution. Several representations are available to calculate the current distribution across the geometric electrode surface (46—50). 

An optimum relationship between the DL and the flow field channels is a key factor in the overall improvement of fhe fuel cell s performance at both high and low current densities. Currently, flow field designs are typically serpentine, interdigitated, or parallel [207,264]. The FF plate performs several functions If is a current collector, provides mechanical support for the electrodes, provides access channels for the reactants to their respective electrode surfaces and for the removal of producf water, and it prevents mixing of oxidant, fuel, and coolant fluids. 

Rs (Figure 1.22a). The double layer capacitance is represented by the capacitance C, and Rs is the series resistance of the EDLC, also named the equivalent series resistance (ESR). This series resistance shows the nonideal behavior of the system. This resistance is the sum of various ohmic contributions that can be found in the system, such as the electrolyte resistance (ionic contribution), the contact resistance (between the carbon particles, at the current collector/carbon film interface), and the intrinsic resistance of the components (current collectors and carbon). Since the resistivity of the current collectors is low when A1 foils or grids are used, it is generally admitted that the main important contribution to the ESR is the electrolyte resistance (in the bulk and in the porosity of the electrode) and to a smaller extent the current collector/active film contact impedance [25,26], The Nyquist plot related to this simple RC circuit presented in Figure 1.22b shows a vertical line parallel to the imaginary axis. 

Some commonly used batteries are shown in Table 15.5, and two are drawn schematically in Fig. 15.10. From these it can be seen that important components are the container, the anode/cathode compartment separators, current collectors to transport current from the electrode material (usually a porous, particulate paste), the electrode material itself, and the electrolyte. It should be noted that the electrode reactions can be significantly more complex than those indicated in Table 15.5, and there will probably be parallel reactions. By stacking the batteries in series, any multiple of the cell potential can be obtained. 

Figure 26 A comparison of the chemical diffusion coefficient of Li into graphite (calculated from PITT), the intensity of the major XRD peaks (e.g., 002, 004) during intercalation (vs. E), and a completed slow scan rate cycling voltammogram of a thin (10 pm) composite graphite electrode (KS-6 from Lonza) in EC-DMC/LiAsF6 solution. Note that as the electrode is thinner and the particles are more oriented (with their basal planes parallel to the current collector), the scan rate is slower and the CV peaks are sharper and better resolved. The various phases (intercalation stages) are indicated [87]. (With copyrights from Elsevier Science Ltd., 1998.)...

If a stationary multiple microband electrode is used, then the collector current is rather sensitive to adventitious vibrations. If the electrode assembly is vibrated parallel to the inter-electrode gap, then although the collection efficiency is reduced the collector current is now insensitive to such random vibrations (of a non-modulatory nature). Repeatable, reliable titration using electrogenerated reagents has been demonstrated in this way [33]. 

Generation-collection experiments can be carried out in UME arrays aside from the double band. An obvious extension is to use a triple band so that the middle electrode serves as a generator and the two flanking electrodes work in parallel as collectors. A more elaborate approach involves an interdigitated array, which is an extensive series of parallel bands, the alternate members of which are connected in parallel. One of the sets serves as the generator and the other as the collector. 

Fig. 6.16. Parallel-plate electrostatic precipitator. 1 — chamber, 2 — collector plate, 3 — discharge electrode, 4 — section switch box, 5 — dust collector...

The electrolyte for the battery is a LiCl/KCl mixture with a temperature of 430—490°C. Batteries are constructed on the parallel-plate principle with alternate anodes and cathodes, and in each inter-electrode space there is a boron nitride cloth or felt separator. Commonly there is one extra negative plate because some lithium is lost during cycling. The plates, typically 5 mm thick, were initially prepared by cold compaction techniques, the active material being compressed into a fine metal lioneycomb material which also acts as the current collector. The negative electrode was just the li/Al alloy in an Fe lattice while the positive electrode was a mixture... 

Various collectors and methods have been adopted to obtain aligned fibers a dynamic collector such as a rotating drum (Xu et al. 2004) a pair of parallel conducting electrodes to create an electric field so that the electrospun fibers are preferentially aligned across the gap between the electrodes (Li and Xia 2004) and a wire screen (Wang et al. 2005). Tubular electrospun fibers can be fabricated on a rotating tube and the deposited fiber layer subsequently extracted from the tube. 

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