Electrode designs, porous

Porous flow-through electrode design (coulometric or amperometric). 

The porous hydrophobic film of previous electrode designs has now been substituted with a new layer based on a mixture of particles of hydrophobic carbon and PTFE binder. This mixture is very similar in composition to the catalytic layer. This particular modification provides several advantages ... 

Liquid membrane electrodes utilize porous polymer materials, such as PVC or other plastics. An organic liquid ion exchanger immiscible with water contacts and saturates the membrane from a reservoir around the outside of the tube containing the water solution of the analyte and the silver-silver chloride wire. See Figure 14.10. Important electrodes with this design are the calcium and nitrate ion-selective electrodes. 

Pocket plate design is not suitable for the positive electrode because of the infiltration of soluble zincate and the consequent decrease in positive electrode capacity. Porous matrix positives do not suffer so badly from... 

There are several things that need to be pointed out on this design. First, the upper electrode is porous, either because it is very thin (10-20 nm) or because it is deposited under such conditions that it cracks. In any case, the polymer beneath it comes into contact with the gas or vapor. Obviously, it is difficult to make robust electrical connections to the top electrode. Fortunately, it is not necessary because it forms an electrically floating plate, which is common to the two capacitors one between the Cr, Ni, Au plate (Ci) and the other between the top and the Ta plate (C2). The corresponding leakage resistances are R and R2. The response of this sensor to water vapor is shown in Fig. 8.14. 

The bipolar plate design is illustrated in Fig. 47. It consists of a cross-flow arrangement where the gas-tight separation is achieved by dense ceramic or metallic plates with grooves for air and fuel supply to the appropriate electrodes. A porous cathode, a dense and thin electrolyte and a porous anode form a composite flat layer placed at the top of the interconnected grooves. The deposition of the porous electrodes can be achieved by mass production methods. Moreover, the bipolar plate configuration technology makes it possible to check for defaults, independently and prior to assembly of the interconnection plate and the anode-electrolyte-cathode structure. 

It is important to understand that increasing the roughness factor of a planar electrode increases the rate of charge transfer but has little effect on the rate of mass transport. On the other hand, the use of correctly designed porous electrodes can increase the rates of both processes. Thus tlie use of porous electrodes is essential whenever gaseous reactants (e.g., or O ) are employed, even if an ideal electrocatalyst could be found. 

The highest order in macroscopic electrode design is represented by insertion electrodes, according to Fig. 3(b). Redox reactions occur in the solid phase. The ions as redox partners form solid solutions. This does not exclude the possibility that in porous insertion electrodes both mechanisms are operative (cf. [28]). 

General aspects of charge transport in active materials have already been discussed in Section 1.5 (cf. Fig. 10). According to this, porous structures are extremely important in this field, as shown in Section 1.3 (cf. Figs. 4 and 5). In the following, four groups of active materials are briefly discussed in connection with their transfer to practical electrode designs ... 

Different electrode designs were developed. Porous conductive electrodes having at least two zones can be used either as reversed dual porosity electrode or as electrode assembly with conductive, noncompressible porous carbon matrices [92]. 

Fig. 16.1 Schematic illustration of an airtight hexagonal cell and electrodes designed for electrochemical measurements in ILs. (a) Vacuum fittings, (b) PEA body, (c) Fixture (stainless steel), (d) O-ring, (e) Cover glass, (f) Cu rod, (g) Heat shrink tube, (h) Pt disc, (i) Glass tube, (j) Ag wire, (k) Inner IL containing Ag(I), (1) Vycol (porous) glass, and (m) Pt wire...

Many of the problems of fluidized-bed cells appear to have been overcome by the development of three-dimensional contiguous-bed reactors (36,37) which mainly evolved from the porous electrode designs usi3 "Tn battery or fuel cell applications. These electrode designs are characterised by very high specific surface areas and space time yields. At the same time the ability to control... 

As can be seen in Fig. 15.1a, the first gas-diffusion electrodes were designed based on back-side metallized porous membranes and the presence of liquid electrolyte. However, there is other approach to diffusion electrode design (Knake et al. 2005). It was found that the liquid electrolyte in a GDE could be replaced by a solid, ionically conductive polymer. Thus, whole electrode-electrolyte assemblies consisting of porous electrodes and ion-exchange polymers were manufactured. This arrangement is depicted in Fig. 15.1b. When using SPE-membrane-based sensors, the electrodes face the sample gas and, therefore, essentially no diffusion barrier is present. Furthermore, they have usually been used in systems with a forced gas flow. 

ESs of both double-layer and battery-Uke materials such as porous carbon and RUO2, respectively, form multilayer electrode stractuies. The two electrodes either combine the two materials or use them separately. Device configuration consists of basic electrode, separator with electrolyte, and electrode design. 

---