Polymer electrolyte membranes construction

Abstract. The constructive and technological features of silicon electrodes of polymer electrolyte membrane fuel cell (PEMFC) are discussed. Electrodes are made with application of modem technologies of integrated circuits, and technologies of macroporous silicon. Also ways of realization of additional functionalities of electrodes to offered constructive - technological performance are considered. 

Fuel cell researchers have also investigated other reference electrodes, such as a pseudo-reference electrode constructed by inserting a micro-sized carbon filament between two polymer electrolyte membranes [73], The main advantage of pseudoreference electrodes is their easy implementation, although one disadvantage is that their DC potential is unknown. However, this DC potential may not be that critical because EIS measurements mainly rely on the AC perturbation signal from which the impedance is calculated. 

For most of the cell types, a layered bipolar construction is state of the art, shown in Fig. 2, for the example of a polymer electrolyte membrane fuel cell. 

The practical details for the construction and operation of polymer electrolyte membrane (PEM) fuel cells are now reasonably familiar topics which do not require further elaboration in this chapter. It should be evident however, that one of the features of primary importance in the operation of such a cell is the efficient conduction of the protons through the membrane. 

Basically, the construction of phosphoric acid fuel cells differs little from what was said in Section 20.4 about fuel cells with a liquid acidic electrolyte. In the development of phosphoric acid fuel cells and, two decades later, in the development of polymer electrolyte membrane fuel cells many similar steps can be distinguished, such as the change from pure platinum catalysts to catalysts consisting of highly disperse platinum deposited on a carbon support with a simultaneous gradual reduction... 

The plane electrodes are separated by isolating spacers, which may lead to the formation of parallel flow channels. In any case, the electrodes are plane sheets which can be replaced and thus made out of any plain material, e.g. nickel, lead, glassy carbon or graphite. Recent technolo cal developments made at the Institute of Microtechniques, Mainz [6, 7], have led to the construction of versatile microchannel electrochemical reactors. Indeed, the pressure can be elevated to up to 35 bar and the electrodes can be stacked in order to increase the overall electrode area. Moreover, polymer electrolyte membranes can be inserted, separating anodic and cathodic compartments if necessary, and finally heat exchangers may be integrated. 

In this section, we construct several analytical polarization curves of PEMFCs and high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In these types of cell, owing to the excellent kinetics of the hydrogen oxidation reaction, the polarization voltage of the anode is negHgible. The voltage loss in a PEMFC is determined by the oxygen transport, ORR kinetics, and the cell resistivity. 

Metal foam (see, for example. Figure 3.5) has already been discussed in the context of heat exchangers. Micro-reactors, highly relevant to the subject of small fuel cells, have also been introduced in earlier chapters. The construction of metal foam based methanol steam micro-reformers to generate hydrogen for polymer electrolyte membrane fuel cells (PEMFCs) has been reported and in Guangzhou, Chinese researchers have looked at laminated micro-reactors in which copper-based catalysts have been supported by metal foams (see Figure 11.11 Yu et al., 2007). 

In this chapter, the electrode construction of a high temperature (HT) polymer electrolyte membrane (PEM) electrode assembly (MEA) will be explained. The different functionalities of the electrode layers like the gas diffusion layer (GDL), the micro porous layer (MPL), and the... 

A more detailed description of the construction and material composition of polymer electrolyte membrane will be given in Chapter 9. 

For this chapter, PEMs and DMs, with solid polymer electrolyte membranes, are of interest. Because of different types of fuels (mainly hydrogen or methanol, H2 or MeOH, respectively) even in this category the materials and construction vary broadly. For example, wtule for portable applications the PEM... 

In proton exchange membrane (PEM) or solid polymer electrolyte (SPE) electrolysis, the electrolyte is replaced by an ion-exchange resin. These units are compact, provide high current densities, but are more expensive, and because of the corrosive nature of the electrolyte, require special construction materials. 

Exciting research is underway to improve the performance and longevity of batteries, fuel cells, and solar cells. Much of this research is directed at enhancing the chemistry in these systems through the use of polymer electrolytes, nanoparticle catalysts, and various membrane supports. Additionally, considerable effort is being put into the construction of three-dimensional microbatteries, see also Electrochemistry AIaterials Science Solar Cells. 

Ion conducting solid polymer electrolytes, such as those used in battery and fuel cell membranes, have been explored for use in supercapacitors [153,159,200,201]. While these electrolytes are environmentally benign and do not leak, conductivities are typically much lower than liquid or gel electrolyte systems, especially at subambient temperatures (important for military and space applications). Nevertheless, capacitance in supercapacitors prepared with solid polymer electrolytes has been reported to be as good as or better than the same devices constructed using liquid electrolytes. Nafion [200], polyethylene oxide [153], and polyvinyl alcohol [153] are the polymers of choice for this application. 

Two special electrochemical cells are used for XRD and XAS measurements. In one case a polymer membrane is pressed on the specimen surface after its electrochemical treatment to reduce the water layer on top, but still permitting potential control during the measurements. In an other case the beam penetrates an electrolyte layer in front of the electrode, which corresponds to the specimen s dimensions, but which is thick enough to reduce the danger of ohmic drops and crevices. Beam lines often provide the exact orientation of the samples with the cell by a goniometer. For XAS measurements a special low cost refraction stage has been constructed which permits the orientation of the sample within 0.01 degrees and which has been used for the study of several systems [108]. 

We note here that the widely employed Clark oxygen electrode differs fundamentally from these devices (18, 63). The Clark device is similar in construction to the apparatus of Figure 2.4.5, in that a polymer membrane traps an electrolyte against a sensing surface. However, the sensor is a platinum electrode, and the analytical signal is the steady-state current flow due to the faradaic reduction of molecular oxygen. 

---