Alkaline fuel cell examples

This edition of the Fuel Cell Handbook is more comprehensive than previous versions in that it includes several changes. First, calculation examples for fuel cells are included for the wide variety of possible applications. This includes transportation and auxiliary power applications for the first time. In addition, the handbook includes a separate section on alkaline fuel cells. The intermediate temperature solid-state fuel cell section is being developed. In this edition, hybrids are also included as a separate section for the first time. Hybrids are some of the most efficient power plants ever conceived and are actually being demonstrated. Finally, an updated list of fuel cell URLs is included in the Appendix and an updated index assists the reader in locating specific information quickly. 

Alkaline fuel cells (AFCs) were the first type of fuel cell to be widely used in space exploration applications-for example, in NASA s Apollo and space shuttle flights. Figure 1.8 shows a schematic of an AFC stmcture. AFCs use H2 and 02 as fuel and oxidant, respectively. The electrolyte is a concentrated KOH solution absorbed into an asbestos matrix. The temperature for AFCs ranges from 100-250°C and the efficiency can be > 60%. OH ions are transported through the electrolyte from cathode to anode. The reactions are as follows ... 

Electrode preparation methods significantly affect fuel cell performance. A variety of methods have been developed. For example, Bevers et al. [17] produced electrodes using a simple and less costly procedure, a modified rolling technique, formerly used in the production of electrodes for alkaline fuel cells and batteries. With these new electrodes, the same power output was obtained as that using commercial ones. 

This is an example of the use of alkaline fuel cells for production of industrially interesting compounds rather than for electricity production (Alcaide et al, 2004). 

In cases where high purity hydrogen is valued, dense metal membranes are an attractive option over polymeric membranes and porous membranes that exhibit much lower selectivities. Two examples where this is true are low-temperature fuel cells (e.g., proton exchange membrane fuel cells [PEMFCs] and alkaline fuel cells [AFCs]) and hydrogen-generating sites where the product hydrogen is to be compressed and stored for future use. 

In early 1960s, some of the metal carbides such as silicone carbide (SiC) and boron carbide (BC) were tested for the first time in fuel cell environment. For example, BC was used as catalyst support in both phosphoric and alkaline fuel cells by GE in the USA [18]. Since then, it took 20 years for other carbides to be evaluated in fuel cells, in particular phosphoric acid fuel cell (PAFC). United Technologies Corporation... 

We have already pointed out that alkaline fuel cells can be operated at a wide range of temperatures and pressures. It is also the case that their range of applications is quite restricted. The result of this is that there is no standard type of electrode for the AFC, and different approaches are taken depending on performance requirements, cost limits, operating temperature, and pressure. Different catalysts can also be used, but this does not necessarily affect the electrode structure. For example, platinum catalyst can be used with any of the main electrode structures described here. 

Since the type of electrolyte material dictates operating principles and characteristics of a fuel cell, a fuel cell is generally named after the type of electrolyte used. For example, an alkaline fuel cell (AFC) uses an alkaline solution such as potassium hydroxide (KOH) in water, an acid fuel cell such as phosphoric acid fuel cell (PAFC) uses phosphoric acid as electrolyte, a solid polymer electrolyte membrane fuel cell (PEMFC) or proton exchange membrane fuel cell uses proton-conducting solid polymer electrolyte membrane, a molten carbonate fuel cell (MCFC) uses molten lithium or potassium carbonate as electrolyte, and a solid oxide ion-conducting fuel cell (SOFC) uses ceramic electrolyte membrane. 

Some improvements in anionic commercial membranes were made possible by irradiation. For example, Hwang and Ohya [133] used accelerated electron radiation to cross-link a commercial membrane based on polysulfone (New-Selemion, Asahi Glass). They proved that these highly cross-linked anion exchange membranes showed a higher coulombic and energy efficiency than Nation membranes when used in an all-vanadium redox flow battery. Application of these membranes in an alkaline fuel cell is also conceivable. 

Several varieties of fuel cells use an electron-conducting porous DM as an interface between the catalyst layer and the current collectors. This DM is not shown in Figure 2.9, since it is not a universal feature of all fuel cells. For example, PEFCs use a carbon-based porous media for this purpose, as shown in Figure 2.14. Either a woven carbon cloth or a carbon fiber structure bonded with a graphitized thermoset resin is typically used for this purpose. Alkaline fuel cells also use a similar porous media to aid electron conduction between the porous electrodes and current collectors. 

Solid alkaline membrane fuel cells (SAMECs) can be a good alternative to PEMFCs. The activation of the oxidation of alcohols and reduction of oxygen occurring in fuel cells is easier in alkaline media than in acid media [Wang et al., 2003 Yang, 2004]. Therefore, less Pt or even non-noble metals can be used owing to the improved electrode kinetics. Eor example, Ag/C catalytic powder can be used as an efficient cathode material [Demarconnay et al., 2004 Lamy et al., 2006]. It has also... 

Solid alkaline membrane fuel cell (SAMFC) working at moderate temperatures (20-80 °C) for which an anion-exchange membrane (AEM) is the electrolyte, electrically conducting by, for example, hydroxyl ions (OH ). 

For example, the electrolyte of alkali fuel cells is a solution of potassium hydroxide (an alkaline, which has a high pH). Solid oxide fuel cells use compoimds of metal oxides as electrolytes. (Fuel cell names are generally... 

Although the Bonnemann method is very interesting by allowing to vary and to control easily the composition and the nanostructure of the catalyst and is adapted to the preparation of real fuel cell electrodes, it displays also some limitations. For example, bismuth-containing colloids could not be prepared with the Bonnemann method, and even in presence of platinum salts. Moreover, the presence of bismuth hinders the reduction of platinum salts [59], However, platinum-bismuth is a good catalyst for ethylene glycol electro-oxidation in alkaline medium [59-62], Moreover, colloid of tin alone could not be obtained, and the reaction was only possible by coreduction in the presence of a platinum salt. Then, other colloidal methods should be developed keeping in mind the necessity of a similar flexibility as that of the Bonnemann method. 

The fundamental principle of SPE reactors is the coupling of the transport of electrical charges, i.e. an electrical current with a transport of ions (cations or anions), through a SPE membrane due to an externally applied (e.g. electrolysis) or internally generated (e.g. fuel cells) electrical potential gradient. For example, in a chlorine/alkaline SPE reactor (Fig. 13.3), the anode and cathode were separated by a cation-SPE membrane (e.g. Nafion 117) forming two compartments, containing the anolyte (e.g. 25 wt% NaCl solution) and the catholyte (e.g. dilute sodium hydroxide), respectively. 

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