Fuel cells design principles

Contrary to traditional fuel cells, biocatalytic fuel cells are in principle very simple in design [1], Fuel cells are usually made of two half-cell electrodes, the anode and cathode, separated by an electrolyte and a membrane that should avoid mixing of the fuel and oxidant at both electrodes, while allowing the diffusion of ions to/from the electrodes. The electrodes and membrane assembly needs to be sealed and mounted in a case from which plumbing allows the fuel and oxidant delivery to the anode and cathode, respectively, and exhaustion of the reaction products. In contrast, the simplicity of the biocatalytic fuel cell design rests on the specificity of the catalyst brought upon by the use of enzymes. 

The domain is as shown in Figure 1. 3-D models have the potential to accurately represent the true operation of a fuel cell. In principle, these models are the ones that should be used to obtain the best designs and optimization of various properties and operating conditions. However, while the current published models are complex on an overall global scale, they are usually not very detailed on the 1-D sandwich scale. For example, almost all of these models have... 

While there are many different fuel cell designs, the basic principle is similar (Figure 1.1). The proton exchange membrane (PEM) fuel cell currently is preferred for use in vehicles because of its low operating... 

NETL s CFD research has demonstrated that CFD-based codes can provide detailed temperature and chemical species information needed to develop improved fuel cell designs. The output of the FLUENT-based fuel cell model has been ported to finite element-based stress analysis software to model thermal stresses in the porous and solid regions of the cell. In principle, this approach can be used for other types of fuel cells as well, as demonstrated by Arthur D. Little and NETL (16,18)... 

Design Principles An individual fuel cell will generate an electrical potential of about 1 V or less, as discussed above, and a current that is proportional to the external load demand. For practical apph-cations, the voltage of an individual fuel cell is obviously too small, and cells are therefore stacked up as shown in Fig. 27-61. Anode/ electrolyte/cathode assemblies are electrically connected in series by inserting a bipolar plate between the cathode of one cell and the anode of the next. The bipolar plate must be impervious to the fuel... 

The implications of this discovery for electrochemical promotion are quite significant since it shows that, at least in principle, the design of an electroche-mically promoted reactor can become much simpler than that of a fuel cell. 

The situation changed drastically in the mid-1990s in view of the considerable advances made in the development of membrane hydrogen-oxygen (air) fuel cells, which could be put to good use for other types of fuel cells. At present, most work in methanol fuel cells utilizes the design and technical principles known from the membrane fuel cells. Both fuel-cell types use Pt-Ru catalyst at the anode and pure platinum catalyst at the cathode. The membranes are of the same type. 

In Fig. 3.52, the efficiency of a reversible PEM fuel cell is depicted. Any fuel cell can in principle be operated in either direction, to produce electricity from hydrogen or to produce hydrogen from electricity. However, in most cases, the cell design is optimised for one intended use and not very efficient... 

An avalanche-like rush of new research activities has evolved around new routes in membrane synthesis and strategies in theoretical and computational modeling that could facilitate a dehberate design of highly functionalized fuel cell membranes. Comprehensive reviews on membrane synthesis highlight principles and fabrication of new membranes particularly those apphcable for DMFC [214], those that are feasible for operation at elevated temperatures (up to 200° C under ambient pressures) [215], and those that are based on various modifications of Nafion-type membranes [216]. 

Practical fuel cell systems are very complex to design and build—especially small, rugged ones for cars, trucks, and buses, which must stand up to bumps and to temperature variations. (This is one reason why it took so long to put the first prototypes on the road.) But the basic principle of how a fuel cell works is fairly straightforward. 

Principles of electrochemical engineering, fuel cell reactors, and electrocatalytic reactor design... 

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