Fuel cells working principle

Oxygen ions are electrons carriers, thus the fuel cell working principles can be described by an adequate electric circuit. An equivalent electric circuit of the fuel cell is illustrated in Fig. 5.8. Because of mixed conductivity of the electrolyte (ionic and electronic), two types of resistance are present in fuel cells ionic resistance R and electrical resistance R2. Resistance R3 is the external load... 

DMFCs and direct ethanol fuel cells (DEFCs) are based on the proton exchange membrane fuel cell (PEM FC), where hydrogen is replaced by the alcohol, so that both the principles of the PEMFC and the direct alcohol fuel cell (DAFC), in which the alcohol reacts directly at the fuel cell anode without any reforming process, will be discussed in this chapter. Then, because of the low operating temperatures of these fuel cells working in an acidic environment (due to the protonic membrane), the activation of the alcohol oxidation by convenient catalysts (usually containing platinum) is still a severe problem, which will be discussed in the context of electrocatalysis. One way to overcome this problem is to use an alkaline membrane (conducting, e.g., by the hydroxyl anion, OH ), in which medium the kinetics of the electrochemical reactions involved are faster than in an acidic medium, and then to develop the solid alkaline membrane fuel cell (SAMFC). 

Fuel cells work on the same principles as a battery (Figure 5.18)—the difference is that instead of the fuel for the reaction being contained in the electrode materials as... 

Consider a manufacturing community of 100,000 persons, the levelized total energy consumption of which (including industry and military) is lOkW/person. Further, assume that one-quarter of these persons are employed in the synthesis of chemicals, using the second fuel cell principle (Section ). As a simplification, assume the manufacture is carried out by fuel cells working at 0.6 V and a current density of 1 A cm-2. The manufactured item has a molecular weight of 300 and requires 8 e0 per mole in its synthesis. 

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. 

Fuel cells work on a basic chemical principle and use some very modern engineering. A cell contains an anode, a cathode and an electrolyte layer, with a typical system being shown in Figure 2.1. 

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. 

Polybasic carboxylic hydroxy and amino acid aided synthetic routes directed towards obtaining mixed inorganic materials, especially for battery and fuel cell applications, are overviewed. It has been shown that, in spite of enormous number of papers on the subject, significant efforts should be undertaken in order to understand the basic principles of these routes. Possible influence of the structure of reactants employed in the process (acids, poly hydroxy alcohols, metal salts) is put forward, and some directions of future work in the field are outlined. 

Stephen J. Paddison received a B.Sc.(Hon.) in Chemical Physics and a Ph.D. (1996) in Physical/Theoretical Chemistry from the University of Calgary, Canada. He was, subsequently, a postdoctoral fellow and staff member in the Materials Science Division at Los Alamos National Laboratory, where he conducted both experimental and theoretical investigations of sulfonic acid polymer electrolyte membranes. This work was continued while he was part of Motorola s Computational Materials Group in Los Alamos. He is currently an Assistant Professor in the Chemistry and Materials Science Departments at the University of Alabama in Huntsville, AL. Research interests continue to be in the development and application of first-principles and statistical mechanical methods in understanding the molecular mechanisms of proton transport in fuel-cell materials. 

After rehearsing the working principles and presenting the different kinds of fuel cells, the proton exchange membrane fuel cell (PEMFC), which can operate from ambient temperature to 70-80 °C, and the direct ethanol fuel cell (DEFC), which has to work at higher temperatures (up to 120-150 °C) to improve its electric performance, will be particularly discussed. Finally, the solid alkaline membrane fuel cell (SAMFC) will be presented in more detail, including the electrochemical reactions involved. 

The improved neutron detector spatial resolution has been a recent advance, with user instruments first available at the end of 2006 and 2007 at NIST and PSI, respectively. The work can be classified as proof-of-principle,9,10 in situ measurement of the steady-state through-plane water content during fuel cell operation," 13 and dynamic through-plane mass transport measurements.14,15... 

Another interesting attempt worth noting is the combination of porphyrin sensitized solar cell with a fuel cell made by Moore and Gust. The hybrid cell can realize an open circuit voltage of 1.2 V. The energy conversion efficiency of this photoelectrochemical biofuel cell can, in principle, produce more power than either a photoelectrochemical cell or a biofuel cell working individually [83],... 

In this chapter, after recalling the working principles and the different kinds of fuel cells, the discussion will be focused on low-temperature fuel cells (AFC, PEMFC, and DAFC), in which several kinds of carbon materials are used (catalyst support, gas-diffusion layer [GDL], bipolar plates [BP], etc.). Then some possible applications in different areas will be presented. Finally the materials used in fuel cells, particularly carbon materials, will be discussed according to the aimed applications. To read more details on the use of carbon in fuel cell technology, see the review paper on The role of carbon in fuel cell technology recently published by Dicks [6],... 

The working principle of fuel cells, the different kinds of fuel cells, the main fuels used and then-possible applications will be first discussed [7-10],... 

Fig. 2.1. Working principle of the Molten Carbonate Fuel Cell (MCFC) with direct internal reforming (DIR).

The working principles behind a solid oxide fuel cell (SOFC) are schematically illustrated in Figure 8.7, where, similar to the other fuel cell types, the three key parts of an SOFC, a cathode, an anode, and an electrolyte, are shown. The electrolyte is, in a majority of cases, an oxygen-anion ceramic conductor, which is, as well, an electronic insulator [5]. In the SOFC the fuel can be methane (CH4). Subsequently, in this case the oxidation reaction in the anode is given by... 

Fig. 5. (a) Working principle of a solid oxide fuel cell, (b) Sketch of possible reaction paths of the oxygen reduction reaction, taking place on a particle of a solid oxide fuel cell cathode. 

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