Working Principles of a Fuel Cell

The cathode s outlet air has a lower oxygen concentration than the inlet air and has to be separated from anode s inlet and outlet gases. The products of the cathodic reaction are water and air with low oxygen and high nitrogen levels. Figure 8.1 shows the working principle of a fuel cell s cathode. 

A good introduction to the principle of a fuel cell is given by the example of the low-temperature cell with an addic electrolyte and working on hydrogen and oxygen (Vetter, 1967 Tanase et al, 1987 Lamy and Leger, 1994 Stevens et al, 2000). The following electrochemical reactions occur at the ... 

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. 

Figure 7.3 Working principle of a hydrogen-powered fuel cell with a proton-conducting electrolyte (Ref. [9])...

Figure 9,1, Working principle of a direct ethanol fuel cell.

The working principle of a MFC with the iron-mediated cathode with a BPM. (Reprinted with permission from A.T. Heijne, H.V.M. Hamelers and C.J.N. Buisman, Microbial fuel cell operation with continuous biological ferrous iron oxidation of the catholyte. Environ. Set. Technol. 41, 2007,4130-4134. Copyright 2007, American Chemical Society.)... 

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). 

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],... 

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... 

In principle, three-electrode EIS measurement is capable of separating the contributions from the anode and the cathode [61], In a three-electrode EIS experiment, as shown in Figure 5.43, the potentiostat, with three electrode probes, is applied to measure signals between the working electrode (WE) and the reference electrode (RE). The counter electrode (CE) is used to collect the induced current from the WE. For a fuel cell, if the anode serves as a WE, the cathode will serve as a CE, and vice versa. In this way, the individual electrode impedances can be determined independently. 

Fig. 3.1 Illustration of a micro-direct methanol fuel cell (a) top view of a planer cell and (b) cross-sectional view with working principle...

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. 

In a generic sensitized PEC design, the molecular excitation and excited state formation are followed by electron transfer injection into the conduction band of a semiconductor. In order to promote multielectron transfer events like water oxidation, multiple redox equivalents must be concentrated in a single site or cluster. The working principles of the cell are schematized in Fig. 6, where solar energy is stored to create a photopotential for water splitting [ 16,17]. In principle, at the cathode, water or CO2 reduction may occur, giving rise to the production of fuels. 

At present, most of the work toward building methanol fuel cells relies on technical and design principles, developed previously for polymer electrolyte membrane fuel cells. In both kinds of fuel cells, it is common to use platinum-ruthenium catalysts at the anode and a catalyst of pure platinum at the cathode. In the direct methanol fuel cells, the membrane commonly used is of the same type as in the hydrogen-oxygen fuel cells. The basic differences between these versions are discussed in Section 19.7. 

---