Fuel working principles

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. 

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],... 

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. 

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. 

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...

Oil applications are based on pressure atomization technology even if small power application solutions are available based on oil evaporation by heat. Electronic control of the fuel/air ratio previews an actuator to move a butterfly for controlling the air flow and an actuator to move the oil pressure regulator. For gas, two actuators control two butterflies, one for gas and one for air, even if fhe gas pneumatic valves (whose working principle is based on a pneumatic feedback) are widely used. More advanced burners control air flow changing the fan speed, reducing the pressure drop in the hydraulic pipes and valves. Despite this, a butterfly valve is often necessary to control startup operation, especially for high power applications. 

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. 

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. 

Polymer Electrolyte membrane Fuel Cells (PEFC) are used to power uninterruptible power supplies, combined heat and power generation systems, vehicles for materials handling as well as electric vehicles, busses and light duty road vehicles. This contribution gives a short introduction into the working principles of PEFC as well as the materials and components used. 

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.

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