Proton-exchange membrane fuel cells principles

Fig. 14.12 Principle of a proton exchange membrane fuel cell (PEMFC).

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). 

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. 

This article provides a basic explanation of fuel cells, especially the fundamentals of proton-exchange membrane fuel cell (PEMFC). Starting with an introduction to fuel cells, it addresses principles, materials, fuel generation processes, and future technological challenges of PEMFC. 

Knights S (2010), PEM Fuel Cell Principles and Introduction to Contamination Issues , in Li H, Knights S, Shi Z VanZee J and Zhang J, Proton Exchange Membrane Fuel Cells Contamination and Mitigation Strategies, Taylor and Francis Group, 1-52. 

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. 

Figure 13.2. Principle of a Proton-Exchange-Membrane (PEM) fuel cell.

The principles of the fuel cell are illustrated in Figure 1.1. The electrochemical cell consists of two electrodes, an anode and a cathode, which are electron conductors, separated by an electrolyte [e.g. a proton exchange membrane (PEM) in a PEMFC or in a DAFC], which is an ion conductor (as the result of proton migration and diffusion inside the PEM). An elementary electrochemical cell converts directly the chemical... 

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... 

Current research is centred on making compact cells of high efficiency. They are described in terms of the electrolyte that is used. The principle types are alkali fuel cells, described above, with aqueous KOH as electrolyte, MCFCs (molten carbonate fuel cells), with a molten alkali metal or alkaline earth carbonate electrolyte, PAFCs (phosphoric acid fuel cells), PEMs (proton exchange membranes), using a solid polymer electrolyte that conducts ions, and SOFCs, (solid oxide fuel cells), with solid electrolytes that allow oxide ion, 0 , transport The... 

The basic principle of a proton exchange membrane (PEM) fuel cell is shown in Fig. 9. 

At the heart of a PEM fuel cell is a polymer membrane that has some unique capabilities. It is impermeable to gases but it conducts protons (hence the name, proton exchange membrane). The membrane that acts as the electrol5q e is squeezed between the two porous, electrically conductive electrodes. These electrodes are typically made out of carbon doth or carbon fiber paper. At the interface between the porous electrode and the polymer membrane there is a layer with catalyst particles, typically platinum supported on carbon [1]. A schematic diagram of cell configuration and basic operating principles is shown in the Figure in.l. 

In this article, each section starts with a brief introduction to techniques, principles, and instrumentation, followed by examples for the purposes of illustration. The illustration is limited to low- to medium-temperature fuel cells such as the proton exchange membrane (PEM), direct liquid, and phosphoric acid fuel cells that involve protons as the ionic charge transport species. 

Such a device needs a well-performing, fast and robust proton-exchange membrane. In principle, a cell designed for water splitting [92] under solar irradiation may also serve for C02-water co-processing. Therefore, work done on solar-driven water splitting [76] can be transferred to CO2 conversion into chemicals/fuels under solar irradiation. 

The principle of PEM-DEFC (proton exchange membrane direct ethanol fuel cell) operation is illustrated in Eigure 15.1. The anode consists of an ethanol solution, while the cathode is composed by humidified air or oxygen, so that good conductivity is maintained in the PEM. 

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