Proton direct ethanol fuel cells

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. 

The direct ethanol fuel cell is based on a proton exchange membrane fuel cell (PBMFC), in which the anodic compartment is fed with an ethanol-water mixture (Fig. 1). 

Direct alcohol fuel cells (DAFCs) are a type of proton exchange membrane fuel cell in which alcohol is directly used as fuel. The majority of the studies about such type of fuel cells have been conducted by using methanol as fuel, leading to the so-called Direct Methanol Fuel Cells (DMFCs). However, the use of ethanol, rather than methanol, as fuel is attracting a great deal of attention. This is because ethanol is, or can be, obtained from renewable sources such as sugarcane in which case, the energy obtained by Direct Ethanol Fuel Cells (DEFCs) could result in net zero CO2 emissions. Furthermore, ethanol is less toxic and less... 

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. 

The third focus of this book centers around fuel cells. Catalysts for fuel cells and for hydrogen production are discussed in one chapter. Catalysts for proton exchange membrane (PEM) fuel cells are described in another chapter. A specific discussion of the aspect of assembly of membrane electrodes in fuel cells is given in another chapter. Catalytic processes in PEM fuel cells are discussed in a separate chapter. The use of nano-size particles of platinum in PEM fuel cells is given in another chapter. Another chapter concerns direct ethanol fuel cells. A separate chapter on alcohol fuel cells generally discusses this area. Another chapter concerns the electrocatalytic oxidation of ethanol which is of key importance in this area of research. 

In recent decades, direct alcohol fuel cells (DAFCs) have been extensively studied and considered as possible power sources for portable electronic devices and vehicles in the near future. The application of methanol is limited due to its high volatility and toxicity, although it is relatively easily oxidized to CO2 and protons. So other short chain organic chemicals especially ethanol, ethylene glycol, propanol, and dimethyl... 

Song S, Tsiakaras P (2006) Recent progress in direct ethanol proton exchange membrane fuel cells (DE-PEMFCs). Appl Catal B Environm 63 187-193... 

For DAFC operated at room and moderate temperamres (lower than 80 °C) perfluoiinated sidfonic acid ionomers (PFSA), mainly Nafion (DuPunt), have been the most studied and used in direct methanol (DMFC) and ethanol fuel cells (DEFQ due to its excellent proton cmiductivity and chemical stability [16, 17]. 

One of the main issues in the direct alcohol fuel cells (DAFCs) is that the fuel can easily permeate into the cathode through the proton exchange membrane, which causes dramatic performance loss since the currently used Pt-containing cathode catalysts have no or little methanol tolerance. One of the advantages of Pd-M alloys over Pt in DAFCs is their high methanol and ethanol tolerance in acid. In particular, methanol tolerance was demonstrated for Pd-Fe, Pd-Co, Pd-Cr, Pd-Ni, and Pd-Pt alloys [19, 41, 53, 77-80]. 

Recent developments in AAEMs have opened up the possibiUty of an alkaline analog of the acidic solid polymer electrolyte fuel cell. This could utilize the benefits of the alkaline cathode kinetics and at the same time eradicate the disadvantages of using an aqueous electrolyte. As the AAEM is also a polymer electrolyte membrane (sometimes abbreviated as PEM), some clarity in abbreviations is required. In this chapter, PEM refers only to the proton exchange membrane fuel cells (acidic), AAEM refers to the anion exchange membrane H2/O2 fuel cells, and AFC exclusively refers to the aqueous electrolyte alkaline H2/O2 fuel cells. Anion exchange membranes are also employed in alkaline direct alcohol fuel cells, discussion of which will refer to them as ADMFC/ADEFC (methanol/ ethanol). 

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