Direct Ethanol Fuel Cell DEFC

Direct ethanol fuel cells (DEFCs) produce power directly from ethanol without prior reforming. Compared with methanol used as the fuel for DMFCs, ethanol is nontoxic, environmentally friendly, and universally available, and making the handling easy. Since ethanol is also a liquid alcohol like methanol, the technological issues of crossover, discharge of carbon dioxide, and passive operation are comparable. 

The main challenge is the electrocatalytic cleavage of the carbon-carbon bond and the complete reaction from ethanol to carbon dioxide. This reaction is enhanced in alkaline compared with acidic chemistry. Additionally, an alkaline environment permits the use of non-precious metals as catalysts. As in alkaline fuel cells, hydroxyl ions are transported from the cathode to the anode, water is produced at 

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Rousseau S, Coutanceau C, Lamy C, Leger JM. 2006. Direct ethanol fuel cell (DEFC) Electrical performances and reaction products distribution under operating conditions with different platinum-based anodes. J Power Sources 158 18-24. 

Shao et al. [35] not only used a similar Ti mesh to the one presented by Scott s group but also used a Ti mesh as the cathode DL in a DMFC. The main difference between both meshes was that the one used on the cathode side was coated on both sides with carbon black (Vulcan XC-72) and PTFE (i.e., with MPLs on each side). It was shown that this novel cathode DL performed similarly to conventional CFP DLs under comparable conditions. Chetty and Scott [36] also used a catalyzed Ti mesh as the anode DL, but in a direct ethanol fuel cell (DEFC) it performed better compared to a cell with a standard DL (CFP). 

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. 

There are several types of direct liquid fuel cells, such as direct methanol fuel cells (DMFCs), direct formic acid fuel cells (DFAFCs), and direct ethanol fuel cells (DEFCs), the most popular being the DMFC, which is the focus of this section. A schematic DMFC system is shown in Figure 1.7. 

The analytical results concerning the electro-oxidation of ethanol in a Direct Ethanol Fuel Cell (DEFC) were obtained by online HPLC analysis coupled with the fuel cell test bench (Scheme 3). 

However, a number of issues, particularly those related to the performance of the electrocatalyst, should be improved in order to implement direct ethanol fuel-cell (DEFC) technology. Among them, the m or challenge is developing electrocatalysts that can break the G-C bond at relative low potentials. 

The Direct Ethanol Fuel Cell (DEFC) is an attractive system since this fuel can be produced by fermentation of sugar-containing raw materials from agriculture. However, despite several advances in recent years, the existing electrocatalyst still possesses very low electrochemical conversion efficiency to CO2 at ambient temperature, particularly at high concentration values of the alcohol molecule (>0.1 mol L ) [3]. In addition to this, the ethanol crossover seems to be even more prominent in the DEFC, causing more severe losses in the fuel cell power. 

Yang CC, Lee YJ, Chiu SJ, Lee KT, Chien WC, Lin CT, Huang CA (2008) Preparation of PVA/HAP composite polymer membrane for a direct ethanol fuel cell (DEFC). J Appl... 

Suresh NS, Jayanti S (2009) Modelling of cross-over effects in direct ethanol fuel cells (DEFCs), AIChE proceedings, paper 161991... 

For direct ethanol fuel cell (DEFC), the alcohol oxidation reaction proceeds on the anode ... 

Hydrogen is the preferred fuel for PEFCs. However, a PEFC can also be fed by liquid or gaseous methanol, called direct methanol fuel cell, DMFC. Other fuels based on alcohols, e.g., the direct ethanol fuel cell, DEFC, are subject to research. 

The polymer electrolyte fuel cell, PEFC, and the phosphoric acid fuel cell, PAFC, are acidic fuel cells the PEFC operates in the temperature range below and around 100 °C (PEFC), respectively, and the PAFC at around 200 °C. Hydrogen is the preferred fuel for both types. A PEFC can also be fed by liquid or gaseous methanol, called direct methanol fuel cell, DMFC. Other fuels based on alcohols, e.g., the direct ethanol fuel cell, DEFC, are subject to research. Fuel cell types utilizing an acidic aqueous electrolyte will not be considered here. 

Methanol and some other liquid foels can be fed to a PEM fuel cell directly without being reformed, thus forming a direct methanol fuel cell (DMFC), direct ethanol fuel cell (DEFC), direct formic acid fuel cell (DFAFC), and so on. 

Figure 4.38. Direct ethanol fuel cell polarization curves at 353 K. Ethanol concentration 2 M, Nation 117, O2 pressure 3 bar [183]. (Reproduced from Journal of Power Sources, 158(1), Rousseau S, Coutanceau C, Lamy C, Leger J-M, Direct ethanol fuel cell (DEFC) electrical performances and reaction products distribution under operating conditions with different platinum-based anodes, 18-24, 2006, with permission from Elsevier.)...

In fuel cells working with a liquid fuel, usually an alcohol such as methanol (a direct methanol fuel cell - DMFC), ethanol (a direct ethanol fuel cell - DEFC), glycerol (a direct glycerol fuel cell - DGEC), etc., in addition to the necessity to activate the ORR at the cathode, the alcohol oxidation reaction at the anode also involves a high overpotential. This high overpotential is mainly due to the formation, after dissociative adsorption of the alcohol at the catalyst surface, of poisoning species which block the catalytic surface the main one adsorbed is carbon monoxide. ... 

Rousseau, S., Coutanceau, C., Lamy, C., etal. (2006). Direct Ethanol Fuel Cell (DEFC) Electrical Performances and Reaction Products Distribution Under Operating Conditions with Different Platinum-based Anodes, J. Power Sources, 158, pp. 18-24. 

It is quite natural that all these considerations have led to enhanced interest in the uses of ethanol in fuel cells. A lot of research went into the development of direct ethanol fuel cells (DEFCs) during the last decade. Much of the research in this direction was performed in France in the group of Claude Lamy (see the review of Lamy et al., 2002). 

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