Direct alcohol fuel cells ethanol

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... 

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). 

Oxidation of Alcohols in a Direct Alcohol Fuel Cell The electrocatalytic oxidation of an alcohol (methanol, ethanol, etc.) in a direct alcohol fuel cell (DAFC) will avoid the presence of a heavy and bulky reformer, which is particularly convenient for applications to transportation and portable electronics. However, the reaction mechanism of alcohol oxidation is much more complicated, involving multi-electron transfer with many steps and reaction intermediates. As an example, the complete oxidation of methanol to carbon dioxide ... 

Besides, it has been shown that palladium is promising for direct alcohol fuel cells applications as it is very active for ethanol electro-oxidation in basic media and that its electroactivity is even higher than that of platinum. Recently, Pd nanoballs and nanowires synthesized by radiolysis in hexagonal mesophases have shown an important elec-trocatalytic activity for ethanol electro-oxidation. ... 

Direct alcohol fuel cells (DAFC) are very attractive as power sources for mobile and portable applications. The alcohol is fed directly into the fuel cell without any previous chemical modification and is oxidized at the anode while oxygen is reduced at the cathode. Methanol has been considered the most promising fuel because it is more efficiently oxidized than other alcohols. Among different electrocatalysts tested in the methanol oxidation, PtRu-based electrocatalysts were the most active [1-3]. In Brazil ethanol is an attractive fuel as it is produced in large quantities from sugar cane and it is much less toxic than methanol. On the other hand, its complete oxidation to CO2 is more difficult than that of methanol due to the difficulty in C-C bond breaking and to the formation of CO-intermediates that poison the platinum anode catalysts. Thus, more active electrocatalysts are essential to enhance the ethanol electrooxidation [3],... 

Ethanol is considered as the ideal fuel for the so-called direct alcohol fuel cells (DAFCs). This is because ethanol has a number of advantages over methanol it can be produced in a sustainable manner, easily stored and transported, and is less toxic or corrosive than methanol. The theoretical mass energy of ethanol is 8.0 kWh kg compared to 6.1 kWh kg" for methanol. The complete oxidation of ethanol releases 12 electrons per molecule its standard electromotive force E° q =1145V, is similar to that of methanol. 

Reviews on DEFC become available since 2006, describing the state of the art of catalysts for ethanol oxidation [31, 76, 77], while more recent works focused oti alkaline DEFC [78-80]. A comprehensive review on alkaline direct alcohol fuel cells was recently published by one of us [30] over viewing catalysts, membranes and cell performance of ADAFC fuelled with methanol, ethanol, and ethylene glycol. 

Rodriguez Varela FJ, Gaona Coronado AA, Jiang Q-Z, Bartolo Perez P (2011) Pt-CeOx/ MWCNT electrocatalysts as ethanol-tolerant ORR cathodes for direct alcohol fuel cells. J New Mater Electrochem Syst 14 75-80... 

Savadogo O, Rodriguez Varela FJ (2008) Palladium-alloy catalysts as ethanol tolerant cathodes for direct alcohol fuel cell applications. J New Mater Electrochem Syst 11 69-74... 

Sen Gupta S, Datta J (2005) An investigation into the electro-oxidation of ethanol and 2-propanol for application in direct alcohol fuel cells (DAECs). J Chem Sci 117(4) 337-344... 

Considering all the types of Direct Alcohol Fuel Cells (DAFC) currently in development, that using methanol (DMFC) is closer to massive commercialization. DMFC exhibits higher current and power densities than fuel cells using ethanol, ethylene glycol, etc., mainly due to the difficulty for breaking the C-C bonds of higher alcohols. For this reason this Chapter will be mainly devoted to review the applications of DMFC. 

The dilution of Pd with non-noble metals in a smart catalytic architecture capable of rapidly and stably oxidizing alcohols on anode electrodes would knock down the main barriers to the commercialization of direct alcohol fuel cells (DAFC), especially those fed with primary alcohols, hi er than methanol, and polyalcohols. Indeed, apart from methanol for which there exist platinnm based catalysts capable of prodncing cnrrent densities of several tens of mW cm, the higher alcohols like ethanol and polyalcohols like glycerol are difficnlt to oxidize on platinum or platinum alloyed with either noble or non-noble metals. 

Abstract The faster kinetics of the alcohol oxidation reaction in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel, and palladium, makes the alkaline direct alcohol fuel cell a potentially low-cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. In this work an overview of catalysts for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol, and ethylene glycol, formed by these materials, is presented. 

In this work an overview of anode catalysts for alkaline direct alcohol fuel cells, and reports of the testing of these materials in alkaline direct alcohol fuel cells fuelled with Ci (methanol) and C2 (ethanol and ethylene glycol) alcohols, is presented. 

Bambagioni V, Bianchini C, Marchionni A, Filippi J, Vizza F, Teddy J, Serp P, Zhiani M (2009) Pd and Pt-Ru anode electrocatalysts supported on multi-walled carbon nanotubes and their use in passive and active direct alcohol fuel cells with an anion-exchange membrane (alcohol = methanol, ethanol, glycerol). J Power Sources 190(2) 241-251... 

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]. 

In direct alcohol fuels cells (DAFCs), some simple organic molecules such as methanol, ethanol, formic acid, and ethylene glycol are used as alternative fuels. Besides the slow kinetics of ORR in the cathode, the slow alcohol oxidation reaction on Pt is another major contribution to low DAFC performance. 

In this context, hydrogen carriers like alcohols feeding a direct alcohol fuel cell (DAFC) appear advantageous for two main reasons they are liquid (which simplifies the problems of storage and distribution) and their theoretical mass energy density is rather high, close to that of gasoUne (6.1 and 8.0 kWh/kg for methanol and ethanol, respectively [4]). The most studied alcohols are methanol [5], which is the simplest mono-alcohol, and ethanol [6]. 

Bambagioni, V, Bianchini, C., Marchionni, A., et al. (1990). Pd and Pt-Ru Anode Electrocatalysts Supported on Multi-waUed Carbon Nanotubes and their Use in Passive and Active Direct Alcohol Fuel Cells with an Anion-exchange Membrane (Alcohol = Methanol, Ethanol, Glycerol), J. Power Sources, 190, pp. 241-251. 

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... 

Another important source of power loss performance in direct alcohol fuel cells is so-called crossover effect, which is the passage of the fuel from the anode to the cathode through the membrane. This crossover effect is responsible for a large part of power losses of DAFCs, especially in the open circuit region. Besides, ethanol can be oxidized at the cathode electrode resulting in mixed potentials that also contribute to the decreasing of the efficiency of the fuel cell. As a rule of thumb the crossover effect increases with the concentration of ethanol and with the increasing temperature and decreases with the thickness of the membrane thus... 

Recently, Chu and Shul [128] have applied combinatorial chemistry to the screening of 66 PtRuSn-anode arrays for investigation of methanol, ethanol, and 2-propanol oxidation. The screening was performed by employing quinine as indicator of the catalytic activity, which allowed for selection of the optimum composition of electrocatalysts for DAFCs (Direct Alcohol Fuel Cells). PtRuSn (80 20 0), PtRuSn (50 0 50), and PtRuSn (50 30 20) furnished the lowest onset potential for methanol, ethanol, and 2-propanol electro-oxidation according to the CV results, respectively. The active area/composition for ethanol electro-oxidation is represented in Figure 15.8 as adapted from Ref. [128]. 

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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