Methanol DMFC

Most fuel cells are powered by hydrogen, which can be fed to the fuel cell system directly or can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol, and hydrocarbon fuels. Direct methanol fuel cells (DMFCs), however, are powered by pure methanol. 

Direct methanol fuel cell technology is relatively new compared to that of fuel cells powered by pure hydrogen, and research and development are roughly 34 years behind that of other fuel cell types. Nonetheless, the DMFC appears to be the most promising as a battery replacement for portable applications such cellular phones and laptop computers, and a number of manufacturers are already introducing commercial versions of these applications. 

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Direct methanol (DMFC) Transport, mobile equipment Polymer 355-475... 

Several types of fuel cell are currently under development, using different electrolyte systems phosphoric acid (PAFC), alkaline, molten carbonate (MCFC), regenerative, zinc-air, protonic ceramic, (PCFC), proton exchange membrane (PEM), direct methanol (DMFC), and solid oxide (SOFC). The last four contain solid electrolytes. 

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]. 

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. 

Schematic representation of ideal water distribution in a neat methanol DMFC.

Fig. 2.1 A schematic presentation of (a) a proton-exchange membrane (PEMFC) and (b) an alkaline membrane fuel cell (AMFC), both fuelled either with H2 gas or directly with methanol (DMFC mode). The stoichiometric ratios of reactants and products are shown in each case...

Direct methanol fuel cells (DMFC) on the other hand represent the only class of fuel cells in which one of the reactants is provided in liquid phase, compared with the other, gas-fed cell types. Due to the comparatively easy handling of methanol, DMFCs are mostly considered for portable and mobile applications. Their reduced power density when compared to hydrogen-driven PEMFCs (the current density is around one-tenth of that compared to PEMFCs) leads usually to... 

Direct methanol (DMFC) H+ 20-90°C Suitable for portable electronic systons of low power, running for long times... 

Two subcategories of PEM fuel cells are currently being widely studied, for allowing the use of other fuels other than hydrogen directly into the cell direct methanol (DMFC) and direct ethanol (DEFC). 

The basic structure of all fuel cells is similar the cell consists of two electrodes which are separated by the electrolyte and which are connected in an external circuit. The electrodes are exposed to gas or liquid flows to supply the electrodes with fuel or oxidant (e.g. hydrogen or oxygen). As it can be seen in Table 12.1, the anode reaction in fuel cells is either the direct oxidation of hydrogen (low temperature fuel cells) or the oxidation of methanol (DMFC). An indirect oxidation via a reforming step can also occur in the case of high temperature operation fuel cells. The cathode reaction is oxygen reduction, in most cases from air. 

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