The Direct Methanol Fuel Cell DMFC

Considering the above limitations, the best next choice would seem to be a methanol/air fuel cell, and this is indeed where the main effort in fuel ceU R D 

10) Note that cars run on natural gas exist, but are not allowed to enter tunnels because of safety considerations. 

The protons produced in this reaction are transported through the cation selective membrane to the cathode, where the reaction taking place is 

water is consumed at the anode and produced at the cathode, and some method of transport of some of the water from the cathode to the anode must be included as part of the fuel cell system. 

On the other hand, methanol is rather toxic, so why not use ethanol, which is less toxic, has similar physical properties (m.p. -114.3 °C b.p. +78,4 C density 0.789 gm cm ) and is also inexpensive It turns out that ethanol and higher alcohols cannot be oxidized all the way to CO2, at least not at the potentials relevant to fuel cell operation. The product of electrochemical oxidation is acetic acid in the case of ethanol and the corresponding higher acid in the case of higher alcohols. It seems that breaking the C-H and the 0-H bonds in methanol is easier that breaking the C-C bond in ethanol. 

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Fuel cells can run on fuels other than hydrogen. In the direct methanol fuel cell (DMFC), a dilute methanol solution ( 3%) is fed directly into the anode, and a multistep process causes the liberation of protons and electrons together with conversion to water and carbon dioxide. Because no fuel processor is required, the system is conceptually vei"y attractive. However, the multistep process is understandably less rapid than the simpler hydrogen reaction, and this causes the direct methanol fuel cell stack to produce less power and to need more catalyst. 

The dynamic behavior of fuel cells is of importance to insure the stable operation of the fuel cells under various operating conditions. Among a few different fuel cell types, the direct methanol fuel cell (DMFC) has been known to have advantages especially for portable... 

The Pt/Ru catalyst is the material of choice for the direct methanol fuel cell (DMFC) (and hydrogen reformate) fuel cell anodes, and its catalytic function needs to be completely understood. In the hrst approximation, as is now widely acknowledged, methanol decomposes on Pt sites of the Pt/Ru surface, producing chemisorbed CO that is transferred via surface motions to the active Pt/Ru sites to become oxidized to CO2... 

The electrodes in the direct methanol fuel cell (DMFC) (i.e. the anode for oxidising the fuel and the cathode for the reduction of oxygen) are based on finely divided Pt dispersed onto a porous carbon support, and the electro-oxidation of methanol at a polycrystalline Pt electrode as a model for the DMFC has been the subject of numerous electrochemical studies dating back to the early years ot the 20th century. In this particular section, the discussion is restricted to the identity of the species that result from the chemisorption of methanol at Pt in acid electrolyte. This is principally because (i) the identity of the catalytic poison formed during the chemisorption of methanol has been a source of controversy for many years, and (ii) the advent of in situ IR culminated in this controversy being resolved. 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

The technically relevant fuel cell types are shown in Fig. 13.5 a newer development of the PEM fuel cell is the direct-methanol fuel cell (DMFC), which uses a diluted... 

Anode Investigations using cyclovoltammetry confirm an important effect of surface oxides (see Vols. 3, 4). A known example of the different anodic activity is the poisoning of platinum by adsorbed carbon monoxide species, for example, in the direct methanol fuel cell (DMFC),... 

In electrochemical systems, metal meshes have been widely used as the backing layers for catalyst layers (or electrodes) [26-29] and as separators [30]. In fuel cells where an aqueous electrolyte is employed, metal screens or sheets have been used as the diffusion layers with catalyst layers coated on them [31]. In direct liquid fuel cells, such as the direct methanol fuel cell (DMFC), there has been research with metal meshes as DLs in order to replace the typical CFPs and CCs because they are considered unsuitable for the transport and release of carbon dioxide gas from the anode side of the cell [32]. 

A particular version of the PEFC is the direct methanol fuel cell (DMFC). As the name implies, an aqueous solution of methanol is used as fuel instead of the hydrogen-rich gas, eliminating the need for reformers and shift reactors. The major challenge for the DMFC is the crossover of methanol from the anode compartment into the cathode compartment through the membrane that poisons the electrodes by CO. Consequently, the cell potentials and hence the system efficiencies are still low. Nevertheless, the DMFC offers the prospect of replacing batteries in consumer electronics and has attracted the interest of this industry. 

One energy application of methanol in its early stages of development is the direct methanol fuel cell (DMFC). A fuel cell is essentially a battery in which the chemicals are continuously supplied from an external source. A common fuel cell consists of a polymer electrolyte sandwiched between a cathode and anode. The electrodes are porous carbon rods with platinum... 

Given these requirements, hybrid and nonhybrid PEMFC systems are the leading contenders for automotive fuel cell power, with additional attention focusing on the direct-methanol fuel cell (DMFC) version of the technology and the possibility of using solid oxide fuel cell (SOFC) systems as auxiliary power units for cars and trucks. 

Havranek A, Wippermann K (2004) Determination of proton conductivity in anode catalyst layers of the direct methanol fuel cell (DMFC). J Electroanal Chem 567(2) 305-15... 

The Methanex Vancouver web site lays emphasis on methanol production and hopes for the direct methanol fuel cell (DMFC). Fiydrogen is mentioned, but not the need for a hydrogen mine for the nearby Ballard Power Inc. 

PEM fuel cells use a solid proton-conducting polymer as the electrolyte at 50-125 °C. The cathode catalysts are based on Pt alone, but because of the required tolerance to CO a combination of Pt and Ru is preferred for the anode [8]. For low-temperature (80 °C) polymer membrane fuel cells (PEMFC) colloidal Pt/Ru catalysts are currently under broad investigation. These have also been proposed for use in the direct methanol fuel cells (DMFC) or in PEMFC, which are fed with CO-contaminated hydrogen produced in on-board methanol reformers. The ultimate dispersion state of the metals is essential for CO-tolerant PEMFC, and truly alloyed Pt/Ru colloid particles of less than 2-nm size seem to fulfill these requirements [4a,b,d,8a,c,66j. Alternatively, bimetallic Pt/Ru PEM catalysts have been developed for the same purpose, where nonalloyed Pt nanoparticles <2nm and Ru particles <1 nm are dispersed on the carbon support [8c]. From the results it can be concluded that a Pt/Ru interface is essential for the CO tolerance of the catalyst regardless of whether the precious metals are alloyed. For the manufacture of DMFC catalysts, in... 

Sundmacher, K. Schultz, T. Zhou, S. Scott, K. Ginkel, M. Gilles, E.D. Dynamics of the direct methanol fuel cell (DMFC) Experiments and model-based analysis. Chem. Eng. Sci. 2001, 56 (2), 333-341. 

Further down the road are more advanced designs, the two most notable being the Direct Methanol Fuel Cell (DMFC) and the Reversible or Regenerative Fuel Cell. 

Fuel cells offer the possibility of reduced emissions and high efficiency for transportation applications. Of the various fuel cells being considered, the direct methanol fuel cell (DMFC) is very attractive due to the key advantages of reducing system complexity and potentially improving transient response compared to reformate-air fuel cell systems. However, DMFCs currently require unsupported noble metal catalysts at high loadings of... 

The Direct Methanol Fuel Cell, DMFC, (see Fig. 7-6 in section 7.2.2.4.) is another low temperature fuel cell enjoying a renaissance after significant improvements in current density. The DMFC runs on either liquid or, with better performance but higher system complexity, on gaseous methanol and is normally based on a solid polymer electrolyte (SPFC). R-Ru catalysts were found to produce best oxidation results at the anode, still the power density is relatively low [5, 29]. Conversion rates up to 34 % of the energy content into electricity were measured, an efficiency of 45 % is expected to be feasible in the future. SPFC in the power order of several kW to be used in automobile applications are currently in the development phase. 

A serious candidate for transportation application is also the direct methanol fuel cell (DMFC) which has been realized already on a laboratory scale. A catalytic burner is requited to evaporate the methanol/water mixture and to bum the exhaust gas at the anode [43]. Considering the complete energy chain, a PEFC is by 50 % more efficient than a diesel engine which consumes 4 1 per 100 km this is also valid for a natural gas driven engine [37]. Fig. 7-6 presents the processing schematics of both IMFC and DMFC. The DMFC offers a much simpler system than the PEFC. The DMFC is currently at an early development stage. It is perceived to offer improved solutions to the need for a small-scale power supply. A program for the construction of a 30 kW stack has recently started [29]. 

Intense international academic and industrial research efforts have recently placed the direct methanol fuel cell (DMFC) on the brink of commercialization [xi,xii]. The major advantage of the DMFC relative to other fuel cells is the simplicity of... 

The purified hydrogen needs to be stored as liquid (at -253°C) or compressed gas at around 200 bar—this is due to the low energy density of hydrogen (0.003 kW h/L at 1 bar and ambient temperature and 0.5 kW h/L at 200 bar). When used in the transport sector, thick steel cylinders for the compressed gas are needed, and stacks of the cylinders must be carried under or on the top of the vehicle (bus, truck, ferry). For private cars, the direct-methanol fuel cell (DMFC—see Figure 7.25) is more attractive. For a DMFC,... 

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