Methanol cross-over

Direct-methanol fuel cells (DMFCs) have attracted considerable attention for certain mobile and portable applications, because of their high specific energy density, low poison emissions, easy fuel handling, and miniaturization [129,130], However, the methanol permeation through electrolyte membranes (usually called methanol cross-over) in DMFCs still is one of the critical problems hindering the commercialization [131,132], Nafion , a... 

SH-Ag clusters, 87 6-FeOOH, Co304,257 colloidal catalysts, 281 coordinatively unsaturated metal atoms, 141 ensembles, 150 methanol cross-over, 289 platforming, 140 volcano shaped curves, 150 chemical anchoring, 143 volcano-shaped curves, 141... 

Sancho T, Lemus J, Urbiztondo M, Soler J, Pina MP. Zeolites and zeotype materials as efficient barriers for methanol cross-over in DMFCs. Micropor Mesopor Mater 200 115(1) 206-213. 

The electro-chemical reactions are assumed to take place in the fluid phase. The explicit introduction of the occupation numbers (0,-, S,- 0,- = 1) as variables is a natural description of the possible lack of catalytic sites and methanol cross over effects. Due to the use of expensive catalysts, electrochemical saturation effects may be reached by fuel cells in some... 

Fang Y, Miao R, Wang T, Wang X (2009) Suppresion of methanol cross-over in novel composite membranes for direct methanol fuel cells. Pure Appl Chem 81 2309-2316... 

Several kind of the reported S-PEEK based composite membranes show also to reduce the hydrophilic/hydrophobic separation and the hydrodynamic solvent transport (water and probably also methanol permeation). Therefore, polymers based on pure S-PEEK and its blends are not only interesting low-cost alternative membrane materials for PEMFC applications but they may also help to reduce the problems associated with high water and methanol cross-over in DMFCs. 

Moreover methanol cross-over through the polymer membrane reduces the efficiency of the Fuel Cell by decreasing the cell voltage as a result of a mixed potential at the oxygen cathode. Improved membranes with low crossover have to be developed. Besides, in order to increase the reaction rate of methanol oxidation (and of oxygen reduction), some works propose to operate the DMFC at higher temperatures with temperature-resistant membranes... 

This performance still requires platinum loadings that are almost ten times higher (around 3 to 5 mg/cm ) than needed in high-performance direct hydrogen PEFC. When feeding concentrated methanol directly, the cross-over can be as high as 30 to 50 percent compared with the amount oxidized electrochemically. If the concentration is reduced, the cross-over is reduced but so is the current density (due to reduced activity of the reactants). Obviously, the methanol crossed over is... 

On the other hand, in the absence of methanol-tolerant oxygen reduction catalysts, high oxygen partial pressures are needed for proper cathode operation in the presence of methanol cross-over. 

Removal of CO2 prodirct gas and methanol cross-over to the cathode where it can react and create a mixed potential, so reducing the efficiency of the cell and decreasing fuel utihsation. 

Research activity in this field has been quite important and is continuing. Thus, the effect of alloys deposited on a support by chemical vapor deposition (Seo et al., 2006b) and by dual ion-beam-assisted deposition (IBAD Gulla et al., 2006) has been studied. Another advantage of such platinum-alloy catalysts that was noted by many workers is their reduced sensitivity to methanol crossing over to the oxygen electrode in DMFCs and the associated improvement in the stability of the electrode s potential (Yuan et al., 2006 Baglio et al., 2007). 

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