Problems to Be Solved in Future DMFCs

In contrast to PEMFCs, and despite the large volume of research performed, DMFC fuel cells are still not in commercial production or in wide practical use. As we have seen from what has been reported earlier in the chapter, the true performance indicators of these fuel cells when used for different needs are difticult to assess from the experience gathered in tests of individual samples performed under a variety of conditions. For such an assessment one would need statistical data obtained from tests on a sufficiently large number of cells of any single type and accounting for all cell parameters and test conditions. 

So far, another potential field of application of DMFCs, as power sources for electric vehicles, is too remote. A large amount of research and engineering still has to be done to master this application, primarily work aimed at improving the technical and economic parameters of these cells. Work is needed more particularly to solve the problems described below. 

The production volume of DMFCs and long-term testing results are still too small for any reliable estimate of the lifetime of methanol fuel cells. Workers therefore look primarily at all the major reasons giving rise to the gradual performance drop and/or premature failure of these cells. The reasons considered in the corresponding section dealing with cells of the PEMFC type must be supplemented in the case of methanol fuel cells by two more, described below. 

At the working potential of an electrode, the Pt-Ru catalyst is rather stable, but in long runs and following the slightest shift of potential in the positive direction 

The operating efficiency of DMFCs is lowered considerably by methanol crossover. This effect leads to unproductive methanol consumption and to a marked decrease in working voltage caused by the action of methanol on the potential of the oxygen electrode. So far, only two possibilities are known to lessen or eliminate this effect completely  

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