Low crossover

R Liu, G. Lu, and G. Y. Wang. Low crossover of methanol and water through thin membranes in direct methanol fuel cells. Journal of the Electrochemical Society 153 (2006) A543-A553. 

In principle, the low-side mosfet does not have any significant crossover loss because there is virtually no overlap between its V and I waveforms — it switches (changes state) only when the voltage across it is almost zero. Therefore, typically, the high-side mosfet is selected primarily on the basis of its high switching speed (low crossover loss), whereas the low-side mosfet is chosen primarily on the basis of its low drain-to-source on-resistance, Rds (low conduction loss). 

When the crossover of DMM was investigated in direct oxidation fuel cells, low crossover rates were observed at both 60 0 and 90 0, as shown in Fig 1.49. Surprisingly, the values were much lower at the higher temperature and sharply declined as a function of current density. This behavior, however, is consistent with the electrical performance in that the cell could not sustain... 

Kumar GG, Kim AR, Nahm KS, Yoo DJ (2011) High proton conductivity and low crossover of polyvinylidene fluoride-hexafluoro propylene-silica sulphuric acid cmnposite mcanbranes for direct methanol fuel cells. Curr Appl Phys 11 896-902... 

The relationship between the OCV and the H2 crossover current density is plotted in Figure 2.4. It can be seen that most of the OCV loss occurs in the extremely low crossover current density region (e.g., <10 mA cm ). 

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... 

TABLE 29.2 Targeted Membrane Properties for High-Temperature PEMFCs and Low Crossover DMECs... 

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