Methanol-depleted domain

Furthermore, surprisingly, very few works have been reported on the study of materials degradation phenomena in DAFCs. For instance, a model for carbon and Ru corrosion in a DMFC anode under strong methanol depletion has been very recently proposed by Kulikovsky [195]. The model is based on the mathematical description of the current conservation in the membrane. In the methanol-depleted domain, methanol oxidation reaction is substituted by the carbon oxidation (corrosion). This is supposed to dramatically lowering the membrane potential and to create an environment for electrochemical oxidation of Ru. His calculations show that 50-100 mV loss in the cell potential manifests quite a significant (above 50 %) methanol-depleted fraction of the cell active area (Fig. 8.21). 

Fig. 8.21 Left) schematic of a DMFC with strong methanol depletion in the second half of the channel (the normalized methanol concentration, membrane potential and carbon phase potentials are shown in the bottom) (right) calculated cell potential and carbon and Ru overpotentials as function of the fraction of methanol-depleted domain (Source [195] reproduced with permission...

FIGURE 5.37 (a) Overpotentials along the channel. For all the curves, = 0.01 and = 0.5168 V. (b) Cell potential and overpotentials for carbon and Ru corrosion versus the fraction of methanol-depleted domain. Note the dramatic drop of Eceii and growth of overpotentials when more than 80% of the channel length is methanol-depleted. The mean cell current density is 100 mA cm . ... 

In this section, we show that electrochemical Ru corrosion is induced in domains with strong methanol depletion. Such domains may arise in cell/stack environment due to nonuniformity of methanol supply over the cell surface. In these domains, methanol oxidation is substituted by the carbon corrosion reaction. This strongly lowers the membrane phase potential, thereby activating Ru electrochemical dissolution. 

In the MD-domain, owing to methanol depletion, the negative membrane phase potential increases by the absolute value (Figure 5.35). This dramatically (by many... 

Figure 5.37b shows the dependence of the cell potential and overpotentials for carbon and Ru corrosion on the fraction of the MD-domain. In this figure, the mean current in the cell is fixed at 100 mA cm . As can be seen, as long as the fraction of MD-domain is below 70%, the variation of the cell potential and overpotentials is not large. Thus, a very substantial methanol-depleted area manifests itself as a... 

He has published a series of seminal papers on the mechanisms of fuel cell degradation and possible scenarios of catastrophic worsening of the fuel cell performance, having described, for example, effects such as the degradation wave along the air channel in PEFCs, and Ru corrosion due to methanol depletion in DMFCs. He contributed to the explanation of exotic direct and reversed performance domains in PFFCs under the lack of hydrogen at the anode (in the reverse domain, carbon... 

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