Membrane degradation fluoride release rate

The open circuit voltage (OCV) condition is generally considered to be the most accelerating condition for chemical degradation of the membrane. Both fluoride release rate and lifetime at OCV are found to be negatively affected under drier... 

Increased temperatures have a strong correlation to some of the key degradation mechanisms. Membrane degradation due to chemical mechanisms as indicated by fluoride release rate has been shown to follow an Arrhenius relationship with temperature, with an increase of 1.8 times for a 10 °C rise. Figure 6.4 shows the relationship between temperature and the fluoride release rate as measured in the cathode and anode effluent at open-circuit voltage operation for an MEA containing DuPont Nafion 112 membrane. This trend is consistent with data reported in the Uterature, e.g. Madden et al. (2009). Sethuraman et al. (2008) showed the effect of temperature on lifetime at open-circuit voltage and found a lifetime of -500 h at 80 °C was dramatically decreased to -60 h at 100 °C and only -30 h at 120 °C (Sethuraman et al., 2008). 

Under steady-state operation, increased cell voltages have been associated with increased fluoride release rates, indicating increased membrane degradation, as shown in Fig. 6.16. 

The OH and OOH radicals generated by reactions 8.32 and 8.34 attack fluoride chains ofperfluoro-sulfonic membranes, leading to accelerated fluoride release rates and membrane degradation. 

For NPC MEA-I, the NPC manbrane was iQiplied. The thickness of the membrane was 40 (im. The conventional MEA failed within lOh of operation, releasing a high amount of fluoride ion. On the other hand, NPC MEA-I showed excellent stability over l,000h, and the fluoride ion release rate was less than 1% of that of the conventional MEA. This result indicates the exceptional chemical stabihty of the NPC MEA against degradation caused by the hydroxyl radical at 120 C and low humidity. 

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