Reversal Tolerance Anode Catalyst Layer

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Alternatively, other additives (for example, graphite, other earbons, or titanium oxide powders) may be employed to reduee the porosity of either layer, thereby impeding the flow of water through the anode. It may be advantageous to employ a porosity-redueing additive mixture of polytetrafluoroethylene and aeetylene earbon blaek, in whieh the anode catalyst layer comprises between about 12% and 32% by weight of polytetrafluoroethylene and between about 0.03 and 0.2 mg cm of acetylene carbon black. 

Another approach for increasing the amount of water in the anode catalyst layer is to boost the water content in the catalyst layer components. A conventional catalyst layer, for instance, may contain up to 30% by weight amount of fully hydrated perfluorosulfonic ionomer. Thus, an increase in water content can be accomplished by increasing the amount of the water-containing ionomer used in the catalyst layer or by employing a different ionomer with higher water content. Alternatively, more hygroscopic materials may be incorporated into the anode catalyst layer to retain more water therein. 

In addition to enhancing the presence of water at the anode through modifications to the anode structure, a PEM fitel cell can be made more tolerant to voltage reversal by incorporating an additional catalyst, a water electrolysis (oxygen evolution reaction, OER) catalyst, at the anode to promote the electrolysis of water [14-16, 18]. In this way, more of the current forced through the cell may be consumed by the electrolysis of water than by the oxidation of the anode components. In a reversal-tolerant fuel cell, the anode comprises a first catalyst composition for evolving protons from the fuel and a second catalyst composition for water electrolysis. 

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