Fuel cells oxygen radical reactions

Ionomer membranes are used in fuel cells in order to separate the anode and cathode compartment and to allow the transport of protons from the anode to the cathode. The typical membrane is Nation , which consists of a perfluorinated backbone and side chains terminated by sulfonic groups. In the oxidizing environment of fuel cells, Nation , as well as other membranes, is attacked by reactive oxygen radicals, which reduce the membrane stability. Direct ESR was used recently in our laboratory to detect and identify oxygen radicals as well as radical intermediates formed in perfluorinated membranes upon exposure to oxygen radicals [73,74]. The three methods used to produce oxygen radicals in the laboratory and the corresponding main reactions are shown below. 

Figure 11.1. Schematic of photocatalytic fuel cell with single compartment (1) single compartment photo-eleetrochemical cell (2) photocatalyst thin film (3) anode substrate (4) aqueous electrolyte (5) cathode support (6) cathode catalyst (7) oxidization reaction of OH by holes in basic media (8) oxidization of organic matter by OH radicals (9) oxidization reaction of organic matter in neutral media (10) proton reduction to produce hydrogen in anaerobic condition (11) oxygen reduction to generate water in aerobic condition (12) light irradiation (13) electric circuit (14) loading (15) quartz window.

Regarding the corrosion mechanism of the carbon support, Hubner and Roduner (1999) reported on the HO radical initiated degradation reactions of sulfonated aromatics for fuel cell membrane. They reported that HO radical addition on the aromatic ring occurs, and is followed by the addition of an oxygen molecule. This will eventually lead to a bond-breaking reaction. Figure 13 indicates the degradation reactions of aromatics. From these results, the carbon support may be similarly decomposed to CO by HO and O. ... 

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