Oxygen in fuel cells

Cobalt porphyrins and phthalocyanines were used as precursors for preparation of carbon supported cobalt catalysts that displayed high activity in reduction of oxygen in fuel cells [9-12], These samples were prepared by deposition of cobalt phtalocyanine on active carbon following by heat treatment at 650-700°C in an inert atmosphere providing formation of Co-N structure deposited on active carbon. 

Fournier, J., G. Lalande, R. Cote, D. Guay, and J.R Dodelet (1997). Activation of various Fe-based precursors on carbon black and graphite supports to obtain catalysts for the reduction of oxygen in fuel cells. J. Electmchem. Soc 144, 218-226. 

Hydrogen combines with oxygen in fuel cells according to the thermochemical equation... 

Hudak NS, Gallaway JW, Barton SC (2009) Mediated biocatalytic cathodes operating on gas-phase air and oxygen in fuel cells. J Electrochem Soc 156 B9-B15... 

Self-Test 4.12B The reaction of H2 and 02 gases to produce liquid H20 is used in fuel cells on the space shuttles to provide electricity. What mass of water is produced in the reaction of 100.0 L of oxygen stored at 25°C and 1.00 atm ... 

Christenn C, Steinhilber G, Schulze M, Friedrich KA (2007) Physical and electrochemical characterization of catalysts for oxygen reduction in fuel cells. J Appl Electrochem 37 1463-1474... 

The situation changed drastically in the mid-1990s in view of the considerable advances made in the development of membrane hydrogen-oxygen (air) fuel cells, which could be put to good use for other types of fuel cells. At present, most work in methanol fuel cells utilizes the design and technical principles known from the membrane fuel cells. Both fuel-cell types use Pt-Ru catalyst at the anode and pure platinum catalyst at the cathode. The membranes are of the same type. 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

Solid alkaline membrane fuel cells (SAMECs) can be a good alternative to PEMFCs. The activation of the oxidation of alcohols and reduction of oxygen occurring in fuel cells is easier in alkaline media than in acid media [Wang et al., 2003 Yang, 2004]. Therefore, less Pt or even non-noble metals can be used owing to the improved electrode kinetics. Eor example, Ag/C catalytic powder can be used as an efficient cathode material [Demarconnay et al., 2004 Lamy et al., 2006]. It has also... 

Bittins-Cattaneo B, Wasmus S, Lopez-Mishima B, Vielstich W. 1993. Reduction of oxygen in an acidic methanol oxygen (air) fuel-cell— An onhne MS study. J Appl Electrochem 23 625 -630. 

The advantages of the presence of Ti02 in fuel cells or electrolyzers have been the subject of growing interest and studies have indicated that the semiconductor significantly influences both the alcohol oxidation [200-203] and the oxygen reduction [204—207] processes. 

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. 

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