Oxygen reduction, in PEMFCs

Gloaguen F, Convert P, Gamhurzev S, Velev OA, Srinivasan S. 1998. An evaluation of the macro-homogeneous and agglomerate model for oxygen reduction in PEMFCs. 

Bouwman, P.J. et al., Platinum-iron phosphate electrocatalysts for oxygen reduction in PEMFCs, J. Electrochem. Soc., 151, A1989, 2004. 

Proietti E, Rugger S, Dodelet J-P (2008) Fe-based electrocatalysts for oxygen reduction in PEMFCs using ball-milled graphite powder as a carbon support. J Electrochem Soc 155 B340-B348... 

Salgado JRC, Antolini E, Gonzalez ER. Pt-Co/C electrocatalysts for oxygen reduction in H2/O2 PEMFCs synthesized by borohydride J Electrochem Soc 2004 151 A2143-9. 

At present there are no alternative cathode electrocatalysts to platinum. Some platinum alloy electrocatalysts prepared on traditional carbon black supports offer a 25 mV performance gain compared with Pt electrocatalysts. However, only the more stable Pt-based metal alloys, such as PtCr, PtZr, or PtTi, can be used in PEMFC, due to dissolution of the base metal by the perfluorinated sulfonic acid in the electrocatalyst layer and membrane [26]. The focus of the continued search for the elusive electrocatalyst for oxygen reduction in acid environment should be on development of materials with required stability and greater activity than Pt. 

Neyerlin KC, Gu W, Jome J, Gasteiger HA. 2006. Determination of catalyst unique parameters for the oxygen reduction reaction in a PEMFC. J Electrochem Soc 153 A1955-A1963. 

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... 

Au has recently received less attention than Pt as a supported catalyst because of its lower impact in PEMFC energy conversion technology, since the ORR is dominated by a two-electron reduction process, at what is a high overpotential, in acidic media. Nevertheless, it is an important oxygen reduction catalyst in alkaline media, and, in contrast to Pt, is oxide-free in the potential range where oxygen reduction occurs. 

Gebeyehu, N., et ah, Ultrathin Ti02-coated MWCNTs with excellent conductivity andsmsi nature as pt catalyst support for oxygen reduction reaction in PEMFCs. Journal of Materials Chemistry, 2012. 

In an acidic medium, a PEMFC fed with ethanol allows power densities up to 60 mW cm to be reached at high temperatures (80-120 °C), but this needs platinum-based catalysts, which may prevent wider applications for portable electronic devices. On the other hand, in an alkaline medium, the activity of non-noble catalysts for ethanol or ethylene glycol oxidation and oxygen reduction is sufficient to reach power densities of the order of 20 mW cm at room temperature. This opens up the hope of developing SAMFCs that are particularly efficient for large-scale portable applications. 

Anodic hydrogen oxidation and even more cathodic oxygen reduction is kinetically hampered at low temperature, so that anodic hydrogen oxidation in AFCs, PEMFCs, and PAFCs demands catalysts of highest activity, that is, platinum metals and platinum in particular. Also Raney nickel is used in... 

Electrocatalysts One of the positive features of the supported electrocatalyst is that stable particle sizes in PAFCs and PEMFCs of the order of 2-3 nm can be achieved. These particles are in contact with the electrolyte, and since mass transport of the reactants occurs by spherical diffusion of low concentrations of the fuel-cell reactants (hydrogen and oxygen) through the electrolyte to the ultrafine electrocatalyst particles, the problems connected with diffusional limiting currents are minimized. There has to be good contact between the electrocatalyst particles and the carbon support to minimize ohmic losses and between the supported electrocatalysts and the electrolyte for the proton transport to the electrocatalyst particles and for the subsequent oxygen reduction reaction. This electrolyte network, in contact with the supported electrocatalyst in the active layer of the electrodes, has to be continuous up to the interface of the active layer with the electrolyte layer to minimize ohmic losses. 

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