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1 1999

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Budowa i właściwości ogniw paliwowych z membranami protonowymiennymi

Tendaj Bogusław, Marczewska-Boczkowska Krystyna

Wiadomości Chemiczne

1999

[Z] 53, 7-8

529-548

The structure and features of different systems of fuel cell depend on the nature of used electrolyte. The main fuel cells are as follows: alkaline fuel cells (AFCs), phosphoric acid fuel cells (PAFCs), solid oxide fuel cells (SOFCs) and proton exchange membrane fuel cells (PEMFCs ). (...) In PEMFC the anode and cathode reactions occur on the platinum or platinum alloy electrocatalyst surfaces; the electrocatalyst is usually supported by carbon. Electrode surfaces contain 1 mg Pt per cm2 or less. Layers (thickness 180 um or less) of perfluorinated sulphonic acid ionomers (e.g. Nafion) are used as electrolyte membranes. The overpotential of the pure hydrogen supplied PEMFC' a anode is low. The contamination of hydrogen by CO restricts the performance of the anode, because CO acts as an anode catalyst poison. Methanol-fed anodes operate at overpotentials as high as 0,3-0,4 V. Oxygen reduction proceeds with rapid fall-off cathode potential. As current density is increasing, formed water disturbs the diffusion of oxygen to the catalyst surfaces. The specific conductivity of the ionomer increases proportionally to the content of absorbed water. The desired water content in membranes of fuel cells is usually supported due to humidification of reactant gases. Reactant gases do not require external humidification, if very thin Nafion membrane (thickness 50 um) contains inside highly dispersed platinum. Pt crystallites catalyse the recombination of the crossover H2 with O2. The generated water humidifies the PEMFC's membrane adequately. (...)