PreparationofGasDiffusion ElectrodeswithSilverCatalysts forAlkalineFuelCells** E. Gülzow 1 , N. Wagner 1 *, and M. Schulze 1 1 Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Technische Thermodynamik, Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany Received 30.10.02 , in revised form 03.02.03, accepted 07.04.03 1 Introduction Low temperature fuel cells like Polymer Electrolyte Fuel Cells (PEFC) and Alkaline Fuel Cells (AFC) represent impor- tant future elements in pollution free energy supply for mobile applications. AFC are an interesting alternative to PEFC. Alkaline fuel cells have the potential to become impor- tant in mobile energy systems, in contrast to other low tem- perature fuel cells, as the alkaline type requires neither expensive noble metal catalysts nor an expensive polymer electrolyte. The advantages of AFC's are not limited to the cheaper components, the AFC also has advantages in the sys- tem technique, because no process gas humidification is needed for AFC operation, which is a significant problem of the present PEFCs, and since the electrolyte is a liquid the temperature management of AFC can be performed with the electrolyte. Some will see a liquid electrolyte as disadvanta- geous, because an AFC needs a circuit for the electrolyte. A similar circuit for liquids is also needed for high efficiency PEFC systems for temperature management, the electrolyte circuit in AFC may be more expensive because of the higher corrosivity of the electrolyte compared with water or other cooling media in the PEFC. The alkaline solution in the AFC must be reconcentrated during long term operation, but this is very simple in comparison to the water management in a PEFC. The most important operational issue for AFCs (CO 2 , life time, costs, etc.) are treated by Gülzow [1] and in a recent review by McLean et al. [2]. Electrochemical investigations on PTFE-bonded gas diffu- sion silver electrodes in alkaline solutions arise for funda- mental and practical interest [3, 4]. Oxygen reduction electro- catalysis is of special importance not only in fuel cells [5] but also in metal-air batteries and industrial chlorine-alkali elec- trolysis [6 ± 8]. The kinetics of oxygen reduction on silver has been investigated by several authors [9 ± 13] with different steady state and potential step techniques on smooth elec- trodes. The reduction process has been found to follow two reaction pathways: the direct 4e ± path and the 2e ± path (gen- erally referred to as the sequential path) involving the forma- tion of peroxide as an intermediate product. The objective of this work is to describe the production and characterization of PTFE-bonded silver gas diffusion ± [ * ] Corresponding author, norbert.wagner@dlr.de [ ** ] ThepaperhasbeenpresentedatSymposium8 oftheInternationalSocietyofElectrochemistry inDüsseldorf,Germany2002 Abstract In alkaline fuel cells (AFC) silver can be used as the cathode catalyst in gas diffusion electrodes. To prepare the gas diffu- sion electrodes, the metal catalyst was mixed with polytetra- flourethylene (PTFE), as the organic binder, in a knife mill and rolled onto a metal web in a calender. The electrodes are manufactured as an endless tape with a thickness of ap- prox. 0.4 mm and widths of up to 20 cm. Raney-silver, car- bon supported silver, or silver deposited as a closed film on PTFE are used as the catalyst. In the gas diffusion electrode preparation process the silver catalyst can be used in this oxidized form. Before using the gas diffusion silver cathodes in the alkaline fuel cell the catalyst will be reduced to the metallic form. Keywords: Alkaline Fuel Cell (AFC), Gas Diffusion Elec- trode (GDE), Ag Catalyst, Oxygen Reduction Reaction (ORR), X-ray Photoelectron Spectroscopy (XPS), REM FUEL CELLS 2003, 3, No. 1±2  2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 67 ORIGINAL RESEARCH PAPER DOI: 10.1002/fuce.200320221