Innovative Production Technique For Pefc Electrodes

DLR, Institut für Technische Thermodynamik Pfaffenwaldring 38-40 D-70569 Stuttgart, Germany Tel.+49 711 6862 324 Fax. +49 711 6862 747 e-mail [email protected]

Abstract

Fuel cells are high efficient and low polluting energy conversation devices. Using hydrogen as a fuel gas they are applicable to solve environmental problems e.g. CO2 impact on the climate. Thus international research efforts have been increased in recent years. Low temperature fuel cells e.g. the PEFC are specially applicable for future transportation and stationary energy supply systems. Application and economics success of his technology is obstructed by the high investment costs with respect to conventional energy conversion devices.

The intent of our activities is the improvement of electrodes and membrane-electrode-assemblies as used in PEFC. Commercial and technical aspects of electrode manufacturing have been considered in early stages of the development of the production procedure.

Two different techniques are developed at DLR. The first is a rolling procedure as used for production for batteries and alkaline fuel cells which has been modified and adapted to the specific demand of PEFC electrodes.- [1] The second technique is a new printing process to produce ultra thin layers of catalyst directly on the electrolyte.

In this paper we will show the first results of the first electrode technique which have been tested in fuel cells and a short description of the second very new method.

Production of electrodes

The technique to produce low temperature fuel cell electrodes by reactive mixing of the components and rolling an endless electrode strip has been developed at the VARTA AG [2,3]

together with the University of Kassel. The principle technique is shown in Fig. 1. The components of the catalytic layer (e.g. Vulcan XC-72 with different Pt/C loadings supplied by E-Tek and PTFE powder Hostaflon TF2053 supplied by Hoechst) are mixed in a fast running knife mill for a short time and water cooling. This mixture is then applied under two different conditions onto a support which consists of an in house hydrophobed carbon cloth (e.g. E-Tek Cloth Type „A"), the powder mixture is either supplied vertical via line fummel under gravity influence (Fig.l) or it is supplied horizontally by sieving it through a silver mesh onto the support just before it enters the calander (Fig.2). The carbon cloth has been made hydrophobic by appling carbon (Vulcan XC-72) / PTFE suspension (Hoechst Hostaflon TF 5032) to both sides of the carbon cloth. This treatment has shown the best result yet concerning the compromise

Fig 1. powder supply under gravity influence

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