Development of Bifunctional Electrodes for Closed-loop Fuel Cell Applications

Kurzfassung

Development of bifunctional Electrodes for closed-loop Fuel Cell Applications Altmann, S., Stuttgart/D, Kaz, T., Stuttgart/D, Friedrich, K. A., Stuttgart/D Sebastian Altmann, Institute of Technical Thermodynamics, German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany Unitized regenerative fuel cells (URFC) in combination with photovoltaic modules are attractive for space missions because they enable extended operation times and low weight. During the planetary day, electrical energy is stored which can be converted into electricity by the fuel cell during the night. All air-independent applications such as spacecraft or space stations would profit significantly from such energy conversion devices. A unitized regenerative fuel cell is a combined energy con¬version and storage system based on H2 and O2 which combines the advantages of fuel cells and secondary batteries. Substantial advantages of the specific energy density can be expected from the use of a URFC (400-1000 Wh/kg) in comparison to secondary batteries (220-250 Wh/kg for future advanced Li-polymer batteries). An important topic is the function of so-called bifunc¬tional oxygen electrodes which generally require the combination of favourable properties for both operating modes. In particular, different catalysts for oxygen reduction and for oxygen evolution are needed. This contribution investigates various electrode designs with Pt and IrO2 catalysts. For that purpose, the DLR dry spraying technique for the manufacturing of electrodes is applied for by mixing the two different catalysts together (Pt and IrO2) or applying the catalyst on different areas of electrode or even realising different layers with both catalysts. In summary, the performances observed in the bifunc¬tional electrodes are quite promising for a URFC. The different configurations open up a wide field for optimi¬zing cell performance, durability and system performance.