Development of Stable Precious Metal-Free Cathodes in Alkaline Fuel Cells

Abstract

The Alkaline Fuel Cells (AFC) have been well developed in the 1960s for on-board power supply for Apollo missions to the moon. Later, in 1990s, the Polymer Electrolyte Membrane Fuel Cell (PEMFC) replaced the AFC due to their advantages such as a lighter and more compact system attributed to solid membranes as electrolyte. However, AFC systems have now reached new attention due to the necessity of using inexpensive non-precious metal catalysts, which is one of the greatest advantages of alkaline media. In this work, precious metal-free oxide catalysts are investigated regarding their performance and long-term stability. Electrodes containing these precious metal-free catalysts are designed, manufactured and in-situ characterized in AFC half-cell tests and single-cell measurements. The main focus lies on increasing the long-term stability of cathodes in alkaline media. Cathodes are manufactured and tested in half-cells for 10,000 h. Tests are performed at different operating conditions: gases (O2, synthetic air, and ambient air), gas flow and temperature are varied. The influence of the operating conditions on the degradation rate and the stability of the cathodes are evaluated accordingly. Furthermore, single cell tests are conducted with non-noble metal anodes, thereby achieving a precious metal-free AFC. Especially the activation processes are investigated. In order to preserve cathode performance, the anode activation is performed separately. Afterwards, the two electrodes are assembled in a custom-made test cell and characterized in fuel cell operation. For comparison of the performance of this precious metal-free AFC, single cells with platinum based catalysts are operated in parallel test cells. The results of the test series will be presented at the meeting.