The Electro-Oxidation of H2, CO in a Model PEM Fuel Cell: Oscillations, Chaos, Pulses

H₂, CO electro-oxidation in a model PEM Fuel Cell (PEMFC) is investigated at 37°C with the help of distributed current measurements. The main purpose of the experiments is to verify the formation of spatio-temporal patterns that have been predicted for a PEMFC with straight channels and a H₂evolving cathode. For galvanostatic operation and a high feed flow rate well expressed globally coupled oscillations are found. For decreasing feed flow rate a period doubling bifurcation cascade appears. Potentiostatic control provokes the breakage of the strict phase relation between adjacent oscillators and the appearance of pulses as well as turbulence is seen. The turbulence is enhanced if an oxygen reducing cathode is introduced instead of a hydrogen evolving cathode. The findings are compared to existing predictions. The study of the patterns is of interest for PEMFC engineers as they directly determine the CO tolerance behavior of the PEMFC.

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Figure caption: Upper row - The segmented anode flow field with 80 segments per channel (channel length: 14.4 cm). The both inner channels are used for current distribution measurement, while the outer channels serve for homogenization. Each segment consists of two sub-segments that face across the channel. Lower row - As seen in the spatio-temporal plots of the measured current signal (corrected for its temporal space dependent average), the system behaves chaotically after a step into the voltage regime at which CO can be oxidized. In this potentiostatic experiment, the cathode was fed with air.