The performance degradation of a passive direct formic acid fuel cell and its improvement by a hydrophobic filter

A direct formic acid fuel cell, DFAFC, can generate a higher power density compared with other direct liquid fuel cells, however, its performance decreases with time. Especially in a passive operation, the performance degradation was caused not only by catalyst poisoning at the anode but also serious flooding at the cathode due to high current operation. In this study, the effect of the flooding on the power generation characteristics of the DFAFC operated with three different air supplying modes, i.e., air breathing, air flowing and oxygen flowing, was investigated by comparing the cathode over-potential before and after 2 h operation at a constant voltage. Moreover, in order to inhibit the flooding, a hydrophobic filter, HF, was introduced at the surface of the cathode, and the effect of the HF on the flooding was investigated. It was found that the water crossover from the anode to the cathode significantly increased by the electroosmotic effect at a high current density, and it caused serious flooding when DFAFC was operated without HF. On the other hand, by inserting the HF, the performance degradation could be inhibited by reducing the flooding at the cathode surface, and the cathode over potentials could be improved. The HF is necessary for higher power generation and a stable operation of the passive DFAFC.

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► The effect of the flooding on the power generation characteristics of the DFAFC was investigated.
► The cathode over-potential significantly increased due to the flooding.
► To inhibit the flooding, a hydrophobic filter was inserted to the cathode surface.
► The cathode over-potential significantly decreased by inserting hydrophobic filter.