Novel Dead-Ended Anode Design for Self-Regulating Humidification in an Air-Breathing H2-PEM Fuel Cell

Water management is a major engineering challenge for proton exchange membrane fuel cells (PEMFCs). Mass transport of hydrogen and/or oxygen is often hindered in flooded electrodes leading to a fuel cell current decrease and irreversible damages. Although optimal PEMFC operation is usually achieved with fully humidified flow-through anode and cathode streams, commercial and portable applications require simpler systems where the size, weight and complexity of the auxiliary systems are minimized. Therefore, dead-ended anode (DEA) operation is usually implemented for compact units. Feeding dry hydrogen with regulated pressure at the anode inlet presumably presents the advantage of requiring no excess hydrogen to be exhausted. In this way, only the stoichiometric amount would be consumed in the fuel cell. However, DEA operation mode usually results in a deterioration of cell performance if the accumulated gas-vapor mixture is not purged to remove liquid water and nitrogen from the anode flow field. Furthermore, this strategy may frustrate the main purpose of the dead-ended anode mode to increase hydrogen utilization while introducing parasitic loads to power the purge system.

A novel design of a PEMFC anode chamber has been implemented in an air-breathing fuel cell allowing for stable long-term operation under stoichiometric H₂ consumption with 100% fuel utilization. The anode chamber consists of a perforated current collector and gas distribution plate in contact with the membrane-electrode assembly. The opposite face of this plate is covered by a gas-tight polymer film selectively permeable to water. This film is fixed to the external face of the anode gas distributor by a tailor-made methacrylate plate and allows for water exchange between the anode internal chamber and the external environment. This gas-tight water permeable film provides a suitable way for excess water removal from the anode. The present study analyzes in detail the operation of this novel design. Impedance spectroscopy and polarization hysteresis curves have been used to explore the cell behavior under several environmental conditions of temperature and relative humidity controlled inside of a climate chamber (Fig. 1). These results are evaluated in comparison with those obtained for a similar cell assembled with a conventional anode operating under continuous flow and dead-ended anode under periodical purge. The stable long-term operation of the 2 W-cell with this novel design ensures 100% efficiency in fuel utilization.

Acknowledgements

The authors gratefully acknowledge financial support from the Spanish Ministry of Economy and Competitiveness under project ELECTROFILM (MAT2011-271 51) and Comunidad de Madrid under DIVERCEL program (S2009/ENE-1475).

Fig. 1. Photograph of the experimental set-up showing the air-breathing fuel cell in the climatic chamber where measurements have been performed. Inset photograph: detail of the anode configuration in the novel H₂-PEM fuel cell design.