The design solves safety as well as reliability issues.
A gravity-independent PEM (proton exchange membrane) fuel cell stack has been developed that will operate at high-pressure H2 and O2 conditions with the requirement for relatively modest H2 and O2 gas circulation. Until now, in order to get higher efficiency, excess reactant gas flow was required to prevent water slug formation in gas channels, thus reducing fuel cell performance. In addition, this excess gas flow is typically supported by mechanical pumps and/or a high-pressure ejector system. All of these in a closed space environment contributed to potential safety as well as reliability issues due to the potential failure of mechanical pumps and ejectors.
ElectroChem’s Integrated Flow Field (IFF) design for a PEM fuel cell solves all these issues. It is based on a multilayered integrated flow-field structure that forms a porous structure with distinct wetting properties. It results in increased exposure of the catalyst to the reactant gas, resulting in higher cell voltage. This results in higher efficiency than the conventional plate designs. In addition, the entire flow field makes full contact between the porous structure and the electrodes, thus avoiding damage to membrane electrode assemblies (MEAs) at elevated operating pressure conditions. The same design also provides transport of product water back to the entire flow field for humidification and greater performance.
In the IFF cell there is no need for excess reactant gas, since the design is based on a non-flow-through operation. The IFF fuel cell allows the operation at 100% reactant gas utilization. The design also enables passive removal of water at various cell orientations.
The figure demonstrates a complete passive water removal at non-flow-through operation condition and a response to 3–1 power ratio demand. It is an IFF fuel cell stack with 4 cells of 200 cm2 electrode surface area.
The results of IFF fuel cell configuration have demonstrated 100% reactant gas utilization, reduced cost and weight penalties, and system simplification with higher reliability.
This IFF design was developed for use in a PEM fuel cell power plant for space application, but it could also be used for high-altitude balloon flight and air-independent applications (e.g., manned and unmanned underwater vehicles). When the IFF design is used in a PEM electrolyzer, it functions as an internal phase separator, which enhances overall system efficiency.
This work was done by Michael Pien of ElectroChem, Inc. for Johnson Space Center.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Michael S. Pien, Ph.D.
Vice-President of Research and Development
400 W Cummings Park # 5600
Woburn, MA 01801
Phone No.: (781) 938-5300