ECS Research Award of the Energy Technology Division Membrane Electrode Assembly Fabrication from Membranes of the DOE High Temperature Membrane Working Group

The Florida Solar Energy Center (FSEC) has led the U.S. Department of Energy (DOE) High Temperature Membrane Working Group (HTMWG) since 2006. The HTMWG investigates membrane performance at elevated temperature/low relative humidity conditions. For the final three years of the project, FSEC has worked with six teams to develop membrane electrode assembly (MEA) fabrication methods for their respective membranes. This presentation details the challenges associated with MEA fabrication of various membrane types, along with the performance results from several HTMWG membranes.

The MEA fabrication technique utilized by FSEC is to suspend the membrane vertically in front of a heated plate, and then spray catalyst-ink slurry onto the membrane. Following electrode application, the CCM is hot pressed to ensure good interfacial contact. Through these procedures, several challenges were identified. First, during electrode application, the membrane can swell due to the high solvent content in the ink and shrink due to the heat from the plate. These combined effects were shown to cause significant internal stresses in a hydrocarbon-based membrane with Teflon support. A second challenge was the ductility (either too high or low) of the membrane, leading to poor mechanical stability. Too high ductility rendered spraying ineffective, while too low ductility led to crack formation, either during spraying or hot pressing. An example is given of a membrane showing a series of pressure-induced cracks after hot pressing. A third challenge relates to the compatibility of the ionomer in the electrode with that in the membrane. For the majority of the teams, the same ionomer was utilized in the electrode, to provide consistency across the tests. However, due to differences in the membrane, the cell performance changed, even though the electrodes were the same. This suggests a performance limiting mechanism is operating at the membrane/catalyst interface.

Notwithstanding these challenges, several cells showed significant progress towards DOE performance and durability targets, including a hydrocarbon-based membrane. One team was able to develop a membrane that exhibited several times-lower fluoride release than NRE 211. Another team’s fuel cell performance exceeded DOE targets, with further optimization possible. These results will be presented.