(28f) Oxidatively Stable Borate-Containing Membranes for H2 Purification for Fuel Cells

Borate-containing membrane was developed for H₂ purification for fuel cell application. The oxidatively stable membrane contained quaternaryammonium hydroxide as a mobile carrier for the facilitated transport of CO₂, quaternaryammonium fluoride-containing polymer as a fixed-site catalyst for the reaction between CO₂ and water molecules, a borate-based additive as another catalyst for the same reaction in a membrane matrix made of crosslinked polyvinylalcohol-polysiloxane. The optimized membrane with a borate-based additive of tetrafluoroboric acid reached a CO₂ permeance of 100 GPU and CO₂/H₂ selectivity >100. The membrane demonstrated oxidative stability at 120°C for at least 144 hours with humid air as the sweep gas. As the membrane thickness was reduced from 15 µm to 10 µm, a significant drop in CO₂/H₂ selectivity was observed due to the increase of the H₂ permeance; while the CO₂ permeance was not significantly improved. Addition of the number of the substrate layers underneath the membrane resulted in a reduction of water permeation through the membrane. As the number of the substrate was increased up to 3 pieces, the water permeance was reduced almost proportionally. A continuous roll-to-roll membrane fabrication machine was used to scale up the fabrication of a 14-inch wide flat-sheet membranes with > 1400 feet in total length. Compared to the lab-scale membranes, a similar performance was obtained from the scale-up membrane. The membrane developed in this work can be used in membrane processes with air as the sweep gas, such as the H₂ purification for fuel cell applications.