Oxidatively stable borate-containing membranes for H2 purification for fuel cells

An oxidatively stable borate-containing membrane for H2 purification in fuel cell application was developed. The membrane comprised a quaternaryammonium hydroxide as the mobile carrier for the facilitated transport of CO2, a quaternaryammonium fluoride-containing polymer as the fixed-site catalyst for the reaction between CO2 and water molecules, a borate-based additive as another catalyst for the same reaction, and a crosslinked polyvinylalcohol-polysiloxane as the membrane matrix. The effect of borate-based additive on the membrane performance was investigated. The optimized membrane containing tetrafluoroboric acid achieved a CO2 permeance of 100 GPU and CO2/H2 selectivity >100. The oxidative stability of the membrane was demonstrated for at least 144 h at 120 °C 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. The water permeation through the membrane was reduced by adding the number of the substrate layers underneath the membrane. The water permeance was reduced almost proportionally as the number of the substrate was increased up to 3 pieces. The membrane was scaled up by using a continuous roll-to-roll machine to fabricate 14-inch. wide flat-sheet membranes with >1400 feet in total length. The scale-up membrane performed similarly compared to the lab-scale membranes. The membrane developed in this work has the potential for membrane processes that use air as the sweep gas including the H2 purification for fuel cell applications.