(111e) New Membranes for Hydrogen Purification and Proton Transport for Fuel Cells

This presentation covers two types of new membranes for fuel cells: (1) carbon dioxide-selective membranes for hydrogen purification and (2) proton-exchange membranes (PEMs). On hydrogen purification for fuel cells, the membranes have been synthesized by incorporating amino groups into polymer networks. These membranes are selective to carbon dioxide and hydrogen sulfide preferentially versus hydrogen since the acid gases permeate through the amine-containing membranes via the facilitated transport mechanism due to their reversible reactions with the amine. The membranes synthesized have shown high carbon dioxide and hydrogen sulfide permeabilities and selectivities vs. hydrogen up to 170oC. Using the membrane synthesized, we have obtained <10 ppm carbon monoxide in the hydrogen product in water gas shift membrane reactor experiments via carbon dioxide removal. The data have been in good agreement with modeling prediction. Since hydrogen sulfide has much higher reaction rate with the amine than carbon dioxide, hydrogen sulfide can permeate through the membrane much faster than carbon dioxide. Our initial experiments have shown a nearly complete removal of hydrogen sulfide from 50 ppm in the synthesis gas feed to about 10 ppb in the hydrogen product, which is good for fuel cell applications. For high temperature PEMs, we have synthesized sulfonated polyimide copolymers containing hydrophilic soft segments to increase the water retention of the membranes at high temperatures and low humidities. In fuel cell performance testing, the new membrane showed similar performance as Nafion® 112 at 70oC and 80% RH, but much better performance than Nafion® 112 at 120oC and 50% RH. Recently, we have also synthesized new sulfonated polybenzimidazole (SPBI)-based membranes. The membrane has exhibited a very high conductivity (> 0.1 S/cm) at high temperatures (> 120oC) and low humidities (even anhydrous). All these new PEMs should be much more cost-effective than Nafion®.