Composite Membranes for Hydrogen Separation Chendong Zuo*, T. H. Lee, S.E. Dorris, U. Balachandran, and Meilin Liu* Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439 * School of Materials Science and Engineering, Georgia Institute of Technology Atlanta, GA 30332 As the demand for hydrogen increases, a practical way of separating pure hydrogen from a gas mixture (e.g., synthesis gas) is becoming more important. Among the various separation techniques, dense membranes of mixed ionic-electronic conductors (MIECs) offer a simple way for obtaining hydrogen from gas streams at high temperatures. Because an MIEC membrane will transport both protons and electronic defects, hydrogen separation can be achieved without electrodes and external circuitry. Although various perovskite-type oxides have been reported to have high proton conductivity in a hydrogen- containing atmosphere, the chemical stability of these materials under practical conditions is still a concern.[1] For example, BaCeO 3 -based proton conductors display the highest conductivity among this class of materials; however, it is unstable in a CO 2 -containing atmosphere.[2] In contrast, BaZrO 3 -based proton conductors have excellent stability but relatively low proton conductivity.[3] These results suggest that the solid solution between cerate and zirconate may offer a good compromise between proton conductivity and chemical stability.[4,5] Compounds in the Ba(Ce x Zr 0.8-x )Y 0.2 O 3-α (0.0≤x≤0.8) system were synthesized by solid-state reaction from stoichiometric mixtures. X-ray diffraction analysis showed that a solid solution was formed over the whole range of x values. As shown in Figure 1, the total conductivities of sintered disks, as determined using impedance spectroscopy, decreased with increasing zirconium content in wet 4% H 2 /helium gas. 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 0.01 Conductivity (S/cm) 1000/T (K -1 ) Ba(Ce 0.7 Zr 0.1 )Y 0.2 O 3 in wet 4% H 2 Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 in wet 4% H 2 Ba(Ce 0.5 Zr 0.3 )Y 0.2 O 3 in wet 4% H 2 Ba(Ce 0.4 Zr 0.4 )Y 0.2 O 3 in wet 4% H 2 Figure 1. Total conductivities of Ba(Ce x Zr 0.8-x )Y 0.2 O 3 in wet 4% H 2 as function of temperature (the humidity was introduced by passing the gas through a water bubbler at room temperature). Because the electronic conductivities of Ba(Ce x Zr 0.8- x )Y 0.2 O 3-α are relatively low, composite membranes consisting of Ni and Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 have been developed for hydrogen separation. As shown in Figure 2, hydrogen flux increased with temperature from 600 to 900 o C. The highest flux, 0.09 cm 3 (STP)/min-cm 2 at 900 o C, was obtained for a membrane of 0.46-mm-thick when wet 4% H 2 was used as the feed gas. Preliminary measurements of membrane stability in atmospheres containing 10% CO 2 showed that this composite (cermet) membrane is stable up to 50 hours, as shown in Figure 3. 600 650 700 750 800 850 900 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 Flux (cm 3 /min-cm 2 ) Temperature ( o C) Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 /Ni, wet 4% H 2 Figure 2. Hydrogen flux through a composite membrane consisting of Ni and Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 ) (0.46 mm thick) using wet 4% H 2 (balance He) as feed gas. 0 10 20 30 40 50 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Flux (cm 3 /min-cm 2 ) Time (h) Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 /Ni, wet 10% CO 2 Figure 3. Time dependence of hydrogen flux for composite membrane consisting of Ba(Ce 0.6 Zr 0.2 )Y 0.2 O 3 and Ni (0.46 mm thick) in wet 10% CO 2 (balance H 2 ) at 900 o C. Acknowledgements This work was supported by U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory's Gasification Technologies Program, under Contract W-31-109-Eng-38. Reference 1. K.D.Kreuer, Solid State Ionics 97, (1997) 1-15. 2. S. V. Bhide and A. V. Virkar, J. Electrochem. Soc., 146, (1999) 4386-4392. 3. K.D.Kreuer; Solid State Ionics 125, (1999) 285-302. 4. K. Katahira, Y. Kohchi, T. Shimura, H. Iwahara, Solid State Ionics 138, (2000) 91-98. 5. K. H. Ryu, S. M. Haile, Solid State Ionics 125, (1999) 355-367. Abs. 1053, 204th Meeting, © 2003 The Electrochemical Society, Inc. View publication stats View publication stats