Hydrogen separation from syngas at high temperatures (>=600°C) is one of the most important H2-producing technologies and it has attracted wide interest in the last decades. Mixed ionic-electronic conductor (MIEC) ceramic materials have received considerable attention due to their potential application as separation membranes in these processes [1]. In MIEC membranes, the separation and transport of H2 occurs electrochemically in the form of protons and electrons. In a non-galvanic mode, the membrane must have both electronic and proton conductivities [2]. Y-doped BaCe1-xZrxO3-? (BCZY) perovskite oxides are promising candidates for the development of such membranes because they combine the high proton conductivity of barium cerates with the chemical stability of barium zirconates in CO2-containing atmospheres, such as syn gas conditions [3]. However, the electronic conductivity exhibited by these materials may be not sufficient to work as H2 separation membranes. The performances of BCZY in this field can be improved by adding a second electronic conductor phase [2]. In the present work, symmetric dense cer-cer membranes for hydrogen separation based on BaCe0.65Zr0.20Y0.15O3-? (BCZ20Y15) and Ce0.85M0.15O2-? (M = Y and Gd, hereafter YDC15 and GDC15) were prepared. After checking the chemical compatibility between precursors, the optimal sintering conditions were individuated, obtaining dense and crack free samples with homogeneous grain distribution. The influence of different composites on electrical properties and H2 permeability performances was thoroughly studied. In particular, BCZ20Y15-YDC15 and BCZ20Y15-GDC15 membranes exhibited an improved hydrogen flow when the sweep side of the membrane was hydrated. In these conditions, the hydrogen flux of BCZ20Y15-GDC15 in the 50:50 volume ratio reached values of 0.27 mL·min-1·cm-2 at 755°C, currently one of the highest H2 flows obtained for bulk mixed protonic-electronic membranes. The stability of these materials under CO2-containing atmosphere was evaluated by thermogravimetry analyses. These composite systems showed a very good chemical stability under CO2-rich atmosphere, supporting their use for hydrogen separation membranes in practical applications. The influence of the different phenomena associated to the permeability mechanism, namely protonic transport, electronic conduction and water splitting, are still to be clarified and should be the beginning for a valuable discussion. [1] T. Norby and R. Haugsrud Dense ceramic mebranes for hydrogen separation in: A. F. Sammels and M.V. Mundschau Nonporous inorganic membranes for chemical processing Wiley-VCH Verlag GmbH & Co. KGaA (2006) 1-48. [2] J.W. Phair, S.P.S. Badwal Ionics 12 (2006) 103-115. [3] S. Barison, M. Battagliarin, T. Cavallin, L. Doubova, M. Fabrizio, C. Mortalò, S. Boldrini, L. Malavasi, R. Gerbasi Journal of Materials Chemistry 18 (2008) 5120-5128.
High hydrogen permeability and CO2-resistance of cer-cer composite membranes based on BaCe0.65Zr0.20Y0.15O3-delta and Y- or Gd-doped CeO2.
Boldrini S;Barison S;Fabrizio M
2015
Abstract
Hydrogen separation from syngas at high temperatures (>=600°C) is one of the most important H2-producing technologies and it has attracted wide interest in the last decades. Mixed ionic-electronic conductor (MIEC) ceramic materials have received considerable attention due to their potential application as separation membranes in these processes [1]. In MIEC membranes, the separation and transport of H2 occurs electrochemically in the form of protons and electrons. In a non-galvanic mode, the membrane must have both electronic and proton conductivities [2]. Y-doped BaCe1-xZrxO3-? (BCZY) perovskite oxides are promising candidates for the development of such membranes because they combine the high proton conductivity of barium cerates with the chemical stability of barium zirconates in CO2-containing atmospheres, such as syn gas conditions [3]. However, the electronic conductivity exhibited by these materials may be not sufficient to work as H2 separation membranes. The performances of BCZY in this field can be improved by adding a second electronic conductor phase [2]. In the present work, symmetric dense cer-cer membranes for hydrogen separation based on BaCe0.65Zr0.20Y0.15O3-? (BCZ20Y15) and Ce0.85M0.15O2-? (M = Y and Gd, hereafter YDC15 and GDC15) were prepared. After checking the chemical compatibility between precursors, the optimal sintering conditions were individuated, obtaining dense and crack free samples with homogeneous grain distribution. The influence of different composites on electrical properties and H2 permeability performances was thoroughly studied. In particular, BCZ20Y15-YDC15 and BCZ20Y15-GDC15 membranes exhibited an improved hydrogen flow when the sweep side of the membrane was hydrated. In these conditions, the hydrogen flux of BCZ20Y15-GDC15 in the 50:50 volume ratio reached values of 0.27 mL·min-1·cm-2 at 755°C, currently one of the highest H2 flows obtained for bulk mixed protonic-electronic membranes. The stability of these materials under CO2-containing atmosphere was evaluated by thermogravimetry analyses. These composite systems showed a very good chemical stability under CO2-rich atmosphere, supporting their use for hydrogen separation membranes in practical applications. The influence of the different phenomena associated to the permeability mechanism, namely protonic transport, electronic conduction and water splitting, are still to be clarified and should be the beginning for a valuable discussion. [1] T. Norby and R. Haugsrud Dense ceramic mebranes for hydrogen separation in: A. F. Sammels and M.V. Mundschau Nonporous inorganic membranes for chemical processing Wiley-VCH Verlag GmbH & Co. KGaA (2006) 1-48. [2] J.W. Phair, S.P.S. Badwal Ionics 12 (2006) 103-115. [3] S. Barison, M. Battagliarin, T. Cavallin, L. Doubova, M. Fabrizio, C. Mortalò, S. Boldrini, L. Malavasi, R. Gerbasi Journal of Materials Chemistry 18 (2008) 5120-5128.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
