BaCe0.85-xZrxY0.15O3-d and Y- or Gd-doped CeO2 ceramic-ceramic composite membranes for Hydrogen separation

The efficient separation of pure H2 from a gas mixture is a critical stage for large scale production of this energy carrier. H2-selective membranes represent an appealing option to recover hydrogen from low-quality gas e.g. from biomass. Protonic-ceramic have received considerable attention due to their potential application as mixed ionic-electronic conductor (MIEC) separation membranes for H2 production. 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 high electronic and high proton conductivities [1]. Still, a stable single phase material with those properties is rather challenging. Indeed, an enhancement of proton conductivity through doping is generally related to a decrease on the electronic conductivity and on the stability of this kind of ceramics. Another strategy is to obtain the desired functional properties through composite membranes formed by two compatible ceramic phases. In this work, BaCe0.85-xZrxY0.15O3-? perovskites and doped CeO2 fluorites have been combined in different volume ratios to fabricate "ceramic-ceramic" composite membranes for H2 separation. It has been demonstrated that barium cerate-zirconate solid solutions BaCe0.85-xZrxY0.15O3-? (x: 0.20, 0.30) stabilize the perovskite structure without sacrificing protonic conductivity [2]. On the other hand, doped ceria oxides shows remarkable n-type electronic conductivity under H2 separation conditions. Furthermore, they enhance the stability against CO2 and H2O of the cerate material in the composite membranes. The optimal preparation and sintering conditions of the dense membranes have been determined through XRD and SEM techniques. OCV and a.c. impedance spectroscopy (EIS) have been carried out to study the electrochemical behaviour of the composites. In addition, the stability against CO2 and syn-gas (mandatory under operational H2 separation conditions) was evaluated by different methods. Finally, the H2-permeation of these dense membranes was measured, reaching hydrogen fluxes among the highest achieved for bulk mixed protonic-electronic membranes reported so far. References [1] T. Norby, R. Hausgrud, Nonporous Inorganic Membranes, 2006, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. [2] S. Barison Et al., J. Mater. Chem., 2010, 18, 5120- 5128.