Ceramic Hydrogen-Permeable Membranes made of Mixed Proton-Electronic Conducting Materials based on the system Ln6WO12

Jose M. Serra 1Sonia Escolastico 1Maria Balaguer 1Wilhelm A. Meulenberg 2Hans Peter Buchkremer 2Tobias Scherb 3Gerhard Schumacher 3Marck W. Lumey 4Richard Dronskowski 4

1. Instituto de Tecnología Química UPV-CSIC (ITQ), avda. de los Naranjos s/n, Valencia 46022, Spain
2. Forschungszentrum Jülich, Institute of Energy Research IEF (FZJ-IEF), Leo-Brandt-Strasse, Jülich 52425, Germany
3. Helmholtz Centre Berlin for Materials and Energy, Glienicker Str. 100, Berlin D-14109, Germany
4. Institute of Inorganic Chemistry, RWTH Aachen University, Landolltweg 1, Aachen 52074, Germany

Abstract

The tungstates Ln6WO12 are proton conducting crystalline materials exhibiting sufficient mixed conductivity (protonic and electronic) and remarkable stability to consider them as potential candidates for the separation of hydrogen at high temperature. Membranes made of this type of materials can be applied for industrial gas separations such as hydrogen separation from hydrogen containing gases, for the implementation of pre-combustion strategies in power plants, and for the application in ceramic proton conducting fuel cells. This contribution summarizes the recent developments achieved on ceramic hydrogen-permeable membranes in the frame of the MEM-BRAIN Alliance. It is shown the preparation of nanocrystalline mixed conducting materials based in the system Ln6WO12 using a sol-gel complexation synthesis method. This method is based on the citrate-complexation route modified to stabilize W- and Ln-containing ions. The influence of the lanthanide (Ln) nature and the partial substitution in the system Ln6-xAxWO12 (Ln= La and Nd; A= Ce, Eu, Gd, La, Nd, Pr, Sm, Tb, Yb; and x =1 and 3) on the total conductivity and crystalline structure was studied systematically. The electrical conductivity measurements were conducted by standard four-point DC technique on the sintered rectangular bars and silver paste and wire were used for contacting. The measurements were carried out under different atmospheres, i.e., helium and H2/D2 saturated with H2O/D2O at 20ºC. For selected samples, it was studied the water up-take process followed by thermogravimetry, XRD and Raman spectroscopy. Hydrogen permeation was studied for different disk-shaped Ln6WO12 membranes in the range of 700-1000ºC. The membrane sides were coated by screen printing with a 20 μm layer of a Pt ink aiming to improve surface hydrogen exchange. Furthermore, stability of these materials at 700 and 800ºC has been evaluated in a CO2-rich gas stream, dry and saturated with water at room temperature. Materials remained unchanged after the treatments, irrespective of its original sintering temperature and lanthanide nature. The experimental work has been supported by ab-initio calculations aiming to give more insight into the fundamentals of protonic conduction through the crystalline lattice.

 

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium G, by Sonia Escolastico
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-14 17:46
Revised:   2009-06-07 00:44