Hydrogen permeability of SrCe 0.7 Zr 0.25 Ln 0.05 O 3  δ membranes (Ln ¼ Tm and Yb) Wen Xing a , Paul Inge Dahl a , Lasse Valland Roaas b , Marie-Laure Fontaine a , Yngve Larring a , Partow P. Henriksen a , Rune Bredesen a,n a SINTEF Materials and Chemistry, Sustainable Energy Technology, POB 124 Blindern, NO-314 Oslo, Norway b Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway article info Article history: Received 13 June 2014 Received in revised form 11 September 2014 Accepted 12 September 2014 Available online 28 September 2014 Keywords: Co-substitution of B site Hydrogen flux Permeability Acceptor doping SrCeO 3 abstract Zr substituted acceptor doped SrCeO 3 materials were synthesized by citric acid route and characterized by XRD and SEM. The hydrogen flux of the materials was measured as a function of temperature and hydrogen partial pressure on the feed side. The hydrogen permeability for SrCe 0.7 Zr 0.25 Tm 0.05 O 3δ and SrCe 0.7 Zr 0.25 Yb 0.05 O 3δ is similar under our measurement window and shows the same hydrogen partial pressure dependency. Under short circuit condition, the hydrogen permeability increased significantly by more than one order of magnitude indicating that the hydrogen transport is limited by electronic conduction under open circuit conditions. The observed data were discussed by applying defect chemistry and the conventional ambipolar transport theory. After the hydrogen permeation measure- ments, the indication of kinetic cation de-mixing was found by XRD analysis. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Dense mixed proton–electron conducting ceramic membranes for hydrogen separation have attracted considerable interests since Iwahara et al. [1] reported proton conductivity in SrCeO 3 based perovskite ceramics at high temperatures ( 4500 1C). Potential appli- cations of hydrogen transport membranes (HTMs) encompass hydro- gen purification and fine chemical production in catalytic membrane reactors [2], where using of HTM process can offer reduction in energy consumption and cost compared to alternative technologies. Attractive membrane candidates are mainly based on perovskite-type materials containing solid solutions with aliovalent parent cations or dopants. The necessary simultaneous transport of both ionic and electronic charge carriers is driven by the hydrogen partial pressure gradient across the membrane. Bulk proton conductivity higher than 10 3 S/cm combined with high electronic conductivity and low grain boundary resistance are deemed necessary for membrane materials in addition to mechanical and chemical stability under process condition. The most extensively studied proton/mixed conductors are acceptor doped SrCeO 3 and BaCeO 3 with their reported high proton conductivities [3–6]. Besides, some other series of perovskite oxides (ABO 3 ), such as SrZrO 3 , CaZrO 3 , and SrTiO 3 have been reported to exhibit appreciably high proton conductivity. The hydrogen permeation of SrCe 1x Ln x O 3 (with x ¼ 0.05, Ln ¼ Eu, Sm, Tm and Yb) has been previously reported [7–10], and perme- ability for these and some other mixed conducting hydrogen separa- tion membrane is summarized in [11,12]. Despite promising hydrogen fluxes SrCeO 3 based materials suffer poor stability in CO 2 and steam containing atmospheres. BaCeO 3 based materials also show rather poor chemical stability towards CO 2 containing atmosphere in con- trast to the BaZrO 3 based ones. It has been demonstrated that for Zr substituted BaCeO 3 the chemical stability towards CO 2 is greatly enhanced, particularly for Zr Z20% [13]. It is also possible to improve chemical stability of SrCeO 3 based materials by Zr substituting of Ce [14]. However, the hydrogen flux for Zr substituted SrCeO 3 materials with different aliovalent dopants, and materials stability remains to be assessed. Here, we focus our investigation on SrCe 0.7 Zr 0.25 Ln 0.05 O 3 with M¼ Tm or Yb, to assess their potentials as HTM candidates. In these materials, the main charge carriers under wet condi- tions are protons, coming from hydration of oxygen vacancies in the structure which are created by the acceptor doping. The substitution reaction forming oxygen vacancies can be written as: M 2 O 3 þ 2SrO ¼ 2Sr X Sr þ 2M = CeðZrÞ þ v dd O þ 5O X O ð1Þ and the homevalent Zr substitution on B site will not create charged defect species. The hydration reaction of oxygen vacancies under wet conditions can be expressed as: H 2 O þ v dd O þ O X O ¼ 2OH d O ð2Þ Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2014.09.027 0376-7388/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Journal of Membrane Science 473 (2015) 327–332