Electrochemical properties of ceramic membranes based on SrTi 0.5 Fe 0.5 O 3Ld in reduced atmosphere A. Murashkina a , V. Maragou b , D. Medvedev a , V. Sergeeva a , A.K. Demin a, **, P. Tsiakaras b, * a Institute of High Temperature Electrochemistry, Laboratory of Solid Oxide Fuel Cells, 22 S. Kovalevskoy, 620990 Yekaterinburg, Russia b Dept. of Mechanical Engineering, School of Engineering, University of Thessaly, Pedion Areos, 383 34 Volos, Greece article info Article history: Received 12 March 2012 Received in revised form 11 June 2012 Accepted 17 June 2012 Available online 31 July 2012 Keywords: Perovskite membrane Strontium titanate Electrical conductivity Oxygen permeation Hydrogen production Ambipolar conductivity abstract The present work aims at the investigation of the electrochemical properties of SrTi 0.5 Fe 0.5 O 3d as a membrane material for hydrogen production via electrochemical reforming. The dependence of the electrical conductivity on the oxygen partial pressure, as well as the oxygen permeability in the range of 10 20 atm  p O2  10 14 atm is examined. The oxygen permeability is measured by an electrochemical method. The dependences of ion current as a function of the electromotive force (EMF) at various temperatures, oxygen partial pressures and the membrane surface conditions (rough and activated by PrO x ) are studied. Finally, the values of hydrogen flux at different temperatures are calculated and a long term investigation during 600 h at p O2 ¼ 10 19 atm, T ¼ 1173 K is carried out. According to the present results, the permeation current increases with the increase of temperature, oxygen partial pressure gradient and activation by PrO x . The long term investigation shows that the electrical resistance of the SrTi 0.5 Fe 0.5 O 3d ceramic membrane increases by 10%, possibly due to the formation of micro-domains into the material’s volume and the decrease in the grain boundary conductivity, because of the segregation of dopant-rich layers near the grain boundaries. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Perovskite-like oxides that present mixed oxygen ioneelec- tron conductivity (MIEC) are considered as promising mate- rials for oxygen permeable membranes. This kind of membranes are used for the electrochemical production of oxygen from gas mixtures, the production of hydrogen through the electrochemical reforming of water, as well as the production of synthesis gas (CO þ H 2 ) through the partial oxidation of methane [1]. A schematic diagram of the transport process that takes place in a membrane with mixed ioniceelectronic conductivity is shown in Fig. 1. For the occurrence of oxygen flux through the membrane, a chemical potential gradient of oxygen (mO 2 ) on opposite sides of the membrane must be created. This moving force of the process can be defined using the various oxygen-containing buffer mixtures (CO þ CO 2 , H 2 O þ H 2 ) and atmospheres based on them (CH 4 þ H 2 O, CO þ H 2 ). From the side with the high oxygen partial pressure, the process of oxygen reduction occurs, which is accompanied with the oxygen introduction to an anion sublattice of the perovskite. From the side with low oxygen partial pressure the reverse process takes place. The opposite electrochemical process results in the directed motion of ions and electrons * Corresponding author. Tel.: þ30 24210 74065; fax: þ30 24210 74050. ** Corresponding author. Tel.: þ7 343 3745431; fax: þ7 343 3745992. E-mail addresses: A.Demin@ihte.uran.ru (A.K. Demin), tsiak@mie.uth.gr (P. Tsiakaras). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 14569 e14575 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2012.06.066