STRUCTURE-PROPERTY RELATIONSHIP IN Mg-DOPED La 0.75 Sr 0.25 Mn 0.5 Cr 0.5 O 3 ANODE FOR SOLID OXIDE FUEL CELL Abul K. Azad*, Firdaus Basheer*, Pg M Iskandar Petra*, Abhijit Ghosh†, John T.S. Irvine †† *Faculty of Integrated Technologies, Universiti Brunei Darussalam, Jalan Tunku Link, Gadong BE 1410, Brunei Darussalam, E mail: abul.azad@ubd.edu.bn † Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India. †† School of Chemistry, University of St-Andrews, Fife KY16 9ST, UK Keywords: Alternative energy, Solid Oxide Fuel Cell, Energy Materials, Electrochemical characterization, Perovskites. Abstract Lanthanum strontium chromium manganite (LSCM) has been found to be a potential candidate for SOFC anode to use in hydrocarbon fuels. Mg -doped LSCM has been synthesized by solid state reaction and tested for its sulphur tolerance when used as anode of solid oxide fuel cells. This material shows redox stability, compatibility with other cell components, acceptable level of cocking and sulphur tolerance. Structural studies using X-ray and neutron powder diffraction shows that the materials crystallize in the rhombohedral symmetry in the R-3C space group. Thermogravimetric analysis shows stable redox behaviour similar to LSCM. Microstructural analysis shows porous structure which is essential for an anode material. Performance of this material as an anode of SOFC has been tested in H2, CH4 and H2S/H2/CH4 atmosphere at different temperatures. Impedance analysis show that best performance can be achieved at about 870 o C corresponding to the polarization resistance of 0.5 ohm/cm 2 in pure H2 and 1.0 ohm/cm 2 in CH4. Microstructural analysis after cell preparations shows a good lamination between the electrolyte and anode. 1 Introduction Solid oxide fuel cell (SOFC) is one of the most exciting electricity producing device and it is made of ceramic materials and operate in the energy range 600-900 o C. SOFC can operate on diverse combustion fuels enabling efficient generation of electrical power. However, most SOFC research has been with the use of hydrogen due to the use of nickel as the fuel electrode catalyst. Development of the fuel electrode is one of the problems to be solved in the use of hydrocarbon fuels [1]. Due to the abundant supply of hydrocarbons e.g. South China Sea gas (CH4 (96-99%), C2H6 (1-3%), C3H8 (0.2%), S (4-10 ppm)), it can be a viable alternative to H2 in SOFC device. Approximately one third of the world's gas fields are highly contaminated and are classified according to their contaminants (H2S and CO2). Other contaminants such as carbonyl sulphide and organic sulphides/disulphides are also present. Such contaminants need to be removed because of greenhouse gas effect and stringent environment protection law. Sulphur de-gassing process reduces the hydrogen sulphide and hydrogen polysulphide content from 250 to 300 ppmv down to less than 10 ppm hydrogen sulphide. Due to the presence of carbon and sulphur, the development of SOFC anodes capable of operating in natural gas, without carbon build up and sulphur poisoning, is still a challenge. Hence, there is a need to investigate alternative materials rather than Nickel- Yttria Stabilized Zirconia (Ni-YSZ) which have good catalytic activity for the various fuel oxidation reactions. The operating conditions in the range 700-900 o C and a low oxygen partial pressure (pO2) in the range of 10 -15 to 10 -20 atm has severely limit the choice of materials available. To date the state-of-the-art anode materials are Ni cermets mixed with either Yttrium stabilized Zirconia (YSZ) or Gadolinium stabilized Ceria (CGO) as the ionic conducting component. However, the most common and widely used anode materials Ni/YSZ suffer from coking of hydrocarbon fuels under the usual operating conditions. It also affects by sintering during high temperature operation as it reduces the catalytically active surface area and, hence, the overall performance. Furthermore carbon deposition on Ni/YSZ anode causes the deterioration of anode performance as well. Several alternatives have been proposed to overcome these problems such as using copper instead of nickel, excess steam in the fuel and the development of novel anode materials [2-6]. Finding alternative materials to overcome these problems seems to be a good option. Recently, strontium doped lanthanum chromium manganite (LSCM) has been found to be a potential anode material for its redox stability, compatibility with the other cell components and acceptable coking and sulphur tolerance [7- 12]. LSCM is a p-type conductor and shows mixed ionic and electronic conductivity (MIEC) with reasonable electronic conductivity. It also shows improved ionic conductivity (~2 Scm -1 ) under fuel conditions but poor ionic conductivity under oxidizing conditions [6]. The substitution of divalent Sr into the A-site with trivalent La results in a charge compensating transition of Mn 3+ to Mn 4+ at the B-site and at low partial pressure of oxygen, the compensation is achieved by the formation of oxygen vacancies. The mixed ionic and electronic conductivity under fuel conditions assists in making LSCM catalytically active for methane (CH4)