Electrochemical behaviour of Co-doped LSGM perovskites prepared by sol-gel synthesis
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Electrochemical behaviour of Co-doped LSGM perovskites prepared by sol-gel synthesis Riccardo Polini1, Alessia Falsetti1, Enrico Traversa1, Oliver Schäf 2 and Philippe Knauth2 1
Dipartimento di Scienze e Tecnologie Chimiche - Università di Roma Tor Vergata Via della Ricerca Scientifica, 00133 ROMA (ITALY) 2 MADIREL (UMR 6121) Université de Provence-CNRS, Centre Saint Jérôme F-13397 Marseille Cedex 20 (FRANCE)
ABSTRACT La0.8Sr0.2Ga0.8Mg0.2-xCoxO3-δ (LSGMC) powders containing different amounts of Co (x = 0.05 and 0.085) were prepared by a citrate sol-gel method. Crystalline powders were obtained by firing at 1000°C (10 h) and dense high-purity pellets were prepared by pressing (300 MPa) and sintering in air at 1475°C (5, 10 and 20 h). The sintered pellets of LSGMC were characterized by X-Ray Diffraction (XRD) Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The conductivity of sintered LSGMC pellets containing different amounts of Co ions in the B sites of the perovskite lattice was assessed by electrochemical impedance spectroscopy (EIS) in the 250-750 °C temperature range. Conductivity values and apparent activation energies were in good agreement with previously published data referring to materials with same composition, but prepared by solid-state reaction.
INTRODUCTION Solid oxide fuel cells (SOFCs) offer a highly efficient power generation system. One of the major requirements for the development and commercialization of low-cost SOFCs is the reduction of the operating temperature. One of the ways to reach this aim is the use of solid electrolytes which exhibit superior ionic conductivity at intermediate temperatures (T < 800 °C). Among these ionic conductors, doped LaGaO3 materials show high oxide ionic conductivity in the 600-800 °C range. The incorporation of divalent cation dopants to form La1-xSrxGa1-yMgyO3-δ (often termed LSGM, where δ = (x+y)/2), gives mobile oxygen vacancies. As a consequence, the resulting ionic conductivity of LSGM at 700 °C is about 4 times larger than that of conventional yttria-stabilized zirconia (YSZ) solid electrolyte [1-3]. Following the initial discovery [1-5], numerous experimental studies have been carried out on LSGM materials, which also include the effect of transition-metal doping [6-11]. It is generally believed that doping with a transition metal cation is undesirable for the ionic conductor due to the appearance of n- or p-type conduction. However, it was found that the oxide ion conductivity was also improved by doping Co for Ga site of LaGaO3-based perovskites [7], although hole conduction was detected at high oxygen partial pressures [7, 11]. Yamada et al. [12] demonstrated that the application of Codoped LSGM for the electrolyte of SOFCs greatly improves the power density of the cell at intermediate temperatures. LSGM materials are usually prepared by time- and energy-consuming solid state reaction [1, 2], although new powder production techniques have been used. Aldinger and coworkers [13,
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14] have studied the pr
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