Synthesis and Characterization of BaZr 0.8 Y 0.2 O 3 Protonic Conductor for Intermediate Temperature Solid Oxide Fuel Ce
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0972-AA01-05
Synthesis and Characterization of BaZr0.8Y0.2O3 Protonic Conductor for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) Alessandra D'Epifanio, Emiliana Fabbri, Elisabetta Di Bartolomeo, Silvia Licoccia, and Enrico Traversa Dept. of Chemical Science and Technology, University of Rome Tor Vergata, Via della Ricerca Scientifica,1, Rome, 00133, Italy
ABSTRACT Barium zirconate BaZr0.8Y0.2O3-δ, to be used as protonic conductor under hydrogen containing atmosphere in intermediate temperature (500-700°C) solid oxide fuel cells (ITSOFCs) was prepared using a sol-gel technique to produce materials with controlled chemical structure and microstructural properties. Several synthetic procedures were investigated, dissolving the metal cations in two solvents (water and ethylene glycol) and using different molar ratios of citric acid with respect to the total metal content. A single phase was obtained at temperature as low as 1100°C. To verify the chemical stability, all the sintered oxides were exposed to CO2 and the phase composition of the resulting specimens was investigated using Xray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Fuel cell polarization curves on symmetric Pt/BZY20/Pt cells of different thickness were measured at intermediate temperatures (500-700°C). INTRODUCTION High temperature proton conducting oxides based on perovskite structures have been widely investigated because of their potential use in several applications. The use of ceramic protonic electrolytes able to operate in a temperature range not exploitable by the present available technologies is a promising alternative that might solve the limits of SOFCs and of polymeric cells [1-3]. In recent years, doped perovskites such as barium cerates (BaCeO3) [1, 45], strontium cerates (SrCeO3) [6-8] and barium zirconate (BaZrO3) [9-14] have been widely studied as proton conducting electrolytes. Among those compounds, yttrium-doped barium cerate has the best performance in terms of fuel cell power density at the lowest temperatures but reacts with CO2, decomposing into BaCO3 and CeO2. On the other hand, barium zirconate has a good chemical stability under CO2 containing atmosphere but requires high sintering temperatures, long annealing, and shows a lower electrical conductivity in the 500-800°C temperature range. Aim of this work is the optimization of a sol-gel method for the synthesis of BaZr0.8Y0.2O3-δ (BZY20) to achieve powders with a stable single phase at reduced temperatures. The chemical stability at high temperature in the presence of CO2 containing atmosphere, the structural and microstructural features of powders and sintered pellets were investigated. Fuel cell polarization curves were measured analyzing the influence of the electrolyte thickness on the performance.
RESULTS AND DISCUSSION Sol-gel method A modified Pechini process was used for preparing BaZr0.8Y0.2O3-δ (BZY20) with controlled compositional homogeneity, high purity and relatively low processing temperatures. Commercial Ba(NO3)
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