Preparation and Powder Characteristics of LNF Compounds for Application in SOFCs

Abstract

LaNi (1-x) Fe x O 3 (LNF) compounds, with 0.0 ≤ x ≤ 0.4, have interesting physical properties such as high ionic and electronic conductivity, good catalytic activity for oxygen reduction, and thermodynamic compatibility with the YSZ electrolyte, which makes them potential candidates for SOFCs (solid oxides fuel cells) cathodes. Order for these excellent properties are achieved, it is necessary to ensure the presence of the homogeneous phase LNF. The methods for preparing these compounds influence the formation and stabilization of the homogeneous phase and therefore the physical properties of these oxides. For this reason, this work deals with the synthesis of the family of compounds LNF and the correlation between the synthesis and the physical properties obtained. In this context, LNF compounds were synthesized by a modified Pechini method for production of powders. Two different synthetic routes were employed, changing the source of nickel: nickel acetate and nickel nitrate. In order to study the thermal evolution of the LNF phase in these compounds, thermal analysis (DTG) and X-ray diffraction (XRD) were performed. The XRD was verified that the series of compounds synthesized by nickel acetate originated monophasic samples different from those obtained with nickel nitrate. We studied the influence of time and sintering temperature on the superficial characteristics of the samples and it was observed the reduction in sintering time allowed obtaining powders of perovskite phase, with grain sizes and smaller clusters than what was observed in the compound -treated for 10 h. To characterize the particle size, the powders were characterized by curves absorption/desorption (BET). The results also show that heat treatment for shorter times resulted in decreased particle size as well as increase the surface area of the compounds. INTRODUCTIONOne of the challenges of the XXI century has been the development of new technologies that optimize the way we store energy. In this context, fuel cells are highlighted, as are systems that convert chemical energy supplied by a fuel and an oxidant into electrical energy. There are different fuel cell types, classified according to the electrolyte that composes themselves. The SOFCs, constituted by a solid electrolyte, are interest subject of several studies and they have the advantage of operating at elevated temperatures. The physical properties of SOFCs depend on the choice of materials that compose the electrodes and the electrolyte. LNF oxides have suitable properties to be used as cathodes for SOFCs, due to their good electrical conductivity (> 100 S cm -1 ) and thermal conductivity and coefficient of thermal expansion (in the range of 10-13·106 K -1 ) compatible with the electrolytes commonly used in SOFCs, such as YSZ [1,2]. EXPERIMENT LNF powder compounds are prepared using polymerized complex process (PC) synthesis route. The preparation samples was carried out starting from two distinct precursor solutions, one containing Ni(NO 3 ) 2 •6H 2 O (99,9985%, Alfa Aesar) and t...