Suitability of strontium and cobalt-free perovskite cathodes with La9.67Si5AlO26 apatite electrolyte for intermediate temperature solid oxide fuel cells.

Adrian Robles-Fernandez,Peter R Slater,Alodia Orera,Rosa I Merino

doi:10.1039/d0dt02987d

Abstract

Aluminium-doped lanthanum silicate (LSAO) apatite-type compounds have been considered as promising candidates for substituting yttria-stabilized zirconia (YSZ) as electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFC). Nevertheless, not many materials have been reported to work as cathodes in a LSAO apatite-based cell. In the present work, eight different strontium and cobalt-free compounds with a perovskite-type structure and the general composition LaM1-xNxO3-δ (where M = Fe, Cr, Mn; N = Cu, Ni; and x = 0.2, 0.3) have been tested. This study includes the synthesis and structural characterization of the compounds, as well as thermomechanical and chemical compatibility tests between them. Functional characterization of the individual components has been performed by electrochemical impedance spectroscopy (EIS). Apatite/perovskite symmetrical cells were used to measure area-specific resistance (ASR) of the half cell in an intermediate temperature range (500-850 °C) both with and without DC bias. According to its electrochemical behaviour, LaFe0.8Cu0.2O3-δ is the most promising material for IT-SOFC among the compositions tested since its ASR is similar to that of the traditional (LaxSr1-x)MnO3 (LSM) cathode.

Highlights

Solid oxide fuel cells (SOFC) are well-known electrochemical devices that transform the chemical energy of a fuel into electricity via a redox reaction in which electrons are generated
A series of strontium and cobalt-free perovskite compounds have been investigated as suitable candidates to work as cathodes on an intermediate temperature solid oxide fuel cells (IT-SOFC) design with an aluminium-doped lanthanum silicate apatite (LSAO) as electrolyte
All compounds have been successfully synthesised, as no secondary phase could be detected by means of x-ray diffraction, neither in the as-prepared powder nor in the sintered pellets manufactured at high temperature

Summary

Introduction

Solid oxide fuel cells (SOFC) are well-known electrochemical devices that transform the chemical energy of a fuel into electricity via a redox reaction in which electrons are generated. This reaction involves oxygen reduction into oxide ions, which are formed in the porous cathode, transported through a dense electrolyte, arriving at the anode where they react with the fuel, liberating electrons and closing the circuit. Among the latest trends seeking an improvement on SOFC technology, reducing operation temperature from 1000°C to 600°C-800°C (intermediate temperatures, IT) is one of the most popular ones.[1,2] The key issue in this research field is finding an electrolyte with higher ionic conductivity at IT than traditional YSZ. Traditional cathodes –such as LaxSr1-xMnO3 (LSM) or LaxSr1xCoyFe1-yO3 (LSCF)– face some issues, like low ionic conductivity and high polarization losses at intermediate temperatures.[16,17] a.Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain

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