Characterisation of La0.6Sr0.4Co0.2Fe0.8O3-d and Ba0.5Sr0.5Co0.8Fe0.2O3-d as Cathode Materials for the Application in Intermediate Temperature Fuel Cells

Abstract

Capable materials for solid oxide fuel cell cathodes have to provide high electrocatalytic activity for oxygen reduction as well as sufficient electronic conductivity and good ionic transport properties (1). This study compares the electrical transport properties and the oxygen exchange properties of two promising cathode materials for operating temperatures between 600 and 800°C: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ . Both materials were synthesized by spray pyrolysis and characterised with respect to phase purity and to the element ratio by XRD and ICP-AES analysis. The sintering behaviour of the calcined powders and the coefficients of thermal expansion of dense sintered samples were studied by dilatometry. As important parameters for the oxygen exchange reaction the chemical surface exchange coefficients ( k ) and chemical diffusion coefficients ( D ) as well as the electrical conductivities are compared.

Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

“…1, LSCF exhibits a significantly higher surface area (a LSCF = 5.41 μm -1 ), according to the higher sintering activity of BSCF (a BSCF = 1.69 μm -1 ). 4,30,31 Implicitly the use of a higher sintering temperature to achieve a good LSCF cathode/electrolyte attachment is justified.…”

“…[4][5][6][7][8] The ALSmodel is an analytical 1D-model developed for semi-infinite thickness, porous, mixed-conducting cathodes with high ionic-electronic conductivity and no gas phase diffusion limitations. It is generally accepted that for thick cathodes the oxygen surface-exchange and the solid-state diffusion processes are coupled and can be described by the following equation, mathematically equivalent to a Gerischer impedance:…”

“…Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] and temperature for LSCF cathodes. 17 Here it should be pointed out that the well-known ALS model can only be applied if the measured impedance shows a Gerischer impedance, which indicates that the surface-exchange and the oxygen bulk diffusion are strongly coupled.…”

“…[1][2][3] The surface-exchange coefficient (k) and the oxygen diffusion coefficient (D) provide key information about the oxygen transport mechanism that dominates the cathodic ORR. Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] or thin-films 9,10 (k δ , D δ ) and by oxygen tracer diffusion experiments for thin-films 11 or powder 12 (k * , D * ). The oxygen transport parameters are usually determined by ex situ experiments for model systems (i.e.…”

In Situ Optical Absorption Studies of Point Defect Kinetics and Thermodynamics in Oxide Thin Films

“…Reported values for k for a given composition at a specific temperature and partial pressure of oxygen vary by orders of magnitude across multiple techniques. For example, in ECR, 197,198,199,200,201 IEDP, 197 and EIS 196 studies investigating the surface exchange kinetics in La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- (LSCF) with temperatures between 700C and 800C and pO 2 between 0.1 and 0.21 atm, values for k chem ranged from 10 -7 -10 -4 cm/s. Similarly, for EIS, 202 ECR, 203,204 and IEDP 205 atm, values for k chem ranged between 10 -5 -10 -7 cm/s from OTR and EIS measurements.…”