Electrochemical characterization of perovskite-based SOFC cathodes

Abstract

The electrochemical performance of La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-d (L58SCF), La 0.78 Sr 0.2 Co 0.2 Fe 0.8 O 3-d (L78SCF) and composite La 0.65 Sr 0.3 MnO 3-d -8 mol% Y 2 O 3 stabilized ZrO 2 (LSM-YSZ, 50:50 wt%) cathode electrodes interfaced to a double-layer electrolyte made of Ce 0.8 Gd 0.2 O 2-d (CGO) and YSZ was studied in the temperature range 600-850°C using impedance spectroscopy and current-overpotential measurements. The experiments were carried out in a single chamber cell using a three electrode set-up with porous Pt films as auxiliary electrodes. The perovskite powders were synthesized using the spray-drying technique starting from nitrate precursors and were deposited on the solid electrolyte via screen-printing. Open circuit impedance measurements on as-prepared electrodes, i.e. before any polarization, and micropolarization measurements have shown that the L78SCF/CGO/YSZ electrode exhibits the lowest area specific polarization resistance R F (R F was approximately equal to 0.4 W cm 2 at 800°C and P O 2 = 21 kPa) or, equivalently, the highest electrocatalytic activity according to the order: LSM/LSM-YSZ/CGO/ YSZ<L58SCF/CGO/YSZ<L78SCF/CGO/YSZ. Current-overpotential data taken over an extended cathodic overpotential (ohmic-drop-free) range (0 to )500 mV) also indicated the aforementioned order of electrocatalytic activity. The Nyquist plots corresponded to at least two overlapping arcs or, equivalently, to at least two rate limiting processes. The relative contribution and degree of overlap of these arcs depended on electrode material, temperature and oxygen partial pressure, the low frequency arc being in general dominant at low temperatures and low oxygen partial pressures. Open circuit impedance experiments carried out at different oxygen partial pressures P O 2 (0.01-100 kPa) revealed an exponential increase of the open-circuit area specific polarization conductance R À1 F with increasing P O 2 .

A Brief Description of High Temperature Solid Oxide Fuel Cell’s Operation, Materials, Design, Fabrication Technologies and Performance

“…Researcher have explored LSM-YSZ (composite) and LSCF cathodes with YSZ-CGO electrolyte by current over potential measurements and impedance spectroscopy, and it is observed that LSM-YSZ has higher area specific polarization resistance (1.8 Ω-cm 2 ) as compared to LSCF (0.4 Ω-cm 2 ) at 850 °C [51]. A lot of efforts/concentrations are being given to increase the performance of electrode for low and intermediate temperature SOFCs [10,37,39,40,[42][43][44][45][46][47].…”

“…Researcher have explored LSM-YSZ (composite) and LSCF cathodes with YSZ-CGO electrolyte by current over potential measurements and impedance spectroscopy, and it is observed that LSM-YSZ has higher area specific polarization resistance (1.8 Ω-cm 2 ) as compared to LSCF (0.4 Ω-cm 2 ) at 850˝C [51]. The solid state reaction that takes place between YSZ electrolyte and MIEC materials during synthesis can be evaded by impregnation of the cathode material into porous electrolyte structure that need low sintering temperature [8,10,12,53].…”

Enhanced Performance of La0.6Sr0.4Co0.2Fe0.8O3-\delta(LSCF) Cathodes with Graded Microstructure Fabricated by Tape Casting

“…4a, the 1-layer LSCF cathodes exhibited area specific resistances (ASR) of 0.088, 0.186, 0.43, and 1.16 Ω·cm 2 at 800 o C, 750, 700, and 650 o C, respectively, similar to those reported in the literature. 15) In contrast, the cells with 3-layer LSCF electrodes of graded microstructure displayed much better performance (Fig. 4b).…”

“…6 are the area specific polarization resistances of LSCF cathodes (3-layer and 1-layer) fabricated by tape-casting in the present work, together with data reported in the literature for LSCF cathode deposited on GDC or YSZ electrolyte. Clearly, the 3-layer LSCF cathodes fabricated by tape-casting display lower interfacial resistance than the 1-layer cathodes fabricated by other methods, including screen printing, 15,16) spray pyrolysis 20) and brush painting. o C, the improvement in performance of the 3-layer graded cathode is more dramatic, approaching an order of magnitude at operating temperatures 650-800 o C. Interfacial resistances of the 1-layer LSCF cathode prepared by tape casting were also indicated in Fig.…”

Spray drying: An alternative synthesis method for polycationic oxide compounds

“…Recently, spray drying of solutions has been used to synthesize some polycationic oxides investigated in view of applications as magnetoresistive materials [6], high temperature superconductors [5], thermoelectric materials [7], piezoelectric materials [8] and electrode materials for lithium-ion batteries [9][10][11] or solid-oxide fuel cells [12]. We have recently reported another, more restricted, application, which is the preparation of composites by spontaneous phase separation of the components during the heat treatment [13].…”