(LaSr)xMnO3 cathode stoichiometry effects on electrochemical performance in contact with AISI 441 steel interconnect

2014

Fuel Cells

Moisture effect on cathode behaviors is a major issue for solid oxide fuel cells servicing under severe high temperature environments. This work studies the effect of dry air and moist air on La 0.8 Sr 0.2 MnO 3 (LSM821) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF6428) cathodes at 800°C by investigating the interfacial reaction and degradation through an AISI 441 interconnect/ LSM821 (LSCF6428) electrode/yttria-stabilized zirconia (YSZ) electrolyte tri-layer structure. Under the same processing condition, the grain size of the LSCF6428 cathode is smaller than that of the LSM821 cathode. Ohmic resistance and polarization resistance of the cathodes are analyzed by deconvoluting the electrochemical impedance spectroscopy (EIS) results. The LSCF6428 cathode has much smaller resistance than the LSM821 cathode. Moisture produces a larger effect on the ohmic resistance and polarization resistance of the LSM821 cathode than on those of the LSCF6428 cathode. More chromium diffuses from the interconnect to the cathode for both LSM821 and LSCF6428 electrodes thermally treated in moist air. Based on the structure, elemental distribution, and EIS analysis, the interaction mechanisms between the electrodes and the AISI 441 alloy interconnect are proposed.

Section: Fundamental Processsupporting

confidence: 93%

Moisture Effect on La_0.8Sr_0.2MnO₃ and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ Cathode Behaviors in Solid Oxide Fuel Cells

2014

Fuel Cells

“…Impedance spectra measured between the cathode and the reference electrode are shown in Figure , and can be deconvoluted by an equivalent circuit R Ω (R H CPE H )(R L CPE L ) (shown in our previous work ) under the AC mode. In the circuit, R Ω is the ohmic resistance from the cathode, the connecting wires, the current collector, and the contact resistance, and corresponds to the intercept of the impedance semicircle with the x ‐axis in the high frequency range.…”

Section: Resultsmentioning

confidence: 99%

Comparison of Different Perovskite Cathodes in Solid Oxide Fuel Cells

2018

Fuel Cells

This study compares the electrochemical performance of three perovskite cathode materials, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), Ba0.5Sr0.5Co0.2Fe0.8O3 (BSCF), and Sm0.5Sr0.5Co0.2Fe0.8O3 (SSCF), at different operating temperatures, in order to provide optimal operating condition and performance for different solid oxide fuel cells. Among these three cathodes, BSCF has the highest power density of 39 mW cm−2 at 600 °C, 88 mW cm−2 at 650 °C, and 168 mW cm−2 at 700 °C; LSCF has the highest power density of 263 mW cm−2 at 750 °C and 456 mW cm−2 at 800 °C. The cathode overpotentials have the same trend as the power densities. Activation energies for the total cathode area specific resistance (ASR) are calculated to be 0.44 eV, 0.38 eV, and 0.52 eV for the LSCF, BSCF, and SSCF cathodes, respectively. Stability testing of 100 h shows that the open circuit voltages of the LSCF and BSCF cathodes drop 16.1% and 22.9% at 800 °C, respectively, as well as 15.3% and 11.3% at 600 °C, respectively, indicating that the LSCF cathode is more stable at 800 °C while the BSCF cathode is more stable at 600 °C. This work should provide important guidance for the solid oxide fuel cell designs and properties.

“…In order to understand the fundamental process in different half-cells and correlate the electrochemical behaviors with the cathode evolution, equivalent circuit R V (R H CPE H )(R L CPE L ) under AC mode, shown in our previous work [26], has been used to fit the EIS spectra and obtain deconvoluted arcs at different frequencies. In the circuit, R V is the ohmic resistance from the cathode, the Pt wires, the Pd paste, the contact between each layer and the cathode, and the electrolyte; however, the major contribution and especially the changes are from the contact resistance between each layer, and the electrolyte.…”

Section: Electrochemical Behaviorsmentioning

confidence: 99%

Perovskite-type La0.6Sr0.4Co0.2Fe0.8O3, Ba0.5Sr0.5Co0.2Fe0.8O3, and Sm0.5Sr0.5Co0.2Fe0.8O3 cathode materials and their chromium poisoning for solid oxide fuel cells

2016

Electrochimica Acta

Self Cite

A B S T R A C TIn the pursuit for solid oxide fuel cell (SOFC) cathode materials that can operate over a wide temperature range, especially at low temperatures such as 600 C, perovskite structure materials La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF), Ba 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 3 (BSCF), and Sm 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 3 (SSCF) are studied. Their electrochemical performance is compared by electrochemical impedance spectroscopy (EIS) at 600 C, 700 C and 800 C for 100 hrs through an AISI 441 interconnect/cathode/yttria-stabilized zirconia (YSZ) electrolyte half-cell structure. The BSCF cathode has the smallest polarization resistance at 600 C, closely followed by the SSCF cathode; the LSCF cathode has the smallest polarization resistance working at 700 C; the SSCF cathode has the smallest polarization resistance working at 800 C, closely followed by the LSCF cathode. From 600-800 C, SrCrO 4 phase forms on the SSCF cathodes near the interconnect while BaCrO 4 phase forms on the BSCF cathodes near the interconnect. For the LSCF cathodes, however, SrCrO 4 phase is only detected at 700 C and 800 C. Cr species diffusion to and poisoning of the cathodes do not directly correlate with the half-cell performance. Lattice constant, stoichiometry, particle size, Cr deposition, and working temperature are important factors to consider.