Performance and Activation Behavior of Surface-Doped Thin-Film La[sub 0.8]Sr[sub 0.2]MnO[sub 3−δ] Cathodes

Abstract

film electrodes of thickness 100, 450, 650, and 700 nm were fabricated on yttria-stabilized zirconia ͑YSZ͒ electrolyte pellets by ultrasonic spray pyrolysis. In addition, 650 nm thick LSM electrodes with a surface doped with La-, Sr-, or Mn-nitrate were studied. Electrodes were deposited on both sides of the YSZ pellets in a symmetric arrangement. The individual electrode impedance spectra were measured at 973 K in laboratory air using a reference electrode placed on the free electrolyte surface. The open-circuit polarization resistance of the pure LSM and Sr and Mn surface-doped electrodes decreased significantly after initial application of cathodic current. In contrast, the La-doped sample showed no activation, with an initial polarization resistance similar to the activated, undoped LSM film. This indicates that surface La species play an important role in LSM electrode activation. All of the electrodes showed a strong, nonlinear decrease in polarization resistance accompanied by a linear decrease in ohmic resistance with increasing applied cathodic current. These changes are attributed to the introduction of a bulk-ion-transport path in the LSM film due to reduction of LSM under polarization. A minimum polarization resistance of 0.17 ⍀ cm 2 was measured for the La surface-doped 650 nm thick electrode at 250 mA/cm 2 .

High‐Performance SOFC Cathodes Prepared by Infiltration

“…[85,123] The following are some of the explanations that have been given for electrode activation: (1) partial reduction of Mn 3þ and generation of oxygen vacancies that extend the three-phase boundary by providing sites for O 2 reduction; [124] (2) reduction of LSM at the LSM/YSZ interface provides a driving force to reduce any La 2 Zr 2 O 7 that could have formed at the LSM/YSZ interface; [120,122] (3) reducing conditions at the TPB remove other species that might passivate the interface; [113,114] (4) cathodic polarization results in the formation of nanopores and causes other microstructural changes that improve diffusion of oxygen species; [124,125] (5) cathodic polarization results in a thin La 2 O 3 oxide film at the LSM/YSZ interface which decreases polarization for unspecified reasons. [126] It is interesting to consider how reducing the environment might be under typical cathode operating conditions. The REVIEW www.advmat.de reduction potential at TPB sites is lowered from atmospheric conditions by, at most, the cathode overpotential.…”

Interface formation and Mn segregation of directly assembled La0.8Sr0.2MnO3 cathode on Y2O3-ZrO2 and Gd2O3-CeO2 electrolytes of solid oxide fuel cells

“…Directly assembled LSM/YSZ and LSM/GDC cells were cathodically polarized at 750 o C and [9,[37][38][39][40][41][42]. For instance, Rp was significantly reduced from 60.0 Ω cm 2 to 0.8 Ω cm 2 and RΩ decreased dramatically from 2.1 Ω cm 2 to 0.9 Ω cm 2 ( Fig.1a) The cathode potential (Ecathode) also drops quickly under the influence of cathodic polarization, from its initial value of 1.3 V to ~0.9 V. For LSM/GDC cell, the electrochemical performance also experiences a significant decrease (see Fig.…”

Interfacial Stability between Air Electrode and Ceria‐Based Electrolyte under Cathodic Polarization in Solid Oxide Fuel Cells

“…The performance of each cell was improved with time due to the reduction in LSM overpotential, of which extent was dependent on the initial overpotential; the enhancement was significant at higher overpotential. This behavior is considered as the current passage effect as is observed for the cell with LSM/YSZ interface [1][2][3][4][5][6][7][8][9][10][17][18][19]. Although in the initial state LSM particles were well adhered to the SDC surface, small closed pores were formed at the LSM/SDC interface after current passage.…”