Electrochemical characterization of mixed conducting and composite SOFC cathodes

The electrochemical performance of La0.58Sr0.4Co0.2Fe0.8O3-delta (L58SCF), La0.9Sr1.1FeO4-6 (LS2F) and LSM (La0.65Sr0.3MnO3-delta)/LSM-YSZ (50 wt.% LSM-50 wt.% ZrO2 (8 mol% Y2O3)) cathode electrodes interfaced to a double layer Ce0.8Gd0.2O2-delta (CGO)/YSZ electrolyte was studied in the temperature range of 600 to 850 degrees C and under flow of 21% O-2/He mixture, using impedance spectroscopy and current density-overpotential measurements. The L58SCF cathode exhibited the highest electrocatalytic activity for oxygen reduction, according to the order: LS2F/CGO/YSZ <= LSM/LSM-YSZ/CGO/YSZ < L58SCF/CGO/YSZ. (c) 2006 Elsevier B.V. All rights reserved

Optimisation of processing and microstructural parameters of LSM cathodes to improve the electrochemical performance of anode-supported SOFCs

To improve the electrochemical performance of LSM-based anode-supported single cells, a systematic approach was taken for optimising processing and materials parameters. Four parameters were investigated in more detail: (1) the LSM/YSZ mass ratio of the cathode functional layer, (2) the grain size of LSM powder for the cathode current collector layer, (3) the thickness of the cathode functional layer and the cathode current collector layer, and (4) the influence of calcination of YSZ powder used for the cathode functional layer. Results from electrochemical measurements performed between 700 and 900 degrees C with H-2 (3 vol.% H2O) as fuel gas and air as the oxidant showed that the performance was the highest using an LSM/YSZ mass ratio of 50/50. A further increase of the electrochemical performance was obtained by increasing the grain size of the outer cathode current collector layer: the highest performance was achieved with non-ground LSM powder. In addition, it was found that the thickness of the cathode functional layer and cathode current collector layer also affects the electrochemical performance, whereas no obvious detrimental effects occurred with the different qualities of YSZ powder for the cathode functional layer. The highest performance, i.e. 1.50 +/- 0.05 A cm(-2) at 800 degrees C and 700 mV, was obtained with a cathode functional layer, characterised by an LSM/YSZ mass ratio of 50/50, a d(90) of the LSM powder of 1.0 mu m, non-calcined YSZ powder, and a thickness of about 30 mu m, and a cathode current collector layer, characterised by d(90) of the LSM powder of 26.0 mu m (non-ground), and a thickness of 50-60 mu m. Also interesting to note is that the use of non-ground LSM for the cathode current collector layer and non-calcined YSZ powder for the cathode functional layer obviously simplifies the production route of this type of fuel cell. (c) 2004 Elsevier B.V. All rights reserved

The influence of noble-metal-containing cathodes on the electrochemical performance of anode-supported SOFCs

In order to enhance the catalytic activity of the cathode for oxygen reduction and thus to increase the electrochemical performance of planar anode-supported solid oxide fuel cells, Pd, Ag, or Pt was added to the cathode. Four routes were used to add these noble metals: infiltration of the cathode with a Pd solution, deposition of Pt on the electrolyte surface, mixing of La0.65Sr0.30MnO3 (LSM) and YSZ cathode powders with different metal precursors (Pt and Pd black, Pd on activated carbon, Ag powder, Ag2O, Ag acetate, Ag citrate, Ag2CO3, colloidal Ag, AgNO3), and synthesis of LSM powder with the addition of AgNO3.Between 750 and 900 degreesC no electrocatalytic effect occurred with respect to the presence of Pt, either added by deposition on the electrolyte or by mixing with cathode powders. Infiltration of the cathode with a Pd solution or mixing with Pd black did not result in a positive effect either. A catalytic effect was only found with Pd on activated carbon and in particular at lower temperatures.Cells prepared with Ag powder and Ag2O showed an improved electrochemical performance compared to Ag-free cells sintered at the same temperature (920 degreesC). However, in comparison to Ag-free cells sintered at the standard temperature (I 100 degreesC) lower current densities were measured. This can be explained by a weak contact between electrolyte and cathode functional layer and an insufficiently sintered cathode. A detrimental effect was observed regarding the addition of the other Ag precursors. Thermal decomposition of these precursors resulted in the formation of large pores in the cathode. (C) 2003 Elsevier B.V. All rights reserved