Performances and Degradation Phenomena of Solid Oxide Anode Supported Cells With LSM and LSCF Cathodes: An Experimental Assessment

The performance of solid oxide fuel cells is affected by various polarization losses, usually grouped in Ohmic, activation, and concentration polarizations. Under typical operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometry: as an example, the performance of a tubular cell is strongly limited by the Ohmic polarization due to the long current path of electrons, while in a planar cell each of these losses has a comparable effect. It is therefore of interest, in the case of planar geometry, to investigate the main performance limiting factors. In this paper, a performance evaluation of planar circular-shaped seal-less SOFC cells was performed. Two different designs of planar cells are considered. Both have a porous NiO-YSZ (yttria stabilized zirconia) anode as mechanical support, a NiO-YSZ anode active layer, and an YSZ electrolyte, and they only differ in the cathode design: (1) strontium doped lanthanum manganate (LSM)-YSZ cathode functional layer and LSM cathode current collector layer; (2) yttria doped ceria blocking layer and lanthanum strontium cobalt ferrite oxide (LSCF) functional layer. The characterization was performed by taking $V-I$ measurements over a range of temperatures between $650°C$ and $840°C$ with hydrogen as fuel and air as oxidant. The experimental data analysis consisted in the analysis of some typical performance indicators (maximum power density (MPD); current density at $0.7V$⁠). The dependence of the cell performance on the various polarization contributions was rationalized on the basis of an analytical model—through a parameter estimation of the experimental data—devoted to the determination of the main polarization losses. Based on the results of the investigation, it is concluded that LSCF cathodes are really effective in decreasing the cathode activation polarization, allowing the reduction in operating temperature.