Polarization behavior of high temperature solid oxide electrolysis cells (SOEC)

The behavior of SOEC was investigated as compared with that of solid oxide fuel cell (SOFC) using small cells prepared on yttria stabilized zirconia (YSZ) planar discs. Ni-YSZ cermet negative electrode showed asymmetric behavior indicating the existence of diffusion limited process in the electrolysis direction, although the behavior was strongly dependent on the electrode preparation. The behavior of positive electrodes made by using perovskite type oxides was also investigated. When polarized anodically, the positive electrode showed degradation behavior which ended up with electrode delamination from electrolyte. The degradation rate was remarkably decreased by improving the initial polarization performance of the electrode or by using a mixed ceria intermediate layer between YSZ and electrode. Polarization measurements of SOEC were conducted at 1173 K, 1223 K and 1273 K with various water content in hydrogen simulating the atmosphere of various water electrolysis rate. The cell was shown to work at a high current density and at high water electrolysis rate without suffering from diffusion limiting current.