Pr- and Co-substitution in rare earth nickelates: Application as SOEC air electrodes

In this work, fundamental material properties of compounds in the system (La,Pr)₂(Ni,Co)O_4+δ as well as their performance as air electrodes in solid oxide electrolysis cells were investigated. Nickelates co-doped with Pr and Co were characterized on a material basis by means of X-ray diffraction and thermogravimetry. Conductivity and conductivity relaxation measurements were performed in order to obtain the electronic conductivity as well as the chemical surface exchange coefficient and the chemical diffusion coefficient of oxygen as a function of temperature and oxygen partial pressure. These parameters can be regarded as the most essential properties at the material level required to assess the suitability of mixed ionic-electronic conducting ceramics for application as air electrode in solid oxide cells. The electrode performance of the materials was then tested on fuel electrode-supported button cells at 800°C. The electrodes were applied by screen-printing and the effect of varying the Pr-content and Co-content of the electrode powder was investigated. Cell tests were performed by means of current-voltage measurements in electrolysis mode. While no significant impact of Pr-doping on the investigated material properties was observed, the electrode performance of Pr-containing materials was significantly better than for the Pr-free compound, which has been discussed in detail.