(High Temperature Materials Division Outstanding Achievement Award) Development of Novel Ion Conducting Materials for Use as Electrolytes and Electrodes in Intermediate Temperature Solid Oxide Cells
Authors: Ishihara Tatsumi 
Published: December 2024

Oxide ion conductor is an important functional material in energy conversion and sensing area. In this presentation, development of new oxide ion conducting materials and their application in high temperature electrochemical cells such as the intermediate temperature solid oxide fuel cells (it-SOFCs) as well as electrolysis cell will be presented. In particular, in 1994, the high oxide ion conductivity in the perovskite structured material La1-xSrxGa1-yMgyO3 (LSGM) was fist time found in our group. LSGM is the first case of a pure oxide ion conducting perovskite oxide and now considered as a viable alternative to Y2O3 stabilized ZrO2 as an electrolyte for the intermediate temperature-SOFC. Not only high ion conductivity but also making thin film are important for achieving the superior electrochemical performance of solid oxide cells. In order to obtain a thin film of LSGM, several processing methods including pulsed laser deposition and conventional wet processing were tried. This resulted in an SOFC with an extremely high power density (3.3W/cm2 at 973K) opening the possibility of intermediate temperature operation at 873K. In addition, a solid oxide cell using an LSGM thin film electrolyte can be used for intermediate temperature (ca.873K) electrolysis and that a reasonable current density (>1A/cm2 at 1.6V) can be achieved at 873K. Preparation of microtubular cell using LSGM film with slurry coat method. In addition to the development of new oxide ion conducting electrolyte materials, highly active cathode and anode materials are also critical for the development of high performance it-SOFCs. In this talk, the development of new electrode materials was also introduced. Examples of the new cathode materials, the perovskite related oxides Pr2NiO4 and Ba(La)CoO3 and, for the anode, Ni-Fe based alloys will be introduced. The surface chemistry of these materials was also analyzed by using the advanced ion beam techniques, i.e., Secondary Ion Mass Spectroscopy (SIMS) and Low Energy Ion Scattering (LEIS). These unique studies showed that three dimensional tensile lattice strain can be successfully introduced by a dispersion of nano size metal particles, mainly, Au, onto the grains of ceramic Pr2NiO4. The resulting tensile strain induces increased oxygen diffusivity and surface activity to oxygen dissociation, providing a new paradigm for the design of the oxygen electrode for solid oxide cells. Using this knowledge, SOFCs with several different designs such as planar, tubular, and metal support cells, which always exhibited the high power densities suitable for commercialization. In particular, cycle stability of SOFC/SOEC was much increased on LSGM/Ni-YSZ tubular cells by infiltration of CeO2 nanoparticles. Figure 1 shows I-V curves of CeO2 infiltrated Ni-YSZ substrate in SOFC mode using LSGM film. It was found that the infiltration of higher concentration of Ce solution increased the maximum power density, because both IR loss and overpotential were significantly decreased. The maximum power density of the cell was 0.95 and 0.42 W cm-2 at 873 and 773 K, respectively at 3 M Ce nitrate infiltrated. The long-term stability of the cell was also measured by using the cell infiltrated with 1.5 M Ce, the stable power generation performance was demonstrated. The steam electrolysis performance of the cell using Ce infiltration was further studied and it was found that Ce also contributes to higher current density in SOEC operation and 1.07 A cm-2 at 1.6 V was achieved at 873 K using 2 M Ce infiltration. In this talk, development of solid oxide cells using LSGM will be introduced from materials to application.
Figure 1 I-V, I-P curves of the SOFC cell using LSGM film deposited on Ce infiltrated Ni-YSZ tubular substrate.

Figure 1