Application of sol-gel processing to synthesis of Ni-YSZ cermet membrane

Optimization of both the internal gelation process (IGP) and EDTA (ethylene-diamine-tetra-acetic acid) complexes-gel reduction process (CGRP) was carried out for manufacturing of Ni-YSZ (yttria-stabilized zirconia) cermet as the membrane electrode. For the IGP, we found the adequate amount of gelling agent and stabilizer such as HMTA (hexamethylenetetramine) and urea for the starting solution, so that precursor gels containing Ni content of 45-61.3 mol% were successfully synthesized. However, the samples prepared via IGP did not show the electronic conductivity but ionic one, although NiO in the samples was completely reduced to Ni. This might be caused by a decrease of Ni content during sintering at high temperatures. On the other hand, for the EDTA CGRP, precursor gels were successfully synthesized by controlling pH value in the preparation of soluble complexes. In addition, the sample synthesized via EDTA CGRP showed the electronic conductivity for Ni content of 60 mol%.