Preparation of YSZ/YDC and YSZ/GDC composite electrolytes by the tape casting and sol-gel dip-drawing coating method for low-temperature SOFC

The composite electrolytes for low-temperature solid oxide fuel cells were fabricated via coating the YSZ sol on tape-casted substrates of yttria doped ceria (YDC) and gadolinia doped ceria (GDC). The doped ceria substrates with 98% of relative density were prepared by the tape-casting method followed by the sintering at 1,500°C for 2 hours. The YSZ polymeric sol for dip-drawing coating was synthesized by the partial hydrolysis of Zr-n-butoxide. The optimum dip-drawing coating rate for obtaining pinhole and crack free YSZ film was 2 cm/min using YSZ polymeric sol with 1.13 mol/l of concentration. After 10 times coating on ceria substrates with YSZ followed by the heat-treatment at 1,400°C for 2 hours, the fully densified YSZ film with 2.0 μm of thickness without pores, cracks, or chemical reactions could be obtained. The results of single cell tests shows that YSZ layer coated doped ceria composite electrolyte prepared by the sol-gel dip-drawing method has an superior single cell performance to YSZ electrolyte without dissociation of ceria substrate.