Materials development for intermediate temperature fuel cells
Abstract
The work in this thesis mainly focuses on the preparation and optimization of materials
for intermediate temperature fuel cells (ITFCs) with the aim of achieving high fuel cell
performance as well as good stability. The fuel cell fabrication was also studied in order
to develop a cost-effective fabrication process. Methods such as solid state reaction,
combustion and carbonate co-precipitation were adopted for the synthesis of the
materials. The densification temperature of Ce0.8Gd0.05Y0.15O1.9 (GYDC) electrolyte was
greatly reduced by the carbonate co-precipitation synthesis and subsequently a simple
one-step co-press-sintering fabrication process was developed. LiNO3 as sintering
additive further reduced the densification temperature of GYDC and up to 96% relative
density was achieved at 800 °C. Lithiated NiO was employed as cathode for IT-SOFCs
and demonstrated good electrocatalytic activity. In addition, lithiated NiO was also
investigated as both anode and cathode for IT-SOFCs and its stability was studied.
Oxide-carbonate composites have demonstrated very high ionic conductivity as the
melting of carbonates greatly enhanced the mobility of ions in materials. High power
densities up to 670 mW cm-2 at 550 °C were achieved for the composite electrolytebased
ITFCs. However, the traditional lithiated NiO cathode can gradually dissolve into
the carbonate melt and scanning electron microscopy studies found obvious
morphology change nearby the cathode/electrolyte interface which may be due to the
dissolution of nickel ions. Perovskite oxide Sm0.5Sr0.5Fe0.8Cu0.2O3-δ (SSFCu) has been
demonstrated to be a compatible and stable cathode for the composite electrolyte based
ITFCs, as a stable current output of about 0.4 A cm-2 was observed under a constant
voltage of 0.7 V during a cell test lasting 100 h. Instead of GYDC,
BaCe0.5Zr0.3Y0.16Zn0.04O3-δ (BCZYZn) was also employed as substrate material for the
carbonate composite electrolyte and SrFe0.7Mn0.2Mo0.1O3-δ (SFMMo) was developed
and used as cathode.