Last years, composite anodes consisted of nickel-gadolinium doped ceria (Ni-GDC) cermet gained a lot of attention as they have potential to be a beneficial solution for the intermediate temperature solid oxide fuel cells. In the range of temperatures below 700o
C, a GDC cermet is characterized by a higher ionic conductivity compared to conventionally used yttria-stabilized zirconia (YSZ) cermet. Moreover, with the use of GDC as the mixed ionic-electronic conductivities (MIEC) material, electrochemical reaction sites are not restricted to triple phase boundaries (TPBs), but also extended to the double phase boundaries (DPBs) which consist of GDC/pore interfaces. Therefore, microstructure of electrodes has the crucial effect for the performance of the SOFCs and the evaluation of its changes are required to predict the deterioration of cell performances. Moreover, the precise mechanism behind observed microstructural reaction kinetics has not been fully revealed yet. For the further understanding of the electrochemical reaction kinetics, evaluation of the influence of TPB and DPB reaction for the overall electrochemical performance of MIEC anodes is required.
In this paper, the influence of the initial microstructure of Ni-GDC anode on the electrochemical performance and its deterioration after 100-h operation are investigated using electrolyte supported cells. The initial microstructure of anode is determined by the different aspect ratios and sizes of GDC powder used in the fabrication of cells. Four types of SOFC anodes were fabricated with the initial composition of NiO:GDC=60:40vol%.
The microstructural parameters of the fabricated anodes have been investigated by the focused-ion-bean – scanning electron microscopy tomography and 3D reconstruction of the representative structures. The parameters such as TPB length, surface area, porosity, tortuosity factor and connectivity have been quantitatively evaluated. From the observed microstructural changes and cell performances, contribution of the Ni-GDC microstructure and electrochemical reaction kinetics on anode performance are discussed.