Electrical and microstructural characterization of Gd-doped Ceria/Y-doped Zirconia bi-layer electrolyte prepared by tape casting

Thiago Dias,Dulcina Pinatti Ferreira De Souza

doi:10.1590/s1517-707620170001.0135

Abstract

GDC-YSZ bi-layer SOFC electrolytes are an interesting manner to protect GDC electrolytes of the low oxygen partial pressure present at anode-electrolyte interface. This oxygen partial pressure condition and high temperatures during the operation of SOFC permit GDC electrolyte reduction injuring the performance of SOFC. In this work, GDC-YSZ bi-layer electrolytes were prepared using double tape casting technique. Single layers of YSZ and GDC electrolytes were also prepared by the same technique for comparison. All samples were sintered at 1600 °C/2 h in air and analyzed by SEM and impedance spectroscopy technique. A good adhesion was established between the layer GDC and YSZ and no cracks were detected despite the differential firing shrinkage. The electrical conductivity of GDC-YSZ bi-layer sample at 350 °C was 7.98x10-5 S.cm-1 and for GDC and YSZ single layer samples electrical conductivities were 1.89x10-4 S.cm-1 and 4.71x10-5 S.cm-1, respectively. These results show that GDC-YSZ bi-layer electrolyte is superior to YSZ single layer electrolyte.

Highlights

One of the main goals on solid oxide fuel cells (SOFC) technology is to achieve viable operation at temperatures lower than 1000 °C, in which high cost materials are required to avoid the cell degradation [1-3]
The oxygen partial pressure at the interface between anode and electrolyte at 800 °C is between 10-18 and 10-20 atm [6]
Under reducing atmosphere, Gadolinia-doped ceria (GDC) becomes a mixed conductor resulting in severe degradation of the cell performance [2,7]

Summary

Introduction

One of the main goals on solid oxide fuel cells (SOFC) technology is to achieve viable operation at temperatures lower than 1000 °C, in which high cost materials are required to avoid the cell degradation [1-3]. Gadolinia-doped ceria (GDC) exhibits ionic conductivity higher than yttria-stabilized zirconia (YSZ) at temperatures below 800 °C and present great potential for SOFC electrolytes applications [4,5]. The oxygen partial pressure at the interface between anode and electrolyte at 800 °C is between 10-18 and 10-20 atm [6]. In these conditions, it occurs the Ce+4 reduction since at 800 °C the equilibrium oxygen partial pressure between Ce2O3 and CeO2 phases is 2.5x10-20 atm. The reduction of ceria causes expansion of the crystal lattice decreasing the mechanical stability of the electrolyte [8]

Methods

Results

Conclusion