Enhanced ionic conductivity in Gd-doped ceria and (Li/Na)2SO4 composite electrolytes for solid oxide fuel cells

• Composite electrolytes Ce0.8Gd0.2O2−δ−x(Li/Na)2SO4 are synthesized.
• The optimum sintering temperature is found to be 870 °C.
• The optimum sulphate-salt content is found to be 20 wt%.
• Composite GDC-20 wt% (Li/Na)2SO4 is a promising electrolyte candidate.

A series of novel composite electrolytes based on 20 mol% Gd doped CeO2 with varying amounts of (Li/Na)2SO4 have been synthesized. X-ray diffraction, thermogravimetry and differential scanning calorimetry, scanning electron microscope and transmission electron microscope were applied to characterize the phase components and microstructures of the composite electrolytes. Their ionic conductivities were determined by AC impedance spectroscopy. It has been found that the optimum sintering temperature and sulphate content for the composite electrolyte is 870 °C and 20 wt% (Li/Na)2SO4, respectively. Above 550 °C, a sharp increase in conductivity occurred, which can be interpreted as superionic phase transitions in the interface phases between GDC and sulphates. Both the high ionic conductivities above the transition temperature, 0.191, 0.298 and 0.372 S cm−1 at 550, 650 and 750 °C respectively, and low activation energy (0.303 eV) highlight composite GDC-20 wt% (Li/Na)2SO4 a promising electrolyte candidate for application in intermediate temperature solid oxide fuel cells.

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