Ionic conductivity increase by one order of magnitude in BCY composite electrolyte added with Li2O

Abstract

The low ionic conductivity of proton conductor electrolytes at low temperatures was one of the key issues that restrict the reduction of operating temperature in ceramic fuel cells. The traditional Y-doped BaCeO3 proton conductor (BCY) has an ionic conductivity of only a few tens of mS·cm−1 at 500 °C, which cannot meet the needs of high-performance low-temperature ceramic fuel cells. In this paper, we found that the ionic conductivity of the composite electrolyte made by adding 20 % Li2O to BCY at 550 °C was 0.526 S cm−1, which was 40 times that of the dense BCY electrolyte sintered at 1550 °C. The maximum power density of a ceramic fuel cell using a BCY- Li2O composite material with a thickness of 1 mm as the electrolyte and porous Ag as the symmetrical electrode was 129 mW cm−2 in H2 at 550 °C. The characterization results of XRD, EPR, and FTIR showed that there may be a region with a large number of oxygen vacancies and lithium vacancies created at the interface of the BCY and Li2O–LiOH composite electrolyte formed in the BCY-Li2O composite electrolyte during the testing conditions for fuel cell performance due to the migration of Li+. The formation of this region should be the main reason for the extremely high conductivity of the BCY-Li2O–LiOH composite electrolytes formed in the cell at low temperatures.