Theoretical description on the interface-enhanced conductivity of SDC/LiNa-carbonate composite electrolytes

Abstract

SDC (Ce0.8Sm0.2O1.9)/LiNa-carbonates composite electrolytes for intermediate temperature SOFCs have been prepared by infiltrating molten LiNaCO3 into the pre-sintered porous SDC pellets with distinctive porosity structures. XRD, SEM and Mercury Porosimetry were employed to structurally characterize the SDC pellets and the composite electrolytes, while AC impedance spectroscopy was used to measure their ionic conductivities. It has been found that the conductivities of SDC-carbonate composites are strongly affected by the porosity structure parameters of SDC pellets including the tortuosity of pore channels and their specific interface area, depending on the dimensions of SDC grains and the built-up pores. According to the ideas of charge transport in tortuous pore channels, a theoretical description on the interface-enhanced conductivities of SDC-carbonates composites has been achieved. It agrees well with the experimental data and reveals that the conductivity of composite electrolytes may be linearly increased with the specific SDC-carbonate interface area, but inversely proportional to the square of tortuosity as well.