Proton conductivity in mixed-conducting BSFZ perovskite from thermogravimetric relaxation

Abstract

The proton conductivity of mixed hole-, oxygen ion- and proton-conducting Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3−δ (BSFZ), a potential cathode material for fuel cells based on oxidic proton-conducting electrolytes, was determined from the weight changes of dense pellets upon changing pH₂O (and pD₂O). The obtained proton concentrations at 20 mbar pH₂O range from 1.3 to 0.32 mol% (350–600 °C). The effective diffusion coefficients extracted from the transients and ranging from 1.4 to 29 × 10⁻⁷ cm² s⁻¹ (350 to 600 °C) represent a lower bound for the proton diffusivity and the directly related proton mobility. The calculated proton conductivities reach values in the range of 0.9 to 3 × 10⁻⁴ S cm⁻¹. Since the real proton conductivity might be underestimated, these values are sufficiently high to render the bulk path in the oxygen reduction mechanism dominant in dense, thin-film electrodes.