Proton conductivity in mixed-conducting BSFZ perovskite from thermogravimetric relaxation

The proton conductivity of mixed hole-, oxygen ion- and proton-conducting Ba0.5Sr0.5Fe0.8Zn0.2O3-delta (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 pH(2)O (and pD(2)O). The obtained proton concentrations at 20 mbar pH(2)O range from 1.3 to 0.32 mol% (350-600 degrees C). The effective diffusion coefficients extracted from the transients and ranging from 1.4 to 29 x 10(-7) cm(2) s(-1) (350 to 600 degrees 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 x 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.