On the systematic selection of perovskite solid electrolytes for intermediate temperature fuel cells

The ability to develop a rationale for predicting new perovskite solid electrolytes discussed here relies in part upon empirical relationships found between activation energy for anionic transport and perovskite crystallographic-related parameters including (i) the average metal-oxygen bond energy of the perovskite lattice, (ii) the degree of openness, or “free volume”, of the lattice, and (iii) the critical radius (rc) saddle point formed by two A and one site through which anionic mediation proceeds. Resulting relationships are found to hold promise for predicting new perovskite solid electrolytes possessing low activation energies and consequent high ionic conductivity for anionic transport. Upon application of principal component analysis to those major empirical factors appearing to influence high ionic mobility in perovskite lattice along with the Goldschmidt tolerance factor S, new materials were selected, three of which were subjected to preliminary evaluation in small fuel cells operating at 600°C. For less than theoretically dense materials, ionic conductivities for sintered disks of BaTb0.9In0.1O3, CaCe0.9Gd0.1O3 and CaCe0.9 Gd0.1O3 and CaCe0.9Er0.1O3 were found to vary between ≊5×10−2Ω−1cm−1and 5×10−3Ω−1cm−1 with activation energies energies varying between 0.53 and 0.35 eV.