Galvanic cell measurements on a fast proton conducting complex perovskite electrolyte

Abstract

The proton conducting Ba 3Ca 1.18Nb 1.82O 9−δ complex oxide electrolyte is shown to have proton conductivity σ H > 10 −2 S/cm with transport number t H > 0.98 at 600 °C. Concentration cell measurements up to 800 °C with different gases show no sign of residual electronic conduction with a total ionic transport number, t H + t o , that is nearly unity. Further, it is found that only 1 3 of the oxygen-ion vacancies, i.e. those that are replaceable by protons, participate in the conduction process, while the remaining deeply trapped V o .. are virtually immobilized. With an electrolyte disc of 1.0 mm thickness, a hydrogen fuel cell operating at 500~600 °C is shown to generate an open circuit voltage of 1.0 V and short circuit current density near 130 mA/cm 2. Also, no electrolytic degradation with respect to the cell EMF was detected after operation in O 2 or CO/CO 2 gases for more than 100 h. These qualities make the compound an excellent candidate as a solid oxide electrolyte for hydrogen fuel cells, humidity/hydrogen sensors and pumps.