Low Temperature Fast Mixed OH−/H+ Ionic Conductor in Doped Strontium Cerates

Abstract

The drawbacks of high temperature solid oxide fuel cells (HT-SOFCs) prompt efforts to lower operating temperatures to near ambient temperatures (NAT). Here the high mixed OH−/H+ ionic conductivity in doped SrCeO3 below 100 °C is reported. The SrCe0.8Y0.2O3−δ (SCYO20) electrolyte demonstrates a high ionic conductivity of 12 mS cm−1 in water and 9 mS cm−1 in wet air at 60 °C and an excellent long-term stability over 100 h. Solid state nuclear magnetic resonance confirms the presence of protons and hydroxide ions in the hydrated oxides and their correlation with Y dopant. Demonstration of direct ammonia fuel cells using the SCYO20 electrolyte indicates the practical application value of this material. The OH− conduction of SrCe0.7Sn0.2Y0.1O3−δ (SCSY721) is demonstrated by electrolysis of D2O. The introduction of KOH significantly increases the availability of OH− feed ions, leading to a remarkable improvement of ionic conductivity of SCSY721 electrolyte which is increased by 27 times, 56.34 mS cm−1 in 6 m KOH at 90 °C. The increased ionic conductivity due to the presence of high concentration of extrinsic conducting ions, here are OH− ions, is called as ‘feeding effect’. This study offers new electrolyte materials for cost-effective, and durable electrochemical devices such as NAT-SOFCs.