The Australian Nuclear Science and Technology Organisation (ANSTO) has collaborated with researchers at the University of Queensland in Australia, and Shandong University and Nanjing Tech Universities in China on research investigating the possible synergistic effects of a new perovskite cathode material for a low-temperature solid-oxide fuel cell (LT-SOFC) that demonstrates impressive and stable electrochemical performance below 500 °C.
Solid-oxide fuel cells (SOFC) convert the chemical energy in fuel into electricity directly by the oxidation of the fuel. These cells are considered to be highly efficient, exhibit long-term stability, produce low emissions, and are relatively low cost.
The study showed that the co-doping of a promising cathode material, strontium cobalt oxide (SrCoO3-6) with niobium (Nb5+) and tantalum (Ta5+), led to improved performance. Experiment and calculations indicated that synergistic effects occurred due to an optimized balance of oxygen vacancies, ionic mobility, and surface electron transfer. Historically, the performance of the cathode in LT SOFCs has been limited by the surface oxygen exchange kinetics of the ORR as well as the mobility of oxide ion in the bulk. New cathode materials, which form oxide ions by the reduction of oxygen, have been explored because the low operating temperature of SOFCs results in sluggish kinetics and limits the performance of the battery. Because the crystal structure of perovskite oxides is not stable below 900 °C, they are doped with rare-earth or alkaline-earth elements.
In the study, strontium cobalt oxide was doped with niobium and tantalum to produce the cathode material SrCo0.8Nb0.1Ta0-1O3-δ (SCNT) and isostructural species. A cubic perovskite structure makes oxygen vacancies in the lattice migrate freely among equivalent oxygen sites. The authors report what they think is the highest reduction of oxygen in a LT-SOFC. The authors suggest the niobium and tantalum may be decreasing the energy barrier for oxygen migration, causing the neighboring cobalt ions to become more active for charge transfer. They attribute the high power density achieved using the pure SCNT cathode to outstanding ORR activity.
The SCNT cathode outperformed the other isostructural cathode compositions at and below 500 °C and surpassed the target of 500 mW cm-2 for SOFCs, suggesting the possibility of operation even below 450°C