(Invited) Performance and Durability of Solid Oxide Cells for Energy Storage

The first part of this talk will discuss the application of reversible solid oxide cells (SOCs) for grid-scale energy storage, focusing on pressurized reduced-temperature cell conditions where co-electrolysis yields methane-rich fuel.  A full analysis of a storage system utilizing low-resistance thin Lanthanum Gallate electrolyte cells and large-scale underground caverns for gas storage indicates that round-trip storage efficiency > 70% can be achieved, along with storage capacity and operating cost values that are comparable or better than pumped hydroelectric storage. 

The second part of the talk will describe results on degradation mechanisms, important for SOC storage technologies to achieve sufficient long-term durability for economic viability. LSM-YSZ and LSCF oxygen electrodes have been studied in both dc electrolysis and reversing-current (alternating between electrolysis and fuel cell operation) modes; similar delamination mechanisms are observed in both cases, although stability is improved by current cycling.  A critical current density and overpotential is observed below which degradation is too slow to measure over ~ 1000 h, but above which degradation rate increases rapidly.  High efficiency storage requires SOCs characterized by low resistance at intermediate temperatures.  This makes it desirable to utilize nano-scale electrodes, but these may be susceptible to degradation by particle coarsening. Accelerated life test results for impregnated oxygen electrode materials are presented and fitted using a combined electrochemical/coarsening model, and the resulting expressions are used to predict long-term performance degradation. Life test results on Ni-based fuel electrodes are also discussed.