Symmetric and reversible solid oxide fuel cells

In the past few years a novel concept of Solid Oxide Fuel Cells (SOFC) has been developed: the symmetrical Solid Oxide Fuel Cells (SSOFC). In this configuration, the same electrode material is used as anode and cathode. Several state-of-the-art SOFC electrode materials have been tested and optimised to operate in such a novel configuration, as is the case of the lanthanum chromites traditionally used as interconnect materials, lanthanum chromium manganites and strontium titanates generally used as anodes and lanthanum manganites typically used as cathodes. Fuel cell performances of approximately 800 mW cm−2 and ∼500 mW cm−2 under H2 and CH4 atmospheres have been obtained using some of these materials in symmetric configuration. Moreover, promising performances have also been reported for interconnect-based materials under city gas containing the impurity H2S. An interesting feature of the compositions evaluated is their potential use as symmetrical electrodes for Solid Oxide Electrolysis Cells (SOEC) with efficiencies in the range of the conventional SOEC systems, i.e. LSM-YSZ/YSZ/Ni-YSZ. Hence, they may be considered all-in-one Symmetric and Reversible SOFCs (SR-SOFCs) with significant advantages compared to traditional configurations, regarding both fabrication and maintenance/operation. In this review, we provide an insight into the most common materials tested as symmetrical electrodes for SOFCs and SOECs, electrolytes employed, configurations tested, new fabrication processes and procedures for microstructural engineering.