High temperature solid oxide cell (SOC) technology is attracting considerable interest in recent decades for clean power generation and hydrogen production (green hydrogen) when combined with low-cost renewable energy. The key driver for such a strong interest is its superior thermodynamic efficiency and high-rate power and hydrogen production. However, the current scale-up and commercialization efforts are hindered by the insufficient durability and high cost, both of which are resulted from the high operating temperature (700-800^oC). A further reduction in operation temperature to, e.g. below 700^oC, is the best solution to address the durability and cost issues. As the operating temperature is reduced, the resistances of cell components increase correspondingly. To decrease the resistances, one can thin out or use high-conductivity electrolyte membranes, open up microstructure of fuel (or hydrogen) electrodes substrate and employ oxygen electrocatalytically active oxygen electrodes. Unfortunately, a direct use of active oxygen electrodes in SOCs has been proven formidable due to their reaction with electrolytes (ZrO₂-based) and very high thermal expansion coefficient. To address the first problem, applying a CeO₂-based barrier layer between electrolytes and oxygen electrodes is currently the solution. However, introduction of such a barrier layer considerably increases the ohmic resistance (sometimes as high as 2-3x), thus defeating the purpose of boosting cell performance. To address the second problem, mixing the active oxygen electrode with CeO₂-based material or infiltrating it into a thermally compatible skeleton is currently the solution, but CeO₂-based barrier layer is still needed.

Therefore, a key development for reduced-temperature ZrO₂-based SOCs is to find an active oxygen electrode without the need of a barrier layer. Here we show that a composite consisting of La_0.8Sr_0.2MnO₃ (LSM), an excellent electronic conductor, and (Bi_0.75Y_0.25)_0.93Ce_0.07O_1.5±δ (BYC), an excellent ionic conductor, is a potential barrier layer free oxygen electrode for reduced-temperature SOCs. We also show fabrication of open structured hydrogen electrode substrate to facilitate H₂/H₂O diffusion and increase the performance of HE.