Composite Solid Oxide/Molten Hydroxide Electrolyte for Hybrid Fuel Cells

ABSTRACT For more than a century, alkaline electrolyzers and fuel cells (AEL and AFC) have been widely used due to their considerable power densities and lifetimes. However, AFCs encounter issues in managing liquid electrolytes, in operating at higher temperatures, and tolerating carbon dioxide. To solve these limitations a hybrid fuel cell is presented that uses a composite electrolyte containing solid oxide and molten hydroxide phases to operate at intermediate temperatures (400‐600°C). These materials are particularly interesting due to their potential to reduce the operating temperature of fuel cells while maintaining high power densities and conductivities. Previous research on oxide‐carbonate composites found conductivity of 0.1 S·cm −1 at 600°C. This paper focuses on the development of a new composite electrolyte based on solid oxide‐molten hydroxide for hybrid fuel cells. Specifically, the hybrid system composed of samarium‐doped ceria (SDC) and different hydroxides (LiOH, NaOH) was studied using a series of thermal, vibrational and electrochemical analyses in different operating conditions. A detailed examination of the electrolyte using differential scanning calorimetry was done to identify the phase transformation temperatures and the stability conditions for the hydroxide phase. A high conductivity of 0.04 S·cm − 1 was achieved with an SDC‐NaOH (70‐30 wt%) composite in a reducing H 2 atmosphere at 400°C. Several challenges remain, particularly in the selection of new electrode materials and ensuring their long‐term stability.