Enhanced Charge Transfer in a Ni_0.8Co_0.15Al_0.05LiO₂|Sm₂Ba_1.33Ce_0.67Cu₃O₉ Bilayer Heterojunction Symmetric Electrode for Protonic Semiconductor Oxide Fuel Cells

Protonic semiconductor oxide fuel cells based on semiconductor oxide proton conductors are emerging as very promising next-generation solid oxide fuel cell (SOFC) technology for low-temperature operation. Currently, Ni_0.8Co_0.15Al_0.05LiO₂ (NCAL) has been widely employed as a symmetric electrode for these novel SOFCs due to its good catalytic activities to both hydrogen oxidization and oxygen reduction reactions, achieving excellent performance at 550 °C. However, the interface between electrode and electrolyte needs to be modified to further reduce electrode polarization. In this study, perovskite-related Sm₂Ba_1.33Ce_0.67Cu₃O₉ (SBCC) was introduced as an interlayer electrode between a layered NCAL electrode and fluorite CeO₂ electrolyte to form a heterojunction regulating the charge transfer at the electrode/electrolyte interface. A symmetric NCAL|SBCC bilayer electrode dropped the polarization resistance of a single cell by 41% compared to the NCAL electrode, from 0.24 to 0.14 Ω·cm² at 550 °C. The peak power density was enhanced by 25% from 744 to 933 mW·cm^-2. Such better performance of bilayer heterojunction electrodes originates from energy band matching at cathode side and Schottky junction effect at anode side, improving charge separation.