Ni/NiO Exsolved Perovskite La 0.2 Sr 0.7 Ti 0.9 Ni 0.1 O 3-δ for Semiconductor-Ionic Fuel Cells: Roles of Electrocatalytic Activity and Physical Junctions.

A semiconductor-ionic fuel cell (SIFC) is recognized as a promising technology and an alternative approach to reduce the operating temperature of solid oxide fuel cells. The development of alternative semiconductors substituting easily reduced transition metal oxide is a great challenge as high activity and durability should be satisfied simultaneously. In this study, the B-site Ni-doped La 0.2 Sr 0.7 Ti 0.9 Ni 0.1 O 3-δ (LSTN) perovskite is synthesized and used as a potential semiconductor for SIFC. The in situ exsolution and A-site deficiency strategy enable the homogeneous decoration of Ni/NiO nanoparticles as reactive sites to improve the electrode reaction kinetics. It also supports the formation of basic ingredient of the Schottky junction to improve the charge separation efficiency. Furthermore, additional symmetric Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ (NCAL) electrocatalytic electrode layers significantly enhance the electrode reaction activity and cells' charge separation efficiency, as confirmed by the superior open circuit voltage of 1.13 V (close to Nernst's theoretical value) and peak power density of 650 mW cm -2 at 550 °C, where the latter is one order of magnitude higher than NCAL electrode-free SIFC. Additionally, a bulk heterojunction effect is proposed to illustrate the electron-blocking and ion-promoting processes of the semiconductor-ionic composite electrolyte in SIFCs, based on the energy band values of the applied materials. Overall, we found that the energy conversion efficiency of novel SIFC can be remarkably improved through in situ exsolution and intentional introduction of the catalytic functionality.