Modulating the Energy Band Structure of the Mg-Doped Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3−δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells

Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3-δ (SPFMg_0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm^-1 along with an attractive fuel cell performance of 0.83 W cm^-2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg_0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO_3-δ and Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg_0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.