Performance Evaluation of the Mixed Conducting Co_0.6Mn_0.4Al_1.6Fe_0.4O₄-Sm_0.2Ce_0.8O₂ Heterostructure Composite Electrolyte Membrane in SOFC and SOEC Mode

A significant improvement in ionic conductivity and charge transportation, coupled with a low activation energy at low operating temperatures, would significantly enhance the widespread application of low-temperature solid oxide electrolysis (450–550 °C). Following this, here we designed an intriguing composite semiconductor heterostructure powder composed of a spine-like structure of Co0.6Mn0.4Fe0.4Al1.6O4 (CMFA) and Sm0.2Ce0.8O2 (SDC) that serves as an effective electrolyte membrane for SOFCs (solid oxide fuel cells) and SOECs (solid oxide electrolysis cells). The composite heterostructure is designed to enhance the fuel cell and electrolysis performance, especially at low operational temperatures. The designed CMFA-SDC heterostructure functions as an electrolyte and NCAL functions as electrodes for SOFC and SOEC. In SOEC mode, the composite heterostructure delivers a high current density of 1.32 A/cm2 with an applied constant voltage of 1.6 V at 550 °C. Besides, in fuel cell mode, the composite electrolyte delivers a peak power density (PPD) of 980 mW/cm2 at 550 °C. This fuel and electrolysis cell, which utilizes lithium compounds as electrodes, has great promise as oxide ion conductive low-temperature SOFC and SOEC, as demonstrated by its exceptional power density and hydrogen production capability. The CMFA-SDC heterostructure composite’s increased ionic conduction was studied by utilizing a variety of transmission and spectroscopic methods, including X-ray diffraction and photoelectron spectroscopy in the visible range. Moreover, the conduction mechanism based on the heterojunction and built-in electric field has been presented in detail. These findings suggest that the heterostructure approach is practical for the LT-SOECs.