Composite Electrolytes for Solid Oxide Fuel Cells

Dear Colleagues,

Solid oxide fuel cells are on the way to entering the market. High efficiency and fuel flexibility are the most attractive properties of SOFC in the field of co-generation or distributed power systems. The revers operation—solid oxide electrolysis cells—is also attracting increasing attention for a huge market of energy storage or H₂ production; however, high costs are still the main obstacle for their application. Reducing the temperature is believed to make it possible to use cheaper materials for interconnects or BOP parts, and is the effective way of reducing costs. However, the operating temperature is strictly limited by ionic conductivity, especially that of electrolyte. Although there has been much progress in recent years in proton conductor and semiconductor electrolytes, which transfer the smallest ions, such electrolytes still have the problem of less stability in CO₂-containing atmospheres, poor sintering properties, and insufficient strength. Therefore, composite electrolytes seem necessary to further decrease operating temperatures. Composite electrolytes may have potential synergistic effects in enhancing ionic conductivity, and can overcome the shortages of each component, for example, to prohibit the electronic conductivity. The most well-known example is to use doped ceria as the barrier layer on zirconia to solve the problem of chemical compatibility. Regarding temperature reduction, further effort should be made for exploring new materials, especially proton conductors. This is the motivation of the current Special Issue.

At reduced temperatures, electrode activity decreases even more sharply than electrolyte conductivity; therefore, the exploration of studies on improving the activities of electrodes, which are compatible with the composite electrolytes, at lower temperatures is important. On the other hand, applications of electrolytes are expanding into broader fields, including SOEC or sensors. Regarding these new applications, new problems of stability and chemical compatibility arise. Furthermore, in addition to studies on the intrinsic properties of materials, the technologies of delivering applicable components, such as electrolyte sheets with a sufficient size, strength, and acceptable resistance, are also important.

This Special Issue highlights composite electrolyte developments and related studies in all aspects of SOFC/EC or other applications.

Prof. Dr. Shaorong Wang
Guest Editor

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