Advanced synthesis of materials for intermediate-temperature solid oxide fuel cells

Solid-oxide fuel cells (SOFCs) technology has a substantial potential in the application of clean and efficient electric power generation. However, the widespread utilization of SOFCs has not been realized because the cost associated with cell fabrication, materials and maintenance is still too high. To increase its competitiveness, lowering the operation temperature to the intermediate range of around 500-800 °C is one of the main goals in current SOFCs research. A major challenge is the development of cell materials with acceptably low ohmic and polarization losses to maintain sufficiently high electrochemical activity at reduced temperatures. During the past few decades, tremendous progress has been made in the development of cell materials and stack design, which have been recently reviewed. SOFCs are fabricated from ceramic or cermet powders. The performances of SOFCs are also closely related to the ways in which the cell materials are processed. Therefore, the optimization of synthetic processes for such materials is of great importance. The conventional solid-phase reaction method of synthesizing SOFCs materials requires high calcination and sintering temperatures, which worsen their microstructure, consequently, their electrochemical properties. Various wet chemical routes have recently been developed to synthesize submicro- to nano-sized oxide powders. This paper provides a comprehensive review on the advanced synthesis of materials for intermediate-temperature SOFCs and their impact on fuel cell performance. Combustion, co-precipitation, hydrothermal, sol-gel and polymeric-complexing processes are thoroughly reviewed. In addition, the parameters relevant to each synthesis process are compared and discussed. The effect of different processes on the electrochemical performance of the materials is evaluated and optimization of the synthesis processes is discussed and some emerging synthetic techniques are also briefly presented.