Nano-structured composite cathodes for intermediate-temperature solid oxide fuel cells via an infiltration/impregnation technique

Solid oxide fuel cells (SOFCs) are high temperature energy conversion devices working efficiently and environmental friendly. SOFC requires a functional cathode with high electrocatalytic activity for the electrochemical reduction of oxygen. The electrode is often fabricated at high temperature to achieve good bonding between the electrode and electrolyte. The high temperature not only limits material choice but also results in coarse particles with low electrocatalytic activity. Nano-structured electrodes fabricated at low temperature by an infiltration/impregnation technique have shown many advantages including superior activity and wider range of material choices. The impregnation technique involves depositing nanoparticle catalysts into a pre-sintered electrode backbone. Two basic types of nano-structures are developed since the electrode is usually a composite consists of an electrolyte and an electrocatalyst. One is infiltrating electronically conducting nano-catalyst into a single phase ionic conducting backbone, while the other is infiltrating ionically conducting nanoparticles into a single phase electronically conducting backbone. In addition, nanoparticles of the electrocatalyst, electrolyte and other oxides have also been infiltrated into mixed conducting backbones. These nano-structured cathodes are reviewed here regarding the preparation methods, their electrochemical performance, and stability upon thermal cycling.