Investigation of a self-assembled Sr0.74La0.26CoO3-δ-SrZr0.79Co0.21O3-δ composite with hierarchical structure as intermediate-temperature solid oxide fuel cell cathode

Abstract

A new series of perovskite composites with nominal compositions of Sr0.8La0.2Co1-xZrxO3-δ (x = 0.2–0.8) are proposed and synthesized via one-pot in-situ self-assembly method, of which the most optimum composite is further investigated as intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode. When the zirconium content (x) is equal to 0.2, the mixed ionic and electronic conducting Sr0.74La0.26CoO3-δ (SLC) and ionic conducting SrZr0.79Co0.21O3-δ (SZC) are incorporated as nanocomposite particles (100 nm) on the well-connected SLC microparticles (200–500 nm). This hierarchical structure is favorable for charge transport, oxygen reduction and gas diffusion. Besides, 74 wt% of SLC self-assembled with 26 wt% of SZC in nanoscale can effectively tailor the thermal expansion coefficient (18.6 × 10−6 K−1), which makes Sr0.8La0.2Co0.8Zr0.2O3-δ (SLC-SZC) composite cathode much matchable with the YSZ and GDC electrolytes (10.8 × 10−6 K−1 and 12.8 × 10−6 K−1). The electrical conductivity of SLC-SZC composite attains 170-107 S cm−1 at 375–700 °C. The single cell with SLC-SZC composite cathode achieves the maximum power density of 1739 mW cm−2 at 650 °C, superior to cells with pure Sr0.8La0.2CoO3-δ cathode. The impedance analysis verifies that oxygen adsorption and dissociation processes of the SLC-SZC composite cathode can be enhanced by its extensive surface area of the hierarchical structure and extensive heterointerface of the nanocomposite.