Novel triple-phase composite cathode materials for proton-conducting solid oxide fuel cells

Ce0.8Sm0.2O2−δ (SDC), BaZr0.1Ce0.7Y0.2O3−δ (BZCY) powders are mechanically mixed with Sm0.5Sr0.5CoO3−δ (SSC) powders to prepare triple-phase SSC–xSDC–(0.3 − x) BZCY (x = 0.1, 0.15, 0.2) composite cathode materials for proton-conducting solid oxide fuel cells (H-SOFCs). The SSC, SDC and BZCY powders are all synthesized via aqueous gelcasting method. Chemical compatibility, sinterability, microstructure, linear thermal expansion coefficients, electrical conductivity and electrochemical performance of the composite cathode materials are investigated and compared with single phase SSC and dual-phase SSC–0.3BZCY composite cathode materials. The results reveal that there have no observable chemical reactions among SSC, SDC and BZCY after co-firing the powder mixes at 1100 °C for 3 h. Adding SDC and BZCY into SSC material decreases open porosity, increases the shrinkage rate of the sintered SSC materials and significantly reduces thermal expansion mismatch between BZCY and SSC materials. Electrical conductivity of the triple-phase composite cathode samples ranges from about 130.8 S cm−1 to 342.3 S cm−1 at temperature 450–800 °C, and increases as SDC content increases. Polarization resistances between the triple-phase composite cathode materials and the BZCY electrolyte decrease with increasing SDC content. The polarization resistance is significantly reduced from 1.57 Ω cm2 for dual-phase SSC–0.3BZCY materials to 0.77 Ω cm2 for triple-phase SSC–0.2SDC–0.1BZCY materials under open circuit conductions at 700 °C in air. The preliminary test results have suggested that triple-phase SSC–xSDC–(0.3 − x) BZCY (x = 0.1, 0.15, 0.2) materials may be a potential candidate of cathode material for H-SOFCs.

► Novel triple-phase SSC–SDC–BZCY composite cathode materials for H-SOFCs were first reported.
► Effects of SDC and BZCY on the sinterability of the composite cathode were revealed.
► The addition of SDC can improve the electrical conductivity of the composite cathode.
► The triple-phase composite cathode has lower polarization resistance than the SSC material.