Sr0.7Ho0.3CoO3−δ as a potential cathode material for intermediate-temperature solid oxide fuel cells

The oxygen-deficient perovskite Sr0.7Ho0.3CoO3−δ (SHCO) operates on the Co(III)/Co(II) redox couple rather than the usual Co(IV)/Co(III) couple for an oxygen reduction reaction(ORR) cathode of an intermediate-temperature solid oxide fuel cell (IT-SOFC). The room-temperature XRD pattern of SHCO prepared by solid-state reaction can be indexed in the tetragonal I4/mmm space group with unit-cell parameters a = 7.617 Å, and c = 15.293 Å. SHCO exhibits an electrical conductivity with values larger than 488 S cm−1 over the temperature range 560–800 °C. The area specific resistance (ASR) of a SHCO cathode measured on a La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) electrolyte reaches a relatively low value of 0.14 Ω cm2 at 800 °C in air. With a 300-μm-thick LSGM disk as the electrolyte and NiO-GDC as the anode, a cell with the SHCO cathode exhibited maximum power densities of 1274, 756, and 493 mW cm−2 at 850, 800, and 750 °C, respectively, with hydrogen as fuel and ambient air as oxidant. Cross-section scanning-electron-microscopy measurements confirmed the porous microstructure of the electrodes and good electrode-buffer layer-electrolyte adherence in a single test cell. The ORR activity of a SHCO cathode operating on the Co(III)/Co(II) couple approaches that of the best cathodes operating on the Co(IV)/Co(III) couple, and higher-spin Co(III) ions provide a compatible thermal expansion.

► We evaluated the electrochemical performance of the oxygen-deficient perovskite Sr0.7Ho0.3CoO3−δ (SHCO) as a cathode material for intermediate-temperature solid oxide fuel cell (IT-SOFC). ► An LSGM electrolyte-supported technique was used for a single cell test. ► A maximum powder density of 756 mW cm−2 at 800 °C satisfies the general requirement for a cathode material for IT-SOFCs.