Hydride reduced LaSrCoO _4-δ as new cathode material for Ba(Zr _0.1Ce _0.7Y _0.2)O ₃ based intermediate temperature solid oxide fuel cells

Cathodes with high catalytic activities are usually required for the preparation of high performance intermediate temperature (600-800 °C) solid oxide fuel cells (IT-SOFCs). In the present study, a new kind of cathode material for IT-SOFCs based on Ba(Zr _0.1Ce _0.7Y _0.2)O ₃ (BZCY) electrolytes is prepared through solid state reduction of the K ₂NiF ₄ structured LaSrCoO _4-δ with CaH ₂. Structural analysis by XRD reveals that the cell parameters of LaSrCoO _4-δ become larger after the reduction. And oxygen stoichiometry of 3.57 is determined by iodometric titration for the CaH ₂ reduced phase (marked as H-LaSrCoO _4-δ). The electrochemical properties of both the H-LaSrCoO _4-δ-BZCY and the LaSrCoO _4-δ-BZCY composite cathodes are investigated through ac impedance spectroscopy and dc polarization measurements. At 750 °C, the H-LaSrCoO _4-δ-BZCY cathode exhibits a polarization resistance of 0.229 Ω cm ², which is about one third smaller than that of the LaSrCoO _4-δ-BZCY cathode. Meanwhile, cathodic overpotential of 25 mV is obtained for the H-LaSrCoO _4-δ-BZCY cathode under a current density of 100 mA cm ^-2 at 750 °C. This value is much lower than 70 mV of the LaSrCoO _4-δ-BZCY cathode obtained at the same condition. Subsequent study on the cathodic reaction process implies that the better electrochemical properties of the H-LaSrCoO _4-δ-BZCY cathode can be attributed to the higher oxygen vacancy concentration in the H-LaSrCoO _4-δ lattice that enhances some key steps of the oxygen reduction reaction (ORR).