Hydride reduced LaSrCoO4-δ as new cathode material for Ba(Zr0.1Ce0.7Y0.2)O3 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 degrees C) solid oxide fuel cells (IT-SOFCs). In the present study, a new kind of cathode material for IT-SOFCs based on Ba(Zr0.1Ce0.7Y0.2)O-3 (BZCY) electrolytes is prepared through solid state reduction of the K2NiF4 structured LaSrCoO4-delta with CaH2. Structural analysis by XRD reveals that the cell parameters of LaSrCoO4-delta become larger after the reduction. And oxygen stoichiometry of 3.57 is determined by iodometric titration for the CaH2 reduced phase (marked as H-LaSrCoO4-delta). The electrochemical properties of both the H-LaSrCoO4-delta-BZCY and the LaSrCoO4-delta-BZCY composite cathodes ware investigated through ac impedance spectroscopy and dc polarization measurements. At 750 degrees C, the H-LaSrCoO4-delta-BZCY cathode exhibits a polarization resistance of 0.229 Omega cm(2), which is about one third smaller than that of the LaSrCoO4-delta-BZCY cathode. Meanwhile, cathodic overpotential of 25 mV is obtained for the H-LaSrCoO4-delta-BZCY cathode under a current density of 100 mA cm(-2) at 750 degrees C. This value is much lower than 70 mV of the LaSrCoO4-delta-BZCY cathode obtained at the same condition. Subsequent study on the cathodic reaction process implies that the better electrochemical properties of the H-LaSrCoO4-delta-BZCY cathode can be attributed to the higher oxygen vacancy concentration in the H-LaSrCoO4-delta lattice that enhances some key steps of the oxygen reduction reaction (ORR). (C) 2011 Elsevier B.V. All rights reserved.