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 °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)O3 (BZCY) electrolytes is prepared through solid state reduction of the K2NiF4 structured LaSrCoO4−δ with CaH2. Structural analysis by XRD reveals that the cell parameters of LaSrCoO4−δ 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−δ). The electrochemical properties of both the H-LaSrCoO4−δ–BZCY and the LaSrCoO4−δ–BZCY composite cathodes are investigated through ac impedance spectroscopy and dc polarization measurements. At 750 °C, the H-LaSrCoO4−δ–BZCY cathode exhibits a polarization resistance of 0.229 Ω cm2, which is about one third smaller than that of the LaSrCoO4−δ–BZCY cathode. Meanwhile, cathodic overpotential of 25 mV is obtained for the H-LaSrCoO4−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 LaSrCoO4−δ–BZCY cathode obtained at the same condition. Subsequent study on the cathodic reaction process implies that the better electrochemical properties of the H-LaSrCoO4−δ–BZCY cathode can be attributed to the higher oxygen vacancy concentration in the H-LaSrCoO4−δ lattice that enhances some key steps of the oxygen reduction reaction (ORR).

► New cathode candidate for SOFC was prepared by the reaction of LaSrCoO4−δ and CaH2. ► With changed lattice parameters, the hydride reduced phase had more oxygen vacancies. ► On base of a BZCY electrolyte, this new phase showed improved cathodic properties. ► Dissociation and charge transfer were rate-determining steps of the cathode reaction. ► Abundant oxygen vacancies in the new phase's lattice enhanced the cathodic kinetics.