Design of interfaces in efficient Ln2NiO4+δ (Ln = La, Pr) cathodes for SOFC applications†
In this work, a novel architecture of Ln2NiO4+δ (LnNO; Ln = La, Pr) cathodes is prepared on the Ce0.9Gd0.1O2−δ (CGO) electrolyte by sequentially using screen-printing (SP) and electrostatic spray deposition (ESD) techniques for the first time. Both LnNO samples crystallize into a single Fmmm orthorhombic layered Ruddlesden–Popper structure. The role of the electrode/air and electrode/electrolyte interfaces has been evaluated by impedance spectroscopy. A drastic reduction in polarization resistance (Rpol) from 3.33 to 0.42 Ω cm2 and from 0.83 to 0.08 Ω cm2 is obtained at 600 °C for LaNO and PrNO, respectively, when the ESD electrode (with a dense thin, ∼100 nm, LnNO sub-layer) is topped by a SP current collector. A further Rpol reduction down to 0.16 and 0.04 Ω cm2 is successfully obtained for LaNO and PrNO, respectively, when the LnNO sub-layer is replaced by a thicker (∼3 μm) porous CGO/LnNO composite sub-layer. This composite sub-layer plays a main role in obtaining the best electrochemical properties of nickelates available in the literature, to the best of our knowledge. Moreover, the values of polarization resistance for both electrodes are constant at 650 °C for 15 days in air, proving their suitability as SOFC cathodes at this intermediate temperature.