Influence of configuration and microstructure on performance of La2NiO4+δ intermediate-temperature solid oxide fuel cells cathodes

• Area specific resistance of La2NiO4+δ (LNO) in symmetric cell lowest for Tsint ∼1000 °C.
• Microstructure dependence indicates role of surface diffusion of oxygen.
• Insertion of dense base-layer of LNO changes impedance from Gerischer dominated to thin layer type dispersion.
• Qualitative model explains the differences in impedance spectra and provides relation with oxygen exchange data.

The influence of sintering temperature on the polarization resistance of screen printed La2NiO4+δ (LNO) cathodes is studied. The electrode dispersion is measured on symmetrical cells with a 100 μm 3% yttria-doped zirconia (TZ3Y) electrolyte and screen-printed yttria-doped ceria (YDC) barrier layers. The as-received commercial LNO powder was used in the formulation of the ink. For cathodes prepared following this procedure the optimum sintering temperature is 1000 °C. Analysis of the impedance spectra shows clearly a Gerischer dispersion (chemical impedance), with an activation energy of 124 kJ mol−1 for the exchange rate parameter KG. The addition of a dense LNO layer between electrolyte and porous electrode lowers the ASR by ∼35%, showing a significant change in the oxygen transfer mechanism. A tentative model, based on a global two step oxygen exchange mechanism, is presented. There are also strong indications that surface diffusion of mono atomic oxygen is a major transport path. The electronic conductivity of LNO is too low at the intended operating temperature of ∼600 °C, resulting in an additional resistance to the apparent electrolyte resistance.