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

The influence of sintering temperature on the polarization resistance of screen printed La2NiO4+delta (LNO) cathodes is studied. The electrode dispersion is measured on symmetrical cells with a 100 mu m 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 degrees 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 K-G. The addition of a dense LNO layer between electrolyte and porous electrode lowers the ASR by similar to 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 similar to 600 degrees C, resulting in an additional resistance to the apparent electrolyte resistance. (C) 2013 Elsevier B.V. All rights reserved.