Stability of nickel-infiltrated anodes in intermediate temperature SOFCs

Nickel-infiltrated La_1-xSr_xGa_0.8Mg_0.2O_3-δ (LSGM) anode functional layers have been shown to yield low polarization resistance in intermediate-temperature solid oxide fuel cells (IT-SOFCs) with thin LSGM electrolytes. A dehydration step after nickel nitrate infiltration and a decrease in the calcination temperature were both shown to decrease the initial NiO particle size, but other factors such as geometry and Ni loading affected the Ni particle size upon reduction. The infiltrated anode polarization resistance, measured during life tests of full cells by separating out the anode component using electrochemical impedance spectroscopy and equivalent circuit fitting, increased continuously, e.g. from 0.08 to 0.16 Ω cm², after 550 h at 650°C. This change was accompanied by approximately a factor of 2 increase in the feature size of the infiltrated Ni. A simple electrochemical model is presented that predicts the observed changes in polarization resistance based on the effect of particle coarsening on triple-phase boundary density.