2D Numerical Model for Identification of Oxygen Reduction Reaction Mechanisms in Patterned Cathodes of La0.6Sr0.4Co0.2Fe0.8O3-delta

Patterned cathodes of La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF-6428) were deposited on 8 mol% yttria-doped stabilized zirconia (YSZ) substrates with a Gd-doped ceria barrier layer by rf-magnetron sputter deposition. Patterns were generated with triple phase boundary (TPB) lengths ranging from 50 to 1200 cm(-1). Electrochemical impedance spectroscopy (EIS) results were collected over a temperature and partial pressure of oxygen, pO(2), range of 600-800 degrees C and 10(-3) - 1.00 atm respectively. Plots of the inverse of the characteristic resistance, R-c(-1) (the maximum of the negative imaginary portion of the impedance), vs. the TPB length indicate the presence of surface transport. Subsequently, the results were fitted to a 2-dimensional numerical model which includes bulk diffusion, surface diffusion, and surface exchange. The model results predict the presence of surface diffusion over all measured temperatures and pO(2). Furthermore, the model results align better with an interstitial type mechanism, compared to a vacancy diffusion mechanism. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.021208jes]