Effect of hetero-structured nano-particulate coating on the oxygen surface exchange properties of La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)

摘要

In this study, dense La0.6Sr0.4Co0.2Fe0.8O3.delta (LSCF) electrodes decorated with the novel hetero-structured ceramic oxide mixture in four different ratios of Ce0.9Gd0.2O2-delta (GDC) and La2Mo2O9 (LMO). The time-dependent conductivity transients were acquire using electrical conductivity relaxation (ECR) technique at a chosen conditions of temperature in the range of 650-850 degrees C and instantaneous pO(2) step change between 0.2 and 0.8. Fitting of time-dependent conductivity to the appropriate non-equilibrium solutions of Fick's diffusion equation has yielded the chemical diffusion coefficient, D-chem, and oxygen surface exchange coefficient, k(chem). As expected, the D-chem of the coated samples remained invariant, whilst the k(chem) is found to vary with the change in GDC-LMO coating mixture ratio. Substantial increase of a factor of 10 in the surface exchange coefficient is noticed for the LSCF coated with a 1:0.75 mixing ratio as compared to bare sample at 850 degrees C. The enhancement in k(chem) is attributed to the optimal triple-phase boundary (TPB) regions which promotes oxygen surface exchange kinetics. Thus, coating of selective ratio of hetero-structured oxide in a form of nano-particulate layer over the LSCF surface is considered to be a promising candidate for solid oxide fuel cell (SOFC) cathode. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.