Enhancement of La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) Activity by Ion Implantation for Low-Temperature SOFC Cathodes

摘要

La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ) (LSCF) has been demonstrated to be one of the best performing mixed ionic-electronic conductors (MIEC) for SOFC cathode materials. Surface exchange on LSCF, however, limits the oxygen transport and the performance. In this study, we investigated a composite cathode with surface modification of LSCF for enhanced oxygen dissociation on the surface, while utilizing LSCFs ability to transport oxygen through the bulk. Manganese ions were ion implanted into LSCF bar samples. Various implantation energies and ion concentrations were used to create samples with different Mn-ion depth profiles. The oxygen transport properties were characterized by electrical conductivity relaxation (ECR), using DC four-point probe measurements during the oxygen re-equilibration processes. The oxygen transport properties, chemical diffusion coefficient (D_(chem)) and chemical surface reaction coefficient (k_(chem)) were obtained by fitting ECR data using the diffusion equations. The changes of k_(chem) for different Mn doping levels and energies were determined. The Mn ion implanted LSCF samples showed an enhanced k_(chem), improving the overall oxygen reduction reaction (ORR) for LSCF cathodes.