Enhancement of La0.6Sr0.4Co0.2Fe0.8O3-δ Surface Exchange through Ion Implantation

Abstract

La0.6Sr0.4Co0.2Fe0.8O3-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 oxygen transport and performance. We investigated surface modified LSCF, by Mn ion implantation, for an enhanced surface oxygen exchange rate while maintaining LSCFs oxygen ion conductivity through the bulk. Various implantation energies and ion concentrations were used to create samples with different Mn-ion depth profiles. The oxygen transport properties, chemical diffusion coefficient (Dchem) and effective chemical surface exchange coefficient (kchem), were characterized by electrical conductivity relaxation (ECR), using DC four-point probe measurements during the oxygen re-equilibration process. The changes of kchem for different Mn doping levels and ion acceleration energies determined with ECR are compared with surface configurations obtained using X-ray photoelectron spectroscopy. The Mn ion implanted LSCF samples show an enhanced kchem, improving the overall oxygen reduction reaction for the LSCF cathode material. Possible factors for the increase in surface exchange for the Mn implanted LSCF samples are discussed.