Co-doped cerium oxide Fe0.25-xMnxCe0.75O2-δ as a composite cathode material for IT-SOFC

Abstract

In this study, Fe-Mn co-doped ceria Fe0.25Mn0.00Ce0.75O2-δ (FMDC1), Fe0.23Mn0.02Ce0.75O2-δ (FMDC2), Fe0.21Mn0.04Ce0.75O2-δ (FMDC3), and Fe0.19Mn0.06Ce0.75O2-δ (FMDC4) powders are synthesized by sol gel method and evaluated as cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC). The combination of Fe and Mn significantly enhanced the ceria catalytic activity and oxygen kinetics for redox-based reactions. The effects of the co-doping mechanism on the phase composition, optical behavior, and electrochemical performance are mainly investigated. The prepared samples are characterized by XRD, SEM, FTIR, UV–vis, and conductivity tests. X-ray diffraction analysis revealed well-developed crystallinity with a single phase cubic structure of synthesized cathode material. SEM depicted the highly porous facet for Fe0.19Mn0.06Ce0.75O2-δ (FMDC4) resulted in the large triple-phase boundaries for the reduction of ambient air. The inclusion of Mn3+and Fe3+ ions into CeO2 network created additional oxygen vacancies (Ov) and simultaneously reduced the optical band gap energy from 2.81 eV for FMDC1 (x = 0.00) to 2.54 eV for FMDC4 (x = 0.06). Among the four samples, FMDC4 possessed the highest electrical conductivity (∼0.89 Scm−1) at 650 °C and corresponding low activation energy of ∼0.301 eV, which lead to good catalytic activity with an enhanced electrochemical performance of the SOFC system. The open-circuit voltage (OCV) attained the value of ∼0.98 V, maximum power density of ∼335 mW cm−2 is obtained at 550 °C, which is comparable to previously reported electrodes. The results suggested that the combination of Fe and Mn into ceria can be used as an effective catalytic promoter for oxygen reduction reactions (ORR), and the composition of FMDC4 resulted in the peak conductivity, short term stability and highest power density as compared to other synthesized samples.