Manipulating the Activity and Thermal Compatibility of NdBaCoFeO5+δ Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells via Fluorine Doping

The use of LnBaCo(2)O(5+delta) (Ln = rare earth) cathodes in intermediatetemperature solid oxide fuel cells (IT-SOFCs) is limited by their high thermal expansion coefficients (TECs). Unfortunately, the electrocatalytic activity of LnBaCo(2)O(5+delta) cathodes is also decreased significantly while reducing the TECs. Here, we report the simultaneous enhancement of the oxygen-reduction activity and thermal expansion compatibility of the NdBaCoFeO5+delta (NBCF) double-perovskite cathode for IT-SOFCs via fluorine doping at the oxygen sites, that is, NdBaCoFeO5+delta-xFx (NBCFFx, x = 0.05 and 0.10). The maximum power density of the single cell with a configuration of NiO-Ce0.8Sm0.2O2/Ce0.8Sm0.2O2/La0.9Sr0.1Ga0.8Mg0.2O3-delta/NBCFF0.05 attains 504 mW cm(-2) at 700 degrees C in dry H-2. Compared with the pristine NBCF, the polarization resistances of NBCFF0.05 are down by 18.9, 17.0, 13.9, and 10.5% from 650 to 800 degrees C with an interval of 50 degrees C, respectively, while the average TEC is decreased by 3.6%. Based on the analysis of distribution of relaxation time from impedance data, the oxygen surface exchange and bulk diffusion are the rate-limiting steps in the oxygen-reduction reaction, which can be improved by fluorine doping. Our results suggest that the fluorine doping at oxygen sites shows a better ability to promote the performance of the cathode material in IT-SOFCs.

Automated summary

This study investigates the enhancement of oxygen-reduction activity and thermal expansion compatibility of double-perovskite cathode materials in IT-SOFCs through fluorine doping at oxygen sites. The results demonstrate that fluorine doping can decrease polarization resistances and reduce thermal expansion coefficients.