Nb and Ta co-substitution in Bi0.5Sr0.5FeO3−δ cathodes for IT-SOFCs: Performance insights

Abstract

This study explores the development of advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) through the co-substitution of niobium (${Nb}^{+5})$ and tantalum (${Ta}^{+5}$) at the B site in the ${Bi}_{0.5}{Sr}_{0.5}Fe{O}_{3-\delta }$ perovskite structure. Both ${Nb}^{+5}$ and ${Ta}^{+5}$ were selected for their identical ionic radii and stable high valence state, which contribute to structural stability, while difference in electronegativity enhances oxidation reduction reaction (ORR) kinetics. The materials were synthesized via a solid-state reaction route. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the formation of a pure cubic phase and high-concentration vacancy in ${Bi}_{0.5}{Sr}_{0.5}{Fe}_{0.8}{Nb}_{0.1}{Ta}_{0.1}{O}_{3-\delta }\left(BiSFN10T10\right)$. Branauer-Emitter-Teller (BET) surface area analysis indicated that $BiSFN10T10$ exhibited highest surface area, enhancing oxygen absorption. Scanning electron microscopy (SEM) revealed excellent adhesion between the cathode, anode and electrolyte materials. The symmetrical cell demonstrated low polarization resistance at $700˚C$, indicating superior electrochemical performance. A single anode-supported cell achieved a peak power density of $590\frac{mW}{{cm}^2}$ and the current density $600\frac{mA}{{cm}^2}$ with $10mol\%$ of $Nb$ and $Ta$ co-substitution in the ${Bi}_{0.5}{Sr}_{0.5}Fe{O}_{3-\delta }$ under dry $H_2\text{.}$ Surpassing the performance of individually substituted ${Bi}_{0.5}{Sr}_{0.5}{Fe}_{0.8}{Nb}_{0.1}{O}_{3-\delta }\left(BiSFN10\right)$.and ${Bi}_{0.5}{Sr}_{0.5}{Fe}_{0.8}{Ta}_{0.1}{O}_{3-\delta }\left(BiSFT10\right)$ materials. Furthermore, the Distribution of Relaxation Time (DRT) analysis provides detailed insight into the electrochemical process across various frequencies. These findings highlight the potential of $BiSFN10T10$ as a high-efficiency cathode material for SOFCs applications, promising a significant advancement in energy conversion technologies.