Nondestructive characterization of solid oxide fuel cell (SOFC) materials has drawn attention owing to the advances in instrumentation that enable in situ characterization during high-temperature cell operation. X-ray photoelectron spectroscopy (XPS) is widely used to investigate the surface of SOFC cathode materials because of its excellent chemical specificity and surface sensitivity. The XPS can be used to analyze the elemental composition and oxidation state of cathode layers from the surface to a depth of approximately 5–10 nm. Any change in the chemical state of the SOFC cathode at the surface affects the migration of oxygen ions to the cathode/electrolyte interface via the cathode layer and causes performance degradation. The objective of this article is to provide a comprehensive review of the adoption of XPS for the characterization of SOFC cathode materials to understand its degradation mechanism in absolute terms. The use of XPS to confirm the chemical stability at the interface and the enrichment of cations on the surface is reviewed. Finally, the strategies adopted to improve the structural stability and electrochemical performance of the LSCF cathode are also discussed.
In this study, cobalt (Co) loaded Sr 2 TiFeO 6-δ (STF) double perovskite was synthesized using a modified nitrate combustion method for the application in catalytic decomposition of methane (CH 4 ) for hydrogen (H 2 ) production in a fixed bed reactor. The physicochemical properties of the catalyst were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy, N 2 adsorption-desorption, thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy. The catalyst showed a stable crystalline behavior with a uniform dispersion of Co over STF. The different compositions with varying Co loading were tested for methane decomposition at 850 C and constant flow rate. The 5% Co/STF achieving a maximum CH 4 conversion of ~95% with an H 2 yield of ~49%. Five percentage Co/STF showed excellent catalytic activity and stability for 46.5 hours time on stream without any indication of performance degradation. The spent catalyst was also analyzed using XRD, SEM, and TGA. The carbon deposited is shaped as carbon nanotubes that are a byproduct and also assist in metal exsolution in high-temperature processes. The use of STF shows the excellent potential showed by perovskites, which are stable in reducing environments, as support materials for methane decomposition.
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