Filmes finos baseados em hexacianoferratos de ferro e bismuto e nanomateriais de carbono para aplicação em dispositivos de armazenamento de energia

Abstract

The objective of this work was the development and characterization of nanocomposite thin films based on iron (HCFFe) and bismuth (HCFBi) hexacyanoferrates combined with carbon nanomaterials (carbon nanotubes and reduced graphene oxide) for application in aqueous rechargeable batteries. The motivation of this study stems from the growing demand for efficient, safe, and low-cost energy storage technologies, such as aqueous electrolyte rechargeable batteries, which emerge as promising alternatives to lithium-ion batteries due to the abundance of metals like sodium and potassium, in addition to the higher intrinsic safety of aqueous systems. The nanocomposite films (HCFFe/NTC, HCFFe/rGO, HCFBi/NTC, and HCFBi/rGO) were prepared using the liquid-liquid interfacial synthesis method. This method allowed the attainment of integral structures, albeit with an irregular compositional distribution, at the toluene-water interface, facilitating their subsequent transfer onto ITO substrates. The materials were structurally and morphologically characterized by Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The analyses confirmed the formation of HCFFe nanoparticles and HCFBi microparticles distributed within the carbon matrices, and an unprecedented diamond-shaped morphology was observed for HCFBi. The electrochemical performance of the films was optimized through a 23 factorial design, evaluating the influence of the cation type (Na+ or K+), pH, and electrolyte concentration. Cyclic voltammetry results, combined with Dunn’s method, indicated that the HCFFe/rGO film exhibited a predominantly faradaic behavior associated with ion intercalation, whereas the HCFBi/rGO film showed more pronounced capacitive and pseudocapacitive contributions. In galvanostatic charge-discharge tests, the HCFFe/rGO composite reached a specific capacity of 160 mA h g-1, while HCFBi/NTC, despite presenting a lower specific capacity (35.85 mA h g-1), demonstrated remarkable cycling stability after 300 cycles. Additionally, the HCFBi/rGO film presented a specific capacitance of 113.30 F g-1, highlighting its potential for capacitor applications.