Heteroestruturas baseadas em manganitas de níquel e sulfetos de cobalto derivados do ZIF-67 para aplicações em supercapacitores híbridos

Abstract

The development of energy storage materials has intensified in response to the growing demand for more efficient and sustainable devices. In this work, a heterostructure based on nickel manganite (NiMn₂O₄) and cobalt sulfide derived from ZIF-67 (Co₃S₄) was developed for application as a positive electrode in hybrid supercapacitors. NiMn₂O₄ was synthesized via a hydrothermal route, while Co₃S₄ was obtained through sulfuration of ZIF-67, with both materials deposited in situ on nickel foam (NF) substrate. Thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses enabled the identification of thermal events associated with precursor decomposition and phase formation after heat treatment. X-ray diffraction (XRD) patterns confirmed the formation of crystalline NiMn₂O₄ and Co₃S₄ phases, as well as the conversion of the ZIF-67 precursor after sulfuration and the coexistence of both phases in the heterostructure, with no evidence of secondary phases within the detection limit of the technique. X-ray photoelectron spectroscopy (XPS) revealed the presence of Ni, Mn, Co, S, and O elements, with multiple oxidation states for Ni, Mn, and Co, in addition to shifts in binding energy peaks, indicating modifications in the chemical environment associated with interfacial interactions between the phases. Morphological analyses by scanning electron microscopy (SEM) showed clear differences among the materials, including the formation of nanosheets for NiMn₂O₄, morphological changes after sulfuration of ZIF-67 to obtain Co₃S₄, and, for the NiMn₂O₄/Co₃S₄ heterostructure, the presence of aggregates composed of interconnected nanostructures, resulting in a heterogeneous morphology across the NF substrate. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) confirmed the crystalline and polycrystalline nature of the materials. Energy-dispersive X-ray spectroscopy (EDS) verified the presence and elemental distribution of the constituent elements in the samples. The electrochemical performance was evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The CV curves displayed well-defined redox peaks, characteristic of faradaic processes and battery-type behavior. The NiMn₂O₄/Co₃S₄ heterostructure delivered a specific capacity of 266.85 mAh g⁻¹ at 1 A g⁻¹, outperforming the individual materials, along with lower charge-transfer resistance, indicating improved electrochemical kinetics. In cycling stability tests, the material retained approximately 71% of its initial capacity after 5000 cycles at 14 A g⁻¹. These results demonstrate that the NiMn₂O₄/Co₃S₄ heterostructure exhibits superior electrochemical performance compared with the individual materials, owing to synergistic interactions between the phases and enhanced charge transport, highlighting its potential for hybrid supercapacitor applications.