Estruturas hierárquicas core@shell baseadas em óxido metálico binário associado a hidróxidos duplos lamelares derivados de MOFs para aplicação em dispositivos avançados de armazenamento de energia

Abstract

Based on rising consumption rates coupled with concerns about energy scarcity, this work explores alternative electroactive materials for the composition of advanced energy storage devices. Given this, this thesis proposes a methodology for obtaining core@shell structures using NiCo2O4 and MOF-derived LDHs. From this perspective, ZIF-67 and Mn-ZIF-67 structures served as models for obtaining CoNiLDH and CoMnNi-LDH, respectively, both of which were used in the construction of core@shell heterostructures. To that end, NiCo2O4 with a morphology similar to sea urchins served as an inner core to anchor CoNi-LDH nanosheets, as well as providing support for ultrathin CoMnNi-LDH nanosheets. Through X-ray diffraction analysis combined with Scanning Electron Microscopy and Transmission Electron Microscopy images, the effectiveness of the processes for obtaining core@shell type structures was proven. XPS spectra indicated the occurrence of metallic ions with oxidation states (Ni2+/Ni3+ and Co2+/Co3+) in all samples. In samples containing CoMnNi-LDH, manganese ions with oxidation states (Mn2+/Mn3+/Mn4+) were identified, and the multiple redox states enabled electron transfers and contributed significantly to increasing the conductivity of the materials. As a result, the NiCo2O4@CoNi-LDH core@shell material exhibited specific capacity values of 81.82 mAh g-1 at 1.0 A g-1 and capacity retention of 77.6% after 10,000 consecutive charge–discharge cycles at 20.0 A g-1 . Such evidence demonstrates the excellent cyclic stability and enhanced electrochemical performance exhibited by the core@shell material, where the charge transfer and diffusional contributions of NiCo2O4@CoNi-LDH coupled with the ordered arrangement of the core@shell structure resulted in an energetic cooperation capable of significantly improving the overall electrochemical characteristics of the material. Furthermore, the NiCo2O4@CoNi-LDH//AC hybrid supercapacitor device achieved a maximum power density of 1,198 W kg⁻¹, keeping a single LED on for more than 5 minutes, highlighting the excellent potential of NiCo2O4@CoNi-LDH in the composition of positive electrodes of advanced energy storage devices requiring high power performance. Furthermore, the insertion of Mn ions into the composition of Mn-ZIF67 and the subsequent production of CoMnNi-LDH enabled the electrochemical improvement of the NiCo2O4@CoMnNi-LDH core@shell heterostructure material xviii when compared to NiCo2O4@CoNi-LDH. The various nanoporous channels of trimetallic hydroxide enabled better ion diffusion, and the multiple redox sites expanded the electroactive surface area, consequently leading to increased electrical conductivity and improved reaction kinetics. As a result, the NiCo2O4@CoMnNiLDH core@shell structure exhibited a specific capacity of 139.42 mAh g-1 at 1.0 A g -1 and good charge capacity retention (51.6%) even after 10,000 consecutive charge and discharge cycles at 20.0 A g-1 .