Esfoliação eletroquímica de grafite natural com eletrólito multifuncional para obtenção de estruturas de grafeno

• Autor(a) principal: Sousa, Nei Carlos Oliveira
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações do Mackenzie
• Texto Completo: http://dspace.mackenzie.br/handle/10899/26504
• topic: esfoliação eletroquímica; grafita; eletrólito multifuncional; grafeno; dispositivos de armazenamento de carga; CNPQ::ENGENHARIAS; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::FISICO-QUIMICA::ELETROQUIMICA

The graphite is an abundant and low-cost precursor for production of graphene materials that include single-layer, few-layer and multi-layers graphene sheets, graphene oxide and reduced graphene oxide. For graphene production from graphite, it is necessary to overcome the van der Waals forces which maintain the carbon nanosheets together in the graphite. Among the several methods used in liquid phase graphite exfoliation, the electrochemical exfoliation methods and, in particular, the anodic exfoliation offers diverse some attractive characteristics such as easy and safety operation, low cost, fast production (≤ 120 minutes), environmentally friendly and suitable for graphene mass production. A disadvantage concerning the anodic exfoliation is related to the oxidation of the carbon lattice which can insert defects or functional groups in the graphene sheets. In this work are described simple and fast procedures (≤ 60 min) for graphene production by using anodic electrochemical exfoliation of graphite electrodes under controlled current and a multifunctional electrolyte. The graphite flakes (area ~ 60 mm2) were exfoliated in two galvanostatic conditions: 10 and 50 mA in electrolytes containing sodium sulfate and phosphate buffer, pH 9.0 and with and without sodium sulfite, utilized to prevent oxidation processes at the graphite electrode. The material characterization by scanning electron microscopy (SEM), Raman spectroscopy and UV-Vis indicated the production of graphene nanosheets with few layers (N ≤ 5) and lateral size ranging between 5 and 30 μm, typically. The graphene yield increases when increase the sodium sulfate concentration and the intercalation current, while the defect density of graphene does not change significantly among different exfoliated materials. With the addiction of sodium sulfite in the electrolyte, the defect density of graphene sheets increased significantly. The different materials produced with current of 50 mA were used to prepare three-dimensional graphene structures in order to evaluate the specific capacitance (SC) by cyclic voltammetry. The specific capacitance values were significantly elevated and ranged from 357.1 F g-1 in 1.0 mol L -1 Na2SO4 electrolyte to 2,913.2 F g-1 in 1.0 mol L-1 H2SO4 at 1.0 mV s-1 scan rate. The materials with higher values of SC were obtained in sulfite-containing electrolytes, indicating their potentialities for application in energy storage devices.