EFFECT OF GRAPHITE PRECURSOR IMMERSION IN SULFURIC ACID/HYDROGEN PEROXIDE (H2SO4/H2O2) MIXTURE ON THE ELECTROCHEMICAL PROPERTIES OF EXFOLIATED GRAPHITE

• Main Author: Bityasmawan A, Oktaviardi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/49007
• Institution: Institut Teknologi Bandung

Graphene is a constituent material of graphite, which is widely studied because of its several attractive properties, including excellent electrical conductivity, large surface area, high flexibility, and high transparency. The large surface area and high electrical conductivity make graphene is suitable as one of the candidates to be applied as a supercapacitor electrode. Electrochemical exfoliation of graphite is a promising method for fabricating graphene because it has several advantages such as an easy processable, inexpensive process, does not require complicated types of equipment, and relatively environmentally friendly. Graphene produced through this process is often called exfoliated graphite (EG). Several studies have reported that the specific capacitance of graphene obtained from this process shows low specific capacitance. The specific capacitance of the supercapacitor can be increased through the functionalization of graphene or EG with oxygen-containing functional groups. However, more oxygen content will decrease specific capacitance due to the low electrical conductivity of the electrode. Therefore, it is necessary to optimize the oxygen content and electrical conductivity of the active material. In this study, the pre-treatment of graphite precursor was carried out in the form of immersion of graphite precursors in a mixture of H2SO4 (sulfuric acid)/H2O2 (hydrogen peroxide) to control the oxidation level of samples and increase the electrochemical properties of EG. The parameters varied in the pre-treatment were the H2SO4/H2O2 mixture volume fraction and the pre-treatment time. The pre-treatment of graphite in a mixture of H2SO4/H2O2 before the electrochemical exfoliation process can cause the expansion of graphite sheet precursors. A larger amount of H2O2 and the longer pre-treatment time will make the graphite sheet expansion more massive. The enormous expansion of graphite sheets results in faster electrochemical peeling. X-Ray Diffraction (XRD) characterization result demonstrates the formation of EG through widening and decreasing the peak intensity of the (002) graphitic plane when compared to graphite precursor. The results of Raman spectroscopy show that the level of crystal defects decreases if the pre-treatment is carried out on a mixture of H2SO4/H2O2, which contains more amount of H2O2. Through Raman spectroscopy and Scanning iv Electron Microscopy (SEM) images, it can also be obtained that the most optimum exfoliation degree is produced in samples undergoing pre-treatment at H2SO4/H2O2 95:5 vol% for 3 minutes indicating the formation of few-layer graphene. The pre-treatment of graphite also affects the oxidation level of produced EG. The results of the Fourier Transform Infrared (FTIR) characterization and Energy Dispersive X-Ray (EDX) spectroscopy confirmed that the EG sample had less oxygen content if the pre-treatment was carried out on H2SO4 / H2O2 mixtures which had more H2O2 content. This phenomenon is allegedly caused by the faster exfoliation time when the H2O2 content in the H2SO4/H2O2 mixture is higher. The faster time is due to the expansion and intercalation of water on graphite sheets resulting from the pre-treatment. Besides, through time variation experiment, it can be obtained that the oxidation level of the sample decreases when the pre-treatment was conducted for 3 minutes and then increases again when the pre-treatment was carried out for 5 minutes. These results indicate that the degree of oxidation of EG can be controlled through the pre-treatment of graphite precursors in the variation of the volume fraction of H2SO4/H2O2 mixture and time variation. The larger amount of H2O2 volume used for pre-treatment obtains higher electrical conductivity of the samples. Meanwhile, optimization of the pre-treatment time using the composition of H2SO4 / H2O2, which produces optimum exfoliation (H2SO4 / H2O2 95: 5 vol%), shows that the highest electrical conductivity is obtained from the pre-treatment for 3 minutes. Electrochemical Impedance Spectroscopy (EIS) characterization results indicate that the lowest charge transfer resistance (Rct) is obtained from the samples with the highest electrical conductivity. The lower the Rct value will cause the capacitive properties of material to be more ideal. From Cyclic Voltammetry (CV) characterization, it was found that the samples obtained through the pre-treatment on H2SO4/H2O2 demonstrate an electric double layer capacitor (EDLC) behavior. The highest specific capacitance value obtained in the sample EG-3 95:5 vol% is 68.59 F/g. This value is 34% higher than the sample obtained from the pre-treatment without the addition of H2O2. The capacitive properties of the sample can be maintained up to a voltage range of 1.5 V. It makes the samples potentially can be applied as a high voltage supercapacitor using the aqueous electrolyte. The method used in this study offers a process that is relatively inexpensive, environmentally friendly, and fast to produce active material supercapacitor electrodes.