THE EFFECT OF ADDITIONAL POLYVINYLPYRROLIDONE ON THE SYNTHESIS AND ELECROCHEMICAL PROPERTIES OF IRON (II) SULFIDES (FES2) NANOPARTICLES VIA HOT-INJECTION METHOD

• Main Author: Fahmi, Haerul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/52622
• Institution: Institut Teknologi Bandung

Iron (II) sulfide or FeS2 is an interesting transition metal material to study because it has a high capacity and specific theoretical energy density, economical, non-toxic and has abundant availability in nature. These various advantages make the FeS2 material one of the candidates for application as an electrode in the supercapacitor. On the other hand, the supercapacitor's low performance is often caused by active material FeS2 with bulk size. So that nanostructuring and supporting materials are needed in the process of making FeS2. FeS2 material can be synthesized by various methods, including the hot-injection method (HIM). This method is one of the promising methods for the synthesis of FeS2 compared to other conventional methods. It has several advantages, such as an easy synthesis process, does not require complicated equipment, short reaction time, energy requirements and temperatures are not too high and relatively environmentally friendly. On the other hand, several studies reported that the specific capacitance of pure FeS2 shows a low specific capacitance. The specific capacitance can be increased by adding polyvinylpyrrolidone (PVP) as a capping agent to inhibit particle growth. However, the higher the concentration of PVP will cause specific capacitance to decrease due to the electrode's low electrical conductivity. Therefore, it is necessary to optimize the variation in PVP concentration to obtain the best spherical capacitance. In addition to optimizing the variation in PVP concentration, this previous study also optimized the reaction time and the ratio of Fe:S precursors to their electrochemical structures and properties. The best precursor ratio optimization can be reviewed through the X-Ray Diffraction (XRD) characterization. Through this characterization, the sample with the precursor ratio Fe: S, namely 1: 4, showed good crystallinity without any other impurities. This can be proven from the diffraction peaks in accordance with the JCPDS FeS2 reference. Furthermore, the 1: 4 precursor ratio is re-optimized by evaluating the variation of synthesis reaction time. The best optimization in this stage is viewed from the XRD characterization results and the Scanning Electron Microscope (SEM). Based on the XRD results, the optimum reaction time was 30 minutes, which showed the best crystallinity of FeS2. In line with this, the SEM results with a reaction time of 30 minutes resulted in a particle size distribution of 0.72 ?m. This value is much smaller than the 1 hour reaction time with a particle size distribution of 1.72 ?m. However, the resulting particle size within 30 minutes is still quite large, so it is necessary to do further optimization with the addition of PVP. Based on the TEM characterization results, the addition of PVP can reduce the particle size of FeS2 to 3.75 nm. Furthermore, it is important to optimize the variation in PVP concentrations. The optimization of PVP concentration variations can be viewed through the electrochemical properties produced through the characterization of Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) in the KOH 3M electrolyte. In general, through this characterization, the best specific capacitance is obtained, which is shown by the addition of PVP of 3 wt% of 911 mF cm-2 at a scanning speed of 10 mV s-1. This is due to the low charge transfer value of the 3wt% FeS2-PVP sample with better electrical conductivity. These results suggest that FeS2-PVP is a promising electrode material for the development of high-performance storage of electrical energy in the future.