Perpustakaan Digital ITB

Supercapacitors are considered as energy storage materials which are believed to provide high-energy density and high-power density. Iron Sulfide (FeS) with hexagonal troilite phase has an antiferromagnetic (AFM) behavior in its z-direction, which results that hexagonal FeS proceed magnetoelectric behavior. Due to its properties, FeS is potential to be applied in many fields such as energy storage devices and spintronics devices. Troilite, a hexagonal FeS phase with 1:1 stoichiometric ratio, is not available in nature and hard to synthesize. This phase tends to form defected FeS rather than the stoichiometric. Besides, the study of the defect effect on the FeS properties is also not yet explored for both experimental and calculation. Therefore, in this study, the first-principles calculation of FeS was brought with Fe deficient as vacancy type to analyze the FeS electronic structure. Below 400K, The FeS are reported to has insulator-AFM phase with a space group of P62c. The first-principles study of FeS with the phase of ????62???? is done in this research by using Density Functional Theory (DFT). Hubbard Correction is brought the Fe atom to accommodate the strong correlated electron interaction in Fe atom. At the first step, lattice parameter was calculated with self-consistency field and obtained that 1 eV Hubbard potential results in lattice parameter of a = 5.93 Å and c = 11.74 Å, which match with experimental results. Then, vacancies are introduced by reducing the Fe atom from the structure, and performed 4 vacancy variations. The density of states and band structure were calculated from the optimized structure. In pristine structure, the energy band gap is 0.65 eV. On the other hand, the vacancy reduce the energy band gap by the occurrence of mid-gap states. The mid-gap states are a result of unpair spin from the defected FeS. The magnetic moment of FeS is also reported in this study, with a value of each vacancy variation is 2.08 ?B, 4.25?B, 6.31 ?B, 10.23 ?B for vacancy variation of 2.08%, 4.16%, 6.24%, and 8.32% respectively. After introducing the defect, semi-metallicity was observed, which raised from the FeS semiconductor behavior. Then, several dopants were introduced into FeS as other defect types. Cobalt, Chromium, and Manganese are selected as the dopants of this study. Besides, the study of magnetic properties and electric properties was purposed in this work. The dopant could induced magnetization with magnetization moment of 1.675 ?B, 0.977 ?B, and -0.053 ?B for Co, Mn, and Cr, respectively. From the density of states calculation, mid-gap states still occur but with smaller mid-gap states. However, mid-gap states,which observed on defected FeS, holds huge potential to results quantum capacitance phenomenon. States near the Fermi level is one of the strong indicators that material could possess quantum capacitance. Theoretically, quantum capacitance could be calculated, as performed in this study. The quantum capacitance was obtained from the density of states with a value of 2280 F/g, 2072 F/g, 2059 F/g, 1975 F/g for concentration defect of 2.08%, 4.16%, 6.24%, and 8.32%, respectively. Compared to the pristine, the quantum capacitance of defected FeS was higher with the quantum capacitance of pristine FeS is 2231 F/g. Besides, after doping Cobalt (Co), Manganese (Mn), and Chromium (Cr), each dopant exhibits a higher quantum capacitance compared to the pristine with the value of 2122 F/g, 2618 F/g, 3076 F/g for Co, Mn, and Cr, respectively. These enhancement indicate that dopants could enhance quantum capacitance significantly in water-based electrolytes. Furthermore, the voltage bias is increased to analyze the supercapacitor performance further. In a doped-type defect, the FeS could be applied as symmetric supercapacitor that differs from asymmetric behavior as in the Fe-deficient defect. The integrated quantum capacitance calculation is also performed to further show and confirmed the real quantum capacitance inside the supercapacitor. From two variation of voltage bias, the FeS show asymmetric supercapacitor behavior for water-based electrolyte use. With the higher voltage bias from the different electrolytes, the supercapacitor behavior changes to symmetric. Moreover, the Cr-doped FeS could results the highest quantum capacitance as presented in this study.