Theoretical Study of Functionalized Two-Dimensional Materials towards their Application in Supercapacitors

Abstract

This thesis investigates possible roots to enhance the quantum capacitance(CQ) of two-dimensional materials based electrodes for supercapacitor applications through density functional theory(DFT) calculations. In this work, various two-dimensional materials such as graphene, molybdenum disulfide(MoS2), and hexagonal boron nitride(h- BN) have been considered, subsequently, chemical functionalization of these systems has been performed to manifest the high quantum capacitance. The quantum capacitance of functionalized systems was estimated from the precise electronic band structures of the system obtained by using DFT calculations. It has been observed that ad-atom functionalization of graphene can significantly enhance the quantum capacitance of the system. Therefore, in the first stage, the quantum capacitance of ad-atom doped graphene with a varying doping concentration has been systematically studied. The effect of temperature on quantum capacitance has also been investigated. The temperature-dependent study of CQ for functionalized graphene shows that the CQ remains very high in a broad range of temperatures close to room temperature. In the second stage, the graphene functionalization has been done by doping with different aliphatic and aromatic molecules and their radicals. Our theoretical investigation reveals that aromatic and aliphatic radicals introduce localized density of states near the Fermi level of the functionalized systems, due to a charge localization which in turn significantly enhances the quantum capacitance of the system. The effects of atomic dislocation on graphene during functionalization has also been incorporated in our investigation. In the third stage, we have carried out our investigation in other two-dimensional materials such as MoS2 and h-BN. Attempts have been made to enhance the quantum capacitance of these systems by introducing defects as well as performing chemical fictionalizations. The detailed study in this thesis suggests an efficient way to produce functionalized materials using two-dimensional materials that could be very suitable electrode materials of highly efficient supercapacitors.