Mxene and Graphene based Nano Composites for Energy Storage Applications

Abstract

With the rapid growth of the human population the energy crisis is also growing in the world. To address this problem, it is essential to design and fabricate energy conversion.and storage devices. Among all available energy storage devices, supercapacitors (SCs) have attracted more attention from the current research community because of their unique features. MXene is regarded as one promising candidate for supercapacitors due to its high electrical conductivity and volumetric capacitance. MXene is a newly developed two-dimensional (2D) material. It is a very suitable substrate for fabrication due to its high electrical conductivity and large specific surface area. The two-dimensional MXene (Ti3C2Tx) sheets stacked quickly, reducing their specific surface area and charge/mass transport properties. However reduced graphene oxide presumed as significant part to improve the electrochemical behaviour. Graphene combined with MXene resolve the restacking problem and promote rapid ion diffusion in electrode materials. In this project, the Mxene/rGO composite will be synthesized through simple and facile hydrothermal treatment. The manufactured nanocomposite will be used as efficient electrode material for energy storage devices such as supercapacitor. Also, the various samples of graphene oxide were prepared using different nitrates as precursors with varying recipes via Modified hummers method and Improved Hummers method. The proposed materials are GtO, XGO, Na-GO, MnGO, Cu-GO, Ni-GO, Zn-GO, GO, 5M-rGO, 10M-rGO and M-GO film. The prepared samples were characterized by different characterization techniques such as Raman, PL, FTIR, UV-VIS and Electrochemical Impedance Spectroscopy (EIS). Raman spectroscopy can be used to examine the chemical components of materials by detecting vibrational, rotational, and other modes in a molecular system. The Raman spectra shows the D, G and 2D bands attributing the defects states and successful oxidation of GO. The broad and asymmetric emission peaks ranging between 500-900nm were observed by photoluminescence spectra. The remarkable sharp emission peak at 600, 599 nm (visible range) for Cu-GO, Ni-GO and Zn-GO is caused by the presence of CO, C=O, and O=C-OH functionalized groups on the GO. The highest PL intensity is occurred at 717, 795 and 721 nm for GO, 5M-rGO and 10M-rGO indicating the red shift for all samples due to some extrinsic defects. FTIR technique is employed to study the chemical composition and its bonding. All the samples accommodate numerous functional groups like epoxy, carbonyl, hydroxyl, and carboxyl. The straight line in lower frequency portion indicates xi

the capacitive behaviour of the electrode material. The EIS analysis investigated the charge transfer property and capacitive nature of the synthesised electrode material. From Nyquist plot of GO, Mxene 5M-rGO and 10M-rGO the slope of the curve decreases in the low frequency region demonstrating the fast ion diffusion/transportation properties. The observed band gap is 2.2eV, 1.53.9eV 2.19eV and 1.6- 3.43eV for GO, Mxene, 5M-rGO and 10M-rGO. It is indicated that all the samples show good absorption in the visible range (300-800nm). The main peak at round about at 230 nm represents the π-π* transitions of C=C bond. The shoulder peaks at round 330 nm stands for n-π* transitions of C=O bonds. Thus, the fabricated Mxene and graphenebased nanocomposite offer to be a promising material in energy devices with high energy. The cyclic voltammogram of our synthesized electrode material was compared with individual materials worked as electrodes at same potential window and scan rates and in same electrolyte as mentioned above. The shapes of CV curves for GO and Mxene were found to be approximately rectangular and symmetric, even at high scan rates, demonstrating excellent capacitive behaviour and rate performance. The CV curve for 5M-rGO can be observed to be well almost rectangular, revealing that it can serve as best electrochemical double layer capacitor (EDLC) electrodes.