Preparation and electrochemical properties of rGO/MIL-101/PANI composites

Due to the increase in investments in renewable energy and the widespread use of portable electronics, electrical energy storage needs have arisen. Lithium ion batteries and supercapacitors are two important technologies that can store electrochemical electrical energy. While supercapacitors stand out with their superior power densities, their energy densities are below lithium ion batteries. For this reason, it has been the subject of research to investigate increasing the energy densities without sacrificing the power densities of the supercapacitors. Materials prepared for use in supercapacitor applications should be porous, long-term stable in the electrolyte, high electrical conductivity and charge transfer capability. Metal organic frameworks are porous materials formed by ligating metal ions to metal ions. MOFs have often sought for supercapacitor applications with their pore structure that can interact well with electrolytes. However, low electrical conductivity affects their performance in electrochemical applications negatively. Supercapacitive properties of MOFs are being investigated, but sufficient information about the electrochemical energy storage mechanism of MOF class materials has not been reached yet. Applications of polyaniline (PANI) from the family of conductive polymers in supercapacitors and lithium-ion batteries have been investigated as conductivity enhancers. It has a significant effect on the result of electrochemical measurement in PANI's morphology. The flexible nature of PANI allows it to be easily composited with other materials. When PANI is composite with materials such as graphene, it creates higher stability, high conductivity nanocomposites. In the thesis, new nanocomposites were prepared with reduced graphene oxide and polyaniline of MIL-101(Cr) and MIL-101(Fe). MIL-101(Cr) and its binary composites were synthesized by both hydrothermal and microwave method. The prepared materials are characterized by elemental analysis, FT-IR, XRD, FE-SEM and N2 adsorption and desorption analysis at 77 K. Electrochemical properties of composites were investigated by cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M Na2SO4 and 2M KOH. While EDLC type capacitive properties improved with the addition of graphene in composites, an improvement in psedocapacitive properties was observed with the addition of PANI. It has been determined with the GCD method that the highest specific capacitance value is reached with the rGO-6/MIL-101(Fe)/PANI composite. It was determined by EIS that the internal resistance of MOFs decreased with the addition of graphene. In the charge / discharge stability tests of the ternary composites gradually increased in the first 500 cycles, the capacitance remained stable up to the 1000th cycle. Te ternary composite containing MIL-101 (Fe) maintained its stability up to the 1000th cycle