Investigation of the magnetic and supercapacitor properties of nanocomposites synthesized by green hydrothermal method with S. officinalis extract

In recent years, energy scarcity and global warming have increased the need for supercapacitors as green energy storage devices. Therefore, new low-cost supercapacitors with high energy density must be developed to meet the needs of society. Faradaic redox reactions of pseudocapacitors, a type of supercapacitor, are usually performed in metal oxides where metal ions have multiple valence states. Transition metal oxide pseudocapacitors have high energy density, high specific capacitance, superior specific energy, and large charge transfer reaction characteristics due to variable oxidation steps, making them unique candidates for high performance supercapacitors. Recently, many studies have been conducted to investigate and develop transition metal oxide based materials for pseudocapacitor applications. In this thesis, the synthesis of nanocomposites using Salvia officinalis (S. officinalis) plant extract-mediated hydrothermal method with Fe3O4, Co3O4, CuO and ZnO transition metal oxides to improve the electrochemical properties of NiO with high theoretical pseudocapacitor properties was carried out at two different operating conditions, 120°C, 12 s (HT-I) and 180°C, 24 s (HT-II). The structural characterization of the synthesized nanocomposites was characterized using Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX) methods. Scherrer and Williamson-Hall (W-H) formulas were used to calculate the full width half maximum (FWHM) values obtained from X-ray diffraction of nanocomponents and crystallite size. In addition, microstrain, stress and energy density were analyzed using with the W-H models of uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM). Magnetic and electrochemical behaviors were elucidated using Vibrating Sample Magnetometer (VSM) and Cyclic Voltammetry (CV) analysis. The nanocomposites synthesized by HT-II method were found to have much smaller particle size and homogeneous surface morphology compared to HT-I method. According to the results of VSM and CV analysis, a significant increase in both saturation magnetization and specific capacitance values of NiO NP and NiO/Fe3O4, NiO/Co3O4, NiO/CuO, NiO/ZnO nanocomposites were determined.