ABSTRACT
Lithium-doped anatase-TiO2 nanoparticles (LixTi1-xO2 NPs, x = 0, 0.05, 0.10, 0.15 and 0.20) could be synthesized by a simple sol-gel process. X-ray diffraction (XRD) results displayed the tetragonal (space group: I41/amd) of polycrystalline TiO2 anatase phase. The spectroscopy results of Raman and FT-IR confirmed the anatase phase of TiO2 through the specific modes of metal oxides vibration in the crystalline TiO2. Surfaces micrographs by scanning electron microscope (SEM) of agglomerated LixTi1-xO2 NPs showed a spongy like morphology. Transmission electron microscope (TEM) illustrated a cuboidal shape of dispersed NPs with particle size distributed in a narrow range 5-10 nm. Bruanauer Emmett-Teller (BET) results showed the increased surface area of LixTi1-xO2 NPs with increasing Li content. LixTi1-xO2 NPs (x = 0.05-0.20) working electrodes illustrated a pseudocapacitive behavior with excellent electrochemical properties through the whole cycles of GCD test. Interestingly, Li0.1Ti0.9O2 NPs electrode illustrated a high performance in terms of maximum specific capacitance 822 F g-1 at 1.5 A g-1 in 0.5 M Li2SO4 electrolyte, with excellent capacitive retention 92.6% after 5000 cycles GCD test.
ABSTRACT
In this work, CoxZn1-xFe2O4 (x = 0.0-0.4) nanoparticles (NPs) were successfully synthesized by a hydrothermal method at 200 °C for 12 h. X-ray diffraction revealed a pure cubic spinel phase of all samples with space group Fd-3m. Fourier transform infrared spectrometry disclosed the vibrational modes of metal oxides in the spinel structure. Scanning electron microscopy and transmission electron microscopy disclosed a uniform distribution of cuboidal shape NPs with a decreased average NPs size from 22.72 ± 0.62 to 20.85 ± 0.47 nm as the Co content increased. X-ray absorption near edge spectroscopy results confirmed the presence of Zn2+, Co2+ and Fe2+/Fe3+ in Co-doped samples. The pore volume, pore size and specific surface area were determined using N2 gas adsorption/desorption isotherms by the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques. Electrochemical properties of supercapacitors, having active CoxZn1-xFe2O4 (x = 0.0-0.4) NPs as working electrodes, indicated pseudo-capacitor performance related to the Faradaic redox reaction. Interestingly, the highest specific capacitance (Csc), 855.33 F/g at 1 A/g, with a capacity retention of 90.41% after 1000 GCD cycle testing was achieved in the Co0.3Zn0.7Fe2O4 electrode.
