Synthesis and characterizations of CoCr2O4/C composite using high energy ball-milling technique as novel anode materials for Li-ion batteries

A chromium cobaltite based ternary composite as an efficient electrode material for hybrid supercapacitors with theoretical investigation

To cater to the growing demand for advanced energy storage devices, the development of efficient electrode materials with brilliant electrochemical response is highly required. Battery-like materials have gained wide research attention as effective electrode materials for hybrid supercapacitors (HSCs). In this account, chromium cobaltite (CrCo2O4) has been synthesized via a facile hydrothermal route. The structural and electronic properties of CrCo2O4 have been investigated using DFT. Activated carbon (AC) and polypyrrole (PPY) have been introduced to hybridize with CrCo2O4 to enhance its electrochemical performance. The high conductivity of PPY, along with the high surface area and excellent cycling stability of AC, synergistically boosts the performance of CrCo2O4. The ternary composite CrCo2O4/AC/PPY exhibited a higher capacitance of 991.25 F g-1 than the pristine CrCo2O4 (301.53 F g-1) at 5 mV s-1. The composite also displayed high cycling stability with 84.25% capacitive retention after ten thousand cycles. The composite also delivered a lower charge transfer resistance (0.36 Ω), which resulted in better charge transfer. A HSC with CrCo2O4/AC/PPY as the positive electrode and MnO2/AC as the negative electrode was fabricated that delivered a high energy density of 97.77 W h kg-1 and power of 1.6 kW kg-1. A high capacitive retention of 76.75% was observed for ten thousand cycles. The practicality of the prepared material was tested by connecting three hybrid cells in series to illuminate a panel of 57 LEDs. The panel was able to glow for 51 minutes. The outstanding performance of the composite reveals the excellent possibility for application in high-performance advanced hybrid SCs.

In Situ TEM Observation of (Cr, Mn, Fe, Co, and Ni)3O4 High-Entropy Spinel Oxide Formation During Calcination at Atomic Scale

High-entropy oxides (HEOs) are promising anode materials for lithium-ion batteries (LIBs), owing to their stable crystal structure, superionic conductivity, and high capacity. In this study, the (Cr, Mn, Fe, Co, and Ni)3O4 HEO via solid-state reaction is prepared. To improve the synthetic efficiency, it is necessary to understand the formation mechanism. Therefore, a high-resolution transmission electron microscopy (HRTEM) is used to record information during calcination at increasing temperature. The overall formation process included MnO2 and NiO aggregation at 500 °C, followed by (Mn, and Ni)3O4 combined with Co3O4 at 600 °C to form (Mn, Co, and Ni)3O4. At higher temperatures, Fe2O3 and Cr2O3 sequentially combined with (Mn, Co, and Ni)3O4 and formed the (Cr, Mn, Fe, Co, Ni)3O4 at 900 °C. In addition, the valence-state-changing mechanisms and ion arrangements of (Cr, Mn, Fe, Co, and Ni)3O4 are determined using electron energy loss spectroscopy (EELS) and extended X-ray absorption fine structure (EXAFS). This study successfully revealed the formation of HEO at atomic scale. The results provide valuable insights for improving the manufacturing process of (Cr, Mn, Fe, Co, and Ni)3O4 HEOs, which is expected to play a vital role in the development of anode materials for next-generation LIBs.

Characterization and photocatalytic activity of CoCr2O4/g-C3N4 nanocomposite for water treatment

One of the materials that has recently been used to remove environmental pollution from industrial effluents with photocatalytic technology is cobalt chromate (CoCr₂O₄) nanoparticles. An effective way to improve the photocatalytic properties of materials is to composite them with other photocatalysts to prevent recombination of electron-holes and accelerate the transfer of oxidation/reduction agents. Graphitic carbon nitride (g-C₃N₄) is an excellent choice due to its unique properties. In this research, CoCr₂O₄ and its composite with g-C₃N₄ (5, 10, and 15%) were synthesized by polyacrylamide gel method and characterized by X-ray diffraction, scanning electron microscopy, FTIR, UV-Vis spectroscopy techniques. The photocatalytic behavior of synthesized nanoparticles was investigated in the degradation process of methylene blue dye. The results showed that the composite samples have higher efficiency in photocatalytic activity than the pure CoCr₂O₄ sample. Using CoCr₂O₄-15 wt%g-C₃N₄ nanocomposite, after 80 min, methylene blue was completely degraded. The mechanism of degradation by CoCr₂O₄-g-C₃N₄ nanocomposite was the superoxide radical produced by the reaction of electrons with oxygen absorbed on the catalyst surface, as well as optically produced holes directly.

Nanochromates MCr2O4 (M = Co, Ni, Cu, Zn): Preparation, Characterization, and Catalytic Activity on the Thermal Decomposition of Fine AP and CL-20

The chromate nanoparticles such as CoCr₂O₄, NiCr₂O₄, CuCr₂O₄, and ZnCr₂O₄ were prepared by a modified sol-gel method. The structural and morphological properties of the chromate nanoparticles were characterized by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The catalytic effects of chromates on the thermal decomposition of fine ammonium perchlorate (FAP) and hexanitrohexaazaisowurtzitane (CL-20) were studied by the TG-DTG measurements. Results show that the addition of CoCr₂O₄, NiCr₂O₄, CuCr₂O₄, and ZnCr₂O₄ nanoparticles makes the activation energies for the thermal decomposition of FAP decrease by 93.9, 94.0, 83.1, and 67.0 kJ·mol^-1, and the thermal decomposition temperatures decrease by 45.0, 24.9, 57.7, and 38.8 K respectively. On the other hand, a similar trend exists in the case of the thermal decomposition of CL-20. Therefore, the addition of nanochromates shows high catalytic efficiency on the thermal decomposition of both FAP and CL-20 components, which would be beneficial to promote the burning rate of propellants containing FAP and CL-20 components.