A novel Fe2O3-decorated N-doped CNT porous composites derived from tubular polypyrrole with excellent rate capability and cycle stability as advanced supercapacitor anode materials

Fishnet-like double active layer-loaded carbon fiber for electrical double-layer capacitors

The rational design and controllable synthesis of high-performance energy storage materials are important measures to address the growing demand for energy storage devices. This work involves the growth of a fishnet-like Fe₂O₃ nanorod@oxygen-rich carbon layer structure directly onto carbon fiber cloth as a binder-free electrode for symmetric capacitors. The growth of Fe₂O₃ nanorods provided a large specific surface area, and the coating of an oxygen-rich carbon layer protected the Fe₂O₃ nanorods as an active substance. Furthermore, oxidation treatment created rich electrochemically active sites by loading oxygen-containing functional groups onto the composite surface. As a result, the optimal OC@Fe₂O₃-ACC sample exhibited a high areal specific capacitance of 1687 mF cm^-2 at a current density of 1 mA cm^-2. Meanwhile, an excellent capacity retention rate of 58.7% was achieved at 15 mA cm^-2. Finally, the long-term cycling stability was verified with an 80% retention rate of the initial capacitance after 12 000 cycles.

Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Metal oxide heterostructures have gained huge attention in the energy storage applications due to their outstanding properties compared to pristine metal oxides. Herein, magnetic Fe₂O₃@SnO₂ heterostructures were synthesized by the sol-gel electrospinning method at calcination temperatures of 450 and 600 °C. XRD line profile analysis indicated that fraction of tetragonal tin oxide phase compared to rhombohedral hematite was enhanced by increasing calcination temperature. FESEM images revealed that hexagonal nanoplatelets of Fe₂O₃ were hierarchically anchored on SnO₂ hollow nanofibers. Optical band gap of heterogeneous structures was increased from 2.06 to 2.40 eV by calcination process. Vibrating sample magnetometer analysis demonstrated that increasing calcination temperature of the samples reduces saturation magnetization from 2.32 to 0.92 emu g^-1. The Fe₂O₃@SnO₂-450 and Fe₂O₃@SnO₂-600 nanofibers as active materials coated onto Ni foams (NF) and their electrochemical performance were evaluated in three and two-electrode configurations in 3 M KOH electrolyte solution. Fe₂O₃@SnO₂-600/NF electrode exhibits a high specific capacitance of 562.3 F g^-1 at a current density of 1 A g^-1 and good cycling stability with 92.8% capacitance retention at a high current density of 10 A g^-1 after 3000 cycles in three-electrode system. The assembled Fe₂O₃@SnO₂-600//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 50.2 Wh kg^-1 at a power density of 650 W kg^-1. The results display that the Fe₂O₃@SnO₂-600 can be a promising electrode material in supercapacitor applications.

A Facile Fabrication of Ordered Mesoporous Carbons Derived from Phenolic Resin and Mesophase Pitch via a Self-Assembly Method

Ordered and disordered mesoporous structures were synthesized by a self-assembly method using a mixture of phenolic resin and petroleum-based mesophase pitch as the starting materials, amphiphilic triblock copolymer F127 as a soft template, hydrochloric acid as a catalyst, and distilled water as a solvent. Then, mesoporous carbons were obtained via autoclave method at low temperature (60 °C) and then carbonization at a relatively low temperature (600 °C), respectively. X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) analyses revealed that the porous carbons with a mesophase pitch content of approximately 10 wt% showed a highly ordered hexagonal mesostructure with a highly uniform pore size of ca. 5.0 nm. In addition, the mesoporous carbons prepared by self-assembly and low-temperature autoclave methods exhibited the amorphous or crystalline carbon structures with higher specific surface area (SSA) of 756 m2/s and pore volume of 0.63 cm3/g, depending on the synthesis method. As a result, mesoporous carbons having a high SSA were successfully prepared by changing the mixing ratio of mesophase pitch and phenolic resin. The electrochemical properties of as-obtained mesoporous carbon materials were investigated. Further, the OMC-meso-10 electrode delivered the maximum SC of about 241 F/g at an applied current density of 1 A/g, which was higher than those of the MC-10 (~104 F/g) and OMC-20 (~115 F/g).

Porous Fe2O3 Nanorods on Hierarchical Porous Biomass Carbon as Advanced Anode for High-Energy-Density Asymmetric Supercapacitors

In this study, a novel negative electrode material was prepared by aligning α-Fe₂O₃ nanorods on a hierarchical porous carbon (HPC) skeleton. The skeleton was derived from wheat flour by a facile hydrothermal route to enhance conductivity, improve surface properties, and achieve substantially good electrochemical performances. The α-Fe₂O₃/HPC electrode exhibits enhanced specific capacitance of 706 F g⁻¹, which is twice higher than that of α-Fe₂O₃. The advanced α-Fe₂O₃/HPC//PANI/HPC asymmetrical supercapacitor was built with an expanded voltage of 2.0 V in 1 M Li₂SO₄, possessing a specific capacitance of 212 F g⁻¹ at 1 A g⁻¹ and a maximum energy density of 117 Wh kg⁻¹ at 1.0 kW kg⁻¹, along with an excellent stability of 5.8% decay in capacitance after 5,000 cycles. This study affords a simple process to develop asymmetric supercapacitors, which exhibit high electrochemical performances and are applicable in next-generation energy storage devices, based on α-Fe₂O₃ hybrid materials.