Polypyrrole-coated Fe2O3 nanotubes constructed from nanoneedles as high-performance anodes for aqueous asymmetric supercapacitors

A crosslinked network polypyrrole coated cobalt doped Fe2O3@carbon cloth flexible anode material for quasi-solid asymmetric supercapacitors

Iron(III) oxide (Fe2O3) exhibits a substantial theoretical specific capacitance and a broad operational voltage window, making it a prospective anode material. The crystal structure of Fe2O3 was altered through cobalt doping, and its electronic conductivity was improved by supporting it with carbon cloth (Co-Fe2O3@CC). Subsequently, a crosslinked network of polypyrrole (PPy) was synthesized onto Co-Fe2O3@CC via an ice-water bath, resulting in the formation of PPy/Co-Fe2O3@CC. This PPy nano-crosslinked network not only established three-dimensional electron transport pathways on the Fe2O3 surface but also amplified the composite material's specific surface area to 45.229 m2 g-1, thereby promoting its electrochemical performance. At a current density of 2 mA cm-2, PPy/Co-Fe2O3@CC displayed an area specific capacitance of 704 mF cm-2, a value 2.2 times higher than that of Co-Fe2O3@CC. The assembled PPy/Co-Fe2O3@CC//Ni-MnO2@CC asymmetric supercapacitor demonstrated an energy density of 1.41 mW h cm-3 at a power density of 54 mW cm-3, making the synthesized electrode material a promising candidate for flexible supercapacitors.

Charge transfer and vacancy engineering of Fe2O3 nanoparticle catalysts for highly selective N2 reduction towards NH3 synthesis

The development of electrocatalysts for N₂ reduction reaction (NRR) is significant for scalable and renewable NH₃ synthesis, but calls for a technology innovation to overcome the specific problems of low efficiency and poor selectivity. Herein, we prepare a core-shell nanostructure by coating polypyrrole (PPy) onto sulfur-doped iron oxide nanoparticles (denoted as S-Fe₂O₃@PPy) as the highly selective and durable electrocatalysts for NRR under ambient conditions. Sulfur doping and PPy coating remarkably improve the charge transfer efficiency of S-Fe₂O₃@PPy, and the interactions between PPy and Fe₂O₃ nanoparticles produce abundant oxygen vacancies as active sites for NRR. This catalyst achieves an NH₃ production rate of 22.1 μg h^-1 mg_cat^-1 and a very-high Faradic efficiency of 24.6%, surpassing other Fe₂O₃ based NRR catalysts. Density functional theory calculations show that the S-coordinated iron site can successfully activate the N₂ molecule and optimize the energy barrier during the reduction process, resulting in a small theoretical limiting potential.

Visible-light-induced photocatalytic response of easily recoverable Mn2O3/SiO2 monolith in centimeter-scale towards degradation of ofloxacin: Performance evaluation and product analysis

Monolithic-photocatalysts being easily recoverable are a suitable alternative to powdered materials for pollutant treatment. This study was conducted to prepare Mn₂O₃/SiO₂ monoliths by wet-impregnating Mn(NO₃)₂^․4H₂O in SiO₂ monoliths. The crystallinity of oxide was affirmed via XRD analyses, whereas EDS and elemental-mapping, and XPS studies revealed the constituent elements and their oxidation states. FESEM images confirmed porous morphology, while BET-analysis confirmed its mesoporous nature (∼8.44 nm) and enormous surface area (∼241 m²/g). The DRS and PL studies disclosed that Mn₂O₃/SiO₂ monoliths consisted of narrow band-gap of ∼2.14 eV and had suitable electron/hole separation. The photocatalytic effectiveness of the monolith had been checked by degrading model dye methylene blue (MB) and antibiotic ofloxacin (OF). The influence of various reaction parameters for degradation, i.e., monolith dose, solution-pH, illumination-area, scavengers, etc., was noted. At optimal reaction conditions, outstanding competence was achieved for MB (95.23%; 0.0225 min^-1) and decent results were obtained for OF-degradation (73.2%; 0.0096 min^-1). The recyclable nature of the catalyst (∼12.7%-reduction in effectiveness after 10 successive cycles) was vindicated by several characterization studies after reusability. The O₂^•-radicals participated majorly in the degradation reaction. The reaction intermediates plus products, generated after the degradation of had been identified via LC/MS study. The mineralization extent of the OF and MB was also gauged through TOC analyses. The photocatalytic treatment of raw textile wastewater manifested ∼57.8% COD and 53% TOC-removal. This study emphasizes the competence of Mn₂O₃/SiO₂ monoliths for the photocatalytic abatement of refractory organic contaminants.

Enhanced catalytic reduction of p-nitrophenol and azo dyes on copper hexacyanoferrate nanospheres decorated copper foams

Catalytic reduction of nitroaromatic compounds using low-cost non-precious metal containing catalyst remains an essential topic in wastewater treatment. Herein, copper hexacyanoferrate nanospheres decorated copper foams (CF) were prepared by a facile method, and it was used as structured catalysts for the reduction of p-nitrophenol (p-NP) and azo dyes. The catalyst obtained by calcination at 200 °C shows the highest catalytic activity, with an almost complete reduction of p-NP within 3 min with a rate of 2.057 min^-1 at room temperature, and it exhibited excellent reusability in successive 6 cycles. The effects of temperature, initial concentration, pH, and flow rate on p-NP reduction were investigated. Moreover, the mechanistic investigation revealed that fast electron transfer ability and enhanced adsorption for p-NP contributed to its enhanced catalytic performances. This work put forward an efficient approach for the construction of structured catalysts with enhanced performance in catalytic reduction applications.

Construction of α-MnO2 on Carbon Fibers Modified with Carbon Nanotubes for Ultrafast Flexible Supercapacitors in Ionic Liquid Electrolytes with Wide Voltage Windows

In this study, α-MnO₂ and Fe₂O₃ nanomaterials are prepared on a carbon fiber modified with carbon nanotubes to produce the nonbinder core–shell positive (α-MnO₂@CNTs/CC) and negative (Fe₂O₃@CNTs/CC) electrodes that can be operated in a wide voltage window in ultrafast asymmetrical flexible supercapacitors. MnO₂ and Fe₂O₃ have attracted wide research interests as electrode materials in energy storage applications because of the abundant natural resources, high theoretical specific capacities, environmental friendliness, and low cost. The electrochemical performance of each electrode is assessed in 1 M Na₂SO₄ and the energy storage properties of the supercapacitors consisting of the two composite electrodes are determined in Na₂SO₄ and EMImBF4 electrolytes in the 2 V and 4 V windows. The 2 V supercapacitor can withstand a large scanning rate of 5000 mV S⁻¹ without obvious changes in the cyclic voltammetry (CV) curves, besides showing a maximum energy density of 57.29 Wh kg⁻¹ at a power density of 833.35 W kg⁻¹. Furthermore, the supercapacitor retains 87.06% of the capacity after 20,000 galvanostatic charging and discharging (GCD) cycles. The 4 V flexible supercapacitor shows a discharging time of 1260 s and specific capacitance of 124.8 F g⁻¹ at a current of 0.5 mA and retains 87.77% of the initial specific capacitance after 5000 GCD cycles. The mechanical robustness and practicality are demonstrated by physical bending and the powering of LED arrays. In addition, the contributions of the active materials to the capacitive properties and the underlying mechanisms are explored and discussed

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.

Spongy p-Toluenesulfonic Acid-doped Polypyrrole with Extraordinary Rate Performance as Durable Anodes of Sodium-Ion Batteries at Different Temperatures

Sodium-ion batteries (SIBs) have potential as an energy storage system because they have similar electrochemical properties as lithium-ion batteries, abundant resource reserves, and extremely high safety performance. Compared with traditional graphite materials, conductive polymers are more suitable as an anode electrode material for SIBs. In this study, a simple and scalable approach has been used to synthesize p-toluenesulfonic acid-doped polypyrrole (p-TSA-PPy). The as-obtained material showed remarkable rate capacities and cyclability. At room temperature (25 °C), its discharge capacities could reach 185, 162, and 135 mAh g^-1 under 10, 30, and 50 C rates after 250 cycles, respectively. More importantly, the capacity of the p-TSA-PPy could still be maintained at 120.5 mAh g^-1 even at the 2000th cycle at 10 C. In addition, it achieves attractive electrochemical performance at different temperatures (0 and 50 °C).