Structure-tunable Mn3O4-Fe3O4@C hybrids for high-performance supercapacitor

N-Doped Porous Carbon-Nanofiber-Supported Fe3C/Fe2O3 Nanoparticles as Anode for High-Performance Supercapacitors

Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe3C/Fe2O3 nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe3C/Fe2O3 during charge-discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g-1 at 2 A g-1, superior to that of NCNF-supported Fe3C nanoparticles (NCFC, 261.7 F g-1), and NCNFs/Fe2O3 (NCFO, 398.3 F g-1). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg-1 at 800 W kg-1. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe3C/Fe2O3.

Boosting the Capacitive Performance of Supercapacitors by Hybridizing N, P-Codoped Carbon Polycrystalline with Mn3O4-Based Flexible Electrodes

Chitosan, a biomass raw material, was utilized as a carbon skeleton source and served as a nitrogen (N) atom dopant in this study. By co-doping phosphorus (P) atoms from H3PO4 and nitrogen (N) atoms with a carbon (C) skeleton and hybridizing them with Mn3O4 on a carbon fiber cloth (CC), an Mn3O4@NPC/CC electrode was fabricated, which exhibited an excellent capacitive performance. The N, P-codoped carbon polycrystalline material was hybridized with Mn3O4 during the chitosan carbonization process. This carbon polycrystalline structure exhibited an enhanced conductivity and increased mesopore content, thereby optimizing the micropore/mesopore ratio in the electrode material. This optimization contributed to the improved storage, transmission, and diffusion of electrolyte ions within the Mn3O4@NPC electrode. The electrochemical behavior was evaluated via cyclic voltammetry and galvanostatic charge-discharge tests using a 1 M Na2SO4 electrolyte. The capacitance significantly increased to 256.8 F g-1 at 1 A g-1, and the capacitance retention rate reached 97.3% after 5000 charge/discharge cycles, owing to the higher concentration of the P-dopant in the Mn3O4@NPC/CC electrode. These findings highlight the tremendous potential of flexible supercapacitor electrodes in various applications.

Oxygen vacancies refilling and potassium ions intercalation of δ-manganese dioxide with high structural stability toward 2.3 V high voltage asymmetric supercapacitors

Oxygen vacancies occupation and coordination environment modulation of the transition-metal based electrodes are effective strategies to improve the structural stability and electrochemical performance. In this work, the 2-methylimidazole (2-MI) doped manganese dioxide (MnO2) anchored on carbon cloth (CC) is fabricated via a simple method (MI-MnO2-x/CC), where the oxygen defects on/inside the K+ doped δ-MnO2 nanosheets are in-situ created by reductive ethanol/Mn2+ and occupied by 2-MI ligands. With the pre-embedded K+ ions and abundant ligand-refilled defects, the electronic coordination structure, structural stability and electron/ion diffusion efficiency can be effectively enhanced. Therefore, the MI-MnO2-x/CC reveals a remarkable specific capacitance of 721.2 mF cm-2 with excellent cycle durability (capacitance retention of 93.4% after 10,000 cycles) under 1.3 V operation potential window. In addition, an asymmetric supercapacitor assembled by MI-MnO2-x/CC and activated mechanical exfoliated graphene oxide yields a maximum energy density of 57.0 Wh kg-1 and a highest power density of 23.0 kW kg-1 under 2.3 V. This effective oxygen defect stabilization strategy by ligands refilling can be extended to various metal oxide-based electrodes for energy storage and conversion.

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

CNT-Strung LiMn2 O4 for Lithium Extraction with High Selectivity and Stability

LiMn₂ O₄ is of great potential for selectively extracting Li⁺ from brines and seawater, yet its application is hindered by its poor cycle stability and conductivity. Herein a two-step strategy to fabricate highly conductive and stable CNT-strung LiMn₂ O₄ (CNT-s-LMO) is reported, by first stringing Mn₃ O₄ particles with multiwalled carbon nanotube (CNT), then converting the hybrids into CNT-s-LMO through hydrothermal lithiation. The as-synthesized CNT-s-LMO materials have a net-like structure with CNTs threading through LMO particles. This unique structure has endowed the CNT-s-LMO electrode with excellent conductivity, high specific capacitance, and enhanced rate performance. Because of this, the CNT-s-LMO electrode in the hybrid capacitive deionization cell (HCDI) can deliver a high Li⁺ extraction percentage (≈84%) in brine and an outstanding lithium selectivity with a separation factor of ≈181 at the Mg²⁺ /Li⁺ molar ratio of 60. Significantly, the CNT-s-LMO-based HCDI cell has a high stability, evidenced by 90% capacity retention and negligible Mn loss in 100 cycles. This method has paved a new way to fabricate carbon-enabled LMO-based absorbents with tuned structure and superior capacity for electrochemical lithium extraction with high Li⁺ selectivity and exceptional cycling stability, which may help to tackle the shortage in supply of Li-ion batteries in industry in the future.

Enhanced capacitive removal of hardness ions by hierarchical porous carbon cathode with high mesoporosity and negative surface charges

Capacitive deionization (CDI), as a promising desalination technology, has been widely applied for water purification, heavy metal removal and water softening. In this study, the hierarchical porous carbon (HPC) with extremely large specific surface area (∼1636 m² g^-1), high mesoporosity and negative surface charges, was successfully prepared by one-step carbonization of magnesium citrate and acid etching. HPC carbonized at 800 ℃ exhibited an excellent specific capacitance (207.2 F g^-1). The negative surface charge characteristic of HPC was demonstrated by potential of zero charge test. With HPC-800 as a CDI cathode, the super high adsorption capacity of hardness ions (Mg²⁺: 472 μmol g^-1, Ca²⁺: 425 μmol g^-1) with ultrafast adsorption rate was realized, attributed to its abundant mesoporous structure and negative surface charges. The priority order of ion adsorption on HPC in the multi-component salt solution was Mg²⁺ > Ca²⁺ > K⁺ ≈ Na⁺. The desalination and softening of the actual brackish water have been simultaneously achieved by three-cell CDI stack after four times of adsorption, with 63% decrease of total dissolved solids and 76% reduction of hardness. The current HPC material with outstanding adsorption performance for hardness ions shows great potential in brackish water purification.

Lithium ion sieve modified three-dimensional graphene electrode for selective extraction of lithium by capacitive deionization

Faced with the strong demand of clean energy, development of lithium source is becoming exceedingly vital. Spinel-type manganese oxide (λ-MnO₂) is a typical lithium ion sieve material. Herein, the conductive three-dimensional (3D) lithium ion sieve electrode material was fabricated by in-situ growth of λ-MnO₂ on 3D reduced graphene oxide (3D-rGO) matrix for Li extraction by capacitive deionization (CDI). The λ-MnO₂ modified rGO (λ-MnO₂/rGO) retained the 3D network structure with uniform distribution of λ-MnO₂ nanosheets on rGO. Electrochemical characterization demonstrated its high conductivity and fast lithium ion diffusion rate. By adjusting the rGO concentration, λ-MnO₂ activity was improved significantly. With λ-MnO₂/rGO as a positive electrode (activated carbon as negative electrode), the corresponding CDI system was successfully applied for the selective extraction of Li⁺. The final rGO content in the λ-MnO₂/rGO was attained by thermogravity analysis. With the appropriate rGO content (15.5%), the obtained λ-MnO₂/rGO electrode achieved the optimal Li⁺ adsorption amount. The corresponding λ-MnO₂/rGO-based CDI cell showed good selectivity and high cycle stability. When applied to the extraction of lithium from synthetic salt lake brine, the electrode also obtained high Li⁺ adsorption amount with good selectivity.

In situ synthesis of advantageously united copper stannate nanoparticles for a new high powered supercapacitor electrode

A novel CuNi2O4@SnS@rGO/NF multicomponent hybrid material leads to fast ion/electron transfers at the electrode/electrolyte interface.

Improving the Fenton-like catalytic performance of MnOx-Fe3O4/biochar using reducing agents: A comparative study

In this work, a Fenton-like system with MnO_x-Fe₃O₄/biochar composite (FeMn/biochar) and reducing agents (RAs) was constructed for pollutant degradation, aiming to enhance Fenton-like performance from both degradation efficacy and operational cost aspects. Batch experiments revealed that five well-characterized RAs (sodium borohydride (SBH), sodium thiosulfate (STS), ascorbic acid (AA), hydroxylamine (HA) and oxalic acid (OA)) could impact performance of FeMn/biochar-H₂O₂ system through multiple mechanisms, including variation of solution pH, competition for H₂O₂, electrostatic attraction and acceleration of metal redox cycle. Significantly, only OA and HA obviously enhanced the catalytic capacity of Fenton-like process and HA increased ciprofloxacin degradation efficiency from 38.2% to 92.8% with a low economic consumption as 4.16 US$/m³, well in agreement with the accelerated Fe(III/II) cycle and Mn(III/II) cycle in FeMn/biochar-H₂O₂-HA system. The accelerated metal redox cycle could enhance the decomposition of H₂O₂ into •OH and •O₂^-, which were verified to be the main reactive oxygen species responsible for ciprofloxacin degradation by radical trapping experiments. Meanwhile, FeMn/biochar-H₂O₂-HA system could also work effectively in real wastewaters, and exhibited favorable catalytic performance towards oxytetracycline, tetracycline, methyl orange, methylene blue, Rhodamine B, and naphthalene, indicating the applicability of FeMn/biochar-H₂O₂-HA system in oxidizing refractory pollutants in wastewaters.