Constructing Mn O C bonds in Mn3O4/Super P composite for superior performance in Li-ion battery

In Situ Growth of Amorphous MnO2 on Graphite Felt via Mild Etching Engineering as a Powerful Catalyst for Advanced Vanadium Redox Flow Batteries

Owing to the advantages of low cost, high safety, and a desirable cycling lifetime, vanadium redox flow batteries (VRFBs) have attracted great attention in the large-scale energy storage field. However, graphite felts (GFs), widely used as electrode materials, usually possess an inferior catalytic activity for the redox reaction of vanadium ions, largely limiting the energy efficiency and rate performance of VRFBs. Here, an in situ growth of amorphous MnO2 on graphite felt (AMO@GF) was designed for application in VRFBs via mild and rapid etching engineering (5 min). After the etching process, the graphite felt fibers showed a porous and defective surface, contributing to abundant active sites toward the redox reaction. In addition, formed amorphous MnO2 can also serve as a powerful catalyst to facilitate the redox couples of VO2+/VO2+ based on density functional theoretical (DFT) calculations. As a result, the VRFB using AMO@GF displayed an elevated energy efficiency and superior stability after 2400 cycles at 200 mA cm-2, and the maximum current density can reach 300 mA cm-2. Such a high-efficiency and convenient design strategy for the electrode material will drive the further development and industrial application of VRFBs and other flow battery systems.

Coordination Engineering of Carbon Dots and Mn in Co-Based Phosphides for Highly Efficient Seawater Splitting at Ampere-Level Current Density

Direct electrolysis of seawater to generate hydrogen is an attractive approach for storing renewable energy. However, direct seawater splitting suffers from low current density and limited operating stability, which severely hinders its industrialization. Herein, a promising strategy is reported to obtain a nano needle-like array catalyst-CDs-Mn-CoxP on nickel foam, in which the Mn─O─C bond tightly binds Mn, Carbon dots (CDs), and CoxP together. The coordination engineering of CDs and Mn not only effectively regulates the electronic structure of CoxP, but also endows the as-prepared catalyst with selectivity and marked long-term stability at ampere-level current density. Low overpotentials of 208 and 447 mV are required to achieve 1000 mA cm-2 for hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER) in simulated seawater, respectively. Cell potentials of 1.78 and 1.86 V are needed to reach 500 and 1000 mA cm-2 in alkaline seawater along with excellent durability for 350 h. DFT studies have verified that the introduction of Mn and CDs effectively shifts the d-band center of Co-3d toward higher energy, thereby strengthening the adsorption of intermediates and enhancing the catalytic activity. This study sheds light on the development of highly effective and stable catalysts for large-scale seawater electrolysis.

Nanocellulose/carbon nanotube/manganese dioxide composite electrodes with high mass loadings for flexible supercapacitors

The increasing commercialization of flexible electronic products has sparked a rising interest in flexible wearable energy storage devices. Supercapacitors are positioned as one of the systems with the most potential due to their distinctive advantages: high power density, rapid charge and discharge rates, and long cycle life. However, electrode materials face challenges in providing excellent mechanical strength while ensuring sufficient energy density. This study presents a method for constructing a flexible composite electrode material with high capacitance and mechanical performance by electrochemically depositing high-quality manganese dioxide (MnO2) onto the surface of a nanocellulose (CNF) and carbon nanotube (CNT) conductive film. In this electrode material, the CNF/CNT composite film serves as a flexible conductive substrate, offering excellent mechanical properties (modulus of 3.3 GPa), conductivity (55 S/cm), and numerous active sites. Furthermore, at the interface between MnO2 and the CNF/CNT substrate, C-O-Mn bonds are formed, promoting a tight connection between the composite materials. The assembled symmetric flexible supercapacitor (FSC) demonstrates impressive performance, with an areal specific capacitance of 934 mF/cm2, an energy density of 43.10 Wh/kg, a power density of 166.67 W/kg and a long cycle life (85 % Capacitance retention after 10,000 cycles), suggesting that they hold promise for FSC applications.

Rational Design of ZnMn2 O4 Quantum Dots in a Carbon Framework for Durable Aqueous Zinc-Ion Batteries

Manganese oxides are promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high energy density and low cost. However, in their discharging processes, the Jahn-Teller effect and Mn³⁺ disproportionation often lead to irreversible structural transformation and Mn²⁺ dissolution, deteriorating the cycling stability of ZIBs. Herein, ZnMn₂ O₄ quantum dots (ZMO QDs) were introduced into a porous carbon framework by in-situ electrochemically inducing Mn-MIL-100-derived Mn₃ O₄ quantum dots and the carbon composite. In such ZMO QDs and carbon composite, the quantum dot structure endows ZnMn₂ O₄ with a shorter ion diffusion route and more active sites for Zn²⁺ . The conductive carbon framework is beneficial to the fast transport of electrons. Furthermore, at the interface between the ZMO QDs and the carbon matrix, the Mn-O-C bonds are formed. They can effectively suppress the Jahn-Teller effect and manganese dissolution of discharge products. Therefore, Zn/ZMO QD@C batteries display remarkably enhanced electrochemical performance.

Electrochemical reaction behavior of MnS in aqueous zinc ion battery

Rechargeable aqueous zinc ion battery (ZIB) is reviving as a promising energy storage device with respect to its distinguished safeness, cost-effectiveness, and eco-friendliness. However, its practical application is still challenged...

Spray Pyrolysis Synthesis of Pure and Mg-Doped Manganese Oxide Thin Films

Pure and Mg-doped manganese oxide thin films were synthesized on heated glass substrates using the spray pyrolysis technique. The surface chemical composition was investigated by the use of X-ray photoelectron spectroscopy (XPS). Structural and morphological properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscopy (AFM). Optical properties were characterized by UV-visible spectroscopy. XPS spectra showed typical Mn (2p3/2), (2p1/2) and O (1s) peaks of Mn3O4 with a slight shift attributed to the formation of different chemical states of manganese. XRD analysis revealed the tetragonal phase of Mn3O4 with a preferred (211) growth orientation that improved with Mg-doping; likewise, grain size is observed to increase with the Mg doping. SEM images of Mn3O4 films showed rough surfaces composed of uniformly distributed nanograins whose size decreases with the Mg-doping. The manganese oxide films surface observed in AFM show a textured, rough and porous surface. The combination of transmittance and absorption data in the UV-visible range allowed determining the energy values of the Eg band gap (1.5–2.5 eV). The decrease of the band gap with the Mg-doping increase is attributed to the influence of the greater size of the Mg2+ ion in the manganese oxide lattice.

Greatly Enhanced Faradic Capacities of 3D Porous Mn3O4/G Composites as Lithium-Ion Anodes and Supercapacitors by C-O-Mn Bonding

Through C-O-Mn bonding, graphene nanosheets are homogeneously dispersed in porous Mn₃O₄ to take full advantages of porous Mn₃O₄ and graphene nanosheets, making the as-formed three-dimensional porous Mn₃O₄/reduced graphene oxide (rGO) composite exhibit good electrochemical performance. Besides, C-O-Mn bonding is demonstrated to greatly promote the Faradic reactions of the composite, resulting in the enhancement of its real capacity in supercapacitor (SC) electrodes as well as lithium-ion battery (LIB) anodes. By simply fine-tuning the content of graphene (<7 wt %), the composite with 2.8 wt % of rGO delivers a high capacitance of 315 F g^-1 at 0.5 A g^-1 with a high rate capability of 64.7% at 30 A g^-1 and an excellent cycling stability of 105% (5 A g^-1, 5000 cycles) as an SC electrode. Also, the one with 6.9 wt % rGO can present a reversible capacity of more than 1500 mAh g^-1 at 0.05 A g^-1 as the LIB anode, the highest value reported to date, which remains 561 mAh g^-1 at 1 A g^-1.

In Situ Synthesis of Mn3 O4 Nanoparticles on Hollow Carbon Nanofiber as High-Performance Lithium-Ion Battery Anode

The practical applications of Mn₃ O₄ in lithium-ion batteries are greatly hindered by fast capacity decay and poor rate performance as a result of significant volume changes and low electrical conductivity. It is believed that the synthesis of nanoscale Mn₃ O₄ combined with carbonaceous matrix will lead to a better electrochemical performance. Herein, a convenient route for the synthesis of Mn₃ O₄ nanoparticles grown in situ on hollow carbon nanofiber (denoted as HCF/Mn₃ O₄ ) is reported. The small size of Mn₃ O₄ particles combined with HCF can significantly alleviate volume changes and electrical conductivity; the strong chemical interactions between HCF and Mn₃ O₄ would improve the reversibility of the conversion reaction for MnO into Mn₃ O₄ and accelerate charge transfer. These features endow the HCF/Mn₃ O₄ composite with superior cycling stability and rate performance if used as the anode for lithium-ion batteries. The composite delivers a high discharge capacity of 835 mA h g^-1 after 100 cycles at 200 mA g^-1 , and 652 mA h g^-1 after 240 cycles at 1000 mA g^-1 . Even at 2000 mA g^-1 , it still shows a high capacity of 528 mA h g^-1 . The facile synthetic method and outstanding electrochemical performance of the as-prepared HCF/Mn₃ O₄ composite make it a promising candidate for a potential anode material for lithium-ion batteries.

Controlling the Sn-C bonds content in SnO2@CNTs composite to form in situ pulverized structure for enhanced electrochemical kinetics

The Sn-C bonding content between the SnO₂ and CNTs interface was controlled by the hydrothermal method and subsequent heat treatment. Electrochemical analysis found that the SnO₂@CNTs with high Sn-C bonding content exhibited much higher capacity contribution from alloying and conversion reaction compared with the low content of Sn-C bonding even after 200 cycles. The high Sn-C bonding content enabled the SnO₂ nanoparticles to stabilize on the CNTs surface, realizing an in situ pulverization process of SnO₂. The in situ pulverized structure was beneficial to maintain the close electrochemical contact of the working electrode during the long-term cycling and provide ultrafast transfer paths for lithium ions and electrons, which promoted the alloying and conversion reaction kinetics greatly. Therefore, the SnO₂@CNTs composite with high Sn-C bonding content displayed highly reversible alloying and conversion reaction. It is believed that the composite could be used as a reference for design chemically bonded metal oxide/carbon composite anode materials in lithium-ion batteries.