MnO2 Heterostructure on Carbon Nanotubes as Cathode Material for Aqueous Zinc-Ion Batteries

Facile synthesis of Bi2Se3/nitrogen-doped carbon dot nanoplates for aqueous zinc ion battery cathodes

Bi2Se3 is a promising cathode material for aqueous zinc ion batteries (AZIBs), but its limited capacity and poor cycling stability deter its further use in the development of AZIBs. To solve this issue, Bi2Se3/NCD composites have been synthesized via a simple two-step solvothermal method. The introduction of nitrogen-doped carbon dots (NCDs) provides more active sites and makes the composite surface rich in functional groups, which facilitates contact with aqueous electrolytes. The results showed that Bi2Se3/NCDs improved the zinc storage properties of Bi2Se3 as a cathode material. The discharge specific capacity is 318 mA h g-1 at 0.1 A g-1. The cycling performance of Bi2Se3/NCDs was also relatively excellent compared to that of Bi2Se3. This work offers a productive and feasible strategy for metal chalcogenides (MCs) as cathode materials for AZIBs to improve the zinc storage capacity.

Kinetics-Driven MnO2 Nanoflowers Supported by Interconnected Porous Hollow Carbon Spheres for Zinc-Ion Batteries

For rechargeable aqueous zinc-ion batteries (ZIBs), manganese dioxide is one of the most promising candidates as a cathode material because of its cost effectiveness, eco-friendliness, and high specific capacities. However, the ZIBs suffer from poor rate performance and low cycle life due to the weak intrinsic electronic conductivity of manganese dioxide, poor ion diffusion of lump manganese dioxide, and its volumetric expansion during the cycle. Herein, we prepare MnO₂@carbon composites (MnO₂@IPHCSs) by in situ growing MnO₂ nanoflowers on an interconnected porous hollow carbon spheres (IPHCSs) template. IPHCSs, as excellent conductors, significantly improve the conductivity of the manganese dioxide cathode. The hollow porous carbon framework of IPHCSs can offer more ion diffusion paths to internal MnO₂@IPHCS carbon composites and acts as a buffer room to cope with the drastic volume contraction and expansion during charge/discharge cycling. The rate performance tests show that MnO₂@IPHCSs with high conductivity have a specific capacity of 147 mA h g^-1 at 3 C. MnO₂@IPHCSs with hollow and nanoflower structures are shown to have excellent ion diffusion performance (ion diffusion coefficient = 10^-11 to 10^-10 cm² s^-1) in the electrochemical kinetics of the galvanostatic intermittent titration technique. Long cycle performance testing and in situ Raman characterization reveal that MnO₂@IPHCSs have high cycling stability (85.5% capacity retention after 800 cycles) and reversibility due to the enhanced structure and increased conductivity. The excellently conductive manganese dioxide supported by IPHCSs has good rate and cycling performance, which can be used to produce superior-performance ZIBs.

Preparation of MnO2-Carbon Materials and Their Applications in Photocatalytic Water Treatment

Water pollution is one of the most important problems in the field of environmental protection in the whole world, and organic pollution is a critical one for wastewater pollution problems. How to solve the problem effectively has triggered a common concern in the area of environmental protection nowadays. Around this problem, scientists have carried out a lot of research; due to the advantages of high efficiency, a lack of secondary pollution, and low cost, photocatalytic technology has attracted more and more attention. In the past, MnO₂ was seldom used in the field of water pollution treatment due to its easy agglomeration and low catalytic activity at low temperatures. With the development of carbon materials, it was found that the composite of carbon materials and MnO₂ could overcome the above defects, and the composite had good photocatalytic performance, and the research on the photocatalytic performance of MnO₂-carbon materials has gradually become a research hotspot in recent years. This review covers recent progress on MnO₂-carbon materials for photocatalytic water treatment. We focus on the preparation methods of MnO₂ and different kinds of carbon material composites and the application of composite materials in the removal of phenolic compounds, antibiotics, organic dyes, and heavy metal ions in water. Finally, we present our perspective on the challenges and future research directions of MnO₂-carbon materials in the field of environmental applications.

Polypyrrole/reduced graphene oxide composites coated zinc anode with dendrite suppression feature for boosting performances of zinc ion battery

Metallic zinc (Zn) anode has been received a great promise for aqueous rechargeable zinc-ion batteries (ZIBs) due to its intrinsic safety, low cost, and high volumetric capacity. However, the dendrite formation regarding the surface corrosion is the critical problems to achieve the high performance and the long lifespans of ZIBs. Here, we purpose the facile cyclic voltammetry deposition of polypyrrole/reduced graphene oxide (PPy/rGO) composites coated onto Zn 3D surface as Zn anode for ZIBs. As results, the deposited PPy/rGO layer demonstrates the homogeneous distribution covering onto Zn surface, effectively suppressing the formation of dendrite. Additionally, a symmetric cell of the PPy/rGO coated Zn remarkably enhances an electrochemical cycling with a low voltage hysteresis for zinc plating/stripping, which is superior to the pristine Zn cell. In addition, the deposited layer of PPy/rGO on Zn effectively improves the reactivity of electrochemically active surface area and the intrinsic electronic configurations, participating in extraction/intercalation of Zn²⁺ ions and leading to enhance ZIBs performance. The coin cell battery of Zn-PPy/rGO//MnO₂ can deliver a high initial discharge capacity of 325 mAh/g at 0.5A/g with a good cycling stability up to 50% capacity retention after 300 cycles. Thus, these achieved results of Zn-PPy/rGO//MnO₂ battery with dendrite-free feature effectively enhance the life-performance of ZIBs and open the way of the designed coating composite materials to suppress dendrite issues.

Enriching Oxygen Vacancy Defects via Ag-O-Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have received great attention due to their environmental friendliness and high safety. However, cathode materials with slow diffusion dynamics and dissolution in aqueous electrolytes hindered their further application. To address these issues, in this work, a MnO₂-2 cathode doped with 1.12 wt % Ag was prepared, and after 1000 cycles of charge/discharge at 1 A·g^-1, the capacity remained at 114 mA·h·g^-1 (only 57.7 mA·h·g^-1 for pristine MnO₂). Cyclic voltammetry (CV), the galvanostatic intermittent titration technique (GITT), the electrochemical quartz crystal microbalance (EQCM) method, and density functional theory (DFT) calculation on pristine δ-MnO₂ and MnO₂-2 also proved the superior performance of MnO₂-2. More investigation disclosed that its superior performance is attributed to the improved diffusion kinetics of the cathode brought by the enriched oxygen vacancy defects due to the formation of Ag-O-Mn bonds. Meanwhile, the kinetic mechanism of the Zn/MnO₂-2 cell can be described as a reversible process of the dissolution/precipitation of the ZHS phase and consequent insertion/extraction of Zn²⁺ and H₃O⁺. Herein, the primary issues of ZIB cathode materials have been addressed and solved to a certain extent. More importantly, such a modification in the design of the advanced manganese-based aqueous ZIB cathode materials can provide further insight and facilitate the development and application of this large-scale energy storage system in the near future.

Polypyrrole nanoparticles embedded nitrogen-doped graphene composites as novel cathode for long life cycles and high-power zinc-ion hybrid supercapacitors

The well-designed network structure of synthetic polypyrrole (PPy) nanoparticles embedded on a nitrogen-doped graphene (N-rGO) surface was utilized as a cathode for aqueous zinc-ion hybrid supercapacitors. Owing to the combination of the redox surface of PPy and the two-dimensional network structure of N-rGO, the PPy/N-rGO cathode affords rapid transport channels for Zn²⁺ ion adsorption/desorption and a faradaic reaction toward the synergistic composite materials. Subsequently, the constructed zinc-ion hybrid supercapacitors with the optimized PPy/N-rGO cathode composites deliver the highest capacity of 145.32 mA h g^-1 at 0.1 A g^-1 and the maximum energy density of 232.50 W h kg^-1 at a power density of 160 W kg^-1. Besides this, excellent cycling stability of 85% retention after 10 000 charge-discharge cycles at 7.0 A g^-1 was achieved. The high-rate capabilities with long life cycle performance of these novel zinc-ion hybrid supercapacitors could find practical use in a wide range of applications, ranging from next-generation electronic devices to large-scale stationary energy storage.

A comparison study of MnO2 and Mn2O3 as zinc-ion battery cathodes: an experimental and computational investigation

The high specific capacity, low cost and environmental friendliness make manganese dioxide materials promising cathode materials for zinc-ion batteries (ZIBs). In order to understand the difference between the electrochemical behavior of manganese dioxide materials with different valence states, i.e., Mn(iii) and Mn(iv), we investigated and compared the electrochemical properties of pure MnO2 and Mn2O3 as ZIB cathodes via a combined experimental and computational approach. The MnO2 electrode showed a higher discharging capacity (270.4 mA h g-1 at 0.1 A g-1) and a superior rate performance (125.7 mA h g-1 at 3 A g-1) than the Mn2O3 electrode (188.2 mA h g-1 at 0.1 A g-1 and 87 mA h g-1 at 3 A g-1, respectively). The superior performance of the MnO2 electrode was ascribed to its higher specific surface area, higher electronic conductivity and lower diffusion barrier of Zn2+ compared to the Mn2O3 electrode. This study provides a detailed picture of the diversity of manganese dioxide electrodes as ZIB cathodes.

Highly Effective Methods of Obtaining N-Doped Graphene by Gamma Irradiation

The design and fabrication of a new effective manufacturing method of heteroatom-doped carbon materials is still ongoing. In this paper, we present alternative and facile methods to obtain N-rich graphene with the use of low energy gamma radiation. This method was used as a pure and facile method for altering the physical and chemical properties of graphene. The obtained materials have an exceptionally high N content-up to 4 wt %. (dry method) and up to 2 wt %. (wet method). High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) studies allowed us to evaluate the quality of the obtained materials. The presented results will provide new insights in designing and optimizing N-doped carbon materials potentially for the development of anode or cathode materials for electrochemical device applications, especially supercapacitors, metal-air batteries and fuel cells. Nitrogen atoms are exclusively bonded as quaternary groups. The method is expandable to the chemical insertion of other heteroatoms to graphene, especially such as sulfur, boron or phosphorus.

Enhanced Cycling Performance of Rechargeable Zinc-Air Flow Batteries Using Potassium Persulfate as Electrolyte Additive

Zinc-air batteries (ZABs) offer high specific energy and low-cost production. However, rechargeable ZABs suffer from a limited cycle life. This paper reports that potassium persulfate (KPS) additive in an alkaline electrolyte can effectively enhance the performance and electrochemical characteristics of rechargeable zinc-air flow batteries (ZAFBs). Introducing redox additives into electrolytes is an effective approach to promote battery performance. With the addition of 450 ppm KPS, remarkable improvement in anodic currents corresponding to zinc (Zn) dissolution and limited passivation of the Zn surface is observed, thus indicating its strong effect on the redox reaction of Zn. Besides, the addition of 450 ppm KPS reduces the corrosion rate of Zn, enhances surface reactions and decreases the solution resistance. However, excess KPS (900 and 1350 ppm) has a negative effect on rechargeable ZAFBs, which leads to a shorter cycle life and poor cyclability. The rechargeable ZAFB, using 450 ppm KPS, exhibits a highly stable charge/discharge voltage for 800 cycles. Overall, KPS demonstrates great promise for the enhancement of the charge/discharge performance of rechargeable ZABs.