Transforming NiCo2O4 nanorods into nanoparticles using citrus lemon juice enhancing electrochemical properties for asymmetric supercapacitor and water oxidation

Recently, the nanostructured nickel-cobalt bimetallic oxide (NiCo₂O₄) material with high electrochemical activity has received intensive attention. Beside this, the biomass assisted synthesis of NiCo₂O₄ is gaining popularity due to its advantageous features such as being low cost, simplicity, minimal use of toxic chemicals, and environment-friendly and ecofriendly nature. The electrochemical activity of spinel NiCo₂O₄ is associated with its mixed metal oxidation states. Therefore, much attention has been paid to the crystal quality, morphology and tunable surface chemistry of NiCo₂O₄ nanostructures. In this study, we have used citrus lemon juice consisting of a variety of chemical compounds having the properties of a stabilizing agent, capping agent and chelating agent. Moreover, the presence of several acidic chemical compounds in citrus lemon juice changed the pH of the growth solution and consequently we observed surface modified and structural changes that were found to be very effective for the development of energy conversion and energy storage systems. These naturally occurring compounds in citrus lemon juice played a dynamic role in transforming the nanorod morphology of NiCo₂O₄ into small and well-packed nanoparticles. Hence, the prepared NiCo₂O₄ nanostructures exhibited a new surface-oriented nanoparticle morphology, high concentration of defects on the surface (especially oxygen vacancies), sufficient ionic diffusion and reaction of electrolytic ions, enhanced electrical conductivity, and favorable reaction kinetics at the interface. The electrocatalytic properties of the NiCo₂O₄ nanostructures were studied in oxygen evolution reaction (OER) at a low overpotential of 250 mV for 10 mA cm^-2, Tafel slope of 98 mV dec^-1, and durability of 40 h. Moreover, an asymmetric supercapacitor was produced and the obtained results indicated a high specific capacitance of (C_s) of 1519.19 F g^-1, and energy density of 33.08 W h kg^-1 at 0.8 A g^-1. The enhanced electrochemical performance could be attributed to the favorable structural changes, surface modification, and surface crystal facet exposure due to the use of citrus lemon juice. The proposed method of transformation of nanorod to nanoparticles could be used for the design of a new generation of efficient electrocatalyst materials for energy storage and conversion uses.

Structural Diversity of Zinc(II), Manganese(II), and Gadolinium(III) Coordination Polymers Based on Two Isomeric N-Heteroaromatic Polycarboxylate Ligands: Structures and Their Derived Mn2O3 for Lithium Storage Applications

Tuning the coordination sites of two isomeric semirigid ligands, 5-(4-pyridin-3-yl-benzoylamino)isophthalic acid (3-H₂PBI) and 5-(4-pyridin-4-yl-benzoylamino)isophthalic acid (4-H₂PBI), afforded six new coordination polymers (CPs), [Zn(3-PBI)(H₂O)]_n (1), {[Mn₂(3-PBI)₂(H₂O)]·DMF·2H₂O}_n (2), {[Gd₂(3-PBI)₃(H₂O)₃]·DMF·3H₂O}_n (3), {[Zn₂(4-PBI)₂]·H₂O}_n (4), {[Mn₂(4-PBI)₂(H₂O)₂]·4H₂O}_n (5), and {(Me₂NH₂)[Gd(4-PBI)₂]·H₂O}_n (6). Structural analysis shows that 1 consists of 2D honeycomb (6,3) net, three sets of networks interlace mutually, generating an unexpected 2D + 2D + 2D → 3D polycatenating interesting system. 2 exhibits a 3D pcu topology. 3 presents a unique 3D with 3,3,6T13 network topology. 4 possesses 3D 2-fold interpenetrated structure with rutile topology. 5 presents an alluring 2D architecture comprising two distinct topologies (kgd and hcb), stacked arrangement in an unexpected ABBABB mode. 6 displays 2D (4,4)-grid network. A differentiation of these structural features indicate that coordination connectivity of metals, together with binding modes of two ligands are accountable for the fascinating structural contrast. In addition, 2 and 5 were then transformed into Mn₂O₃ via a simple heat treatment. Electrochemical test results show that both of the obtained Mn₂O₃ moieties exhibit stable lithium storage properties and excellent rate capabilities.

Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

An Ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance

The efficient charge accumulation of an ideal supercapacitor electrode requires abundant micropores and its fast electrolyte-ions transport prefers meso/macropores. However, current electrode materials cannot meet both requirements, resulting in poor performance. Herein, we creatively constructed three-dimensional cabbage-coral-like graphene as an ideal electrode material, in which meso/macro channels are formed by graphene walls and rich micropores are incorporated in the surface layer of the graphene walls. The unique 3D graphene material can achieve a high gravimetric capacitance of 200 F/g with aqueous electrolyte, 3 times larger than that of commercially used activated carbon (70.8 F/g). Furthermore, it can reach an ultrahigh areal capacitance of 1.28 F/cm² and excellent rate capability (83.5% from 0.5 to 10 A/g) as well as high cycling stability (86.2% retention after 5000 cycles). The excellent electric double-layer performance of the 3D graphene electrode can be attributed to the fast electrolyte ion transport in the meso/macro channels and the rapid and reversible charge adsorption with negligible transport distance in the surface micropores.

Mesoporous Mn2O3/reduced graphene oxide (rGO) composite with enhanced electrochemical performance for Li-ion battery

Transition metal oxides are the most promising candidates in low-cost and eco-friendly energy storage/conversion applications.

Conversion Reaction-Based Oxide Nanomaterials for Lithium Ion Battery Anodes

Developing high-energy-density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion reaction-based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.

Reconstruction of Mini-Hollow Polyhedron Mn2O3 Derived from MOFs as a High-Performance Lithium Anode Material

A mini-hollow polyhedron Mn2O3is used as the anode material for lithium-ion batteries. Benefiting from the small interior cavity and intrinsic nanosize effect, a stable reconstructed hierarchical nanostructure is formed. It has excellent energy storage properties, exhibiting a capacity of 760 mAh g-1 at 2 A g-1 after 1000 cycles. This finding offers a new perspective for the design of electrodes with large energy storage.

A thermally activated manganese 1,4-benzenedicarboxylate metal organic framework with high anodic capability for Li-ion batteries

Mn-1,4-BDC@200 was synthesized, with a capacity of 974 mA h g⁻¹after 100 cycles at a rate of 100 mA g⁻¹.

MnO nanocrystals incorporated in a N-containing carbon matrix for Li ion battery anodes

In this study, MnO nanocrystals incorporated in a N-containing carbon matrix were fabricated by the facile thermal decomposition of manganese nitrate-glycine gels.

Influence of TiO2 surface coating on the electrochemical properties of V2O5 micro-particles as a cathode material for lithium ion batteries

Based on V₂O₅ micro-particle, TiO₂-coated V₂O₅ micro-particle was obtained by hydroxylation of tetrabutyl titanate, whose electrochemical cyclic stability as cathode for LIBs is improved due to the protective role of TiO₂ coating layer.

Facile synthesis of MOF-derived Mn2O3 hollow microspheres as anode materials for lithium-ion batteries

In this article, we report a facile and scalable route for the fabrication of Mn₂O₃ hollow microspheres by direct pyrolysis of Mn-based metal–organic frameworks at 450 °C with a heating rate of 10 °C min⁻¹ in air.

FeMnO3: a high-performance Li-ion battery anode material

FeMnO₃particles were synthesized and evaluated as a Li-ion battery anode, exhibiting a high capacity and long-term cycling stability.

A simple synthesis of hollow Mn2O3 core–shell microspheres and their application in lithium ion batteries

Hollow Mn₂O₃ core–shell microspheres were successfully fabricated via a mixed method including a solution method and a subsequent thermal decomposition.

Electrochemical energy storage in Mn2O3 porous nanobars derived from morphology-conserved transformation of benzenetricarboxylate-bridged metal–organic framework

MOF-derived Mn₂O₃ shows a high capacity of ∼410 mA h g⁻¹ as a 2 V anode and an ultrahigh energy density of 147.4 W h kg⁻¹ as a supercapacitor.

N-doped carbon/MoS2 composites as an excellent battery anode

N-doped carbon/MoS₂ composites manifested high specific capacity of 611 mA h g⁻¹ and excellent cycling performance than bare MoS₂ and N-doped carbon.

Three-Dimensional (3D) Bicontinuous Hierarchically Porous Mn2O3 Single Crystals for High Performance Lithium-Ion Batteries

Bicontinuous hierarchically porous Mn₂O₃ single crystals (BHP-Mn₂O₃-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn₂O₃-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn₂O₃-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn₂O₃-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g⁻¹ at 100 mA g⁻¹ after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g⁻¹ at 1 Ag⁻¹). These values are among the highest reported for Mn₂O₃-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn₂O₃-SCs are suitable for charge transfer at the electrode/electrolyte interface.

Hierarchical Mn₂O ₃Hollow Microspheres as Anode Material of Lithium Ion Battery and Its Conversion Reaction Mechanism Investigated by XANES

Hierarchical Mn2O3 hollow microspheres of diameter about 6-10 μm were synthesized by solvent-thermal method. When serving as anode materials of LIBs, the hierarchical Mn2O3 hollow microspheres could deliver a reversible capacity of 580 mAh g(-1) at 500 mA g(-1) after 140 cycles, and a specific capacity of 422 mAh g(-1) at a current density as high as 1600 mA g(-1), demonstrating a good rate capability. Ex situ X-ray absorption near edge structure (XANES) spectrum reveals that, for the first time, the pristine Mn2O3 was reduced to metallic Mn when it discharged to 0.01 V, and oxidized to MnO as it charged to 3 V in the first cycle. Furthermore, the XANES data demonstrated also that the average valence of Mn in the sample at charged state has decreased slowly with cycling number, which signifies an incomplete lithiation process and interprets the capacity loss of the Mn2O3 during cycling.

Manganese oxide/carbon yolk-shell nanorod anodes for high capacity lithium batteries

Transition metal oxides have attracted much interest for their high energy density in lithium batteries. However, the fast capacity fading and the low power density still limit their practical implementation. In order to overcome these challenges, one-dimensional yolk-shell nanorods have been successfully constructed using manganese oxide as an example through a facile two-step sol-gel coating method. Dopamine and tetraethoxysilane are used as precursors to obtain uniform polymer coating and silica layer followed by converting into carbon shell and hollow space, respectively. As anode material for lithium batteries, the manganese oxide/carbon yolk-shell nanorod electrode has a reversible capacity of 660 mAh/g for initial cycle at 100 mA/g and exhibits excellent cyclability with a capacity of 634 mAh/g after 900 cycles at a current density of 500 mA/g. An enhanced capacity is observed during the long-term cycling process, which may be attributed to the structural integrity, the stability of solid electrolyte interphase layer, and the electrochemical actuation of the yolk-shell nanorod structure. The results demonstrate that the manganese oxide is well utilized with the one-dimensional yolk-shell structure, which represents an efficient way to realize excellent performance for practical applications.

Pristine hollow microspheres of Mn2O3 as a potential anode for lithium-ion batteries

Ascorbic acid aided inside-out Ostwald ripening promotes the formation of Mn₂O₃ microspheres with a hollow interior surface that exhibits an appreciable capacity of 610 mA h g⁻¹, even after completing 100 cycles.

Nanoflake driven Mn2O3 microcubes modified with cooked rice derived carbon for improved electrochemical behavior

Mn₂O₃ microcubes, symmetrically formed out of the systematic stacking of nanoflakes, built with nanoparticles in the 30–50 nm range have been obtained from a simple co-precipitation method.

pH-Regulated Synthesis of Multi-Shelled Manganese Oxide Hollow Microspheres as Supercapacitor Electrodes Using Carbonaceous Microspheres as Templates

Multi-shelled Mn2O3 hollow microspheres have been achieved through a pH-regulated method and used as supercapacitor electrodes. The designed unique architecture allows efficient use of pseudo-capacitive Mn2O3 nanomaterials for charge storage with facilitated transport for both ions and electrons, rendering them high specific capacitance, good rate capability, and remarkable cycling performance.

Hierarchical MnCo2O4 nanosheet arrays/carbon cloths as integrated anodes for lithium-ion batteries with improved performance

To solve the reduced output voltage caused by the high lithium redox potential of Co3O4 when applied as an anode material in full cells, an effective strategy is to partially replace Co by Mn to form MnCo2O4 without changing the original crystal structure. Herein, 3D hierarchical MnCo2O4 nanosheets arrays grown via a hydrothermal method on carbon cloths, as binder-free anodes for lithium-ion batteries, exhibit a high areal capacity of 3.0 mA h cm(-2) at a current density of 800 μA cm(-2), excellent cycling stability, good rate performances and a discharge voltage plateau of 0.25 V which is lower than that of their Co3O4 nanosheet counterparts. Due to the increased output voltage of the full cell induced by the introduction of Mn species with a lower lithium extraction potential, MnCo2O4 based full cells display higher or comparative capacity in a certain voltage range compared with Co3O4, while still retaining the excellent conductivity of Co3O4 electrodes. Our work here paves the way for the design of high performance full cells with Co-based oxide electrodes.

All-nanowire based Li-ion full cells using homologous Mn2O3 and LiMn2O4

We report an all-nanowire based flexible Li-ion battery full cell, using homologous Mn2O3 and LiMn2O4 nanowires for anodes and cathodes, respectively. The same precursors, MnOOH nanowires, are transformed from hydrothermally grown MnO2 nanoflakes and directly attached on Ti foils via reaction with poly(vinyl pyrrolidone). The Mn2O3 anode and LiMn2O4 cathode are subsequently formed by thermal annealing and reaction with lithium salt, respectively. The one-dimensional nanowire structures provide short lithium-ion diffusion path, good charge transport, and volume flexibility for Li(+) intercalation/deintercalation, thus leading to good rate capability and cycling performance. As proof-of-concept, the Mn2O3 nanowire anode delivers an initial discharge capacity of 815.9 mA h g(-1) at 100 mA g(-1) and maintains a capacity of 502.3 mA h g(-1) after 100 cycles. The LiMn2O4 nanowire cathodes show a reversible capacity of 94.7 mA h g(-1) at 100 mA g(-1) and high capacity retention of ∼ 96% after 100 cycles. Furthermore, a flexible Mn2O3//LiMn2O4 lithium ion full cell is fabricated, with an output voltage of >3 V, low thickness of 0.3 mm, high flexibility, and a specific capacity of 99 mA h g(-1) based on the total weight of the cathode material. It also exhibits good cycling stability with a capacity of ∼ 80 mA h g(-1) after 40 charge/discharge cycles.

Synthesis of Mn₂O₃ nanomaterials with controllable porosity and thickness for enhanced lithium-ion batteries performance

Mn₂O₃ has been demonstrated to be a promising electrode material for lithium-ion batteries. Thus, the fabrication of Mn₂O₃ nanomaterials with high specific capacity and cycling stability is greatly desired. Here we report a simple but effective method to synthesis Mn₂O₃ nanomaterials from a Mn(OH)₂ precursor, which was prepared from manganese acetate in ethylene glycol and water at 180 °C for 12 h. The morphology and sheet thickness of Mn(OH)₂ precursor could be tuned by controlling the ethylene glycol/H₂O volume ratio, resulting in a further tunable morphology and sheet thickness of the porous Mn₂O₃ nanomaterials. In the electrochemical tests the prepared Mn₂O₃ nanomaterials, with the porous architecture and thin thickness exhibited a high and stable reversible capacity, indicating that both small thickness and porous sheets structure are crucial for improving the electrochemical performance of Mn₂O₃ in terms of specific capacity and stability.

Morphology-mediated tailoring of the performance of porous nanostructured Mn2O3 as an anode material

The experiments determined the effects of different morphologies of synthesized porous Mn₂O₃ on its performance as an anode material in Li-ion batteries.

Recent advances in Mn-based oxides as anode materials for lithium ion batteries

The Mn-based oxides including MnO, Mn₃O₄, Mn₂O₃, MnO₂, CoMn₂O₄, ZnMn₂O₄and their carbonaceous composite/oxide supports with different morphologies and compositions as anode materials are reviewed.