Ultrahigh Rate Capability and Lifespan MnCo2O4/Ni-MOF Electrode for High Performance Battery-Type Supercapacitor

MnCo₂O₄ is derived from a Co/Mn bimetallic metal-organic framework (MOF). Then Ni-MOF is directly grown on the surface of the obtained MnCo₂O₄ to form a nano-flower structure with small balls. A large surface area, abundant active sites of MnCo₂O₄ and porosity of Ni-MOF allow the prepared MnCo₂O₄/Ni-MOF composite material to deliver an excellent electrochemical performance. At the same time, an appropriate thermal treatment temperature of the MnCo₂O₄ precursor is also very important for controlling the morphology of the obtained MnCo₂O₄ and electrochemical performances of the resulted composite material including electric conductivity, specific capacitance and rate performance. The prepared MnCo₂O₄-600/Ni-MOF shows an ultrahigh rate performance (when the current density increases from 1 to 10 A g⁻¹, the capacitance retention rate is as high as 93.41 %) and good cycle stability (the assembled asymmetric supercapacitor advice delivers a capacitance retention rate of 94.74 % after 20 000 charge and discharge cycles) as well as a relatively high specific capacitance. These excellent electrochemical properties indicate that MnCo₂O₄/Ni-MOF has a good application prospect in the market.     

Nitrogen-doped porous carbon coated on MnCo2O4 nanospheres as electrode materials for high-performance asymmetric supercapacitors

Spinel-based nanostructured materials are commonly used as promising electrode materials for supercapacitor applications. The combination of heteroatom-doped carbon material with spinel oxides substantially improves the specific capacitance and cyclic stability. In this work, dopamine-derived nitrogen-doped carbon was coated on spinel phase MnCo₂O₄ nanospheres using simple solvothermal and calcination methods. Surface morphology and the crystalline structure of the prepared MnCo₂O₄@Nitrogen-doped carbon were confirmed by FESEM and X-ray diffraction. The electrochemical performance of MnCo₂O₄@Nitrogen-doped carbon electrode material was analyzed by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. MnCo₂O₄@nitrogen-doped carbon exhibits the highest specific capacitance of 1200 F/g compared to MnCo₂O₄ spheres are 726 F/g at 1 A/g and exhibits excellent cyclic stability (capacitance retention of 87% at 7 A/g after 3000 cycles). The enhanced performance of the composite might be benefitted from the synergistic effect between nitrogen-doped carbon on porous MnCo₂O₄ spheres. Furthermore, an asymmetric supercapacitor device was fabricated by using the optimized composition of MnCo₂O₄@NC-2 as a positive electrode and nitrogen, sulfur-doped reduced graphene oxide (NS-rGO) as a negative electrode, respectively. This asymmetric supercapacitor device achieves a maximum energy density of 61.0 Wh/kg at a power density of 2889 W/kg and possesses excellent capacitance retention of 95% after 5000 cycles at 7 A/g.     

Hydrothermal synthesis of reduced graphene sheets/Fe2O3 nanorods composites and their enhanced electrochemical performance for supercapacitors

Reduced graphene nanosheets/Fe₂O₃ nanorods (GNS/Fe₂O₃) composite has been fabricated by a hydrothermal route for supercapacitor electrode materials. The obtained GNS/Fe₂O₃ composite formed a uniform structure with the Fe₂O₃ nanorods grew on the graphene surface and/or filled between the graphene sheets. The electrochemical performances of the GNS/Fe₂O₃ hybrid supercapacitor were tested by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests in 6 M KOH electrolyte. Comparing with the pure Fe₂O₃ electrode, GNS/Fe₂O₃ composite electrode exhibits an enhanced specific capacitance of 320 F g⁻¹ at 10 mA cm⁻² and an excellent cycle-ability with capacity retention of about 97% after 500 cycles. The simple and cost-effective preparation technique of this composite with good capacitive behavior encourages its potential commercial application.     

Bismuth oxide coated amorphous manganese dioxide for electrochemical capacitors

With MnSO₄, NaOH and K₂S₂O₈ as the raw materials, the amorphous and δ-type manganese dioxide (MnO₂) is separately prepared by using different chemical precipitation-oxidation methods. The results of charge–discharge and electrochemical impedance spectroscopy (EIS) tests show that (i) the specific capacitance of the amorphous MnO₂ reaches to 301.2 F g⁻¹ at a current density of 200 mA g⁻¹ and its capacitance retention rate after 2000 cycles is 97%, which is obviously higher than 250.8 F g⁻¹ and 71% of the δ-type one, respectively; (ii) good electrochemical capacitance properties of the amorphous MnO₂ should be contributed to easy insertion/extraction of ions within the material; (iii) when 5 wt% Bi₂O₃ is coated on the amorphous MnO₂, its specific capacitance increases to 352.8 F g⁻¹ and the capacitance retention rate is 90% after 2000 cycles.     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

High reversible capacity and rate capability of ZnCo2O4/graphene nanocomposite anode for high performance lithium ion batteries

A facile and straightforward method was adopted to synthesize ZnCo₂O₄/graphene nanocomposite anode. In the first step, pure ZnCo₂O₄ nanoparticles were synthesized using urea-assisted auto-combustion synthesis followed by annealing at a low temperature of 400 °C. In the second step, in order to synthesize ZnCo₂O₄/graphene nanocomposite, the obtained pure ZnCo₂O₄ nanoparticles were milled with 10 wt% reduced graphene nanosheets using high energy spex mill for 30 s. The ZnCo₂O₄ nanoparticles, with particle sizes of 25–50 nm, were uniformly dispersed and anchored on the reduced graphene nanosheets. Compared with pure ZnCo₂O₄ nanoparticles anode, significant improvements in the electrochemical performance of the nanocomposite anode were obtained. The resulting nanocomposite delivered a reversible capacity of 1124.8 mAh g⁻¹ at 0.1 C after 90 cycles with 98% Coulombic efficiency and high rate capability of 515.9 mAh g⁻¹ at 4.5 C, thus exhibiting one of the best lithium storage properties among the reported ZnCo₂O₄ anodes. The significant enhancement of the electrochemical performance of the nanocomposite anode could be credited to the strong synergy between ZnCo₂O₄ and graphene nanosheets, which maintain excellent electronic contact and accommodate the large volume changes during the lithiation/delithiation process.     

Synthesis of Co3O4/CoOOH via electrochemical dispersion using a pulse alternating current method for lithium-ion batteries and supercapacitors

We report a convenient, low-cost and ecofriendly approach for the fabrication of a Co₃O₄/CoOOH electrode material intended for lithium ion batteries (LIBs) and supercapacitors (SCs) using the electrochemical dispersion of the cobalt foil through the pulse alternating current (PAC) method. The synthesized material is a Co₃O₄/CoOOH composite (with about 10–15 wt% CoOOH) in the form of nanosheets with a length of approximately 200 nm and a thickness of 10–20 nm. It is found to exhibit high reversible discharge specific capacities and good cycling behavior while tested as the anode material in LIBs. Measuring the reversible capacitance at high (2C) and low (C/20) cycling rates gives the values of 610 mAh g⁻¹ and 1030 mAh g⁻¹, respectively. The specimen possesses excellent performance as the electrode for SCs with the retention of capacitance up to 98% at the current density increasing from 0.5 to 10 A g⁻¹. After 1000 cycles at a current density of 10 A g⁻¹ the electrode maintains about 90% of its initial capacitance which evidences the long cycle life. Hence, electrochemically prepared Co₃O₄/CoOOH seems to be a promising candidate for high-performance LIBs and SCs applications.     

Na4Co2.4Mn0.3Ni0.3(PO4)2P2O7: High potential and high capacity electrode material for sodium-ion batteries

Na₄Co_2.4Mn_0.3Ni_0.3(PO₄)₂P₂O₇ has been evaluated as a positive electrode for sodium-ion batteries. The novel material has two redox couples around 4.2 V and 4.6 V and can deliver the high capacity of ca. 103 mAh g^− 1 at the high current density of 850 mA g^− 1 (5 C). X-ray absorption spectroscopy (XAS) results show that the redox reactions of Co, Mn and Ni ions proceed simultaneously in the charge process and it is indicated the novel material provide high mixed potential by the redox reactions of Co, Mn and Ni ions. These findings suggest that the derivatives of Na₄Co₃(PO₄)₂P₂O₇ should be employed as high potential and high capacity electrode materials.     

Central role of TiO2 anatase grain boundaries on resistivity of CaCu3Ti4O12-based materials probed by Raman spectroscopy

This study focuses on characterization and control of grain boundaries to enhance the properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics capacitors for industrial applications. A novel factor deals with TiO₂ anatase revealed by Raman scattering in grain boundaries, found as a dominant parameter of largest sample resistivity, consistent with higher grain boundary resistivity and higher breakdown voltage. Four selected samples of CCTO-based compositions showing very different properties in terms of permittivity ranging from 1000 to 684 000 measured at 1 kHz, capacitance of grain boundaries ranging from 8 10⁻¹⁰ to 4.5 10⁻⁷ F cm⁻¹, grain boundary resistivity ranging from 193 to 30,000,000 Ω cm and sample resistivity extending from 450 to 10¹¹ Ω cm. The relationship between permittivity weighted by grain size and capacitance of grain boundaries confirms the internal barrier layer capacitance model over 5 orders of magnitude.     

Mesoporous Fe2O3 nanoparticles as high performance anode materials for lithium-ion batteries

This work introduces an effective, inexpensive, and large-scale production approach to the synthesis of Fe₂O₃ nanoparticles with a favorable configuration that 5 nm iron oxide domains in diameter assembled into a mesoporous network. The phase structure, morphology, and pore nature were characterized systematically. When used as anode materials for lithium-ion batteries, the mesoporous Fe₂O₃ nanoparticles exhibit excellent cycling performance (1009 mA h g^− 1 at 100 mA g^− 1 up to 230 cycles) and rate capability (reversible charging capacity of 420 mA h g^− 1 at 1000 mA g^− 1 during 230 cycles). This research suggests that the mesoporous Fe₂O₃ nanoparticles could be suitable as a high rate performance anode material for lithium-ion batteries.     

Mesoporous MnCo2O4 with a Flake‐Like Structure as Advanced Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A mesoporous flake‐like manganese‐cobalt composite oxide (MnCo₂O₄) is synthesized successfully through the hydrothermal method. The crystalline phase and morphology of the materials are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller methods. The flake‐like MnCo₂O₄ is evaluated as the anode material for lithium‐ion batteries. Owing to its mesoporous nature, it exhibits a high reversible capacity of 1066 mA h g^?1, good rate capability, and superior cycling stability. As an electrode material for supercapacitors, the flake‐like MnCo₂O₄ also demonstrates a high supercapacitance of 1487 F g^?1 at a current density of 1 A g^?1, and an exceptional cycling performance over 2000 charge/discharge cycles.     

Impact of titanium precursors on formation and electrochemical properties of Li4Ti5O12 anode materials for lithium-ion batteries

This work describes comparative study on the application of Li₄Ti₅O₁₂ (LTO) as anode materials for lithium-ion batteries which were successfully prepared by sol-gel synthesis with the use of two titanium sources. One of them was anatase-type titanium dioxide (TiO₂), whereas the second was tetrabutyl titanate (TBT). Both obtained LTO materials were very similar in terms of their crystallinity and purity. In turn, the sample synthetized with TBT source revealed better particle dispersibility, and its particles were slightly lower in size. These particular features resulted in higher Li⁺ diffusion coefficient and better kinetic of Li⁺ ions during charge transfer reactions for the LTO synthetized with TBT source. This reflected in specific capacitance values for both electrodes which equalled 150 mAh g⁻¹, 120 mAh g⁻¹, and 63 mAh g⁻¹ for TBT-LTO and 120 mAh g⁻¹, 80 mAh g⁻¹, and 58 mAh g⁻¹ for TiO₂-LTO at C-rates of 1, 5, and 10 C, respectively.

     

Synthesis of Co3O4/Carbon Heteroaerogels with Ultrahigh Capacitance via Polyethyleneimine Intercalation of Co2BIM4 Nanosheets

The development of metal–organic frameworks (MOFs)-based supercapacitors have attracted intense concentration in recent years due to their regularly arranged porous and tunable pore sizes. However, the performance of the MOFs-derived supercapacitors is also low because of their poor electrical conductivity and rarely accessible active sites. In the present work, we developed a Co-MOF (namely Co₂BIM₄, BIM=benzimidazole) nanosheets derived Co₃O₄/nitrogen-doped carbon (Co₂BIM₄-Co₃O₄/NC) heteroaerogel as a novel supercapacitor electrode. The 3D Co₂BIM₄-Co₃O₄/NC heteroaerogels were obtained by directly intercalating polyethyleneimine (PEI) into the interlayers of Co₂BIM₄ nanosheets and following by carbonizing the resulting Co₂BIM₄/PEI composite. The Co₂BIM₄-Co₃O₄/NC electrode possessed 3D conductive framework with an overlapped hetero-interface and expanded interlayers, leading to fast and stable charge transfer/diffusion and an enhanced pseudocapacitance performance. Therefore, the Co₂BIM₄-Co₃O₄/NC electrode showed ultrahigh capacitance of 2568 F g⁻¹ at 1 A g⁻¹, 1747 F g⁻¹ at 10 A g⁻¹, and excellent long cycling time with a capacitance preservation of 92.7 % following 10000 cycles at 10 A g⁻¹, which is very promising for applications in supercapacitors and other energy storage devices.     

Enhanced Supercapacitor Performance Using a Co3O4@Co3S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃O₄ and Co₃S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃O₄@Co₃S₄ nanocomposite, the nanostructure of Co₃S₄ was fabricated from Co₃O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm⁻² (5651.24 F g⁻¹) at a current density of 6 mA cm⁻² compared to the Co₃O₄/rGO/NF electrode with a capacitance of 3.06 F cm⁻² (1230.77 F g⁻¹) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg⁻¹, specific power density of 6048.03 W kg⁻¹ and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s⁻¹). Finally, by using Co₃O₄ @Co₃S₄/rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm⁻² at the applied current density of 1 mA cm⁻², and delivered an energy density of 0.143 Wh kg⁻¹ at the power density of 5.42 W kg⁻¹.     

Mesoporous Mn promoted Co3O4 oxides as an efficient and stable catalyst for low temperature oxidation of CO

Mesoporous Mn-doped Co₃O₄ catalysts were successfully prepared via a dry soft reactive grinding method based on solid state reaction, and their catalytic performances on CO oxidation were evaluated at a high space velocity of 49,500 mL g⁻¹ h⁻¹. A significant promoted effect was observed once the atomic ratios of Mn/(Co+Mn) were lower than 10%, for instance, the temperature for 50% conversion decreased to about −60 °C, showing superior catalytic performance compared to the single metal oxide. Especially, the Mn-promoted Co₃O₄ catalyst with a Mn/(Co+Mn) molar ratio of 10% could convert 100% CO after 3000 min of time-on-steam without any deactivation at room temperature. As prepared catalysts were characterized by XRD, N₂-adsorption/desorption, TEM, H₂-TPR, O₂-TPD and CO-titration analysis. The significant enhancement of performance for oxidation of CO over Mn-Co-O mixed oxides was associated with the high active oxygen species concentrations formed during the pretreatment in O₂ atmosphere.     

General Formation of MxCo3−xS4 (M=Ni,Mn, Zn) Hollow Tubular Structures for Hybrid Supercapacitors

A simple and versatile method for general synthesis of uniform one‐dimensional (1D) M_xCo_3−xS₄ (M=Ni, Mn, Zn) hollow tubular structures (HTSs), using soft polymeric nanofibers as a template, is described. Fibrous core–shell polymer@M‐Co acetate hydroxide precursors with a controllable molar ratio of M/Co are first prepared, followed by a sulfidation process to obtain core–shell polymer@M_xCo_3−xS₄ composite nanofibers. The as‐made M_xCo_3−xS₄ HTSs have a high surface area and exhibit exceptional electrochemical performance as electrode materials for hybrid supercapacitors. For example, the MnCo₂S₄ HTS electrode can deliver specific capacitance of 1094 F g⁻¹ at 10 A g⁻¹, and the cycling stability is remarkable, with only about 6 % loss over 20 000 cycles.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2O4 for Low-Temperature Battery Operation

Binary transition-metal oxides (BTMOs) with hierarchical micro–nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe₂O₄ (cl-CoFe₂O₄) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro–nano-structure can promote fast ion transport and stable electrode–electrolyte interfaces. As a result, the cl-CoFe₂O₄ can deliver a high specific capacity (1019.9 mAh g⁻¹ at 0.1 A g⁻¹), excellent rate capability (626.0 mAh g⁻¹ at 5 A g⁻¹), and good cyclability (675.4 mAh g⁻¹ at 4 A g⁻¹ for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and −25 °C, the cl-CoFe₂O₄ anode can deliver high capacities of 907.5 and 664.5 mAh g⁻¹ at 100 mA g⁻¹, respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO₄ cathode exhibits a high rate performance (214.2 mAh g⁻¹ at 5000 mA g⁻¹) and an impressive cycling performance (612.7 mAh g⁻¹ over 140 cycles at 300 mA g⁻¹) in the voltage range of 0.5–3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe₂O₄ is dominated by pseudocapacitive behavior, leading to fast Li⁺ insertion/extraction and good cycling life.     

Perovskite SrCo0.9Nb0.1O3−δ as an Anion‐Intercalated Electrode Material for Supercapacitors with Ultrahigh Volumetric Energy Density

We have synthesized and characterized perovskite‐type SrCo_0.9Nb_0.1O_3−δ (SCN) as a novel anion‐intercalated electrode material for supercapacitors in an aqueous KOH electrolyte, demonstrating a very high volumetric capacitance of about 2034.6 F cm⁻³ (and gravimetric capacitance of ca. 773.6 F g⁻¹) at a current density of 0.5 A g⁻¹ while maintaining excellent cycling stability with a capacity retention of 95.7 % after 3000 cycles. When coupled with an activated carbon (AC) electrode, the SCN/AC asymmetric supercapacitor delivered a specific energy density as high as 37.6 Wh kg⁻¹ with robust long‐term stability.     

A Polyoxometalate-Based Binder-Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

Capacitive deionization is a promising technique in sea water desalination. Compared with common electrodes, mixed capacitive-deionization electrodes exhibit better performance in sea water desalination because they integrate pseudocapacitance and electric double-layer capacitance in one system. Herein, a 3D binder-free mixed capacitive-deionization electrode was fabricated by direct electrodeposition of SiW₁₂O₄₀⁴⁻ and polyaniline on a 3D exfoliated graphite carrier. In this electrode, SiW₁₂O₄₀⁴⁻/polyaniline composite particles with a size of about 100–120 nm are dispersed homogenously on the 3D exfoliated graphite carrier. Its specific capacitance reaches 352 F g⁻¹ at 1 A g⁻¹. With increasing current from 1 to 20 A g⁻¹, the specific capacitance only decays by 32 %. When employed in sea water desalination, the performance of this mixed capacitive-deionization electrode is also excellent. At 1.2 V, the salt adsorption capacity of this mixed electrode reaches 23.1 mg g⁻¹ with a salt adsorption rate of 1.38 mg g⁻¹ min⁻¹ in 500 mg L⁻¹ NaCl. The performance of this electrode is well retained after 30 cycles. The excellent sea water desalination performance originates from the synergistic effect between SiW₁₂O₄₀⁴⁻ and polyaniline. This work has developed polyoxometalate as a new material for capacitive-deionization electrodes.