Synergy of Oxygen Vacancy and Surface Modulation Endows Hollow Hydrangea-like MnCo2O4.5 with Enhanced Capacitive Performance

Surface chemistry and bulk structure jointly play crucial roles in achieving high-performance supercapacitors. Here, the synergistic effect of surface chemistry properties (vacancy and phosphorization) and structure-derived properties (hollow hydrangea-like structure) on energy storage is explored by the surface treatment and architecture design of the nanostructures. The theoretical calculations and experiments prove that surface chemistry modulation is capable of improving electronic conductivity and electrolyte wettability. The structural engineering of both hollow and nanosheets produces a high specific surface area and an abundant pore structure, which is favorable in exposing more active sites and shortens the ion diffusion distance. Benefiting from its admirable physicochemical properties, the surface phosphorylated MnCo2O4.5 hollow hydrangea-like structure (P-MnCoO) delivers a high capacitance of 425 F g-1 at 1 A g-1, a superior capability rate of 63.9%, capacitance retention at 10 A g-1, and extremely long cyclic stability (91.1% after 10,000 cycles). The fabricated P-MnCoO/AC asymmetric supercapacitor achieved superior energy and power density. This work opens a new avenue to further improve the electrochemical performance of metal oxides for supercapacitors.

A Review on the Application of Cobalt-Based Nanomaterials in Supercapacitors

Among many electrode materials, cobalt-based nanomaterials are widely used in supercapacitors because of their high natural abundance, good electrical conductivity, and high specific capacitance. However, there are still some difficulties to overcome, including poor structural stability and low power density. This paper summarizes the research progress of cobalt-based nanomaterials (cobalt oxide, cobalt hydroxide, cobalt-containing ternary metal oxides, etc.) as electrode materials for supercapacitors in recent years and discusses the preparation methods and properties of the materials. Notably, the focus of this paper is on the strategies to improve the electrochemical properties of these materials. We show that the performance of cobalt-based nanomaterials can be improved by designing their morphologies and, among the many morphologies, the mesoporous structure plays a major role. This is because mesoporous structures can mitigate volume changes and improve the performance of pseudo capacitance. This review is dedicated to the study of several cobalt-based nanomaterials in supercapacitors, and we hope that future scholars will make new breakthroughs in morphology design.

Porous MCo2O4(M = Zn, Cu, Fe, Mn) as high efficient bi-functional catalysts for oxygen reduction and oxygen evolution reaction

High-efficiency bi-functional electrocatalysts with long-term stability are critical to the development of many kinds of fuel cells, because that the performance of battery is limited by the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, porous MCo₂O₄(M = Zn, Cu, Fe, Mn) were prepared by hydrothermal method with NH₄F and urea as surfactants. FeCo₂O₄with porous structure has more oxygen defects and the larger specific surface area than other MCo₂O₄(M = Zn, Cu, Mn), and it not onlysupplies more active sites but also avails the transmission of electrolyte and O₂in the process of ORR and OER in 0.1 M KOH aqueous solution. Porous FeCo₂O₄electrode material produces less intermediate H₂O₂, and its ORR is mainly controlled by a 4e^-reaction path. Compared with commercial Pt/C, the prepared FeCo₂O₄has comparable ORR activity and excellent OER activity. At the same time, the stability of FeCo₂O₄to ORR is significantly higher than that of commercial Pt/C. The porous FeCo₂O₄was prepared by facile synthesis procedure could be a potential promising bi-functional catalyst due to its high electrocatalytic activities and long-term stability for both the ORR and OER.

MnCo2O4/Ni3S4 nanocomposite for hybrid supercapacitor with superior energy density and long-term cycling stability

MnCo₂O₄ is regarded as a good electrode material for supercapacitor due to its high specific capacity and good structural stability. However, its poor electrical conductivity limits its wide-range applications. To solve this issue, we integrated the MnCo₂O₄ with Ni₃S₄, which has a good electrical conductivity, and synthesized a MnCo₂O₄/Ni₃S₄ nanocomposite using a two-step hydrothermal process. Comparing with individual MnCo₂O₄ and Ni₃S₄, the MnCo₂O₄/Ni₃S₄ nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor. The specific capacity value of the MnCo₂O₄/Ni₃S₄ electrode was 904.7 C g^-1 at 1 A g^-1 with a potential window of 0-0.55 V. A hybrid supercapacitor (HSC), assembled using MnCo₂O₄/Ni₃S₄ and active carbon as the cathode and anode, respectively, showed a capacitance of 116.4 F g^-1 at 1 A g^-1, and a high energy density of 50.7 Wh kg^-1 at 405.8 W kg^-1. Long-term electrochemical stability tests showed an obvious increase of the HSC's capacitance after 5500 charge/discharge cycles, reached a maximum value of ∼162.7% of its initial value after 25,000 cycles, and then remained a stable value up to 64,000 cycles. Simultaneously, its energy density was increased to 54.2 Wh kg^-1 at 380.3 W kg^-1 after 64,000 cycles.

Suppressed Jahn-Teller Distortion in MnCo2 O4 @Ni2 P Heterostructures to Promote the Overall Water Splitting

Jahn-Teller distortion in cobalt based spinel electrocatalysts causes poor activity and stability in potentially promising catalysts for water splitting. Here, a novel strategy to resolve this problem by interface engineering is reported, in which, Jahn-Teller distortion in MnCo₂ O₄ is significantly suppressed by in situ growth Ni₂ P nanosheets onto the MnCo₂ O₄ . The significance of interface engineering in suppressing Jahn-Teller distortion of Mn³⁺ is further investigated by X-ray photoelectron spectroscopy, the resulting increased catalytic activity and the effects of suppressed distortion demonstrated by density functional theory calculations. The resulting MnCo₂ O₄ @Ni₂ P heterostructures exhibit superior electrocatalytic activity for the both oxygen evolution reaction and hydrogen evolution reaction with small overpotentials of 240 and 57 mV at 10 mA cm^-2 , respectively. Furthermore, the heterogeneous composite electrode demonstrates a superior current density of 10 mA cm^-2 at a voltage of 1.63 V with excellent durability in a water splitting cell.

In-Situ Synthesis of Heterostructured Carbon-Coated Co/MnO Nanowire Arrays for High-Performance Anodes in Asymmetric Supercapacitors

Structural design is often investigated to decrease the electron transfer depletion in/on the pseudocapacitive electrode for excellent capacitance performance. However, a simple way to improve the internal and external electron transfer efficiency is still challenging. In this work, we prepared a novel structure composed of cobalt (Co) nanoparticles (NPs) embedded MnO nanowires (NWs) with an N-doped carbon (NC) coating on carbon cloth (CC) by in situ thermal treatment of polydopamine (PDA) coated MnCo₂O_4.5 NWs in an inert atmosphere. The PDA coating was carbonized into the NC shell and simultaneously reduced the MnCo₂O_4.5 to Co NPs and MnO NWs, which greatly improve the surface and internal electron transfer ability on/in MnO boding well supercapacitive properties. The hybrid electrode shows a high specific capacitance of 747 F g⁻¹ at 1 A g⁻¹ and good cycling stability with 93% capacitance retention after 5,000 cycles at 10 A g⁻¹. By coupling with vanadium nitride with an N-doped carbon coating (VN@NC) negative electrode, the asymmetric supercapacitor delivers a high energy density of 48.15 Wh kg⁻¹ for a power density of 0.96 kW kg⁻¹ as well as outstanding cycling performance with 82% retention after 2000 cycles at 10 A g⁻¹. The electrode design and synthesis suggests large potential in the production of high-performance energy storage devices.

Rational design of flower-like cobalt–manganese-sulfide nanosheets for high performance supercapacitor electrode materials

The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors.

Electrochemical water splitting exploration of MnCo2O4, NiCo2O4 cobaltites

One-step solvothermal synthesis is used to produce Mn and Ni based cobaltites.

Porous layered stacked MnCo2O4 cubes with enhanced electrochemical capacitive performance

The development of new electrode materials with various components, structures, morphologies and porosities is critical for improving the performance of supercapacitors. Here, we report a facile strategy for synthesizing porous layered stacked MnCo₂O₄ cubes through a hydrothermal method, followed by annealing treatment. Compared with other morphologies of MnCo₂O₄, the specific capacitance of porous layered stacked MnCo₂O₄ cubes reaches 480.5 F g^-1 at a current density of 1 A g^-1. Furthermore, porous layered stacked MnCo₂O₄ cubes show an ultrahigh capacity retention of 75.7% even at a current density of 25 A g^-1 and good cycling stability with 96.6% specific capacitance retained after 3000 cycles, which makes porous layered stacked MnCo₂O₄ cubes a great potential electrode material for supercapacitor applications.

Crystal morphology evolution of Ni–Co layered double hydroxide nanostructure towards high-performance biotemplate asymmetric supercapacitors

Hierarchical three-dimensional (3D) porous structures of nickel–cobalt layered double hydroxide (LDH) are grown on diatomite biotemplate via one-step hydrothermal method.

V. Muralee Gopi C, Rana PJS, Vinodh R, Kim S, Padma R, Kim HJ. Hierarchical nanostructured MnCo2O4–NiCo2O4 composites as innovative electrodes for supercapacitor applications

Hierarchical MnCo₂O₄–NiCo₂O₄ nanostructures deliver a higher electrochemical performance than MnCo₂O₄ and NiCo₂O₄ electrodes.

Hierarchical Ni-Co layered double hydroxide nanosheets entrapped on conductive textile fibers: a cost-effective and flexible electrode for high-performance pseudocapacitors

Hierarchical three-dimensional (3D) porous nanonetworks of nickel-cobalt layered double hydroxide (Ni-Co LDH) nanosheets (NSs) are grown and decorated on flexible conductive textile substrate (CTs) via a simple two-electrode system based electrochemical deposition (ED) method. By applying a proper external cathodic voltage of -1.2 V for 15 min, the Ni-Co LDH NSs are densely deposited over the entire surface of the CTs with good adhesion. The flexible Ni-Co LDH NSs on CTs (Ni-Co LDH NSs/CTs) architecture with high porosity facilitates enhanced electrochemical performance in 1 M KOH electrolyte solution. The effect of growth concentration and external cathodic voltage on the electrochemical properties of Ni-Co LDH NSs/CTs is also investigated. The Ni10Co5 LDH NSs/CTs electrode exhibits a high specific capacitance of 2105 F g(-1) at a current density of 2 A g(-1) as well as an excellent cyclic stability as a pseudocapacitive electrode due to the advantageous properties of 3D interconnected porous frameworks of Ni10Co5 LDH NSs/CTs. This facile fabrication of bimetallic hydroxide nanostructures on CTs can provide a promising electrode for low-cost energy storage device applications.

Facile synthesis of NiCoMnO4 nanoparticles as novel electrode materials for high-performance asymmetric energy storage devices

Hydrothermally synthesized NiCoMnO₄ NPs showed a high capacitance of 510 F g⁻¹ with high mass loaded electrodes (∼10 mg cm⁻²). Integrated with RGO NSs, their viability was testified for high-performance asymmetric supercapacitors.

Flexible heterostructured supercapacitor electrodes based on α-Fe2O3 nanosheets with excellent electrochemical performances

Hybrid α-Fe₂O₃@Co₃O₄ and α-Fe₂O₃@MnCo₂O₄ composites are successfully synthesized on flexible carbon cloth, respectively. These as-obtained products as the supercapacitor electrodes show enhanced discharge areal capacitance.

Facile synthesis of three-dimensionally ordered macroporous silicon-doped La0.8K0.2CoO3 perovskite catalysts for soot combustion

Three-dimensionally ordered macroporous (3DOM) silicon-doped La_0.8K_0.2CoO₃ perovskite catalysts were successfully prepared by a colloidal crystal templating method. The catalysts showed a well-ordered macroporous structure and exhibited high activity for soot removal.

Electrodeposition of spinel MnCo₂O₄ nanosheets for supercapacitor applications

Herein, we report a facile, low-cost and one-step electrodeposition approach for the synthesis MnCo2O4 (MCO) nanosheet arrays on indium doped tin oxide (ITO) coated glass substrates. The crystalline phase and morphology of the materials are studied by x-ray diffraction, energy dispersive x-ray analysis and field-emission scanning electron microscopy. The supercapacitor performance of the MCO nanosheets are studied in a three-electrode configuration in 2 M KOH electrolyte. The as-prepared binder-free electrode shows a high specific capacitance of 290 F g(-1) at 1 mV s(-1) with excellent cyclic stability even after 1000 charge/discharge cycles. The obtained energy density and power density of the MCO nanosheets are 10.04 Wh kg(-1) and 5.2 kW kg(-1) respectively. The superior electrochemical performances are mainly attributed to its nanosheet like structure which provides a large reaction surface area, and fast ion and electron transfer rate.

Controllable synthesis of micro/nano-structured MnCo2O4 with multiporous core–shell architectures as high-performance anode materials for lithium-ion batteries

Various micro/nano-structured MnCo₂O₄ with excellent lithium storage performance were synthesized controllably.

Advanced asymmetric supercapacitors based on Ni3(PO4)2@GO and Fe2O3@GO electrodes with high specific capacitance and high energy density

Ni₃(PO₄)₂@GO and Fe₂O₃@GO have been successfully synthesized as electrode materials, and they have been used to assemble an asymmetric supercapacitor (Fe₂O₃@GO//Ni₃(PO₄)₂@GO), which exhibited a high energy density.

A 1-D/2-D hybrid nanostructured manganese cobaltite–graphene nanocomposite for electrochemical energy storage

A novel method to bridge the advantages of 1D and 2D nanomaterials for energy storage applications.