Hierarchical Core-Shell Nanosheet Arrays with MnO2 Grown on Mesoporous CoFe2O4 Support for High-Performance Asymmetric Supercapacitors

Advances in porous carbon materials for a sustainable future: A review

Developing clean and renewable energy sources is key to a sustainable future. For human society to progress sustainably, environmentally friendly energy conversion and storage technologies are critical. The use of nanostructured advanced functional materials heavily influences the functionality of these systems. Porous carbons are multifunctional materials boasting considerable industrial utility. They possess many remarkable physiochemical and mechanical characteristics which have garnered interest in various fields. In this review, the application of porous carbon materials in electrocatalysis (HER, OER, ORR, NARR, and CO2RR) and rechargeable batteries (LIBs, LiS batteries, NIBs, and KIBs) for renewable energy conversion and storage are discussed. The suitability of porous carbon materials for these applications is discussed, and some recent works are reviewed. Finally, a few viewpoints on developing porous carbons in electrocatalysis and rechargeable batteries are given. This review aims to generate interest in current and upcoming researchers in porous carbon application for a sustainable future.

MnO2-based materials for supercapacitor electrodes: challenges, strategies and prospects

Manganese dioxide (MnO₂) has always been the ideal electrode material for supercapacitors due to its non-toxic nature and high theoretical capacity (1370 F g^-1). Over the past few years, significant progress has been made in the development of high performance MnO₂-based electrode materials. This review summarizes recent research progress in experimental, simulation and theoretical studies for the modification of MnO₂-based electrode materials from different perspectives of morphology engineering, defect engineering and heterojunction engineering. Several main approaches to achieve enhanced electrochemical performance are summarized, respectively increasing the effective active site, intrinsic conductivity and structural stability. On this basis, the future problems and research directions of electrode materials are further envisaged, which provide theoretical guidance for the adequate design and synthesis of MnO₂-based electrode materials for use in supercapacitors.

Observation of morphology resembling Hydrangea macrophylla flower in SILAR-deposited MFe2O4 (M=Co2+, Ni2+, Mn2+) nanocrystallites: synergetic effect on electrochemical performance

The successive ionic layer adsorption and reaction (SILAR) experimental process has been used to develop a high-efficiency electrode of MFe₂O₄ (M = Ni, Co and Mn) on substrates at ambient temperature. Structural, morphological and electrochemical properties have been investigated using x-ray diffraction (XRD), a scanning electron microscope (SEM) and an electrochemical test station, respectively. A morphology resembling the Hydrangea macrophylla flower has been observed and tuned with varying Fe concentration. The formation of MFe₂O₄ demonstrates the efficient electrochemical behavior and the specific capacitance has been evaluated as ∼1380, ∼972 and ∼815 Fg^-1 for CoFe₂O₄ (CF), NiFe₂O₄ (NF) and MnFe₂O₄ (MF), respectively, at a current density of 1 Ag^-1. Also, the developed electrodes maintain excellent cyclic retention of ∼92%, ∼89% and ∼86% for CF, NF, and MF, respectively, up to 5000 cycles. Further, asymmetric solid-state supercapacitor (ASC) devices have been fabricated using the best compositions of MFe₂O₄ as a positive electrode and carbon black (CB) as a negative electrode, and successfully illuminate a 1.8 V commercial LED.

Two-Dimensional Transition Metal Oxide and Hydroxide-Based Hierarchical Architectures for Advanced Supercapacitor Materials

The supercapacitor has been widely seen as one of the most promising emerging energy storage devices, by which electricity is converted from chemical energy and stored. Two-dimensional (2D) metal oxides/hydroxides (TMOs/TMHs) are revolutionizing the design of high-performance supercapacitors because of their high theoretical specific capacitance, abundance of electrochemically active sites, and feasibility for assembly in hierarchical structures by integrating with graphitic carbon, conductive polymers, and so on. The hierarchical structures achieved can not only overcome the limitations of using a single material but also bring new breakthroughs in performance. In this article, the research progress on 2D TMOs/TMHs and their use in hierarchical structures as supercapacitor materials are reviewed, including the evolution of supercapacitor materials, the configurations of hierarchical structures, the electrical properties regulated, and the existence of advantages and drawbacks. Finally, a perspective covering directions and challenges related to the development of supercapacitor materials is provided.

Pulsed laser deposited CoFe2O4 thin films as supercapacitor electrodes

The influence of the substrate temperature on pulsed laser deposited (PLD) CoFe2O4 thin films for supercapacitor electrodes was thoroughly investigated. X-ray diffractometry and Raman spectroscopic analyses confirmed the formation of CoFe2O4 phase for films deposited at a substrate temperature of 450 °C. Topography and surface smoothness was measured using atomic force microscopy. We observed that the films deposited at room temperature showed improved electrochemical performance and supercapacitive properties compared to those of films deposited at 450 °C. Specific capacitances of about 777.4 F g-1 and 258.5 F g-1 were obtained for electrodes deposited at RT and 450 °C, respectively, at 0.5 mA cm-2 current density. The CoFe2O4 films deposited at room temperature exhibited an excellent power density (3277 W kg-1) and energy density (17 W h kg-1). Using electrochemical impedance spectroscopy, the series resistance and charge transfer resistance were found to be 1.1 Ω and 1.5 Ω, respectively. The cyclic stability was increased up to 125% after 1500 cycles due to the increasing electroactive surface of CoFe2O4 along with the fast electron and ion transport at the surface.

Spinel ferrite (AFe2O4)-based heterostructured designs for lithium-ion battery, environmental monitoring, and biomedical applications

The development of spinel ferrite nanomaterial (SFN)-based hybrid architectures has become more popular owing to the fascinating physicochemical properties of SFNs, such as their good electro-optical and catalytic properties, high chemothermal stability, ease of functionalization, and superparamagnetic behaviour. Furthermore, achieving the perfect combination of SFNs and different nanomaterials has promised to open up many unique synergistic effects and advantages. Inspired by the above-mentioned noteworthy properties, numerous and varied applications have been recently developed, such as energy storage in lithium-ion batteries, environmental pollutant monitoring, and, especially, biomedical applications. In this review, recent development efforts relating to SFN-based hybrid designs are described in detail and logically, classified according to 4 major hybrid structures: SFNs/carbonaceous nanomaterials; SFNs/metal–metal oxides; SFNs/MS₂; and SFNs/other materials. The underlying advantages of the additional interactions and combinations of effects, compared to the standalone components, and the potential uses have been analyzed and assessed for each hybrid structure in relation to lithium-ion battery, environmental, and biomedical applications.

We have summarized recent developments in SFN-based hybrid designs. The additional interactions, combination effects, and important changes have been analyzed and assessed for LIB, environmental monitoring, and biomedical applications.

Hierarchical core-shell structures of P-Ni(OH)2 rods@MnO2 nanosheets as high-performance cathode materials for asymmetric supercapacitors

The hierarchical porous structure with phosphorus-doped Ni(OH)₂ (P-Ni(OH)₂) rods as the core and MnO₂ nanosheets as the shell is fabricated directly by growth on a three-dimensional (3D) flexible Ni foam (NF) via a two-step hydrothermal process. As a binder-free electrode material, this unique hybrid structure exhibits excellent electrochemical properties, including an ultrahigh areal capacitance of 5.75 F cm^-2 at a current density of 2 mA cm^-2 and great cyclic stability without capacitance loss at a current density of 20 mA cm^-2 after 10 000 cycles. Moreover, an all-solid-state asymmetric supercapacitor (AAS) based on a P-Ni(OH)₂@MnO₂ hybrid structure on Ni foam as the cathode and activated carbon (AC) as the anode is successfully assembled to enhance value the electrochemical properties. The AAS device also shows excellent electrochemical properties including a large potential window of 0∼1.6 V, an areal capacitance is 911.3 mF cm^-2 at a current density of 1 mA cm^-2 and long-term cycling performance. Meanwhile, the AAS device also delivers a high energy density of 0.324 mW h cm^-2 at a power density of 0.8 mW cm^-2; and can easily light colorful light-emitting diode (LED) lights, suggesting that 3D P-Ni(OH)₂@MnO₂ hybrid composite has promising potential for practical use in high-performance supercapacitors.

The synthesis of hierarchical ZnCo2O4@MnO2core–shell nanosheet arrays on Ni foam for high-performance all-solid-state asymmetric supercapacitors

ZnCo₂O₄@MnO₂core–shell nanosheet arrays synthesizedviaa two-step hydrothermal method exhibited an extraordinary electrochemical performance.