Ni(OH) 2 /NiO/Ni composite nanotube arrays for high-performance supercapacitors

Current Trends and Promising Electrode Materials in Micro-Supercapacitor Printing

The development of scientific and technological foundations for the creation of high-performance energy storage devices is becoming increasingly important due to the rapid development of microelectronics, including flexible and wearable microelectronics. Supercapacitors are indispensable devices for the power supply of systems requiring high power, high charging-discharging rates, cyclic stability, and long service life and a wide range of operating temperatures (from -40 to 70 °C). The use of printing technologies gives an opportunity to move the production of such devices to a new level due to the possibility of the automated formation of micro-supercapacitors (including flexible, stretchable, wearable) with the required type of geometric implementation, to reduce time and labour costs for their creation, and to expand the prospects of their commercialization and widespread use. Within the framework of this review, we have focused on the consideration of the key commonly used supercapacitor electrode materials and highlighted examples of their successful printing in the process of assembling miniature energy storage devices.

Core-Shell Carbon Nanofibers@Ni(OH)2/NiO Composites for High-Performance Asymmetric Supercapacitors

The application of transition metal oxides/hydroxides in energy storage has long been studied by researchers. In this paper, the core-shell CNFs@Ni(OH)₂/NiO composite electrodes were prepared by calcining carbon nanofibers (CNFs) coated with Ni(OH)₂ under an N₂ atmosphere, in which NiO was generated by the thermal decomposition of Ni(OH)₂. After low-temperature carbonization at 200 °C, 250 °C and 300 °C for 1 h, Ni(OH)₂ or/and NiO existed on the surface of CNFs to form the core-shell composite CNFs@Ni(OH)₂/NiO-X (X = 200, 250, 300), in which CNFs@Ni(OH)₂/NiO-250 had the optimal electrochemical properties due to the coexistence of Ni(OH)₂ and NiO. Its specific capacitance could reach 695 F g^-1 at 1 A g^-1, and it still had 74% capacitance retention and 88% coulomb efficiency after 2000 cycles at 5 A g^-1. Additionally, the asymmetric supercapacitor (ASC) assembled from CNFs@Ni(OH)₂/NiO-250 had excellent energy storage performance with a maximum power density of 4000 W kg^-1 and a maximum functional capacity density of 16.56 Wh kg^-1.

Ternary NiCeCo-Layered Double Hydroxides Grown on CuBr2@ZIF-67 Nanowire Arrays for High-Performance Supercapacitors

Ternary layered double-hydroxide-based active compounds are regarded as ideal electrode materials for supercapacitors because of their unique structural characteristics and excellent electrochemical properties. Herein, an NiCeCo-layered double hydroxide with a core-shell structure grown on copper bromide nanowire arrays (CuBr₂@NCC-LDH/CF) has been synthesized through a hydrothermal strategy and calcination process and utilized to fabricate a binder-free electrode. Due to the unique top-tangled structure and the complex assembly of different active components, the prepared hierarchical CuBr₂@NCC-LDH/CF binder-free electrode exhibits an outstanding electrochemical performance, including a remarkable areal capacitance of 5460 mF cm^-2 at 2 mA cm^-2 and a capacitance retention of 88% at 50 mA cm^-2 as well as a low internal resistance of 0.163 Ω. Moreover, an all-solid-state asymmetric supercapacitor (ASC) installed with CuBr₂@NCC-LDH/CF and activated carbon electrodes shows a high energy density of 118 Wh kg^-1 at a power density of 1013 W kg^-1. Three assembled ASCs connected in series can operate a multifunctional display for over three and a half hours. Therefore, this innovative work provides new inspiration for the preparation of electrode materials for supercapacitors.

Recent Advancements in Electrochemical Deposition of Metal-Based Electrode Materials for Electrochemical Supercapacitors

The demand for energy storage devices with high energy and power densities has increased tremendously in this rapidly growing world. Conventional capacitors, fuel cells, and lithium-ion batteries have been used as energy storage devices for the long term. However, supercapacitors are one of the most promising energy storage devices because of their high specific capacitance, high power density, and longer cycle life. Recent research has focused on synthesizing transition-metal oxides/hydroxides, carbon materials, and conducting polymers as supercapacitor electrode materials. The performance of supercapacitors can be improved by altering electrolytes, electrode materials, current collectors, experimental temperatures, and film thickness. Thousands of papers on supercapacitors have already been published, reflecting the significance and elucidating how much demanding such energy storage devices for this fast-growing generation. This review aims to illustrate the electrode materials loaded on various conductive substrates by electrochemical deposition employed for supercapacitors to provide broad knowledge on synthetic pathways, which will pave the way for future research. We also discussed the basic parameters involved in supercapacitor studies and the advantages of the electrochemical deposition techniques through literature analysis. Finally, future trends and directions on exploring metals/metal composites toward designing and constructing viable, high-class, and even newly featured flexible energy storage materials, electrodes, and systems are presented.

Novel Dealloying-Fabricated NiS/NiO Nanoparticles with Superior Cycling Stability for Supercapacitors

NiS/NiO nanoparticles are successfully fabricated through a simple dealloying method and an ion-exchange process. X-ray diffraction demonstrates the existence of NiO and NiS phases, and scanning electron microscopy and transmission electron microscopy imply the nanopore distribution nature and the nanoparticle morphology of the produced material. The electrochemical behaviors are studied by cyclic voltammetry and galvanostatic charge-discharge measurements. The NiS/NiO electrode shows an enhanced specific capacitance of 1260 F g-1 at a current density of 0.5 A g-1. The NiS/NiO//AC device provides a maximum energy density of 17.42 W h kg-1, a high power density of 4000 W kg-1, and a satisfactory cycling performance of 93% capacitance retention after 30,000 cycles.

Green and facile preparation of graphene/resveratrol/polyaniline composites for high-performance supercapacitors

A novel and environmentally-friendly resveratrol (RA) was used as an effective reagent for the preparation of reduced graphene oxide (rGO).

Overview of transition metal-based composite materials for supercapacitor electrodes

Supercapacitors (SCs) can bridge the gap between batteries and conventional capacitors, playing a critical role as an efficient electrochemical storage device in intermittent renewable energy sources. Transition metal-based electrode materials have been investigated extensively as a class of electrode materials for SC application, but they have some limitations due to the sluggish ion/electron diffusion and inferior electronic conductivity, restricting their electrochemical performances towards energy storage. Developing advanced transition metal-based electrode materials is crucial for high energy density along with high specific power and fast charging/discharging rates towards high performance SCs. In this review, we highlight the state-of-the-art of transition metal-based electrode materials (transition metal oxides and their composites, transition metal sulfides and their composites, and transition metal phosphides and their composites), focusing on specific morphologies, components, and power characteristics. We also provide future prospects for transition metal-based electrode materials for SCs and hope this review will shed light on the achievement of higher performance and hold great promise in vast applications for future energy storage and conversion.

Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures’ electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.

Porous Fiber Processing and Manufacturing for Energy Storage Applications

The objective of this article is to provide an overview on the current development of micro- and nanoporous fiber processing and manufacturing technologies. Various methods for making micro- and nanoporous fibers including co-electrospinning, melt spinning, dry jet-wet quenching spinning, vapor deposition, template assisted deposition, electrochemical oxidization, and hydrothermal oxidization are presented. Comparison is made in terms of advantages and disadvantages of different routes for porous fiber processing. Characterization of the pore size, porosity, and specific area is introduced as well. Applications of porous fibers in various fields are discussed. The emphasis is put on their uses for energy storage components and devices including rechargeable batteries and supercapacitors.

Ingenious preparation of N/NiOx co-doped hierarchical porous carbon nanosheets derived from chitosan nanofibers for high-performance supercapacitors

It is still a key challenge to find suitable materials and methods to obtain super capacitors (SCs) with high specific capacitance due to the difficulty of balancing low theoretical capacity of conventional carbon materials and the poor ion transportability of transition metal oxide. In this work, N Ni dual-doped porous carbon nanosheets (NiO_x-NCNSs) are prepared through a novel way using original N-doped chitosan nanofibers and nickel nitrate to form honeycomb layered structure constructed by 2D fiber network as precursors. NiO_x-NCNS exhibits a high specific surface area of 1847.4 m² g^-1 with a rich N content of up to 5.16 wt% and shows a higher specific capacitance of 614.6 F g^-1 at a current density of 1 A g^-1 than that of carbon nanosheets of undoped Ni (NCNS) (427.5 F g^-1). More specifically, the SC assembled using NiO_x-NCNS electrodes achieves a high energy density of 20.3 W h kg^-1 at a power density of 240.9 W kg^-1, which is superior to most of the CNS-based SCs that have been reported. After 10 000 cycles, the symmetric SC retains approximately 85.61% of the initial capacitance. The strategy provided in this work probes the feasibility of high-performance SCs.

Atomic cobalt catalysts for the oxygen evolution reaction

Atomically dispersed Co/N-codoped graphene electrocatalysts require an ultra-low onset overpotential of approximately 210 mV on a glassy carbon electrode in both 1.0 M KOH and 0.1 M KOH solutions.

Ni(OH)2@Ni core-shell nanochains as low-cost high-rate performance electrode for energy storage applications

Energy storage performances of Ni-based electrodes rely mainly on the peculiar nanomaterial design. In this work, a novel and low-cost approach to fabricate a promising core-shell battery-like electrode is presented. Ni(OH)₂@Ni core-shell nanochains were obtained by an electrochemical oxidation of a 3D nanoporous Ni film grown by chemical bath deposition and thermal annealing. This innovative nanostructure demonstrated remarkable charge storage ability in terms of capacity (237 mAh g⁻¹ at 1 A g⁻¹) and rate capability (76% at 16 A g⁻¹, 32% at 64 A g⁻¹). The relationships between electrochemical properties and core-shell architecture were investigated and modelled. The high-conductivity Ni core provides low electrode resistance and excellent electron transport from Ni(OH)₂ shell to the current collector, resulting in improved capacity and rate capability. The reported preparation method and unique electrochemical behaviour of Ni(OH)₂@Ni core-shell nanochains show potential in many field, including hybrid supercapacitors, batteries, electrochemical (bio)sensing, gas sensing and photocatalysis.

Synthesis of a novel Au nanoparticles decorated Ni-MOF/Ni/NiO nanocomposite and electrocatalytic performance for the detection of glucose in human serum

A nonenzymatic glucose electrochemical sensor was constructed based on Au nanoparticles (AuNPs) decorated Ni metal-organic-framework (MOF)/Ni/NiO nanocomposite. Ni-MOF/Ni/NiO nanocomposite was synthesized by one-step calcination of Ni-MOF. Then AuNPs were loaded onto the Ni-based nanocomposites' surface through electrostatic adsorption. Through characterization by transmission electron microscopy (TEM), high resolution TEM (HRTEM) and energy disperse spectroscopy (EDS) mapping, it is found that the AuNPs were well distributed on the surface of Ni-based nanocomposite. Cyclic voltammetric (CV) study showed the electrocatalytic activity of Au-Ni nanocomposite was highly improved after loading AuNPs onto it. Amperometric study demonstrated that the Au-Ni nanocomposites modified glassy carbon electrode (GCE) exhibited a high sensitivity of 2133.5 mA M^-1 cm^-2 and a wide linear range (0.4-900 μM) toward the oxidation of glucose with a detection limit as low as 0.1 μM. Moreover, the reproducibility, selectivity and stability of the sensor all exhibited outstanding performance. We applied the as-fabricated high performance sensor to measure the glucose levels in human serum and obtained satisfactory results. It is believed that AuNPs decorated Ni MOF/Ni/NiO nanocomposite provides a new platform for developing highly performance electrochemical sensors in practical applications.

Development of high-utilization honeycomb-like α-Ni(OH)2 for asymmetric supercapacitors with excellent capacitance

The low utilization rate of active materials has been a critical obstacle for the industrialization of ultracapacitors. In this study, a thin layer of cross-structured ultrathin α-Ni(OH)₂ nanosheets was successfully grown in situ on the surface of a nickel foam as a high-conductivity framework by a vibratory water bath route under a low temperature (80 °C) and mild conditions. Combining the ultrathin α-Ni(OH)₂ nanosheets and ultrashort electron transport, the strategy of a perfect intercalation structure of α-Ni(OH)₂ and a thin layer of active material on a continuous conductive framework resulted in a high utilization rate of active material, which further achieved high specific capacitance of 213.55 F g⁻¹ at 1 A g⁻¹ in a two-electrode system and high capacitance retention from three to two electrode system (753.79 F g⁻¹ at 1 A g⁻¹ in the three-electrode system). Meanwhile, the device also achieved high energy density of 74.94 W h kg⁻¹ at power density of 197.4 W kg⁻¹ and still retained 24.87 W h kg⁻¹ at power density of 3642 W kg⁻¹.

The low utilization rate of active materials has been a critical obstacle for the industrialization of ultracapacitors.

Controllable synthesis of hierarchical nickel hydroxide nanotubes for high performance supercapacitors

Hierarchical Ni(OH)₂ nanotubes synthesized by a self-sacrificial template method exhibit superior capacitance and stability as electrode materials for supercapacitors.

Annealing effects on the magnetic properties of highly-packed vertically-aligned nickel nanotubes

Hysteresis loops showing the decrease of the saturation magnetic moment (left) through a dense array of vertically-aligned Ni nanotubes after their progressive thermal conversion into hybrid ferromagnetic/antiferromagnetic Ni/NiO nanotubes (right).

NiO@MnO2 core–shell composite microtube arrays for high-performance lithium ion batteries

The NiO@MnO₂ core–shell microtube array electrode with excellent lithium storage performance is fabricated by self-corrosion and electrodeposition.

Controllable synthesis of ultrathin nickel oxide sheets on carbon cloth for high-performance supercapacitors

Controllable synthesis of ultrathin nickle oxide sheets on carbon cloth for high-performance supercapacitors.

Nanofoaming to Boost the Electrochemical Performance of Ni@Ni(OH)2 Nanowires for Ultrahigh Volumetric Supercapacitors

Three-dimensional free-standing film electrodes have aroused great interest for energy storage devices. However, small volumetric capacity and low operating voltage limit their practical application for large energy storage applications. Herein, a facile and novel nanofoaming process was demonstrated to boost the volumetric electrochemical capacitance of the devices via activation of Ni nanowires to form ultrathin nanosheets and porous nanostructures. The as-designed free-standing Ni@Ni(OH)₂ film electrodes display a significantly enhanced volumetric capacity (462 C/cm³ at 0.5 A/cm³) and excellent cycle stability. Moreover, the as-developed hybrid supercapacitor employed Ni@Ni(OH)₂ film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm³ (at 0.25 A/cm³) and excellent cycle performance (only 14% capacitance reduction for 4500 cycles). Furthermore, the volumetric energy density can reach 33.9 mWh/cm³, which is much higher than that of most thin film lithium batteries (1-10 mWh/cm³). This work gives an insight for designing high-volume three-dimensional electrodes and paves a new way to construct binder-free film electrode for high-performance hybrid supercapacitor applications.

Assembly of NiO/Ni(OH)2/PEDOT Nanocomposites on Contra Wires for Fiber-Shaped Flexible Asymmetric Supercapacitors

Fiber-shaped solid-state supercapacitors have aroused much interest in the fields of portable devices because of their attractive features such as high flexibility and safety, tiny volume, and high power density. In this work, NiO/Ni(OH)2 nanoflowers encapsulated in three-dimensional interconnected poly(3,4-ethylenedioxythiophene) (PEDOT) have been fabricated on contra wires through a mild electrochemical route. The as-formed hybrid electrode made of NiO/Ni(OH)2/PEDOT delivered a high specific capacitance of 404.1 mF cm(-2) (or 80.8 F cm(-3)) at a current density of 4 mA cm(-2) and a long cycle life with 82.2% capacitance retention after 1000 cycles. Furthermore, a fiber-shaped flexible all-solid-state asymmetric supercapacitor based on the resulting hybrid electrode was assembled. The energy density of 0.011 mWh cm(-2) at a power density of 0.33 mW cm(-2) was achieved under an operating voltage window of 1.45 V. This work provides an effective strategy to fabricate high-performance electrodes for fiber-shaped flexible asymmetric supercapacitors through a facile and low-cost route.

Dealloying Behavior of NiCo and NiCoCu Thin Films

Porous metals and alloys, such as those fabricated via electrochemical dealloying, are of interest for a variety of energy applications, ranging from their potential for enhanced catalytic behavior to their use as high surface area supports for pseudocapacitor materials. Here, the electrochemical dealloying process was explored for electrodeposited binary NiCo and ternary NiCoCu thin films. For each of the four different metal ratios, films were dealloyed using linear sweep voltammetry to various potentials in order to gain insight into the evolution of the film over the course of the linear sweep. Electrochemical capacitance, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used to examine the structure and composition of each sample before and after linear sweep voltammetry was performed. For NiCo films, dealloying resulted in almost no change in composition but did result in an increased capacitance, with greater increases occurring at higher linear sweep potentials, indicating the removal of material from the films. Dealloying also resulted in the appearance of large pores on the surface of the high nickel percentage NiCo films, while low nickel percentage NiCo films had little observable change in morphology. For NiCoCu films, Cu was almost completely removed at linear sweep potentials greater than 0.5 V versus Ag/AgCl. The linear sweep removed large Cu-rich dendrites from the films, while also causing increases in measured capacitance.

MOF-derived NixCo1−x(OH)2 composite microspheres for high-performance supercapacitors

NixCo_1−x(OH)₂ composite microspheres are successfully synthesized with the assistance of alkali solution by employing a bimetallic Co–Ni–MOF as both the precursor and the self-sacrificing template, demonstrating excellent electrochemical performance.

Facile morphology controlled synthesis of nanostructured Co3O4 films on nickel foam and their pseudocapacitive performance

The as-synthesized 3D hierarchically porous Co₃O₄ network film on nickel foam shows prominent pseudocapacitive performance.

Facile synthesis of three-dimensional NiCo2O4 with different morphology for supercapacitors

The morphology of NiCo₂O₄ can be controlled by changing the kinds of alkali source and the addition of NH₄F, influencing its electrochemical properties.

High supercapacitive performance of Ni(OH)2/XC-72 composite prepared by microwave-assisted method

A Ni(OH)₂/XC-72 composite with CNTs as a conductive agent has a unique 3-D conductive network structure and shows high specific capacitance of 1560 F g⁻¹ at 1 A g⁻¹.