Amorphous Ni-Co Binary Oxide with Hierarchical Porous Structure for Electrochemical Capacitors

Influence of Ni and Sn Perovskite NiSn(OH)6 Nanoparticles on Energy Storage Applications

New NiSn(OH)₆ hexahydroxide nanoparticles were synthesised through a co-precipitation method using various concentrations of Ni²⁺ and Sn⁴⁺ ions (e.g., 1:0, 0:1, 1:2, 1:1, and 2:1; namely, N, S, NS-3, NS-2, and NS-1) with an ammonia solution. The perovskite NiSn(OH)₆ was confirmed from powder X-ray diffraction and molecule interactions due to different binding environments of Ni, Sn, O, and water molecules observed from an FT-IR analysis. An electronic transition was detected from tin (Sn 3d) and nickel (Ni 2p) to oxygen (O 2p) from UV-Vis/IR spectroscopy. Photo luminescence spectroscopy (PL) identified that the emission observed at 400-800 nm in the visible region was caused by oxygen vacancies due to various oxidation states of Ni and Sn metals. A spherical nanoparticle morphology was observed from FE-SEM; this was due to the combination of Ni²⁺ and Sn⁴⁺ increasing the size and porosity of the nanoparticle. The elemental (Ni and Sn) distribution and binding energy of the nanoparticle were confirmed by EDAX and XPS analyses. Among the prepared various nanoparticles, NS-2 showed a maximum specific capacitance of 607 Fg^-1 at 1 Ag^-1 and 56% capacitance retention (338 Fg^-1 and 5 Ag^-1), even when increasing the current density five times, and excellent cycle stability due to combining Ni²⁺ with Sn⁴⁺, which improved the ionic and electrical conductivity. EIS provided evidence for NS-2's low charge transfer resistance compared with other prepared samples. Moreover, the NS-2//AC (activated carbon) asymmetric supercapacitor exhibited the highest energy density and high-power density along with excellent cycle stability, making it the ideal material for real-time applications.

Encapsulation of spinel CuCo2O4 hollow sphere in V2O5-decorated graphitic carbon nitride as high-efficiency double Z-type nanocomposite for levofloxacin photodegradation

In this study, spinel CuCo₂O₄ (CCO) with a hierarchical hollow sphere morphology was encapsulated in V₂O₅-decorated ultra-wrinkled graphitic carbon-nitride (VO-UCN) for the first time via a facile glycerol-assisted solvothermal method in the interest of developing a novel high-efficiency double Z-type nano-photocatalyst (denoted as VO-UCN@CCO). The remarkable physicochemical features of the as-prepared nano-photocatalysts were verified using diverse characterization techniques including TGA, XRD, FT-IR, FE-SEM, TEM, BET, UV-vis DRS, PL, EIS, and transient photocurrent techniques. Herein, VO-UCN@CCO nanocomposite was employed for the photodisintegration of levofloxacin (LVOF) antibiotic under visible-light irradiation and the impact of certain operative reaction system variables was explored in an effort to optimize the photocatalytic capability. The 40% loading of CCO in VO-UCN@CCO nanocomposite was found to display maximum photocatalytic performance (about 95%) for LVOF photodecomposition, which was 9.3, 6.6, and 13.8 times greater when compared with pristine VO, UCN, and CCO, respectively. A high capability was observed for as-prepared photocatalyst during reusability tests and near 90% degradation efficiency was obtained in the sixth run. The complete mineralization of LVOF was achieved by the VO-UCN@CCO photocatalyst process after 300 min of reaction. An excellent synergy factor towards the degradation of LVOF was obtained for VO-UCN@CCO compared to each of its components alone. This peculiar design is envisaged to provide new inspirations for ameliorating the photocatalytic decontamination of tenacious and non-biodegradable species present in real wastewater.

Hierarchical WS2@NiCo2O4 Core-shell Heterostructure Arrays Supported on Carbon Cloth as High-Performance Electrodes for Symmetric Flexible Supercapacitors

Nowadays, rationally preparing heterostructure materials can not only make up for the shortage of individual components, but also exert unexpected performance through synergistic interactions between the components. Herein, a core-shell of WS₂@NiCo₂O₄ screw-like heterostructure arrays grown on carbon cloth (CC) was prepared by a two-step solvothermal method for supercapacitors. As a binder-free flexible electrode, a high areal capacitance of 2449.9 mF cm^-2 can be achieved for WS₂@NiCo₂O₄/CC at a current density of 1 mA cm^-2. Benefiting from the core-shell of the WS₂@NiCo₂O₄ heterostructure, the capacitive property of the flexible WS₂@NiCo₂O₄/CC electrode is better than those of WS₂/CC and NiCo₂O₄/CC electrodes. Based on WS₂@NiCo₂O₄/CC electrodes, the assembled flexible solid-state symmetric supercapacitor (FSS) device shows a high energy density of ∼45.67 W h kg^-1 at a power density of 992.83 W kg^-1. Meantime, the WS₂@NiCo₂O₄/CC-assembled FSS device also exhibits high cycling stability with an excellent capacity retention of ∼85.59% after 5000 cycles.

Octahedral morphology of NiO with (111) facet synthesized from the transformation of NiOHCl for the NOx detection and degradation: experiment and DFT calculation

NiO with polar (111) facets was successfully synthesized from the transformation of a layered NiOHCl, exhibiting excellent NO_x detection and degradation activity.

Highly Active Core-Shell Carbon/NiCo2 O4 Double Microtubes for Efficient Oxygen Evolution Reaction: Ultralow Overpotential and Superior Cycling Stability

Developing highly efficient electrocatalysts with earth abundant elements for oxygen evolution reaction (OER) is a promising way to store light or electrical energy in the form of chemical energy. Here, a new type of electrocatalyst with core-shell carbon/NiCo₂ O₄ double microtubes architecture is successfully synthesized through a hydrothermal method combined with the calcination process with wet tissues as the template and carbon resource. The outer NiCo₂ O₄ nanosheet arrays contain abundant defects, which come from reduction of the carbon in wet tissues. This indicates that carbon is a very excellent defect inducer. The inner carbon microtubes can act as the robust structure skeleton and these core-shell double microtubes provide abundant diffusion channels for oxygen and electrolyte, both of which contribute to improving the stability by avoiding damage to the electrode from produced O₂ bubbles and the collapse of the outer NiCo₂ O₄ microtubes. Electrochemical results show that the electrode, core-shell carbon/NiCo₂ O₄ double microtubes loaded on carbon cloth, exhibits prominent electrocatalytic activity with an overpotential of only 168 mV at 10 mA cm^-2 and a Tafel slope as low as 57.6 mV dec^-1 in 1.0 mol L^-1 KOH. This new type of electrocatalyst possesses great potential in water electrolyzers and rechargeable metal-air batteries.

Metal Oxide and Hydroxide-Based Aqueous Supercapacitors: From Charge Storage Mechanisms and Functional Electrode Engineering to Need-Tailored Devices

Energy storage devices that efficiently use energy, in particular renewable energy, are being actively pursued. Aqueous redox supercapacitors, which operate in high ionic conductivity and environmentally friendly aqueous electrolytes, storing and releasing high amounts of charge with rapid response rate and long cycling life, are emerging as a solution for energy storage applications. At the core of these devices, electrode materials and their assembling into rational configurations are the main factors governing the charge storage properties of supercapacitors. Redox-active metal compounds, particularly oxides and hydroxides that store charge via reversible valence change redox reactions with electrolyte ions, are prospective candidates to optimize the electrochemical performance of supercapacitors. To address this target, collaborative investigations, addressing different streams, from fundamental charge storage mechanisms and electrode materials engineering to need-tailored device assemblies, are the key. Over the last few years, significant achievements in metal oxide and hydroxide-based aqueous supercapacitors have been reported. This work discusses the most recent achievements and trends in this field and brings into the spotlight the authors' viewpoints.

Research Advances of Amorphous Metal Oxides in Electrochemical Energy Storage and Conversion

Amorphous metal oxides (AMOs) have aroused great enthusiasm across multiple energy areas over recent years due to their unique properties, such as the intrinsic isotropy, versatility in compositions, absence of grain boundaries, defect distribution, flexible nature, etc. Here, the materials engineering of AMOs is systematically reviewed in different electrochemical applications and recent advances in understanding and developing AMO-based high-performance electrodes are highlighted. Attention is focused on the important roles that AMOs play in various energy storage and conversion technologies, such as active materials in metal-ion batteries and supercapacitors as well as active catalysts in water splitting, metal-air batteries, and fuel cells. The improvements of electrochemical performance in metal-ion batteries and supercapacitors are reviewed regarding the enhancement in active sites, mechanical strength, and defect distribution of amorphous structures. Furthermore, the high electrochemical activities boosted by AMOs in various fundamental reactions are elaborated on and they are related to the electrocatalytic behaviors in water splitting, metal-air batteries, and fuel cells. The applications in electrochromism and high-conducting sensors are also briefly discussed. Finally, perspectives on the existing challenges of AMOs for electrochemical applications are proposed, together with several promising future research directions.

Recent Progress in Some Amorphous Materials for Supercapacitors

A breakthrough in technologies having "green" and sustainable energy storage conversion is urgent, and supercapacitors play a crucial role in this area of research. Owing to their unique porous structure, amorphous materials are considered one of the best active materials for high-performance supercapacitors due to their high specific capacity, excellent cycling stability, and fast charging rate. This Review summarizes the synthesis of amorphous materials (transition metal oxides, carbon-based materials, transition metal sulfides, phosphates, hydroxides, and their complexes) to highlight their electrochemical performance in supercapacitors.

Cobalt-Doped Nickel Phosphite for High Performance of Electrochemical Energy Storage

Compared to single metallic Ni or Co phosphides, bimetallic Ni-Co phosphides own ameliorative properties, such as high electrical conductivity, remarkable rate capability, upper specific capacity, and excellent cycle performance. Here, a simple one-step solvothermal process is proposed for the synthesis of bouquet-like cobalt-doped nickel phosphite (Ni₁₁ (HPO₃ )₈ (OH)₆ ), and the effect of the structure on the pseudocapacitive performance is investigated via a series of electrochemical measurements. It is found that when the cobalt content is low, the glycol/deionized water ratio is 1, and the reaction is under 200 °C for 20 h, the morphology of the sample is uniform and has the highest specific surface area. The cobalt-doped Ni₁₁ (HPO₃ )₈ (OH)₆ electrode presents a maximum specific capacitance of 714.8 F g^-1 . More significantly, aqueous and solid-state flexible electrochemical energy storage devices are successfully assembled. The aqueous device shows a high energy density of 15.48 mWh cm^-2 at the power density of 0.6 KW cm^-2 . The solid-state device shows a high energy density of 14.72 mWh cm^-2 at the power density of 0.6 KW cm^-2 . These excellent performances confirm that the cobalt-doped Ni₁₁ (HPO₃ )₈ (OH)₆ are promising materials for applications in electrochemical energy storage devices.

NiCo2O4 nanowire based flexible electrode materials for asymmetric supercapacitors

The rational design and construction of supercapacitor electrode materials with prominent energy and power density play an indispensable role for their potential application in energy storage devices.

Carbon-Induced Generation of Hierarchical Structured Ni0.75Co0.25(CO3)0.125(OH)2 for Enhanced Supercapacitor Performance

Hierarchical nanostructures with heteroatom doping have been considered as an important component in electrode materials for advanced supercapacitors. Herein, with the aid of C, N, and S codoped Ni_0.75Co_0.25(CO₃)_0.125(OH)₂/C (NSH) with a hierarchical structure was synthesized through a facile one-step hydrothermal method. Notably, it is the first report on a carbon precursor as a structure inducer for designing a three-dimensional (3D) carnation-like hierarchical structure. Thanks to the carbon induction effect and the introduction of N/S dopants, the obtained NSH with a 3D architecture exhibits superior performances as electrode materials for supercapacitors. For example, NSH offers a high specific capacity of 277.3 mAh/g at 0.5 A/g. Moreover, the assembled NSH//reduced graphene oxide hydrogel-based hybrid supercapacitor exhibits high energy densities of 44.4 and 11.7 Wh/kg at power densities of 460 W/kg and 9.8 kW/kg, respectively. This result opens up opportunities for carbon-induced methods to control the morphology and structure of other similar materials.

Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni3 S2 Nanowire Films for High-Performance Supercapacitors

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni₃ S₂ core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni₃ S₂ nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730 C cm^-3 at 0.25 A cm^-3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni₃ S₂ core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni₃ S₂ as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm^-3 (based on the total volume of both electrodes) at 0.5 A cm^-3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm^-3 , which is much larger than those of thin-film lithium batteries (1-10 mWh cm^-3 ). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.

Nanotubular Iridium-Cobalt Mixed Oxide Crystalline Architectures Inherited from Cobalt Oxide for Highly Efficient Oxygen Evolution Reaction Catalysis

Here, we report the unique transformation of one-dimensional tubular mixed oxide nanocomposites of iridium (Ir) and cobalt (Co) denoted as Ir_xCo_1-xO_y, where x is the relative Ir atomic content to the overall metal content. The formation of a variety of Ir_xCo_1-xO_y (0 ≤ x ≤ 1) crystalline tubular nanocomposites was readily achieved by electrospinning and subsequent calcination process. Structural characterization clearly confirmed that Ir_xCo_1-xO_y polycrystalline nanocomposites had a tubular morphology consisting of Ir/IrO₂ and Co₃O₄, where Ir, Co, and O were homogeneously distributed throughout the entire nanostructures. The facile formation of Ir_xCo_1-xO_y nanotubes was mainly ascribed to the inclination of Co₃O₄ to form the nanotubes during the calcination process, which could play a critical role in providing a template of tubular structure and facilitating the formation of IrO₂ by being incorporated with Ir precursors. Furthermore, the electroactivity of obtained Ir_xCo_1-xO_y nanotubes was characterized for oxygen evolution reaction (OER) with rotating disk electrode voltammetry in 1 M NaOH aqueous solution. Among diverse Ir_xCo_1-xO_y, Ir_0.46Co_0.54O_y nanotubes showed the best OER activity (the least-positive onset potential, greatest current density, and low Tafel slope), which was even better than that of commercial Ir/C. The Ir_0.46Co_0.54O_y nanotubes also exhibited a high stability in alkaline electrolyte. Expensive Ir mixed with cheap Co at an optimum ratio showed a greater OER catalytic activity than pure Ir oxide, one of the most efficient OER catalysts.

Hierarchical CuCo2O4@nickel-cobalt hydroxides core/shell nanoarchitectures for high-performance hybrid supercapacitors

Ni_0.5Co_0.5(OH)₂ nanosheets coated CuCo₂O₄ nanoneedles arrays were successfully designed and synthesized on carbon fabric. The core/shell nanoarchitectures directly served as the binder-free electrode with a superior capacity of 295.6mAhg^-1 at 1Ag^-1, which still maintained 220mAhg^-1 even at the high current density of 40Ag^-1, manifesting their enormous potential in hybrid supercapacitor devices. The as-assembled CuCo₂O₄@Ni_0.5Co_0.5(OH)₂//AC hybrid supercapacitor device exhibited favorable properties with the specific capacitance as high as 90Fg^-1 at 1Ag^-1 and the high energy density of 32Whkg^-1 at the power density of 800Wkg^-1. Furthermore, the as-assembled device also delivered excellent cycling performance (retaining 91.9% of the initial capacitance after 12,000 cycles at 8Ag^-1) and robust mechanical stability and flexibility, implying the huge potential of present hierarchical electrodes in energy storage devices.

NiCo₂O₄-Based Supercapacitor Nanomaterials

In recent years, the research on supercapacitors has ushered in an explosive growth, which mainly focuses on seeking nano-/micro-materials with high energy and power densities. Herein, this review will be arranged from three aspects. We will summarize the controllable architectures of spinel NiCo₂O₄ fabricated by various approaches. Then, we introduce their performances as supercapacitors due to their excellent electrochemical performance, including superior electronic conductivity and electrochemical activity, together with the low cost and environmental friendliness. Finally, the review will be concluded with the perspectives on the future development of spinel NiCo₂O₄ utilized as the supercapacitor electrodes.

Low-crystalline mesoporous CoFe2O4/C composite with oxygen vacancies for high energy density asymmetric supercapacitors

A low-crystalline mesoporous cobalt ferrite and carbon composite (L-CoFe₂O₄/C) material was prepared via a sol–gel approach and calcination process. An L-CoFe₂O₄/C//AC asymmetric supercapacitor exhibited high energy density and power density.

Enhanced microwave absorption capacity of hierarchical structural MnO2@NiMoO4 composites

MnO₂@NiMoO₄ exhibits enhanced microwave absorption capacity, which originates from the hierarchical hybrid nanostructures, multi-effective components, good impedance matching, and interfacial polarization between MnO₂ and NiMoO₄.

Facile synthesis of mesoporous hierarchical ZnS@β-Ni(OH)2 microspheres for flexible solid state hybrid supercapacitors

Mesoporous hierarchical ZnS@β-Ni(OH)₂ microspheres have been successfully synthesized via a facile route and exhibited good performance as electrode materials for supercapacitors.