NiCo-layered Double Hydroxide Research Articles

Activated Carbon Supported Ni-Co Layered Double Hydroxides Nanowires: An Effective and Low-Cost Electrocatalyst for Ethanol Electro-Oxidation in Alkaline Media

Developing nanostructured electrocatalysts by utilizing low-cost, non-noble metals with good activity and stability to replace noble metals such as Pt and Pd has gained significant interest in the area of sustainable energy production technologies. To that effect, we adopted a facile synthesis route to synthesize NiCo-LDH (layered double hydroxides) nanowires with activated carbon (AC) as support using a one-pot hydrothermal synthesis method. The role of AC on the activity of NiCo-LDH catalyst was studied. The activity of the electrocatalysts was characterized using Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Chronoamperometry (CA) techniques. The NiCo-LDH/AC, with Ni:Co molar ratio of 1:2, exhibited a good electrocatalytic activity of 12.5 mA cm−2 at 1.1 V vs SCE (saturated calomel electrode) at a scan rate of 50 mV s−1 and retained a remarkable cyclic stability of 74.4% even after 200 cycles in 0.1 M NaOH and 1 M EtOH. The better electrocatalytic activity of NiCo-LDH/AC catalyst can be ascribed to the presence of extremely active sites and porous structures as well as a good electron transfer conductivity of AC. The facile synthesis of NiCo-LDH/AC and its attractive performance highlights its potential application as an anodic electrocatalyst in direct ethanol fuel cells (DEFCs).

Insights into the enhanced performance of NiCo-LDH modified Pd/NF cathode for electrocatalytic hydrodechlorination

To obtain an electrocatalytic hydrodechlorination (ECH) cathode with low noble metal content, low energy consumption and high catalytic activity, a novel electrode that arming Pd with NiCo-layered double hydroxide (Pd/NiCo-LDH/NF) was prepared. The Pd/NiCo-LDH/NF electrode shows excellent ECH activity, having a mass activity of 32.80 min−1 gPd−1 for dechlorination of 2,4-dichlorophenol (2,4-DCP), which is 5 ∼ 10 times higher than other reports on ECH cathodes. The higher ECH activity is due to the synergistic effect between NiCo-LDH interlayer and Pd2+. The influence of preparation parameters on morphology, composition, conductivity and hydrogen evolution performance of the NiCo-LDH was investigated by means of scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma emission spectrometer, cyclic voltammetry, electrochemical impedance spectroscopy, and linear scanning voltammetry. Density functional theory (DFT) analysis results showed that the NiCo-LDH containing OH− vacancies enhanced the generation of Hads*, weakened the toxicity of phenol to the electrode, and improved the ECH activity of the electrode. This work designed a robust electrocatalytic cathode with low energy consumption, low cost and high efficiency for the ECH of chlorinated phenols.

Cr-Doped NiCo-Layered Double Hydroxide/N-Doped Graphene for a Bifunctional Electrocatalyst for Rechargeable Zinc Air Batteries

Rechargeable zinc air batteries (RZABs), which repeatedly store and release charges through the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) using oxygen electrocatalysts, are considered a promising energy storage system owing to their low cost and safety. Controlling the chemical structure and morphology of multifunctional electrocatalysts is crucial for improving their electrocatalytic activities and stabilities for high performance RZABs. Herein, we report hierarchically structured Cr-doped NiCo-layered double hydroxides (LDHs) nanoplates chemically grown on the surface of nitrogen-doped reduced graphene oxide nanosheets (NiCoCr LDH/N-rGO) for an application into bifunctional electrocatalysts of RZABs. As verified by the spectroscopic and electrochemical characterizations, Cr doping modulates the electronic configuration and surface structure of both LDHs and N-rGO nanosheets, thereby improving bifunctional catalytic activity and reaction kinetics. In particular, the electrocatalytic activity and kinetics of NiCoCr LDH/N-rGO for both ORR and OER are greatly improved owing to the increased active sites by Cr doping and hierarchical porous structure as demonstrated by low overpotential and Tafel’s slope. Thus, the electrochemical performance of RZAB with NiCoCr LDH/N-rGO catalyst is superior to that with Pt/C+RuO2, as confirmed by higher power density of 97 mW cm-2 and better cycling stability of 18 h for the former than 59 mW cm-2 and 6 h for the latter.

Microwave-Assisted Hierarchically Grown Flake-like NiCo Layered Double Hydroxide Nanosheets on Transitioned Polystyrene towards Triboelectricity-Driven Self-Charging Hybrid Supercapacitors.

Recently, there is a need to explore the utilization of various heterostructures using the designed nanocomposites and tuning the surfaces of electrodes for improving the electrochemical performance of supercapacitors (SC). In this work, a novel approach is successfully employed through a facile two-step synthetic route with the assistance of a microwave for only 1 min. Depending on the glass transition of a polystyrene (PS) substrate and electrochemical deposition (ECD) of electroactive Ni-Co layered double hydroxides (LDHs), a hierarchically designed flake-like morphology can be readily prepared to enhance the surface-active sites, which allows a rhombohedral Ni-Co LDHs electrode to obtain superior electrochemical properties. Further, the interactions between electrode and electrolyte during the diffusion of ions are highly simplified using multiple enhanced electroactive sites and shorter pathways for electron transfer. The unique surface architecture of the PS substrate and the synergistic effect of the bimetallic components in Ni-Co LDHs enable this substrate to obtain desired electrochemical activity in charge storage systems. The optimized MWC Co0.5Ni0.5 electrode exhibited an areal capacity of 100 µAh/cm2 at a current density of 1 mA/cm2 and a remarkable capacity retention of 91.2% over 5000 continuous charging and discharging cycles due to its remarkable synergistic effect of abundant faradaic redox reaction kinetics. The HSC device is assembled with the combination of optimized MWC Co0.5Ni0.5 and activated carbon as a positive and negative electrode, respectively. Further, the electrochemical test results demonstrated that MWC Co0.5Ni0.5 //AC HSC device showed a high areal capacitance of 531.25 mF/cm2 at a current density of 5 mA/cm2. In addition, the fabricated an aqueous HSC device showed a power density of 16 mW/cm2 at an energy density of 0.058 mWh/cm2, along with the remarkable capacity retention of 82.8% even after 10,000 continuous charging and discharging cycles. Moreover, the assembled hybrid supercapacitor (HSC) device is integrated with a triboelectric nanogenerator (TENG) for the development of energy conversion and storage systems. Not only an extensive survey of materials but also an innovative solution for recent progress can confirm the wide range of potential SC applications. Remarkably, this study is a new way of constructing self-powered energy storage systems in the field of sustainable wearable electronics and future smart sensing systems.

Surface Selenization of NiCo-Layered Double Hydroxide Nanosheets for High-Performance Supercapacitors

Due to their unique spatial structures, layered double hydroxides (LDHs) have been considered as prospective electrode materials for supercapacitors. In this work, several NiCo-LDH materials are obtained via a facile selenization process. This can improve the conductivity and reduce the electrochemical impedance of the samples. The 0.4Se-NiCo-LDH materials deliver a specific capacitance of 1396 F/g at 1 A/g. The capacity retention rate can reach 91.38% after 10,000 cycles. In addition, using the prepared materials as a positive electrode, an asymmetric supercapacitor is constructed. It offers an energy density of 60 Wh/kg at a power density of 2700 W/kg, demonstrating that the synthesized samples possess promising applications in future flexible energy-storage systems.

MXene supported nickel-cobalt layered double hydroxide as efficient bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

An inexpensive and noble metal free electrocatalyst with high anion exchange capacity and intrinsic conductivity is highly desirable for renewable energy applications like hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this turn, low cost and earth abundant nickel cobalt hydroxides (NiCo(OH)2) based layered double hydroxides (LDHs) have been considered for a long time. However, aggregation of their flakes and structural instability lead to less accessible active sites and hence poor electrical conductivity which limit their electrocatalytic performance as an electrocatalyst. Therefore, MXene supported NiCo(OH)2 samples (with different ratios of Co) were prepared using one-step hydrothermal method possessing enlarged surface area and numerous active sites for enhanced electrochemical activity. As an electrocatalyst, MXene supported NiCo LDHs with 1:1.2 ratio (Ni:Co) (NCM-1.2) illustrated a convincing electrocatalytic activity for HER and OER as compared to NiCo(OH)2, MXene and other MXene supported samples. The improved electrocatalytic activity of NCM-1.2 can be attributed to active redox couples (Ni2+/3+ and Co2+/3+), improved accessible active sites (Ni2+ for HER and Co3+ for OER) and reduced interfacial charge transfer resistance.

Solvent-free oxidation of benzyl C-H to ketone with Co-Ni layered double hydroxide as the catalyst and O2 as the sole oxidant.

The aerobic oxidation of ethylbenzene is an effective way to produce acetophenone, in which solvent-free conditions and oxygen as the sole oxidant are the best choice. At present, the catalytic activity and selectivity are still at an unsatisfactory level, because efficient catalysts need to achieve both C-H bond activation and O2 activation. In this work, the 2-methylimidazole-induced hydrolysis strategy was used to prepare a new class of CoNi-layered double hydroxide (CoNi-LDH) materials with different metal ratios. High-Resolution Transmission Electron Microscopy (HRTEM) showed that CoNi-LDH had obvious weak crystallinity and a thin lamellar structure. X-ray Photoelectron Spectroscopy (XPS) reveals the consistency between the content of the M-O component in the host layer and the proportion of Co3+, among which CoNi-LDH with a feed ratio (Co : Ni) of 2 : 1 (Co2Ni-LDH) has the highest M-O content and Co3+ ratio. The formation of M-O is due to the H-vacancy generated by the breaking of the hydroxyl group, which can be used for the H abstraction of C-H bonds. The redox effect caused by M2+/M3+ facilitates the transfer of electrons, which promotes the activation of O2 to the superoxide radical anion (˙O2-). Thereby, Co2Ni-LDH shows the highest catalytic activity for the oxidation of ethylbenzene. Under solvent-free conditions and with oxygen as the sole oxidant, 97.8% conversion of ethylbenzene and 98.8% selectivity of acetophenone can be obtained. The excellent catalytic performance is related to the structure of CoNi-LDH, and is also the best when compared with the reported results. Various types of aromatic hydrocarbons containing benzyl C-H bonds can be effectively oxidized by CoNi-LDH to produce the corresponding ketone products.

In situ growth of NiCo-MOF and the derived NiCo2O4/NiCo2O4/Ni foam composite with a wire-penetrated-cage hierarchical architecture for an efficient oxygen evolution reaction.

A NiCo2O4/NiCo2O4/Ni foam (NCO/NCO/NF) hybrid composite with a wire-penetrated-cage hierarchical structure was synthesized by in situ growth of bimetallic NiCo metal-organic frameworks (NiCo-MOF) on a NiCo layered double hydroxide (NiCo-LDH) nanowire-modified Ni foam (NF) surface and subsequent heat treatment in air. The NCO/NCO/NF hybrid composite shows higher specific surface area and more active sites than its individual components. The wire-penetrated-cage hierarchical structure of NCO/NCO/NF and the synergistic coupling of NCO hollow nanocages (NCO HNCs), NCO nanowires (NCO NWs) and NF provide a fast electron transfer path, improve the conductivity, accelerate the kinetic reaction rate, and enhance the structural stability. When assessed as an electrode for the oxygen evolution reaction (OER), the NCO/NCO/NF hybrid composite exhibits a low overpotential of 310 mV at 10 mA cm-2 and current density retention of 91% after a 100 h oxidation reaction, which indicates that it has excellent catalytic activity and durability in the electrocatalytic OER.

NiCo LDH nanozymes with selective antibacterial activity against Gram-negative bacteria for wound healing.

Bacterial infections have been a major threat to human health. Especially, Gram-negative (G-) bacterial infections have been an increasing problem worldwide. The overuse of antibiotics leads to an emergence of drug resistance, and thus the development of novel antimicrobial agents is important, particularly against G- bacteria. Nanozymes use reactive oxygen species (ROS) to kill bacteria, reducing the risk of bacterial resistance and providing new opportunities to meet the challenges of strain selectivity. Here, we synthesized NiCo layered double hydroxide (LDH) nanozymes, which exhibit selective antibacterial activity based on their peroxide-like (POD-like) activity. To obtain the highest antibacterial activity, the POD-like activity of NiCo LDH nanozyme was further optimized by tuning the ratio of nickel and cobalt, and Ni4Co6 LDHs showed the highest POD activity and antibacterial activity. More importantly, Ni4Co6 LDHs can achieve selective sterilization of G- bacteria due to their electrostatic adsorption and hydrophilic interactions with the bacterial cell wall. Animal experiments further indicated that the healing of G- bacteria-infected wounds was effectively promoted without damaging their normal biological tissues. In conclusion, we provide a selective antibacterial agent through a simple strategy, which provides a new direction for the application of nanozymes.

Introducing high-valence molybdenum to stimulate lattice oxygen in a NiCo LDH cathode for chloride ion batteries.

Layered double hydroxides (LDHs) have been intensively investigated as promising cathodes for the new concept chloride ion battery (CIB) with multiple advantages of high theoretical energy density, abundant raw materials and unique dendrite-free characteristics. However, driven by the great compositional diversity, a complete understanding of interactions between metal cations, as well as a synergetic effect between metal cations and lattice oxygen on LDH host layers in terms of the reversible Cl-storage capability, is still a crucial but elusive issue. In this work, we synthesized a series of chloride-inserted trinary Mox-doped NiCo2-Cl LDH (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) with gradient oxygen vacancies as enhanced cathodes toward CIBs. The combination of advanced spectroscopic techniques and theoretical calculations reveals that the Mo dopant facilitates oxygen vacancy formation and varies the valence states of coordinated transition metals, which can not only tune the electronic structure effectively and promote Cl-ion diffusion, but improve the redox activity of LDHs. The optimized Mo0.3NiCo2-Cl LDH delivers a reversible discharge capacity of 159.7 mA h g-1 after 300 cycles at 150 mA g-1, which is almost a triple enhancement compared to that of NiCo2Cl LDH. The superior Cl-storage of trinary Mo0.3NiCo2Cl LDH is attributed to the reversible intercalation/deintercalation of chloride ions in the LDH gallery along with the oxidation state changes in Ni0/Ni2+/Ni3+, Co0/Co2+/Co3+ and Mo4+/Mo6+ couples. This simple vacancy engineering strategy provides critical insights into the significance of the chemical interaction of various components on LDH laminates and aims to effectively design more LDH-based cathodes for CIBs, which can even be extended to other halide-ion batteries like fluoride ion batteries and bromide ion batteries.

Multifunctional Ni3S2@NF-based electrocatalysts for efficient and durable electrocatalytic water splitting.

Transition-metal sulfides (TMSs) have indeed drawn dramatic interest as a potential species of electrocatalysts by virtue of their unique structural features. However, their poor stability and inherent activity have impeded their use in electrocatalytic water splitting. Here, we provide a rational design of a hierarchical nanostructured electrocatalyst containing CeOx-decorated NiCo-layered double hydroxide (LDH) coupled with Ni3S2 protrusions formed on a Ni foam (NF). Specifically, the as-prepared electrocatalyst, denoted as Ni2Co1 LDH-CeOx/Ni3S2@NF, presents only 250 and 300 mV overpotential at ±100 mA cm-2, respectively, along with the Tafel slope values of 92 and 52 mV dec-1, as well remarkable long-term life for water splitting in an alkaline electrolyte. Based on systematic experiments and theoretical analysis, the superior electrocatalytic property in terms of Ni2Co1 LDH-CeOx/Ni3S2@NF can be imputed to the following reasons: the porous framework of Ni3S2@NF provides a largely surface area and high conductivity; the NiCo LDH nanosheets provide enriched active sites and favorable adsorption ability; the oxygen-vacancy-rich CeOx optimizes the electronic configuration. Overall, these factors work synergistically to expedite the catalytic kinetics of splitting water. Our work concentrates on a rational interface to devise efficient, multifunctional, and serviceable electrocatalysts for future applications.

MXene-Coated Nickel Ion-Exchanged ZIF Skeleton-Cavity Layered Double Hydroxides for Supercapacitors

A NiCo layered double hydroxide (LDH) has been regarded as a promising electrode material for supercapacitors. However, the low electronic conductivity, limited electroactive sites, and self-agglomeration hinder its large-scale application. Herein, MXene-coated nickel ion-exchanged ZIF skeleton-cavity LDHs (ZSC-LDH@MXene) were fabricated to enhance the electrochemical performance of NiCo LDHs. The ZSC-LDH@MXene integrated the advantages of various materials, providing abundant metal active sites and fast redox reaction kinetics and enhancing the specific capacity of the electrode. The MXene nanosheets can construct abundant conductive networks, enhancing the electronic conductivity of the NiCo LDH. The nanosheet-assembled ZIF skeleton-cavity structure can facilitate electron/ion transport, enlarge the electrolyte accessibility, and expose abundant electroactive sites. Furthermore, the hollow cavity can relieve the volume expansion during the charging/discharging cycles. Ultimately, the as-obtained ZSC-LDH@MXene electrode manifested a large specific capacity of 1029.6 C g–1 at 1 A g–1, a superior rate capability of 62.6% at 30 A g–1, as well as outstanding cycling performance with a 92.0% capacity retention at 10 A g–1 over 10,000 cycles. The assembled ZSC-LDH@MXene//AC hybrid supercapacitor exhibited a superb energy density of 43.7 W h kg–1 at 789 W kg–1.

Facile syntheses of Fe2O3-rGO and NiCo-LDH-rGO nanocomposites for high-performance electrochemical capacitors

Faraday-type electrode materials and devices for electrochemical capacitors have been widely investigated. However, their applications are severely limited by the preparation method and cost of electrode materials. In this work, high-performance electrochemical capacitors were successfully assembled using Fe2O3-decorated reduced graphene oxide (rGO) nanocomposites and NiCo-Layered Double Hydroxides (LDH) as the anode and cathode, respectively. An easy and efficient approach (the modified precipitation method) for the large-scale fabrication was used to prepare Fe2O3 and NiCo-LDH, supported by rGO sheets, respectively. The anode material, Fe2O3-rGO, exhibited an excellent specific capacitance (Csp) of 1073 F g−1 at a current density of 1 A g−1 and a retention rate of 92 % at 10 A g−1, while the NiCo-LDH-rGO cathode material provided a Csp of 1850 F g−1 at 1 A g−1 and maintained 84 % at 10 A g−1. The effective combination of these electrodes for the NiCo-LDH-rGO//Fe2O3-rGO electrochemical capacitors resulted in an excellent energy density of 108 Wh/kg at a power density of 884 W/kg, with remarkable cycling stability (80 % after 1000 cycles at 10 A g−1). We believe that this work, including the proposed method and electrode materials, will advance the further development and commercialization of electrochemical capacitors.

Nickel–cobalt layered double hydroxide/NiCo2S4/g-C3N4 nanohybrid for high performance asymmetric supercapacitor

Graphitic carbon nitride (g-C3N4) with semiconducting nature can be considered for energy storage system by modifying its electrical conductivity and structural properties through formation of hybrid with materials such as bimetallic metal sulfide and nickel-cobalt layered double hydroxide (LDH). g-C3N4 as a N-rich compound with basic surface sites can change the surface properties of nanohybrid and impress the charge transfer. In this study, a nanohybrid based on nickel-cobalt LDH and sulfide and graphitic carbon nitride (NiCo LDH/NiCo2S4/g-C3N4) was synthesized through a three-step method. At first, Ni doped ZIF-67 was formed at the surface of g-C3N4 nanosheets and then the product was calcined in a furnace to form NiCo2O4/g-C3N4. At next step, the sample was hydrothermally converted to NiCo2S4/g-C3N4 using thioacetamide and finally modified with NiCo LDH nanoplates to form porous structure with high surface area. The NiCo LDH/NiCo2S4/g-C3N4 nanohybrid showed high specific capacitance of 1610 F g−1 at current density of 1 A g−1 and also excellent stability of 108.8% after 5000 cycles at potential scan rate of 50 mV s−1, which makes it promising candidate for energy storage. An asymmetric system was prepared using nickel foams modified with NiCo LDH/NiCo2S4/g-C3N4 and g-C3N4 as positive and negative electrodes, respectively. The specific capacitance of 246.0 F g−1 was obtained at 1 A g−1 in 6 M KOH solution and system maintained 90.8% cyclic stability after 5000 cycles at potential scan rate of 50 mV s−1. The maximum energy density and power density of the system were calculated as 82.0 Wh kg−1 and 12,000 W kg−1, respectively, which demonstrate its capability for energy storage.

Heterostructure tailoring of carbon nanotubes grown on prismatic NiCo clusters for high-efficiency electromagnetic absorption

The employment of electromagnetic (EM) absorbers integrating elaborate architecture, enhanced microwave absorption and multifunctional features remains a formidable challenge in practical applications including military stealth and incoming 5G electronic information era. Herein, a novel microwave absorber has been fabricated by in-situ growing carbon nanotubes (CNTs) on the prismatic nickel–cobalt (NiCo) clusters derived from Ni-Co layered double hydroxides (NiCo-LDH) via catalytic carbonization of ethyl acetate. The NiCo/CNTs composites with highly porous texture could provide sufficient open space to balance the impedance and introduce magnetic loss mechanism. Accordingly, the absorbers achieved remarkable EM absorption performance with a minimum reflection loss of –46.2 dB at 1.5 mm and broad bandwidth of 5.8 GHz owing to synergistic magnetic-dielectric effects and distinct structural merits. The NiCo/CNTs absorber manifests superior radar wave attenuation by the radar cross section simulation and density functional theory (DFT) was also performed to elucidate the potential mechanisms of the heterostructure formation and performance enhancement in the NiCo/CNTs composites. This work is expected to provide new insights or inspirations to modulate EM properties by rationally designing heterostructure for the elimination of severe EM pollution.

Facile synthesis of Co-Ni layered double hydroxides nanosheets wrapped on a prism-like metal-organic framework for efficient oxygen evolution reaction

The construction of low-cost oxygen evolution reaction (OER) electrocatalysts with high activity and good durability is a considerable challenge for facilitating the efficient utilization of green energy. Herein, the prism-like materials of institute lavoisier frameworks-88 (MIL-88) was first synthesized by a hydrothermal method. Then, Co-Ni layered double hydroxides (CoNi-LDHs) nanosheets were directly wrapped on the MIL-88 surface by electrodeposition to form core-shell MIL-88@CoNi-LDHs composites. Due to the distinct structure and synergistic effect between the MIL-88 core and CoNi-LDHs shell, it was found that MIL-88@CoNi-LDHs had outstanding OER activity with a small Tafel slope (45.55 mV dec-1), low overpotential (314 mV) at 10 mA cm−2, and superior durability. This study provides a prospective pathway to exploit highly efficient low-cost electrocatalysts for OER.

Fabrication of hierarchical Ni nanowires@ NiCo-layered double hydroxide nanosheets core-shell hybrid arrays for high-performance hybrid supercapacitors.

Layered double hydroxides (LDHs) are electrode materials with high specific capacity due to their structure which has a tunable interlayer spacing, however, the disadvantages of their low conductivity and electrochemically limited sites prevent their application in supercapacitors. In this study, we synthesized a high electrochemical performance electrode material with a core-shell structure based on hierarchical nickel nanowires (core) and NiCo LDHs nanosheets (shell). First, hierarchical nickel nanowires, h-Ni NWs, were prepared by the reduction of Ni2+ ions by hydrazine N2H4. Then with the hydrothermal method, the hierarchical nickel nanowires were coated with NiCo LDHs to improve the electrical conductivity of the latter. The electrochemical results showed that the NiCo LDHs@h-Ni NWs electrode had a specific capacity of 1486 C/g at a current density of 1 A/g in 6 M KOH electrolyte with excellent capacity retention (89.7%) after 10,000 charge-discharge cycles at 20 A/g. Due to the synergistic interaction between nickel nanowires and NiCo LDHs which provides excellent conductivity, durability, efficient mesoporous network, and suitable channels for fast ion/electron transfer. In addition, a hybrid supercapacitor (HSC) was fabricated by combining the NiCo LDHs@h-Ni NWs electrode (battery type) with activated carbon (EDLC). The fabricated device provided a high energy density of 72.22 Wh/kg at 800 W/kg, and a maximum power density of 16 kW/kg, the HSC provided an energy density of 50.44 Wh/kg and outstanding cycling stability (88.1% retention after 10,000 cycles).

Mechanistic insights into efficient peroxymonosulfate activation by NiCo layered double hydroxides

The efficient removal of organic refractory pollutants such as dyes and antibiotics in wastewater is crucial for protecting the environment and human health. In this work, a NiCo-layered double hydroxide (NiCo-LDH) with a uniform microspherical, hierarchical structure and a high surface area was successfully synthesized as an effective peroxymonosulfate (PMS) activator for the degradation of various organic dyes and antibiotics. The influence of various parameters on the catalytic activity of the NiCo-LDH was determined. Radical scavenger studies unveiled the major reactive oxygen species (ROSs) generated in the NiCo-LDH/PSM system to be 1O2, SO4•−, and O2•−. Ex-situ X-ray photoelectron spectroscopy (XPS) analysis uncovered the role of Co sites and oxygen vacancy as active sites and revealed the reversible redox properties of NiCo-LDH based on Co2+/Co3+ cycles. The activation mechanism and Rhodamine B (RhB) degradation pathways were experimentally studied and proposed. The NiCo-LDH is highly versatile, reusable and stable as shown by post-catalysis characterizations. This work shows the excellent catalysis performances and provides insights into the activation mechanism of PMS by NiCo-LDH for organic pollutant remediation.

One-pot synthesis of flower-like Ni-Co/reduced graphene oxide layered double hydroxide nanocomposites as advanced electrodes for high-performance asymmetric supercapacitors

Novel electrode materials with appropriate architectures are always desired to increase the energy density of supercapacitors. Here, the design and fabrication of NiCo-layered double hydroxides (NC-LDH) in composition with reduced graphene oxide (rGO) were prepared as high-performance electrodes for supercapacitors. In particular, a facile and one-pot scheme was designed for the growth of NC/rGO-LDH composites, which exhibited a high specific surface area of 204 m2/g. The compositional features of the composites, i.e., a two-dimensional flower-like layered architecture and conductive rGO, contributed to their highly impressive specific capacitance (1913.5 F/g at 1 A/g) and excellent cyclic performance. Furthermore, an asymmetric supercapacitor was designed using NC/rGO-LDH composites as the positive electrode and activated carbon as the negative electrode, which displayed a high energy density of 59.2 Wh/kg at a power density of 750 W/kg.

Self-supporting electrode for flexible supercapacitors: NiCo-layered double hydroxide derived from metal organic frameworks wrapped on graphene/polyaniline nanotubes@cotton cloth

Nowadays, constructing hetero-structure materials is an efficacious procedure to uplift the electrochemical performance of layered double hydroxide (LDH) materials. The logical design of such elegant nanostructures is still challenging. Herein, NiCo-LDH nanosheets derived from Co-ZIF grown on graphene/polyaniline nanotube (G/PANI-NT)@cotton cloth (CC) was synthesized by a facile and novel two-step strategy for supercapacitors. Such hetero-structures give a 30.63 m2 g−1 surface area and more subjected electrochemical active sites. The supercapacitor performance results exhibit that the NiCo-LDH/G/PANI-NT@CC electrode has the best supercapacitor performance when it is used as a pseudocapacitor. By the ratio of Ni/Co = 2:1 in the precursor solution, the electrode shows an areal specific capacitance of 88.15 mF cm−2 at a current density of 0.075 mA cm−2. The electrochemical performance of the electrodes was perused using a redox-additive electrolyte. The electrochemical performance of the NiCo-LDH/G/PANI-NT@CC electrode was amended using K2S2O8 in a 3 M KOH solution. Considerably, the areal specific capacitance of NiCo-LDH/G/PANI-NT@CC (181.17 mF cm−2) increased to 431.30 mF cm−2, by changing the K2S2O8 concentration in KOH solution at a current density of 0.075 mA cm−2. Long-term stability test demonstrates that 84.05 % of the original capacitance remains after 10,000 cycles at the current density of 0.2 mA cm−2. The results indicate that NiCo-LDH/G/PANI-NT@CC will be an appropriate candidate for high-performance supercapacitors. The NiCo-LDH/G/PANI-NT@CC//NiCo-LDH/G/PANI-NT@CC flexible solid-state supercapacitor was assembled with the PVA/KOH gel electrolyte.