Hierarchical Nanocages Assembled by NiCo-Layered Double Hydroxide Nanosheets for a High-Performance Hybrid Supercapacitor

Hierarchical NiGa-LDH/Ti3C2Tx MXene composites for enhanced capacitance in alkaline all-solid-state energy storage

In recent years, the rapid advancement of safe energy storage devices with high energy and power densities has generated significant interest in all-solid-state supercapacitors (SCs). MXene-based nanomaterials have emerged as promising candidates for energy storage owing to their exceptional redox properties, extensive surface area, and high metallic conductivity. Additionally, layered double hydroxides (LDHs), distinguished by their distinct nanostructures, and efficient ion channels, with elevated specific capacitance, have attracted interest. Consequently, a novel all-solid-state supercapacitor(AASCs) was fabricated by employing a hydrothermal method to integrate NiGa-LDH nanosheets with Ti3C2Tx MXene, resulting in enhanced energy storage properties. The NiGa-LDH/Ti3C2Tx MXene exhibits excellent properties, including a specific capacitance of 618.66 F g-1 at 1 mA cm-2 and 93.75 % capacitance retention after 5,000 cycles at 1 mA cm-2. The all-solid-state NiGa-LDH/Ti3C2Tx MXene//activated carbon(AC) asymmetric supercapacitor (AASCs) demonstrates an impressive energy density of 20 Wh kg-1 and a high power density of 400 W kg-1. Density-functional theory (DFT) studies show that NiGa-LDH/Ti3C2Tx MXene has a high density of states (DOS) around the Fermi level and possesses a potassium ion adsorption energy of -2.36 eV. This study provides technical and theoretical insights into the design of intricate nanostructures utilizing MXene-based nanomaterials for all-solid-state energy storage device.

Advances in anion-intercalated layered double hydroxides for supercapacitors: study of chemical modifications and classifications

Hybrid material-based electrochemical supercapacitors (SCs) possessing improved energy density (ED), enhanced stability, high porosity, and a large accessible surface area have attracted attention as promising energy storage devices. SCs also demonstrate excellent specific capacitance (Cs) across various current densities, increased capacitance, and high cell voltages, all contributing to improved ED. Layered double hydroxides (LDHs), with their anionic exchange capabilities and laminar structures, offer significant potential for boosting charge transfer in SCs. This review provides a comprehensive overview of the recent advances in anion-based LDHs, discussing their storage mechanisms, chemical modifications, and classification based on interlayer anions. The roles of different anions, including monovalent, divalent, and polyoxometalates, in enhancing storage properties are examined. In addition, the challenges, future research directions, and practical perspectives of anion-storing LDHs are presented. Hence, this review provides a concise overview of anion-based LDHs for SCs, highlighting their potential significance in energy storage applications.

High-performance disposable electrochemical sensors for creatinine derived from hollow CoNi-LDH@Creatinine-imprinted Poly(methacrylic acid) (i-PMA) composites

BACKGROUND

Layered double hydroxides (LDHs), featuring a 2D layered structure, are an emerging class of inorganic porous materials for electrochemical biosensors. Presently, they are primarily utilized in the electrochemical detection of oxygen-containing biomolecules. However, there are currently no reported LDH sensors, particularly CoNi-LDH ones, designed for the electrochemical detection of creatinine (Cre), a widely studied nitrogen-containing biomolecule. Here, to realize electrochemical detection of creatinine, a unique hollow CoNi-LDH/creatinine imprinted polymethacrylic acid (H-LDH@i-PMA) composite is developed through a pioneering combination of a hollow CoNi-LDH (H-LDH) structure and the molecular imprinting polymer (MIP) coating technique.

RESULTS

The materials are comprehensively characterized using FT-IR, PXRD, XPS, TEM, CV, and EIS. Disposable Au-screen printed electrodes are fabricated with both H-LDH and H-LDH@i-PMA, and the sensing of Cre is subsequently investigated via cyclic voltammetry and differential pulse voltammetry methods. The H-LDH@i-PMA sensor exhibits superior porosity, a larger electroactive area, and enhanced electron-transfer kinetics in comparison to H-LDH sensor. The H-LDH@i-PMA sensor achieves a wide detection range of 0-1000 nM, accompanied by a low detection limit of 236 pM, and five-times more sensitivity for Cre than non-imprinted H-LDH sensor. Futhermore, it demonstrates robust selectivity against interferents such as ascorbic acid, uric acid, guanine, and glutamine. When tested with real salivary samples, it exhibits a recovery rate of 99.0 ± 1.80 %, and maintains excellent reusability over a period of four weeks.

SIGNIFICANCE

These exceptional results are due to superior electroactive area, tailor-made recognition sites, and greater electron-transfer kinetics of H-LDH@i-PMA as compared to the non-imprinted LDH sensor. This is the first reported use of an LDH-based sensor for the detection of Cre, providing valuable insights into developing high-performance electrochemical sensors for various biomolecules.

Zeolitic Imidazolate Framework-67-Derived NiCoMn-Layered Double Hydroxides Nanosheets Dispersedly Grown on the Conductive Networks of Single-Walled Carbon Nanotubes for High-Performance Hybrid Supercapacitors

A supercapacitor's energy storage capability is greatly dependent on electrode materials. Layered double hydroxides (LDHs) were extensively studied as battery-type electrodes because of their 2D structure and quick intercalation/deintercalation of electrolyte ions. However, the energy storage capability for pristine LDHs is limited by their large aggregation tendency and poor electrical conductivity. Herein, a novel NiCoMn-LDH/SWCNTs (single-walled carbon nanotubes) composite electrode material, with ultrathin NiCoMn-LDH nanosheets dispersedly grown among the highly conductive networks of SWCNTs, was prepared via a facile zeolitic imidazolate framework-67 (ZIF-67)-derived in situ etching and deposition procedure. The NiCoMn-LDH/SWCNTs electrode demonstrates a specific capacitance as large as 1704.3 F g-1 at 1 A g-1, which is ascribed to its exposure of more active sites than NiCoMn-LDH. Moreover, the assembled NiCoMn-LDH/SWCNTs//BGA (boron-doped graphene aerogel) hybrid supercapacitor exhibits a superior capacitance of 167.9 F g-1 at 1.0 A g-1, an excellent energy density of 45.7 Wh kg-1 with a power density of 700 W kg-1, and an outstanding cyclic stability with 82.3% incipient capacitance maintained when subjected to 5000 charge and discharge cycles at the current density of 10 A g-1, suggesting the significant potential of NiCoMn-LDH/SWCNTs as the electrode material applicable in supercapacitors.

Coexistence of Redox-Active Metal and Ligand Sites in Copper-Based Two-Dimensional Conjugated Metal-Organic Frameworks as Active Materials for Battery-Supercapacitor Hybrid Systems

Two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) are promising materials for supercapacitor (SC) electrodes due to their high electrochemically accessible surface area coupled with superior electrical conductivity compared to traditional MOFs. In this work, porous and non-porous HHB-Cu (HHB=hexahydroxybenzene), derived through surfactant-assisted synthesis are studied as representative 2D c-MOF models with different characteristics, showing diverse reversible redox reactions with Na+ and Li+ in aqueous (10 M NaNO3) and organic (1.0 M LiPF6 in ethylene carbonate and dimethyl carbonate) electrolytes, respectively. These redox activities were here deployed to design negative electrodes for hybrid SCs (HSCs), combining the battery-like property of HHB-Cu at the negative electrode and the high capacitance and robust cyclic stability of activated carbon (AC) at the positive electrodes. In the organic electrolyte, porous HHB-Cu-based HSC achieves a maximum cell specific capacity (Cs) of 22.1 mAh g-1 at 0.1 A g-1, specific energy (Es) of 15.55 Wh kg-1 at specific power (Ps) of 70.49 W kg-1, and 77 % cyclic stability after 3000 gravimetric charge-discharge (GCD) cycles at 1 A g-1 (specific metrics calculated on the mass of both electrode materials). In the aqueous electrolyte, porous HHB-Cu-based HSC displays a Cs of 13.9 mAh g-1 at 0.1 A g-1, Es of 6.13 Wh kg-1 at 44.05 W kg-1, and 72.3 % Cs retention after 3000 GCD cycles. The non-porous sample, interesting for its superior electrical conductivity despite its limited surface area compared to its porous counterpart, shows lower Es performance but better rate capability compared to the porous one. This study indicates the potential of assembling a battery-SC hybrid system by rationally exploiting the battery-like behavior of 2D c-MOFs and the electrochemical double-layer capacitance of AC.

Engineering intervention to disrupt the evolution of ZIF-67: Ultra-fast synthesis of arrayed Co(OH)2@ZIF-L in dozens of seconds for high-energy charge storage

Designing rational heterostructures of high-performance electroactive materials on conductive substrates with hierarchical structures is critical for advancing electrochemical energy storage technologies. In this study, a unique spatial structure is fabricated by vertically aligning two-dimensional (2D) structures of Co-ZIF-L on conductive nickel foam (NF) substrate through interruption of ZIF-67 formation. This is followed by an innovative electrochemical synthesis method that disrupts unstable surface coordination bonds in Co-ZIF-L, enabling the in-situ generation of Co(OH)2. The resulting Co(OH)2@ZIF-L/NF binder-free electrodes feature a hierarchical spatial structure and are synthesized in approximately 30 s. These electrodes showcase exceptional area capacity of 3.1 C cm-2 at 1 mA cm-2, attributed to their high specific surface area and layered architecture that promotes electrolyte penetration. Density Functional Theory (DFT) calculations reveal that the Co(OH)2@ZIF-L nanostructures have superior electrical conductivity compared to the individual components. Furthermore, a hybrid supercapacitor (HSC) based on Co(OH)2@ZIF-L/NF//AC exhibits an impressive energy density of 42 Wh kg-1 at a power density of 184.7 W kg-1. This research provides new insights into the efficient synthesis of high-performance electroactive materials with unique spatial structures and expands the potential applications of ZIF materials.

High-Performance Supercapacitors Using Hierarchical And Sulfur-Doped Trimetallic NiCo/NiMn Layered Double Hydroxides

A supercapacitor features high power density and long cycling life. However, its energy density is low. To ensemble a supercapacitor with high power- and energy-densities, the applied capacitor electrodes play the key roles. Herein, a high-performance capacitive electrode is designed and grown on a flexible carbon cloth (CC) substrate via a hydrothermal reaction and a subsequent ion exchange sulfuration process. It has a 3D heterostructure, consisting of sulfur-doped NiMn-layered double hydroxide (LDH) nanosheets (NMLS) and sulfur-doped NiCo-LDH nanowires (NCLS). The electrode with sheet-shaped NMLS and wire-shaped NCLS on their top (NMLS@NCLS/CC) increases the available surface area, providing more pseudocapacitive sites. It exhibits a gravimetric capacity of 555.2 C g-1 at a current density of 1 A g-1, the retention rate of 75.1% when the current density reaches up to 20 A g-1, as well as superior cyclic stability. The assembled asymmetric supercapacitor that is composed of a NMLS@NCLS/CC positive electrode and a sulfurized activated carbon negative electrode presents a maximum energy density of 24.2 Wh kg-1 and a maximum power density of 16000 W kg-1. In this study, a facile strategy for designing hierarchical LDH materials is demonstrated as well as their applications in advanced energy storage systems.

Tip effect of NiCo-LDH with low crystallinity for enhanced energy storage performance of yarn-shaped supercapacitors

Layered double hydroxides (LDHs) are considered promising materials for supercapacitor applications. However, the development of yarn-shaped supercapacitors (YSCs) with high electrochemical performance utilizing LDHs remains challenging. In this study, the NiCo-LDHs with various morphologies (nano-needles, nano-sheets, needle-sheet composites, and nano-flowers) were grown on carbon nanotubes (CNTs)-functionalized cotton yarn via a co-precipitation technique for YSC applications. Among these, the yarn incorporating nano-needle NiCo-LDHs exhibited reduced crystallinity yet demonstrated a superior areal capacitance compared to other morphologies, following a diffusion-controlled process. Finite element simulations were subsequently conducted to investigate this phenomenon, revealing that the lower-crystallinity nano-needle NiCo-LDHs accumulated a greater charge at their tips, thereby enhancing redox reactions and achieving higher energy storage capacitance. Subsequently, the yarns with nano-needle NiCo-LDHs were assembled into flexible quasi-solid-state symmetric YSCs, achieving a peak areal capacitance of 124.27 mF cm-2 and an exceptionally high energy density of 39.4 μWh cm-2 at a current density of 0.2 mA cm-2. Furthermore, our YSCs can be scaled up through serial or parallel connections and integrated into fabrics, making them suitable for wearable energy storage applications. This work provides an efficient method for fabricating high-performance YSCs and demonstrates significant potential for wearable energy storage devices.

Switch-Type Electrochemiluminescence Aptasensor for AFB1 Detection Based on CoS Quantum Dots Encapsulated in Co-LDH and a Ferrocene Quencher

Among the various aflatoxin B1 (AFB1) assays, performing accurate detection is difficult because false positives and false negatives are frequent due to limited sensitivity, expensive equipment, or inadequate pretreatment during operation. Here, an "off-on" switch-type electrochemiluminescence (ECL) aptasensor armed with cobalt-sulfur quantum dots was encapsulated in hollow cobalt-layered double hydroxide nanocages as an enhanced luminescent probe (Co-LDH@QDs), and a ferrocene-modified aptamer (Fc-APT) was used as a luminescent quencher. In general, when Fc-APT was hybridized with complementary DNA modified with a DNA nanotetrahedron, electron transfer between ferrocene and Co-LDH@QDs was facilitated, leading to efficient quenching of the ECL intensity into an "off" state in the absence of AFB1. In the presence of AFB1, the intensity of ECL increased with an increasing AFB1 concentration after Fc-APT specifically recognized that AFB1 was detached from the electrode interface to achieve an "on" state. The linear range of the proposed ECL aptasensor for AFB1 detection was 0.1 pg mL-1 to 10 ng mL-1, with a detection limit of 0.03 pg mL-1. We successfully employed the proposed ECL aptasensor for corn application, which provides an economical and simple alternative to complex and costly enzyme-linked immunoassays. The switch-type ECL aptasensor provides quick, accurate, and prospective technological support for pinpoint management of food safety.

Optimizing nickel-aluminium layered double hydroxides for supercapacitors: The role of 3D structural assembly

Nickel-aluminium layered double hydroxides (NiAl-LDHs) have emerged as promising electrode materials for supercapacitors (SCs) due to their inherently high specific surface area and theoretical specific capacitance, which are primarily attributed to the rapid pseudocapacitive response at the surface. However, NiAl-LDHs typically form agglomerated nanosheets, leading to a significant reduction in specific surface area, which is crucial for enhancing the number of active sites and improving the capacitive properties of the materials. To overcome this limitation, 2D nanostructures were assembled into 3D architectures by synthesizing NiAl-LDHs with distinct morphologies in a one-step hydrothermal process using an alkaline agent (NH4F). This approach resulted in the formation of 3D NiAl-LDH/HN4F structures, which exhibit a larger contact area and a greater number of redox-active sites. Consequently, the 3D NiAl-LDH/HN4F electrodes demonstrated a significantly higher specific surface area, leading to remarkable improvements in specific capacitance (1219 ± 30F g-1) and energy density (61 ± 1 Wh kg-1) compared to their 2D counterparts. This structural enhancement increases both the surface area and active site density while providing a new framework for designing high-performance LDH-based electrodes.

One-Step Synthesis of NiCo-LDH@Ni(OH)2 Heterostructure Foams on Biomass-Derived Porous Carbon for High-Performance Supercapacitors

Layered double hydroxides (LDHs) have attracted much attention as pseudocapacitor supercapacitor electrodes because of their high theoretical specific capacity. However, LDHs have drawbacks such as poor electrical conductivity, and their specific capacities are lower than the theoretical values. In this work, NNCLDH@OPC electrodes are constructed via in situ synthesis of heterostructure foams (NNCLDH) consisting of NiCo-LDH and Ni(OH)2 on pomelo peel-derived porous carbon (OPC) through a one-step solvothermal method using ZIF-67 as a template. Owing to the synergistic effect of the 3D nanofoam structure and the multicomponent heterostructure as well as the conductive porous carbon support, the NNCLDH/OPC exhibited ultrahigh electrochemical performance as well as excellent cycling stability: a specific capacity of 3290 F g-1 at 1 A g-1 and a capacitance retention of 77.8% after 4000 cycles at a current density of 10 A g-1. In addition, the assembled NNCLDH@OPC//OPC asymmetric supercapacitor (ASC) has a maximum energy density of 51 Wh kg-1 with a power density of 812 W kg-1 and a maximum power density of 16 kW kg-1 at a current density of 20 A g-1. These results demonstrate the significant application potential of NNCLDH/OPC composites in supercapacitor electrodes.

One-Step Cooperative Growth of High Reaction Kinetics Composite Homogeneous Core-Shell Heterostructure

Reaction kinetics can be improved by the enhanced electrical contact between different components growing symbiotically. But so far, due to the necessity for material synthesis conditions match, the component structures of cooperative growth are similar, and the materials are of the same type. The collaborative growth of high-reaction kinetics composite homogeneous core-shell heterostructure between various materials is innovatively proposed with different structures in one step. The NiCo-LDH and PPy successfully symbiotically grow on activated carbon fiber fabric in one step. The open channel structure of the NiCo-LDH nanosheets is preserved while PPy effectively wrapped around the NiCo-LDH. The well-defined nanostructure with abundant active sites and convenient ion diffusion paths is favorable for electrolyte entry into the entire nanoarrays. In addition, owing to the enhanced electronic interaction between different components through XPS analysis, the NiCo-LDH@PPy electrode shows outstanding reaction kinetics and structural stability. The as-synthesized NiCo-LDH@PPy exhibited excellent super-capacitive storage capabilities, robust capacitive activity, and good rate survival. Furthermore, an asymmetric supercapacitor (ASC) device made of NiCo-LDH@PPy and activated carbon (AC) is able to maintain a long cycle life while achieving high power and energy densities.

Fabrication of the hollow dodecahedral NiCoZn layered double hydroxide for high-performance flexible asymmetric supercapacitor

Layered double hydroxides (LDHs) with unique layered structure have excellent theoretical capacitance. Nevertheless, the constrained availability of electrically active sites and cationic species curtails their feasibility for practical implementation within supercapacitors. Most of the reported materials are bimetallic hydroxides, and fewer studies are on trimetallic hydroxides. In here, the hollow dodecahedron NiCoZn-LDH is synthesized using CoZn metal-organic frameworks (CoZn-MOFs) as template. Its morphology and composition are studied in detail. Concurrently, the effect of the amount of third component on the resulting structure of NiCoZn-LDH is also researched. Benefiting from its favorable structural and compositional attributes to efficient transfer of ions and electrons, NiCoZn-LDH-200 demonstrates outstanding specific capacitance of 1003.3F g-1 at 0.5 A/g. Furthermore, flexible asymmetric supercapacitor utilizing NiCoZn-LDH-200 as the positive electrode and activated carbon (AC) as the negative electrode reveals favorable electrochemical performances, including a notable specific capacitance of 184.7F g-1 at 0.5 A/g, a power density of 368.21 W kg-1 at a high energy density of 65.66 Wh kg-1, an energy density of 31.78 Wh kg-1 at a high power density of 3985.97 W kg-1, a capacitance retention of 92 % after 8000 cycles at 5 A/g, and a good capacitance retention of 90 % after 500 cycles of bending. The template method presented herein can effectively solve the problem of easy accumulation and improve the electrochemical properties of the materials, which exhibits a broad research prospect.

NiCo-LDH Hollow Nanocage Oxygen Evolution Reaction Promotes Luminol Electrochemiluminescence

Conventional luminol co-reactant electrochemiluminescence (ECL) systems suffer from low stability and accuracy due to factors such as the ease of decomposition of hydrogen peroxide and inefficient generation of reactive oxygen species (ROS) from dissolved oxygen. Inspired by the luminol ECL mechanism mediated by oxygen evolution reaction (OER), the nickel-cobalt layered double hydroxide (NiCo-LDH) hollow nanocages with hollow structure and defect state are used as co-reaction promoters to enhance the ECL emission from the luminol-H2 O system. Thanks to the hollow structure and defect state, NiCo-LDH hollow nanocages show excellent OER catalytic activity, which can stabilize and efficiently produce ROS and enhance the ECL emission. Additionally, mechanistic exploration suggests that the ROS involved in the co-reaction of the luminol-H2 O system are derived from the OER reaction process, and there is a positive correlation between ECL intensity and the OER catalytic activity of the co-reaction promoter. The selection of catalysts with excellent OER catalytic activity is a key factor in improving ECL emission. Finally, a dual-mode immunosensor is constructed for the detection and analysis of alpha-fetoprotein (AFP) based on the promoting effect of NiCo-LDH hollow nanocages on the luminol-H2 O ECL system.

Microfluidic Printing of Vertically-Oriented Nanosheets/MOFs Hetero-Interface for Intensive Pseudocapacitive Storage

Efficient manufacture of electroactive vertically-oriented nanosheets with enhanced electrolyte mass diffusion and strong interfacial redox dynamics is critical for realizing high energy density of miniature supercapacitor (SC), but still challenging. Herein, microfluidic droplet printing is developed to controllably construct vertically-oriented graphene/ZIF-67 hetero-microsphere (VAGS/ZIF-67), where the ZIF-67 is coordinately grown on vertically-oriented graphene framework via Co─O─C bonds. The VAGS/ZIF-67 shows ordered porous channel, high electroactivity and strong interfacial interaction, providing rapid electrolyte diffusion dynamics and high faradaic capacitance in KOH solution (1674 F g-1 , 1004 C g-1 ), which are verified by computational fluid dynamics (CFD) and density functional theory (DFT). Moreover, the VAGS/ZIF-67 based SC exhibits large energy density (100 Wh kg-1 ), excellent durability (10 000 cycles and high/low temperature), and robust power-supply applications in portable electronics.

Efficient improvement in the electrochemical performance of petal-like lamellar NiMn-LDHs with affluent oxygen vacancies derived from Mn MOF-74

Supercapacitors (SCs) as a kind of novel energy storage devices have emerged to meet the urgent requirement of environmentally friendly clean energy storage equipment. However, unsatisfactory energy density and low operating voltage tremendously restrict their practical application. Herein, petal-like lamellar NiMn-layered double hydroxide (NiMn-LDH) was successfully fabricated through a simple Ni(NO3)2 etching method with Mn MOF-74 as a sacrificial template. This NiMn-LDH 3/NF electrode exhibited an improved specific capacitance of 1410.2 F g-1 at a current density of 1 A g-1 (Mn MOF-74/NF: 172.2) owing to its high redox activity, compositional flexibility and intercalating capability. Importantly, NiMn-LDH was further optimized via a facile hydroperoxide treatment to harvest NiMn-LDH (O-LDH) with abundant oxygen vacancies, exhibiting remarkable improvement in specific capacitance (990%) compared to original MOF-74 before modification. The preparation of O-LDH enriches the electrode material engineering strategy and achieves improved electrochemical performance for application in new-generation SCs.

"Improving with using" effect and mechanism analysis of electrodeposited poly(1,5-diaminoanthraquinone)/carbon cloth electrode for high-performance flexible supercapacitors

As a robust and conductive substrate, carbon cloth (CC) has been modified with various pseudocapacitive materials to boost its electrochemical performance in flexible supercapacitors. Here, poly(1,5-diaminoanthraquinone) (PDAA) electrodeposited CC electrodes were developed and much higher areal specific capacitance was obtained in comparison with the functionalized CC (FCC). Most importantly, an unusual phenomenon of "improving with using" was found for the optimized one, FCC@PDAA-3, which exhibited the increased capacitance retention from 150.4% to 194.8% with increasing the number of cycles from 10,000 to 50,000. Such extraordinary cyclic life was mainly ascribed to the doping and electropolymerization of the encapsulated 1,5-diaminoanthraquinone (DAA) in the immobilized PDAA during the electrochemical cycles. These findings are expected to contribute to a deeper understanding of the pseudocapacitive materials evolution during long charging/discharging cycles, favoring the design of long-life supercapacitors for practical application.

CoCx‑induced interfacial octahedral Co2+ sites of NiCo-LDH electrode with improved faradic reactivity toward high-performance supercapacitor

Battery-like electrode materials are characterized by large theoretical capacitance but suffer from poor surface reactivity and insufficient electroactive sites thus limiting their practical charge storage capacity. To overcome this challenge, an effective strategy for vacancy modulation on battery-like electrode materials is necessary. Herein, we report for the first time an elaborately designed three-dimensional (3D) hierarchical heterostructure consisting of CoCx@NiCo-LDH on conductive nickel foam as a freestanding supercapacitor electrode. Benefiting from the weakening of the coordination of CoO bonds, the CoCx structure induces in-situ reconstruction of the NiCo-LDH lattice, resulting in the formation of abundant oxygen vacancies (interfacial octahedral Co2+ sites) that lower the OH- adsorption energy as determined by the density functional theory (DFT) calculation. The resulting CoCx@NiCo-LDH/NF electrode exhibits an ultrahigh rate capability (2330 mF cm-2 at 0.3 mA cm-2, with capacitance retention of 51.5 % at 30 mA cm-2) and remarkable cycling performance (capacitance retention of 81.6 % after 10,000 cycles). Additionally, the assembled asymmetric devices deliver an extremely high energy density of 246 μWh cm-2 at the power density of 798 μW cm-2, with 87.8 % capacitance retention after 10,000 cycles at 8 mA cm-2. Overall, this study presents a simple yet effective strategy to construct high-performance battery-like electrodes for potential applications in energy storage, transportation, and communication.

012 facets modulated LDH composite for neurotoxicity risk assessment through direct electrochemical profiling of dopamine

Rising concerns of pesticide-induced neurotoxicity and neurodegenerative diseases like Parkinson's, Alzheimer's, and Multiple Sclerosis, are exacerbated by overexposure to contaminated waterbodies. Therefore, evaluating the risk accurately requires reliable monitoring of related biomarkers like dopamine (DA) through electrochemical detection. Layered double hydroxides (LDHs) have shown great potential in sensors. However, to meet the challenges of rapid detection of large patient cohorts in real-time biological media, they should be further tailored to display superior analytical readouts. Herein, a ternary LDH (Ni2CoMn0.5) was integrated with the sheets of thermally reduced graphene oxide (trGO), to expose more highly active edge planes of the LDH, as opposed to its generally observed inert basal planes. The improvement in detection performance through such a modulated structure-property is a prospect that hasn't been previously explored for any other LDH-based materials employed in sensing applications. The 2 folds superior electrochemical activity exhibited by the face-on oriented LDH with trGO as compared to the pristine LDH material was further employed for direct detection of DA in real blood plasma samples. Moreover, the designed sensor exhibited exceptional selectivity towards the detection of DA with a limit of detection of 34.6 nM for a wide dynamic range of 0.001-5 mM with exceptional stability retaining 88.56% of the initial current even after storage in ambient conditions for 30 days.

Hierarchical NiCo@NiOOH@CoMoO4 Core-Shell Heterostructure on Carbon Cloth for High-Performance Asymmetric Supercapacitors

The fabrication of low-cost, effective, and highly integrated nanostructured materials through simple and reproducible methods for high-energy-density supercapacitors is highly desirable. Herein, an activated carbon cloth (ACC) is designed as the functional scaffold for supercapacitors and treated hydrothermally to deposit NiCo nanoneedles working as internal core, followed by a dip-dry coating of NiOOH nanoflakes core-shell and uniform hydrothermal deposition of CoMoO4 nanosheets serving as an external shell. The structured core-shell heterostructure ACC@NiCo@NiOOH@CoMoO4 electrode resulted in exceptional specific areal capacitance of 2920 mF cm-2 and exceptional cycling stability for 10 000 cycles. Moreover, the fabricated electrode is developed into an asymmetric supercapacitor which demonstrates excellent areal capacitance, energy density, and power density within the broad potential window of 1.7 V with a cycling life of 92.4% after 10 000 charge-discharge cycles, which reflects excellent cycle life. The distinctive core-shell structure, highly conductive substrate, and synergetic effect of coated material results in more electrochemical active sites and flanges for effective electrons and ion transportation. This unique technique provides a new perspective for cost-efficient supercapacitor applications.

Mixed solvent-assisted synthesis of high mass loading amorphous NiCo-MOF as a promising electrode material for supercapacitors

The pursuit of high mass loading metal-organic framework (MOF) materials via a simple method is crucial to achieve high-performance supercapacitors. Herein, an amorphous NiCo-MOF material with a high mass loading of up to 10.3 mg cm-2 was successfully prepared using a mixed solvent system of ethanol and water. In addition, by adjusting the volume ratio of ethanol to water, amorphous NiCo-MOFs with three different morphologies including nanospheres, nanopores, and ultra-thick plates were obtained. It was found that the different solvent systems not only affected the growth rate of MOFs, but also controlled their nucleation rate by changing the coordination environment of the metal ions, and thus achieved morphology and mass loading regulation, thereby influencing their energy storage behavior. Notably, the optimum NiCo-MOF exhibited the superior specific capacitance of up to 9.7 F cm-2 (941.8 F g-1) at a current density of 5 mA cm-2 and high-rate capability of 71.1% even at 20 mA cm-2. Moreover, the corresponding assembled solid-state supercapacitor exhibited an excellent energy density of 0.65 mW h cm-2 at a power density of 2 mW cm-2 and capacity retention of 84.7% after 8000 cycles at 30 mA cm-2. Overall, this work proposes a feasible and effective strategy to achieve high mass loading NiCo-MOFs, impacting their ultimate electrochemical performance, which can possibly be further extended to other MOFs with superior capacitance.

Co(II)-Based Metal-Organic Framework Derived CA-CoNiMn-CLDHs with Peroxidase-like Activity for Colorimetric Detection of Phenol

Given the serious harm of toxic phenol to human health and the ecological environment, it is urgent to develop an efficient, low-cost and sensitive nanoenzyme-based method to monitor phenol. MOF-derived nanozyme has attracted wide interest due to its hollow polyhedra structure and porous micro-nano frameworks. However, it is still a great challenge to synthesize MOF-derived multimetal synergistic catalytic nanoenzymes in large quantities with low cost. Herein, we reported the synthetic strategy of porous hollow CA-CoNiMn-CLDHs with ZIF-67 as templates through a facile solvothermal reaction. The prepared trimetallic catalyst exhibits excellent peroxidase-like activity to trigger the oxidative coupling reaction of 4-AAP and phenol in the presence of H2O2. The visual detection platform for phenol based on CA-CoNiMn-CLDHs is constructed, and satisfactory results are obtained. The Km value for CA-CoNiMn-CLDHs (0.21 mM) is lower than that of HRP (0.43 mM) with TMB as the chromogenic substrate. Because of the synergistic effect of peroxidase-like activity and citric acid functionalization, the built colorimetric sensor displayed a good linear response to phenol from 1 to 100 μM with a detection limit of 0.163 μM (3σ/slope). Additionally, the CA-CoNiMn-CLDHs-based visual detection platform possesses high-chemical stability and excellent reusability, which can greatly improve economic benefits in practical applications.

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.

Series of Halogen Engineered Ni(OH)2 Nanosheet for Pseudocapacitive Energy Storage with High Energy Density

Ni(OH)2 nanosheet, acting as a potential active material for supercapacitors, commonly suffers from sluggish reaction kinetics and low intrinsic conductivity, which results in suboptimal energy density and long cycle life. Herein, a convenient electrochemical halogen functionalization strategy is applied for the preparation of mono/bihalogen engineered Ni(OH)2 electrode materials. The theoretical calculations and experimental results found that thanks to the extraordinarily high electronegativity, optimal reversibility, electronic conductivity, and reaction kinetics could be achieved through F functionalization . However, benefiting from the largest ionic radius, INi(OH)2 contributes the best specific capacity and morphology transformation, which is a new finding that distinguishes it from previous reports in the literature. The exploration of the interaction effect of halogens (F, INi(OH)2 , F, BrNi(OH)2 , and Cl, INi(OH)2 ) manifests that F, INi(OH)2 delivers a higher specific capacity of 200.6 mAh g-1 and an excellent rate capability of 58.2% due to the weaker electrostatic repulsion, abundant defect structure, and large layer spacing. Moreover, the F, INi(OH)2 //FeOOH@NrGO device achieves a high energy density of 97.4 Wh kg-1 and an extremely high power density of 32426.7 W kg-1 , as well as good cycling stability. This work develops a pioneering tactic for designing energy storage materials to meet various demands.

Controlled Synthesis of Flower-like Hierarchical NiCo-Layered Double Hydroxide Integrated with Metal-Organic Framework-Derived Co@C for Supercapacitors

Layered double hydroxides (LDHs) have come to the foreground recently, considering their unique layered structure and short ion channels when they act as electrode materials for supercapacitors (SCs). However, due to their poor rate and cycle performance, they are not highly sought after in the market. Therefore, a flower-like hierarchical NiCo-LDH@C nanostructure with flake NiCo-LDH anchored on the carbon skeleton has emerged here, which is constructed by calcination and hydrothermal reaction and applying flake ZIF-67 as a precursor. In this structure, NiCo-LDH grows outward with abundant and homogeneously distributed Co nanoparticles on Co@C as nucleation sites, forming a hierarchical structure that is combined tightly with the carbon skeleton. The flower-like hierarchical nanostructures formed by the composite of metal-organic frameworks (MOFs) and LDHs have successfully enhanced the cycle and rate performance of LDH materials on the strength of strong structural stability, large specific surface area, and unique cooperative effect. The NiCo-LDH@C electrode displays superb electrochemical performance, with a specific capacitance of 2210.6 F g^-1 at 1 A g^-1 and 88.8% capacitance retention at 10 A g^-1. Furthermore, the asymmetric supercapacitor (ASC) constructed with NiCo-LDH@C//RGO reveals a remarkable energy density of 45.02 W h kg^-1 with a power density of 799.96 W kg^-1. This project aims to propose a novel avenue to exploit NiCo-LDH electrode materials and provide theory and methodological guidance for deriving complex structures from MOF derivatives.

Layered bimetallic hydroxide nanocage assembled on MnO2 nanotubes: A hierarchical porous sugar gourd-like electrocatalyst for the sensitive detection of hydrogen peroxide in food

Hydrogen peroxide is used widely as a disinfection or bleaching additive during processing in the food industry. However, excessive residues of hydrogen peroxide in food have serious human health implications. In the present study, a novel electrochemical sensing electrode (MnO₂/ZIF-67@LDH) with hierarchical porous sugar gourd-like structure was fabricated through a multi-step hydrothermal method using ZIF as the precursor. The unique porous nanocage structure of the sensing electrode provided multidimensional charge transfer channels and accelerated the electron transfer rate. As a hydrogen peroxide sensor, the electrode had two detection linear ranges of 1×10^-3-4 mmol L^-1 and 4-8 mmol L^-1, and the detection limit was 0.26 µmol L^-1. The MnO₂/ZIF-67@LDH sensor was also applied to determine the content of hydrogen peroxide in actual food samples of juice and milk, and satisfactory recovery were achieved. The present study provides a novel and effective design strategy for the construction of electrochemical sensing electrodes.

An electrochemiluminescence resonance energy transfer biosensor based on Luminol-LDH and CuS@Pt for detection of alpha-fetoprotein

Alpha-fetoprotein (AFP) is the best diagnostic marker for hepatocellular carcinoma (HCC) and plays an important role in the general surveillance of the population. Therefore, the establishment of an ultra-sensitive AFP assay is essential for the early screening and clinical diagnosis of HCC. In this work, we designed a signal-off biosensor for ultra-sensitive detection of AFP based on an electrochemiluminescent resonance energy transfer (ECL-RET) strategy using luminol intercalated layered bimetallic hydroxide (Luminol-LDH) as an ECL donor and Pt nanoparticles-grown on copper sulfide nanospheres (CuS@Pt) as ECL acceptor. The (Au NPs/Luminol-LDH)_n multilayer nanomembrane synthesized by our intercalation and layer-by-layer electrostatic assembly process not only effectively immobilizes luminol but also significantly enhances the ECL signal. The CuS@Pt composite has well visible light absorption ability and can burst the light emitted from luminol by ECL-RET. The biosensor showed good linearity in the range from 10^-5 ng mL^-1 to 100 ng mL^-1 and a minimum detection limit of 2.6 fg mL^-1. Therefore, the biosensor provides a novel and efficient strategy for the detection of AFP, which is important for the early screening and clinical diagnosis of HCC.

Electrochemically activated 3D Mn doped NiCo hydroxide electrode materials toward high-performance supercapacitors

Metal doping and electrochemical reconstruction had been demonstrated to play a significant role in the preparation of advanced electrode materials, which is helpful to achieve high-performance supercapacitors. However, there was no report about the combination of two technologies to construct electrode materials and their applications in supercapacitors. Herein, a rational Mn doped NiCo sulfide compound with open structure composed of 2D ultra-thin nanosheets was designed via a Mn doping route. In order to further improve the energy storage performance of the resulted product, we adopted a simple electrochemical activation strategy to reconstruct it. It was found that the reconstructed sample not only exhibited an irreversible evolution of structure (from 2D sheet to 3D channel), but also the phase transformation (from metal sulfide to metal hydroxide). Benefiting from the stable 3D curved structure with numerous channels, multitudinous charge transfer provided by numerous valence states of metals and copious active sites by low crystalline state, the in-situ self-reconstructed sample exhibited superior capacitance. In details, the optimized product delivered excellent specific capacitance of 1462C g^-1 (3655F/g) at 1 A g^-1 and high rate capability of 66 % even at 5 A g^-1. Moreover, the corresponding assembled asymmetric supercapacitor exhibited an excellent energy density of 141.8 Wh kg^-1 at a power density of 850.1 W kg^-1, and the capacitance retention rate was 96.6 % even after 5000 cycles, which was distinctly superior than thoseofthe previous similarmaterialsreported. In a word, this work provided a feasible and effective strategy to construct 3D Mn doped NiCo hydroxide electrode materials toward high-performance supercapacitors.

Hierarchical Nickel-Cobalt Hydroxide Composite Nanosheets-Incorporated Nitrogen-Doped Carbon Nanotubes Embedded with Nickel-Cobalt Alloy Nanoparticles for Driving a 2 V Asymmetric Supercapacitor

A class of electrode materials with favorable structures and compositions and powerful electrochemical (EC) properties are needed to boost the supercapacitor capacity significantly. In this study, an inventive technique was established to produce a well-aligned nickel-cobalt alloy nanoparticles-encapsulated N-doped carbon nanotubes with porous structure and good conductivity on carbon cloth (NiCo@NCNTs/CC) as a substrate. Then, nanosheets of nickel-cobalt layered double hydroxide (NiCo-LDH) were grown on NiCo@NCNTs/CC via a simple EC deposition method to construct a self-supported monolithic hierarchical nanosheets/nanotubes composite electrode of NiCo-LDH/NiCo@NCNTs/CC. In such a composite electrode, the NiCo@NCNTs can act as a good conductor and structural scaffold to grow NiCo-LDH nanosheets with a three-dimensional open and porous structure, which helps to improve the electron/ion-transfer performance, increase the number of exposed reactive sites, and inhibit the aggregation of NiCo-LDH nanosheets, thereby boosting the capacitance and stability. As a positive electrode, the NiCo-LDH/NiCo@NCNTs/CC hierarchical nanosheets/nanotubes electrode displays 1898 mF cm^-2 (1262 A g^-1) of high capacitance, long-term stability with a capacitance retention of around 100% after 8000 cycles, and nearly 103% Coulombic efficiency. After assembling into an asymmetric supercapacitor with a Co(OH)₂/NiCo@NCNTs/CC negative electrode, 2 V of operating voltage with 73.1 μW h cm^-2 (52.8 W h kg^-1) of energy density was achieved. Our investigation gives a potential approach for constructing the integrated composite electrode of transition-metal compounds-carbon materials for high-performance supercapacitors.