Assembly of Ni-Al layered double hydroxide and graphene electrodes for supercapacitors

Fabrication of Sandwiched NiCo-Layered Double Hydroxides/Carbon Nanoballs for Sustainable Energy Storage

This study presents a promising method for creating high-performance supercapacitor electrodes. The approach involves crafting a unique composite material-nickel-cobalt-layered double hydroxides (NiCo-LDH) grown on carbon nanoballs (CNBs). This is achieved by first creating a special carbon material rich in oxygen and nitrogen from a polybenzoxazine source. At first, eugenol, ethylene diamine and paraformaldehyde undergo Mannich condensation to form the benzoxazine monomer, which undergoes self-polymerization in the presence of heat to produce polybenzoxazine. This was then carbonized and activated to produce CNBs containing heteroatoms. Then, through a hydrothermal technique, NiCo-LDH nanocages are directly deposited onto the CNBs, eliminating the need for complicated templates. The amount of CNBs used plays a crucial role in performance. By optimizing the CNB content to 50%, a remarkable specific capacitance of 1220 F g-1 was achieved, along with excellent rate capability and impressive cycling stability, retaining 86% of its capacitance after 5000 cycles. Furthermore, this NiCo-LDH/CNB composite, when combined with active carbon in a supercapacitor configuration, delivered outstanding overall performance. The exceptional properties of this composite, combined with its simple and scalable synthesis process, position it as a strong contender for next-generation sustainable energy storage devices. The ease of fabrication also opens doors for its practical application in advancing energy storage technologies.

Visible-Light-Driven Photocatalytic H2 Production Using Composites of Co-Al Layered Double Hydroxides and Graphene Derivatives

The direct conversion of solar energy into chemical energy represents an enormous challenge for current science. One of the commonly proposed photocatalytic systems is composed of a photosensitizer (PS) and a catalyst, together with a sacrificial electron donor (ED) when only the reduction of protons to H2 is addressed. Layered double hydroxides (LDH) have emerged as effective catalysts. Herein, two Co-Al LDH and their composites with graphene oxide (GO) or graphene quantum dots (GQD) have been prepared by coprecipitation and urea hydrolysis, which determined their structure and so their catalytic performance, giving H2 productions between 1409 and 8643 μmol g-1 using a ruthenium complex as PS and triethanolamine as ED at 450 nm. The influence of different factors, including the integration of both components, on their catalytic behavior, has been studied. The proper arrangement between the particles of both components seems to be the determining factor for achieving a synergistic interaction between LDH and GO or GQD. The novel Co-Al LDH composite with intercalated GQD achieved an outstanding catalytic efficiency (8643 μmol H2 g-1) and exhibited excellent reusability after 3 reaction cycles, thus representing an optimal integration between graphene materials and Co-Al LDH for visible light driven H2 photocatalytic production.

Capacitive deionization of high concentrations of hexavalent chromium using nickel-ferric-layered double hydroxide/molybdenum disulfide asymmetric electrode

To decontaminate wastewater affected by high concentrations of aqueous hexavalent chromium (Cr(VI)) and improve the capability of layered double hydroxide (LDH) as an electrode in the capacitive deionization (CDI) process, nickel-ferric-LDH (NiFe-LDH) and NiFe-LDH/molybdenum disulfide (NiFe/MoS₂) were synthesized using a hydrothermal method. Characterization results indicated that the flower-like cluster framework of MoS₂ was decorated with the NiFe-LDH. Addition of MoS₂ improved the conductivity, capacitance reversibility, charge efficiency, coulombic efficiency, and stability of NiFe/MoS₂. The CDI performance of aqueous Cr(VI) was evaluated using NiFe/MoS₂ and activated carbon as the anode and cathode, respectively. The process reached equilibrium within 240 min. The deionization capacity and removal ratio for Cr(VI) (100 mg/L, 100 mL) were 49.71 mg/g and 99.42 %, respectively, at 1.2 V and 20 mL/min. The isothermal data were accurately described using the Langmuir model, and the theoretical maximum deionization capacity of NiFe/MoS₂ for Cr(VI) was 106.2 mg/g. The interaction mechanisms included electrostatic attraction, surface complexation, and reduction. These findings indicate that NiFe/MoS₂ has feasible applications in practical wastewater treatment for Cr(VI) removal.

Preparation of Manganese Oxide Nanoparticles with Enhanced Capacitive Properties Utilizing Gel Formation Method

Development of efficient and environmentally benign materials is important to satisfy the increasing demand for energy storage materials. Nanostructured transition-metal oxides are attractive because of their variety in morphology, high conductivity, and high theoretical capacitance. In this work, the nanostructured MnO₂ was successfully fabricated using a gel formation process followed by calcination at 400 °C (MNO4) and 700 °C (MNO7) in the presence of air. The suitability of the prepared materials for electrochemical capacitor application was investigated using graphite as an electrode substrate. The chemical, elemental, structural, morphological, and thermal characterizations of the materials were performed with relevant techniques. The structural and morphological analyses revealed to be a body-centered tetragonal crystal lattice with a nano-tablet-like porous surface. The capacitive performances of the MNO4- and MNO7-modified graphite electrodes were examined with cyclic voltammetry and chronopotentiometry in a 0.5 M Na₂SO₄ aqueous solution. The synthesized MNO7 demonstrated a higher specific capacitance (627.9 F g^-1), energy density (31.4 Wh kg^-1), and power density (803.5 W kg^-1) value as compared to that of MNO4. After 400 cycles, the material MNO7 preserves 100% of capacitance as its initial capacitance. The highly conductive network of nanotablet structure and porous morphologies of MNO7 are most likely responsible for its high capacitive behavior. Such material characteristics deserve a good candidate for electrode material in energy storage applications.

Adsorption of UO2 2+ by AlBaNi-layered double hydroxide nano-particles: kinetic, isothermal, and thermodynamic studies

AlBaNi-LDH nanoparticles have been synthesized by the co-precipitation method. A series of characterization analyses (Scanning Electron Microscope, Energy Dispersive X-ray, Transmission Electron Microscope, X-ray Diffraction, Atomic Force Microscope, and Infrared spectroscopy) proved that the surface structure of AlBaNi-LDH nano-particles was the key mechanism for UO2 2+ adsorption. The synthesized product showed good performance in UO2 2+ adsorption efficiency in neutral pH with a maximal adsorption capacity of 137 mg/g. The results demonstrated the adsorption process fitted well with pseudo-second-order and Langmuir isotherm models. Also, the effects of coexisting ions and different eluents are briefly described. These results confirm that AlBaNi-LDH is an effective material for the adsorption of UO2 2+ from an aqueous solution with reusable availability.

Rational design of Ti3C2Cl2 MXenes nanodots-interspersed MXene@NiAl-layered double hydroxides for enhanced pseudocapacitor storage

Although electrodes based on two dimensional hybrids with interstratification-assemble have been widely studied for supercapacitors, the performance enhancement still remains challenge mainly due to the random dispersion of surface passivated two dimensional nanosheets. Herein, a new covalent surface functionalization of MXene-based Ti₃C₂Cl₂ nanodots-interspersed MXene@NiAl-layered double hydroxides (QD-Ti₃C₂Cl₂@NiAl-LDHs) hybrid electrode with superior pseudocapacitor storage performance has been elaborately designed by electrostatic-assembled. As a result, the QD-Ti₃C₂Cl₂@NiAl-LDHs electrode exhibits a super specific capacitance of 2010.8F g^-1 at 1.0 A g^-1 and high energy density of 100.5 Wh kg^-1 at a power density of 299.8 W kg^-1. In addition, 94.1% capacitance retention is achieved after cycling for 10,000 cycles at 1.0 A g^-1, outperforming previously reported of two dimensional hybrids electrode for supercapacitor. Furthermore, density functional theory (DFT) calculations show that the superior pseudocapacitor storage performance of the QD-Ti₃C₂Cl₂@NiAl-LDHs may be attributed to the creation of numerous electrochemical active sites and the enhancement of electrical conductivity by the QD-Ti₃C₂Cl₂ MXene. This work provides new strategy for developing excellent pseudocapacitor supercapacitor based on two dimensional hybrid electrode.

Synthesis of CNTs/CoNiFe-LDH Nanocomposite with High Specific Surface Area for Asymmetric Supercapacitor

Ternary layered double hydroxide (LDH) materials have shown promising application in hybrid supercapacitors. However, the low electrical conductivity of LDHs is still a restriction to their performance. Herein, carbon nanotubes/cobalt-nickel-iron LDH (CNTs/CoNiFe-LDH) hybrid material was prepared by a one-step hydrothermal approach for the first time. The presence of CNTs improved the conductivity and surface area of the electrode, leading to an enhanced electrochemical performance. The CNTs/CoNiFe-LDH hybrid electrode exhibited high specific capacity 170.6 mAh g-1 at a current density of 1 A g-1, with a capacity retention of 75% at 10 A g-1. CNTs/CoNiFe-LDH//AC asymmetric supercapacitor (ASC) was also assembled, which had high specific capacitance (96.1 F g-1 at the current density of 1 A g-1), good cycling stability (85.0% after 3000 cycles at 15 A g-1) and high energy density (29.9 W h kg-1 at the power density of 750.5 W kg-1). Therefore, the CNTs/CoNiFe-LDH material could be used for hybrid supercapacitor electrodes.

Synthesis of NiFeAl LDHs from electroplating sludge and Their excellent supercapacitor performance

This work demonstrated that electroplating sludges (EPS) of specific composition may be used for the synthesis of layered double hydroxide (LDH) materials for energy applications after appropriate treatment. The unique composition and structure of EPS render it with good electrochemical energy storage performance. The EPS containing Ni, Fe, and Al was dissolved by acid and added with urea precipitator. The LDH material was prepared by a facile hydrothermal method. The increase of urea in a certain range is conducive to the formation of intact LDH. However excessive urea levels promoted the transformation from LDH to Ni(HCO₃)₂. Various active Ni bridged by N in ‒O‒CN promoted electron transfer, ‒O‒CN content in LDHs was proportional to the urea amount. The prepared LDHs exhibited a specific capacitance of 1652.20 F g^-1 at 0.5 A g^-1, and the value remained at 766.69 F g^-1 after 1000 cycles. The prepared LDH has excellent supercapacitor performance, which is closely related to its structure. Therefore, the proposed recycling strategy of EPS resources can be used to prepare LDH supercapacitors, paving the way for new applications of EPS in the field of energy storage.

Electronic modulation of oxygen evolution on metal doped NiFe layered double hydroxides

The bottleneck of electrochemical water splitting is the sluggish kinetics of oxygen evolution reaction (OER). Layered double hydroxides (LDHs) have been proposed as active and affordable electrocatalysts in OER. It has been reported that the activity of LDHs can be effectively tuned by doping of other metals. Despite previous experimental synthesis and improved catalytic performance, the in-depth OER mechanism on metal doped LDHs remains ambiguous. In the present work, transition metals (Cr, Mn and Co) doped NiFe LDHs were designed to investigate the doping effect in OER by both experimental analysis and density functional theory calculations. Based on experimental results, the intrinsic OER activity is Cr-NiFe LDHs > Co-NiFe LDHs > Mn-NiFe LDHs > NiFe LDHs, while the enhanced catalytic performance upon doping can be attributed to the interface effect, which results in the tuning of the binding energies of the intermediate states in OER.

Efficient immobilization of aptamers on the layered double hydroxide nanohybrids for the electrochemical proteins detection

Despite the use of layered double hydroxides (LDH) in different electrochemical (bio)sensors, the construction of aptasensors using LDH-based surfaces was not reported to the best of our knowledge. This may be due to the lack of a suitable linker to attach aptamers to the LDH-modified surface. LDH-based aptasensors are established here as very sensitive and reliable devices in serum and cerebrospinal fluid (CSF) analysis. 5'-NH₂ DNA aptamer probes were immobilized on the LDH-based surfaces in a vertical conformation without any linker materials. Due to the low electron conductivity of the LDH, carbon nanotubes (CNT) with high electronic conductivity and high surface area were combined with LDH. Thrombin was used as a model protein for aptasensing. The sensor shows a linear range of 0.005-12,000 pmol L^-1 and a limit of detection of 0.1 fmol L^-1. Moreover, the aptasensor was used for the sensing of thrombin in CSF and serum samples acquired from both healthy and patients with different disease.

Performance of CuAl-LDH/Gr Nanocomposite-Based Electrochemical Sensor with Regard to Trace Glyphosate Detection in Water

Glyphosate, which has been widely reported to be a toxic pollutant, is often present at trace amounts in the environment. In this study, a novel copper-aluminum metal hydroxide doped graphene nanoprobe (labeled as CuAl-LDH/Gr NC) was first developed to construct a non-enzymatic electrochemical sensor for detection trace glyphosate. The characterization results showed that the synthesized CuAl-LDH had a high-crystallinity flowered structure, abundant metallic bands and an intercalated functional group. After mixed with Gr, the nanocomposites provided a larger surface area and better conductivity. The as-prepared CuAl-LDH/Gr NC dramatically improved the enrichment capability for glyphosate to realize the stripping voltammetry detection. The logarithmic linear detection range of the sensor was found to be 2.96 × 10-9-1.18 × 10-6 mol L-1 with the detection limit of 1 × 10-9 mol L-1 with excellent repeatability, good stability and anti-interference ability. Further, the sensor achieved satisfactory recovery rates in spiked surface water, ranging from 97.64% to 108.08%, demonstrating great accuracy and practicality.

Graphene Oxide-Polypyrrole Coating for Functional Ceramics

Ceramic substrates were metallized with a Ni-Mo-P electroless coating and further modified with a polypyrrole (PPy) coating by the electrodeposition method. The properties of the polypyrrole coating were studied with the addition of a graphene oxide (GO) nanomaterial prior to the electrodeposition and its reduction degree. Fourier Transform Infrared Spectroscopy, Field-Emission Scanning Electron Microscopy, Raman spectroscopy and cyclic voltammetry were employed to characterize the properties of the coatings. The results indicated the successful synthesis of conductive electrodes by the proposed approach. The electrodeposition of PPy and its charge storage properties are improved by chemically reduced GO. The surface capacitive contribution to the total stored charge was found to be dominant and increased 2–3 fold with the reduction of GO. The chemically reduced GO-modified PPy exhibits the highest capacitance of 660 F g⁻¹ at 2 mV s⁻¹, and shows a good cyclability of 94% after 500 charge/discharge cycles. The enclosed results indicate the use of an NiMoP electroless coating, and modification with a carbon nanomaterial and conducting polymer is a viable approach for achieving functional ceramics.

Recent Progress in Two-Dimensional Layered Double Hydroxides and Their Derivatives for Supercapacitors

High-performance supercapacitors have attracted great attention due to their high power, fast charging/discharging, long lifetime, and high safety. However, the generally low energy density and overall device performance of supercapacitors limit their applications. In recent years, the design of rational electrode materials has proven to be an effective pathway to improve the capacitive performances of supercapacitors. Layered double hydroxides (LDHs), have shown great potential in new-generation supercapacitors, due to their unique two-dimensional layered structures with a high surface area and tunable composition of the host layers and intercalation species. Herein, recent progress in LDH-based, LDH-derived, and composite-type electrode materials targeted for applications in supercapacitors, by tuning the chemical/metal composition, growth morphology, architectures, and device integration, is reviewed. The complicated relationships between the composition, morphology, structure, and capacitive performance are presented. A brief projection is given for the challenges and perspectives of LDHs for energy research.

Effect of Deposition Parameters on Electrochemical Properties of Polypyrrole-Graphene Oxide Films

Graphene oxide (GO)-modified polypyrrole (PPy) coatings were obtained by electrochemical methods in the presence of the anionic surfactant, sodium dodecyl sulfate (SDS). The structure, morphology, and electrochemical properties of the coatings were assessed by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry at varying scan rates, respectively. The properties of the obtained coatings were analyzed with the GO and PPy loadings and electrodeposition mode. The hybrid coatings obtained galvanostatically showed a coarser appearance than those deposited by cyclic voltammetry CV mode and improved performance, respectively, which was further enhanced by GO and PPy loading. The capacitance enhancement can be attributed to the SDS surfactant that well dispersed the GO sheets, thus allowing the use of lower GO content for improved contribution, while the choice of suitable electrodeposition parameters is highly important for improving the applicability of GO-modified PPy coatings in energy storage applications.

Cobalt-based layered double hydroxides revisited: evidence for oxidizing radical generation

Layered double hydroxides (LDHs) containing transition metal elements such as cobalt show interesting reactivity related to the complexity of cobalt chemistry.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties. Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit, we have synthesized bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on reduced graphene oxide core-shells using template based wet chemical approach. The material synthesized have been characterized structurally and electrochemically. The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^-1. A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.

Surface Engineering of Graphene Oxide Shells Using Lamellar LDH Nanostructures

The discovery of graphene oxide (GO) has made a profound impact on varied areas of research due to its excellent physicochemical properties. However, surface engineering of these nanostructures holds the key to enhanced surface properties. Here, we introduce surface engineering of reduced GO (rGO) shells by radially grafting Ni-Co layered double hydroxide (LDH) lamella on rGO shells to form Ni-Co LDH@rGO. The morphology of synthesized Ni-Co LDH@rGO mimics dendritic cell-like three-dimensional (3D) hierarchical morphologies. Silica nanospheres form self-sacrificial templates during the reduction of GO shells to form rGO shells during the template-assisted synthesis. The radial growth of LDH lamellae during hydrothermal process on GO shells provides access to a significantly larger number of additional active redox sites and overcompensates the loss of pseudocapacitive charge storage centers during the reduction of GO to form rGO shells. This enables in the synthesis of novel surface-engineered rGO nanoshells, which provide large surface area, enhanced redox sites, high porosity, and easy transport of ions. These synthesized 3D dendritic cell-like morphologies of Ni-Co LDH@rGO show a high capacitance of ∼2640 F g^-1. A flexible hybrid device fabricated using this nanomaterial shows a high energy density of ∼35 Wh kg^-1 and a power density of 750 W kg^-1 at 1 A g^-1. No appreciable compromise in device performance is observed under bending conditions. This synthesis strategy may be used in the development of functional materials useful for potential applications, including sensors, catalysts, and energy storage.

Retracted Article: A layered double hydroxide assembled on a g-C3N4-modified hollow carbon sphere as an adsorbent for the removal of uranium(vi)

A layered double hydroxide assembled on a g-C₃N₄-modified hollow carbon sphere with unique flower-like morphology was prepared to capture U(vi).

Electrostatic Self-Assembly of Sandwich-Like CoAl-LDH/Polypyrrole/Graphene Nanocomposites with Enhanced Capacitive Performance

A novel sandwich-like composite with ultrathin CoAl-layered double hydroxide (LDH) nanoplates electrostatically assembled on both sides of two-dimensional polypyrrole/graphene (PG) substrate has been successfully fabricated using facile hydrothermal techniques. The PG not only serves as an excellent conductive and structural scaffold to enhance the transmission of electrons and prevent aggregation of CoAl-LDH nanoplates but also contributes to the enhancement of the specific capacitance. Owing to the homogeneous dispersion of CoAl-LDH nanoplates and its intimate interaction with PG substrate, the resulting CoAl-LDH/PG nanocomposite material exhibits excellent capacitive performance, for example, enhanced gravimetric specific capacitance (864 F g^-1 at 1 A g^-1 ), high rate performance (75% retention at 20 A g^-1), and excellent cycle life (almost no degradation in supercapacitor performance after 5000 cycles) in aqueous KOH solution. Furthermore, the assembled asymmetric capacitor is able to deliver a superhigh energy density of 46.8 Wh kg^-1 at 1.2 kW kg^-1 and maintain 90.1% of its initial capacitance after 10 000 cycles. These results indicate a rational assembly strategy toward a high-performance pseudocapacitive electrode material with excellent rate performance, high specific capacitance, and outstanding cycle stability.

Synthesis of Fluorinated Graphene/CoAl-Layered Double Hydroxide Composites as Electrode Materials for Supercapacitors

CoAl-layered double hydroxide/fluorinated graphene (CoAl-LDH/FGN) composites were fabricated via a two-step hydrothermal method. The synthesized CoAl-LDH/FGN composites have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and electrochemical measurements. The results indicated that the fluorinated carbon with various configuration forms were grafted onto the framework of graphene, and the C-F bond configuration and fluorine content could be tuned by the fluorination time. Most of semi-ionic C-F bonds were formed at an appropriate fluorination time and, then, converted into fluorine rich surface groups (such as CF₂, CF₃, etc.) which were electrochemically inactive as the fluorination time prolonged. Moreover, the CoAl-LDH/FGN composites prepared at the optimal fluorination time exhibited the highest specific capacitance (1222 F/g at 1 A/g), the best rate capability, and the most stable capacitance retention, which offered great promise as electrode materials for supercapacitors.

Electrostatic-Induced Assembly of Graphene-Encapsulated Carbon@Nickel-Aluminum Layered Double Hydroxide Core-Shell Spheres Hybrid Structure for High-Energy and High-Power-Density Asymmetric Supercapacitor

Achieving high energy density while retaining high power density is difficult in electrical double-layer capacitors and in pseudocapacitors considering the origin of different charge storage mechanisms. Rational structural design became an appealing strategy in circumventing these trade-offs between energy and power densities. A hybrid structure consists of chemically converted graphene-encapsulated carbon@nickel-aluminum layered double hydroxide core-shell spheres as spacers among graphene layers (G-CLS) used as an advanced electrode to achieve high energy density while retaining high power density for high-performance supercapacitors. The merits of the proposed architecture are as follows: (1) CLS act as spacers to avoid the close restacking of graphene; (2) highly conductive carbon sphere and graphene preserve the mechanical integrity and improve the electrical conductivity of LDHs hybrid. Thus, the proposed hybrid structure can simultaneously achieve high electrical double-layer capacitance and pseudocapacitance resulting in the overall highly active electrode. The G-CLS electrode exhibited high specific capacitance (1710.5 F g^-1 at 1 A g^-1) under three-electrode tests. An ASC fabricated using the G-CLS as positive electrode and reduced graphite oxide as negative electrode demonstrated remarkable electrochemical performance. The ASC device operated at 1.4 V and delivered a high energy density of 35.5 Wh kg^-1 at a 670.7 W kg^-1 power density at 1 A g^-1 with an excellent rate capability as well as a robust long-term cycling stability of up to 10 000 cycles.

Synthesis of Ni/Co/Al-layered triple hydroxide@brominated graphene hybrid on nickel foam as electrode material for high-performance supercapacitors

The determined need for a sustainable energy economy has evoked the increasing interest of researchers concerning the discovery of smart material designs of layered double hydroxide (LDH) nanocomposites for energy-based applications.

Surface and interface engineering of CoNi layered double hydroxides for efficient methanol oxidation reaction

Surface and interface engineering (P doping and coupling with rGO) were adopted to enhance the MOR activity of CoNi LDHs.