Nickel-cobalt Layered Double Hydroxide Research Articles

Plasmonic Au-NPs Photodecorated on NiCoLDH Nanosheets as a Flexible SERS Sensor for the Real-Time Detection of Fipronil

Rapid extraction and detection of probe molecules from curved surfaces is critical for on-site and real-time detection. In this study, a flexible platform was developed using carbon cloth (CC) to create honeycomb-like nickel cobalt layered double hydroxides (NiCoLDH) nanosheets via a simple electrodeposition technique, which were then decorated with gold nanoparticles (Au-NPs) via photodeposition process. The Au-NPs/NiCoLDH/CC was designed as a surface-enhanced Raman scattering (SERS) substrate for detecting the broad-spectrum pesticide, Fipronil (FP). The fabricated sensor achieves a superior SERS activity due to the electrodeposited NiCoLDH, which provides the charge-transfer effect, and the photodeposited Au-NPs, which generate efficient SERS hotspots through the electromagnetic effect. The Density Functional Theory (DFT) calculation was used to estimate the optimal geometry and frontier molecular orbital diagrams of the FP molecules. The influence of electrodeposition time on NiCoLDH production and Au-NPs decorating quantity was investigated in detail. Furthermore, the flexible SERS sensor has excellent sensitivity, homogeneity, a low limit of detection (LOD), and high reproducibility for FP detection. Even after 40 cycles of bending and torsion, the SERS substrate maintained excellent mechanical endurance. Using this substrate, FP molecules on the surfaces of grape and tomato were successfully examined through a direct-sampling approach, achieving LODs of 10-8M and 10-9M, respectively. These findings highlight the outstanding potential of the produced flexible SERS sensor for real-time and on-site pesticide detection, making it valuable for food security analysis and monitoring.

In situ construction of sea urchin-like structural NiCo-LDH coated cobalt‑nitrogen co-doped carbon as high-performance electrode for supercapacitor

Nickel‑cobalt layered double hydroxide (NiCo-LDH) has received much attention in the field of supercapacitor electrodes due to its multiple oxidation states and good electrochemical activity. However, NiCo-LDH often suffers from structural instability and low conductivity in practical applications. In this study, sea urchin-like structural NiCo-LDH coated cobalt‑nitrogen co-doped carbon (NiCo-LDH@Co-NC-x) electrode materials were prepared by in situ growth of NiCo-LDH on the surface of cobalt‑nitrogen co-doped carbon nanosheets (Co-NC) using a one-step hydrothermal method. The results show that the NiCo-LDH@Co-NC-2 electrode material exhibits excellent electrochemical performance, its specific capacitance is up to 1909 F g−1 at a current density of 1 A g−1, and capacitance retention of 69.5 % (only 26.2 % for NiCo-LDH) can be achieved after 10,000 cycles at a current density of 10 A g−1. This is because the abundant and uniformly distributed Co nanoparticles on Co-NC provide nucleation sites for the in-situ growth of NiCo-LDH, effectively improving the interface binding between Co-NC and NiCo-LDH, enhancing the structural stability of NiCo-LDH, and ensuring highly efficient electron transport throughout the NiCo-LDH@Co-NC-2 electrode. An asymmetric supercapacitor (NiCo-LDH@Co-NC-2//AC) was further assembled with NiCo-LDH@Co-NC-2 and activated carbon (AC) as positive and negative electrodes, respectively, achieving an energy density as high as 36.8 Wh kg−1 at a power density of 750 W kg−1. These findings suggest that the NiCo-LDH@Co-NC-2 composite can be a promising candidate for high-performance supercapacitor electrode.

Oxygen vacancies are generated in the inner layer of the core-shell structure by in-situ electrochemical activation to promote electrochemical energy storage

Alkaline zinc ion batteries have attracted attention as potential energy storage devices but remain challenging due to the low utilization rate of active substances, poor conductivity, and few active sites. In order to solve these shortcomings, we grow ultrathin nickel-cobalt layered double hydroxides (NiCo LDH) by electrodeposition on Co3O4 surfaces, and generated abundant oxygen vacancies in the inner layer of the core-shell structure by electrochemical method. The special core-shell structure improves the contact between the active material and the electrolyte, bringing a positive effect on ion diffusion and charge transfer during the energy storage process. At the same time, the abundant oxygen vacancies not only effectively improve the conductivity and the number of active sites of the material, but also improve the valence state conversion ability of the cobalt element. As expected Co3O4-OV/NiCo LDH exhibits a specific capacity of 338.47 mAh g−1 at a current density of 1 A g−1 and a high average discharge potential of 1.65 V relative to Zn2+/Zn. Furthermore, the characterizations combined with density functional theory (DFT) calculations indicate that the generation of oxygen vacancies improves the conductivity and the number of active sites which results in excellent reversible electrochemical activity. This work not only provides new insight into designing advanced electrodes by introducing oxygen vacancies but also opens up avenues for the development of high-performance zinc-cobalt batteries.

Designing a Microstructure of NiCo-LDH@CNTs@Carbon Foam for Efficient Electromagnetic Wave Absorption and Excellent Environmental Tolerance.

The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

Regulating the microstructure and catalytic activity of metal selenides via calcination strategy for lithium-sulfur battery

Metal selenides obtain a series of advantages such as high electronic conductivity, excellent catalytic activity and facile fabrication approach, which are considered as promising catalysts in lithium sulfur (Li-S) battery. Traditional research based on metal selenides focuses on designing novel/complex microstructures or composites, however, the catalytic ability can be greatly affected by internal properties such as defect or vacancy. In this work, hollow nickel-cobalt layered double hydroxide (NiCo-LDH) is first fabricated and applied as a precursor to fabricate NiCoSe, and Se vacancy accompanied with crystal phase, microstructure and catalytic activity can be regulated by simply adjusting selenization atmosphere and temperature. Involving the application of NiCoSe in Li-S battery, the optimum fabrication parameter is perform the selenization at 600 °C under argon/5 % hydrogen, and the battery can exhibit a high discharge specific capacity of 1042.8 mAh g−1, excellent cycling performance of 500 cycles with a decay rate of 0.083 % at 1 C. This work highlights the importance of calcination process and also provides reference for further modifying the microstructure and performance of metal selenides in Li-S battery.

Facile synthesis and electrochemical performance of bacterial cellulose/reduced graphene oxide/NiCo-layered double hydroxide composite film for self-standing supercapacitor electrode

This study employs a cost-efficient method to create a pliable BC/rGO-NiCo-LDH electrode film on a bacterial cellulose base. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analyses verified the incorporation of reduced graphene oxide (rGO) and nickel–cobalt layered double hydroxide (NiCo-LDH) into the bacterial cellulose structure. The BC/rGO-NiCo-LDH composite material exhibited high-temperature stability and achieved a specific capacitance of 311 F g−1 at a scan rate of 0.1 mV/s, surpassing that of earlier cellulose electrodes. The electrode film showed exceptional mechanical capabilities, displaying flexibility and load resistance without any structural damage. The film’s flexibility and lightweight properties were improved due to the low density of 0.656 g cm−3, which is a result of the nanoporous structure and intrinsic low density of rGO and cellulose. A retention ratio of 0.40 for storage modulus at a glass transition temperature of around 90°C demonstrated positive mechanical performance. This cost-effective and uncomplicated synthesis approach produced a BC/rGO-NiCo-LDH electrode with potential. The material possessed favourable mechanical and electrochemical characteristics, making it suitable for wearable electronics.

Hollow dodecahedral Zn0.3Cd0.7S@NiCo-mixed metal oxide p-n heterojunction with high-efficiency photocatalytic hydrogen production activity

The growing demand for clean and sustainable energy has driven extensive research into efficient photocatalysts for hydrogen production. However, many semiconductor photocatalysts in this field still face the challenges such as wide band gap, limited visible light absorption, and inefficient separation and transport of photoinduced charges. In this study, nickel–cobalt layered double hydroxide (NiCo-LDH) was synthesized using an “etch-and-grow” method with zeolitic imidazolate framework-67 (ZIF-67) as a sacrificial template, followed by high-temperature calcination to produce nickel–cobalt mixed metal oxide (NiCo-MMO). Zn0.3Cd0.7S quantum dots were used to modify NiCo-MMO resulting in a hollow dodecahedral Zn0.3Cd0.7S@NiCo-MMO composite photocatalyst. In hydrogen production performance test, the optimized Zn0.3Cd0.7S@NiCo-MMO exhibited excellent performance (8177.5 μmol·g−1·h−1) and demonstrated good cycling stability. The hollow dodecahedral structure of the Zn0.3Cd0.7S@NiCo-MMO enhanced the light trapping ability and provided large surface area. The p-n heterojunction formed within Zn0.3Cd0.7S@NiCo-MMO accelerated carrier separation and transfer, effectively inhibited the recombination of photogenerated electrons and holes, and significantly improved the hydrogen production activity.

Hierarchical triplet-metallic oxide/carbon nanocomposites constructed from 2D layered double hydroxides and metal-organic frameworks for high-performance microwave absorption

In the face of increasingly severe electromagnetic wave radiation and interference, it is of great significance to design and prepare excellent absorbing materials. Particularly, hierarchical structure has emerged with enhanced physicochemical properties, offering enormous potential for designing absorbing materials. Here, a hierarchical structure composite constructed by ZIF-8 and fungus-like nickel-cobalt layered double hydroxide (Ni, Co-LDH) nanosheets were synthesized by in-situ self-assembly growth process. A series of Zn@NiCo-Lc composites were obtained by calcination under air. Calcined derivatives of dielectric and magnetic metallic oxides and carbon give rise to multiple polarizations and magnetic losses. The matching of the dielectric and magnetic losses of the hybrid material is further tuned by varying the feed ratio of the bimetallic LDH nanosheets, resulting in a sample with tunable EMA performance. All samples exhibit comparable EMA performance, especially large EABmax of above 5.5 GHz, and Zn@NiCo-Lc-2 has the strongest EMA intensity performance (RLmin is −67.61 dB at an ultra-thin thickness of 1.71 mm). This study provides a tractable method for the fabrication of hierarchical structural composites of high-performance MOF/LDH-derived absorbers, further broadening the application and development of novel electromagnetic wave absorption materials.

Synergistic SERS enhancement of NiCo-LDHs microurchins and silver nanoparticles for ultra-sensitive and reusable detection of thiabendazole

Two-dimensional layered semiconductor materials as a distinctive class of materials are comprehensively explored for widespread applications due to narrow bandgap, controllable morphology, and tunable metal cation composition. Herein, we constructed a sensing platform of surface enhanced Raman spectroscopy (SERS) by combination of nickel‑cobalt layered double hydroxide (NiCo-LDH) microurchins and plasmonic silver nanoparticles (Ag NPs) for fungicide detection of thiabendazole (TBZ). The NiCo-LDHs/Ag-NPs microcomposites consist of NiCo-LDHs microurchins having a large number of nanoneedles deposited with photoreduced Ag NPs. The SERS platform with NiCo-LDHs/Ag-NPs shows an excellent SERS performance for TBZ detection, including an ultra-low detection limit of 1.49 × 10−11 M, a sublime enhancement factor of 1.71 × 109, high uniformity, good reproducibility, and long-term storage stability. The ultrahigh SERS activity of NiCo-LDH/Ag-NPs can be attributed to strong electromagnetic enhancement in the nanoscale gaps between Ag NPs, massive charge transfer through large-area NiCo-LDH/Ag-NPs interfaces, and the synergistic action of electromagnetic and charge transfer mechanisms. Besides, the unique morphology of NiCo-LDHs/Ag-NPs microcomposite provides a broad surface area for adsorption of TBZ molecules for further Raman signal enhancement. The practicability of the proposed SERS platform is confirmed by detecting TBZ in the real samples of apple juice and river water. The exceptional self-cleaning capability of the NiCo-LDHs/Ag-NPs microcomposite with an retention rate of 81.97 % even after the fifth degradation cycle underscores its impressive sustainable reusability and cost-effectiveness. The findings in this work lay the foundation for the development of high-performance SERS platforms to ensure food safety and environmental protection.

NiCo-LDH sheets and Ag3PO4 nanoparticles decorated on graphitic carbon nitride for efficient oxygen evolution reaction

Ternary heterostructure engineering enables highly efficient interfacial charge transfer, which can enhance the efficiency of electrocatalysts for the oxygen evolution reaction (OER), and has thus attracted widespread interest in electrocatalysis. NiCo-LDH/CN/AgPO was synthesized via ultrasonication and subjected to morphological analyses using X-ray diffraction, scanning electron microscopy, and (high-resolution) transmission electron microscopy. The synergistic effects in the ternary heterostructured NiCo-LDH/CN/AgPO nanocomposite comprising 2D nickel-cobalt layered double hydroxide (NiCo-LDH) and silver phosphate (Ag3PO4) nanospecies anchored on graphitic carbon nitride (g-C3N4) nanosheets will provide promising features as an electrode for the alkaline oxygen evolution reaction (OER). The NiCo-LDH/CN/AgPO heterostructure demonstrated exceptional electrocatalytic OER performance compared to AgPO/NiCo-LDH, AgPO/CN, and CN, achieving a low overpotential of 289 mV for the OER at 10 mA cm−2 in 1.0 M KOH. This superior catalytic activity is attributed to the relatively large electroactive surface area, rapid charge transfer capability, and intimate interactions between the components. The innovative design and synthesis of the NiCo-LDH/CN/AgPO heterostructure provide significant potential for constructing electrocatalysts with superior efficacy in oxygen evolution reactions.

Hydrothermal synthesis of Ni, Co hydroxide nanosheet array on vertically suspended carbon cloth for flexible high-performance supercapacitors

The investigation of Ni(OH)2 electrode materials has been a prominent issue in the field of electrochemical energy. The slow ion diffusion kinetics and inherent low electronic conductivity of Ni(OH)2 restrict its electrochemical performance and application in practice. In this work, mixed-phase nickel-cobalt layered double hydroxide (NiCoLDH) array structures are successfully grown directly on vertically suspended carbon cloth (CC). In contrast to the traditional hydrothermal method, the vertically suspended carbon cloth affordes adequate reaction sites to ensure optimum array structure growth. This unique structure realizes a large mass loading of the active material. Meanwhile, the introduction of flexible electrode substrate carbon cloth effectively enhances the mechanical properties of the electrode. Due to the powerful electrochemistry kinetics, NiCoLDH/CC-1.5 exhibites a great capacitive and excellent rate performance of 1516.5 F g−1 at 1 A g−1 and 1073.75 F g−1 even at 20 A g−1. The assembled asymmetric supercapacitor demonstrates a favorable cycling stability (capacitance retention of 90.11 % after 10,000 cycles at 5 A g−1).

Introduction of bimetallic oxide-modified carbon nanotubes for boosting the energy storage performance of NiCo-LDH based in-plane micro-supercapacitors on paper

In-plane micro-supercapacitors (IMSCs) have greater promise for use in flexible wearable electronics than traditional stacked configurations due to their ease of integration and conformability. Nickel-cobalt layered double hydroxide (NiCo-LDH) has garnered significant interest as a stellar material for supercapacitors because of its affordable price, regular morphology, and high theoretical capacity. Unfortunately, the intrinsic poor conductivity of LDH materials prevents supercapacitors from achieving long-term stable cycling and the desired energy density. This research successfully applies the self-templated approach to prepare carbon nanotubes (CNTs) with heterogeneous architectures and numerous phase interfaces, thereby mitigating this disadvantage. Carbon nanosheets adorned with WO2 and MoO2 nanoparticles assemble the CNT with a typical three-dimensional structure. When combined with LDH in a suitable ratio, the composite electrode’s conductivity significantly improves, providing increased capacity and cycling stability. Compared to commercial CNTs, the larger size of the prepared WO2/MoO2@P, N-CNTs serves a superior supporting and connecting role, thereby preventing the NiCo-LDH from aggregating. Under the best conditions, the composite electrode demonstrates a capacity of 1237 C/g at 1 A g−1 and an optimal capacity retention of more than 92%. For the IMSC devices, the composite materials as the positive electrode achieve an energy density of 0.0590 mWh cm−2, and no capacity degradation is observed after 10,000 cycles. In addition, bending tests have demonstrated the mechanical stability of the IMSCs. Therefore, this strategy of mixing highly conductive WO2/MoO2@P, N-CNTs can effectively improve the conductivity of the composite material and the mechanical properties of the overall device. Furthermore, this concept can be further extended to the preparation and application of other wearable devices.

Preparation and evaluation of S-rGO/ZnFe2O4/NiCoLDH nanocomposite electrocatalyst in oxygen reduction reaction

This study introduces a novel combination of sulfur-doped reduced graphene oxide (S-rGO), zinc ferrite (ZnFe2O4) and nickel cobalt layered double hydroxide (NiCoLDH) as an efficient and low-cost electrocatalyst for oxygen reduction reaction (ORR) for the first time. The hydrothermal method is used to synthesize all samples including graphene oxide (GO), S-rGO, NiCoLDH, ZnFe2O4 and S-rGO/ZnFe2O4/NiCoLDH hybrids. X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), energy dispersive x-ray analysis (EDX), electrochemical surface area (ECSA), and fourier transform infrared spectroscopy (FTIR) analysis are used to determine the structure of synthesized electrocatalysts, physical properties, and morphology. The electrochemical measurements are carried out using cyclic voltammetry (CV), linear scanning voltammetry (LSV), chronoamperometry (ChA), and electrochemical impedance spectroscopy (EIS). The results for all samples are compared with the Pt/C commercial catalyst. According to the electrochemical results, the S-rGO/ZnFe2O4/NiCoLDH electrocatalyst has the best electrochemical performance. Moreover, the nanocomposite exhibited better electrocatalysis, a high diffusion limiting current density of −5.4 mA cm−2 and an onset potential of 0.03 V. Based on the results of this study, the LDH enhances electrical conductivity, electrocatalytic activity, active surface area, and stability of the catalyst for ORR after combining with carbon bases and ferrite.

Efficient photocatalytic hydrogen production of Ni-Co layered double hydroxides (Ni-Co LDHs) anchored with reduced graphene oxide (rGO) hybrid composite

Using a suitable co-catalyst to boost photocatalytic H2 evolution from water splitting is crucial. Herein, we designed pristine NiCo-LDH and reduced graphene-oxide supported nickel-cobalt layered double hydroxide nanosheets (NiCo-LDH/rGO) as photocatalyst for the first time to evaluate the hydrogen production performance. Adding graphene has the potential to significantly increase electrical conductivity, and the supported NiCo-LDH has the potential to significantly reduce the likelihood of graphene self-aggregation. The effectiveness of its photocatalytic hydrogen generation was analyzed using a set of characterizations. The H2 evolution rates for pure rGO were 345.2 μmolh−1g−1, whereas those for Ni-Co LDH/rGO were 578.2 μmolh−1g−1. Average hydrogen generation per hour for the Ni-Co LDH/rGO composite material was 2032.1 μmolh−1g−1, which was 5.8 and 3.5 times that of rGO and Ni-Co LDH/rGO, respectively, NiCo-LDH@rGO's synergistic impact on the NiCo-LDH boosts the H2 generation pathway by increasing the catalyst's stability as well as performance by exposing active sites and speeding up electron transport. The produced nanocomposite shows excellent spatial charge separation and quicker electron transport across the conductive network of rGO, as shown by the photocurrent response test and photoluminescence (PL) spectra. The results of this study provide a fresh perspective on the practical use and synthesis of the inexpensive and effective NiCo-LDH/rGO, demonstrating the standard deviation of logical planning and preparation of high-performance photocatalysts.

Nickel aerogel @ ultra-thin NiCo-LDH nanosheets integrated freestanding film as a collaborative adsorption and accelerated conversion cathode to improve the rate performance of lithium sulfur batteries

It is a great challenge to develop freestanding ultralight cathodes for lithium–sulfur battery exhibiting good electrochemical performances. Herein, ultrathin porous nickel–cobalt layered double hydroxide (NiCo-LDH) nanosheets were grown on the surface of ultra-light nickel microwire aerogels (NMWAs), and there is capillary action in the gaps formed by the ordered arrangement due to the presence of magnetic filed in the preparation process, which has the advantages of synergistic adsorption and accelerated conversion kinetics of lithium polysulfide. Because of the abundant hydrophilic hydroxyl groups on the surface of NiCo-LDH and the capillary action of NMWAs, the integrated freestanding film cathode sulfur host (NMWAs@NiCo-LDH/S) provides excellent rate performance as well as cycling stability. The film cathode has an ultra-high initial specific capacity of 1238.4 mAh g−1 at 0.1C and an excellent reversible capacity of 805.8 mAh/g at 5.0C. Even after 700 cycles at a high current density of 5.0C, it still provides a reversible capacity of 647.1 mAh g−1 with a capacity decay rate of only 0.018 % per cycle. This work provides a simple and new way for the design of high rate lithium–sulfur battery film cathodes with good cycle stability.

Simple preparation of V-doped NiCo-LDH as cathode of high energy density supercapacitor

One of the most promising cathode materials for supercapacitors is nickel-cobalt layered double hydroxide (NiCo-LDH). Doping atoms are widely used to solve the problems of poor electrical conductivity and structural defects of electrode materials. Vanadium (V) has received widespread attention due to its multiple oxidation states and low cost. In this article, we use one-step hydrothermal method to synthesize V-doped NiCo-LDH (V-NC1.5). By regulating the doping amount of V, 2V-NC1.5 exhibits superb specific capacitance of 1835 F g−1 at 1 A g−1. An asymmetric aqueous supercapacitor was assembled with 2V-NC1.5 and activated carbon. Its maximum energy density can reach 60.9 Wh kg−1 at 800 W kg−1 of power density. When the two units are connected in series, they can effectively power a white LED bulb and maintain its brightness for more than 30 min. This result provides a potential opportunity for the efficient deployment of innovative energy storage technologies in the coming years.

Compositionally engineered NiCoLDH@rGO as bifunctional cathode catalyst for rechargeable Li-O2/Li-CO2 battery

Compositionally tuned nickel-cobalt layered double hydroxides (NCLDHs) and NCLDH@reduced graphene-oxide (NCLDH@rGO) were synthesized through a facile solvothermal synthesis route. The formation of the synthesized NCLDH and the NCLDH@rGO with the intercalated carbonate and nitrate anions, has been confirmed utilizing different characterization techniques. Microscopic results revealed the flaky morphology with thickness about 30 nm. Rotating ring disc electrode (RRDE) voltammetry was utilized to analyze the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO2RR) kinetics on each of the pristine (1:1), (2:1), (3:1) and (4:1) NCLDH catalysts and the NCLDH@rGO composites. The RRDE data revealed that the electrochemical activity towards ORR/OER/CO2RR could be largely increased by tuning mole ratio of the (Ni2+/Co3+) or the amount of the rGO in the NCLDH. It turned out that among the pristine electrocatalysts, the (1:1) NCLDH catalyst exhibited enhanced ORR/OER kinetics. While the NCLDH acted as a catalyst center, the rGO provided conductive network that facilitated passable overpotential with increased current density for the ORR/OER/ CO2RR. Better adsorption of O2 and CO2 on the NCLDH@rGO catalyst also contributed for the electrocatalytic activity. Consequently, the NCLDH@rGO composites as cathode catalyst for Li-O2 battery in the CR2032 prototype coin-cell exhibited a stable open circuit voltage (OCV). Among the NCLDH@rGO composites, the NCLDH with 15 wt.% rGO (NCRGO15) exhibited a high discharge capacity of 3616 mAh g−1 at 50 Ag−1 for the Li-O2 battery and a discharge capacity of 45 mAh g−1 at a current density of 100 Ag−1 for the CR2032 coin-type Li-CO2 battery. As a practical use, a commercial 2.8 V green LED bulb was lit continuously for about 20 h using the fabricated Li-O2 battery that consisted of lithium anode and (1:1) NCLDH@rGO15 wt.% (NCRGO15) air-breathing cathode.

Effect of synthesis temperature on the structural morphology of a metal–organic framework and the capacitor performance of derived cobalt–nickel layered double hydroxides

Three-dimensional interconnected nickel–cobalt layered double hydroxides (NiCo-LDHs) were prepared on nickel foam by ion exchange using a cobalt-based metal–organic framework (Co-MOF) as a template at different temperatures. The effects of the Co-MOF preparation temperature on the growth, mass, morphology, and electrochemical properties of the Co-MOF and derived NiCo-LDH samples were studied. The synthesis temperature from 30 to 50 °C gradually increased the mass of the active material and the thickness of the Co-MOF sheets grown on the nickel foam. The higher the temperature is, the larger the proportion of Co3+. β-Cobalt hydroxide (β-Co(OH)2) sheets were generated above 60 °C. The morphology and mass loading pattern of the derived flocculent layer clusters of NiCo-LDH were inherited from metal-organic frameworks (MOFs). The areal capacitance of NiCo-LDH shows an inverted U-shaped curve trend with increasing temperature. The electrode material synthesized at 50 °C had a tremendous specific capacitance of 7631 mF·cm−2 at a current density of 2 mA·cm−2. The asymmetric supercapacitor assembled with the sample and active carbon (AC) achieved an energy density of 55.0 Wh·kg−1 at a power density of 800.0 W·kg−1, demonstrating the great potential of the NiCo-LDH material for energy storage. This work presents a new strategy for designing and fabricating advanced green supercapacitor materials with large power and energy densities.

Nickel-cobalt layer double hydroxide @ lignin-based hollow carbon quasi core-shell structure for high-performance supercapacitors

The physicochemical properties of an advanced supercapacitor electrode material can be co-tailored by incorporating various active materials into a hierarchical micro-/nano-architecture with a core-shell structure. Herein, we presented the development of high-performance supercapacitor electrode materials of quasi core-shell architectures based on nickel-cobalt layered double hydroxides supported on lignin-based hollow carbon (NiCoLDH@LHC) nanocomposites. The synthesis involves a novel approach combining enzymatic hydrolysis lignin (EHL) as a carbon source and magnesium oxide (MgO) as a template, utilizing evaporation-induced self-assembly (EISA) followed by carbonization. The manipulation of the mass ratio of NiCoLDH/LHC can induce alterations in its apparent morphology, stratified porosity, and active site, thereby an influence on its electrochemical performance. The optimal NiCoLDH@LHC90 nanocomposites display a unique flower-like spherical structure with open pores, a substantial specific surface area (SSA), and numerous electrochemically active sites. In addition, the density functional theory (DFT) calculations demonstrate that the higher density of Ni3+/Co3+ cations induced by the incorporation of LHC can increase the conductivity of NiCoLDH materials. Notably, these nanocomposites exhibit a remarkable specific capacitance of up to 640 C g−1 at 1 A g−1, with exceptional cycling stability (93.66% retention over 10,000 cycles). Furthermore, an assembled NiCoLDH@LHC90//LHC asymmetric supercapacitor demonstrates an impressive energy density (power density) of 35.44 Wh kg−1 (200.01 W kg−1). The physicochemical properties of an advanced supercapacitor electrode material can be finely tuned by incorporating various active materials into a hierarchical micro-/nano-architecture with a core-shell structure.

C3N4 improved nickel-cobalt layered double hydroxide (NiCoLDH) supercapacitive property

A flower-like composite of NiCoLDH/C3N4 is prepared using a simple one-step hydrothermal method. The morphologies and structure information of samples are observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties are measured by an electrochemical workstation and Land. The effects of the C3N4 mass loading on the capacitance of NiCoLDH/C3N4 composite are studied. The results show that the NiCoLDH/C3N4 composite exhibits a flower-like morphology and presents an impressive specific capacitance of 2677 F g−1 at 1 A g−1 for the optimized sample with C3N4 mass loading of 5 mg, higher than that of the pristine NiCoLDH (1676 F g−1). In addition, the assembled NiCoLDH/C3N4//YP50 supercapacitor device could achieve a maximum energy density of 33 Wh kg−1 and show a good capacitance retention of 97 % after 9000 cycles.