Ni-Co LDH Research Articles

Unique 3D flower-on-sheet nanostructure of NiCo LDHs: Controllable microwave-assisted synthesis and its application for advanced supercapacitors

Two-dimensional (2D) nanostructures, though promising in energy storage, suffer from aggregation and subsequent deterioration of performance in practical applications. Hence, assembly of 2D nanostructures into three-dimensional (3D) architectures is highly desirable. Here, we report a microwave-assisted approach to the controllable synthesis of 2D materials with tunable 3D structures simply by adjusting the ratio of water/ethylene glycol (H2O/EG). Novel flower-on-sheet 3D hierarchical structures of nickel cobalt double hydroxide (NiCo LDHs) are obtained at EG content of 40%, while microspheres and 2D nanosheets are obtained when the EG content is 0% and 75%, respectively. We propose that under microwave irradiation, EG molecules disperse the nuclei and facilitate the initial formation of 2D sheets. Subsequently, the dominating hydrophobicity of the assembling results in the formation of nanoflowers on the sheets. When tested as electrode materials in supercapacitors, the flower-on-sheet NiCo LDH exhibits superior capacitance (1187.2 F g−1 at 1 A g−1), good rate capability (71% retention at 30 A g−1), and high stability (only 0.3% cyclic decay per cycle with respect to the first charge capacitance), which is ascribed to that ‘sheet’ could act as buffer substrate while ‘flower’ expose more active site. Our results demonstrate an energy-saving and one-pot approach for controllable construction of 2D derived 3D nanostructure that can be applied in next-generation energy storage materials.

Room‐Temperature Ultrafast Synthesis of NiCo‐Layered Double Hydroxide as an Excellent Electrocatalyst for Water Oxidation

AbstractDesigning and synthesis of efficient, highly active with longer stability and earth abundant catalysts for the oxygen evolution reaction (OER) is urgent need for the electrochemical production of fuels. In this aspect, herein, facile room‐temperature electrodeposited NiCo layered double hydroxide (NiCo‐LDH) is reported as a highly active and stable electrocatalyst for OER in aqueous solution. In alkaline media, as obtained NiCo LDH shows superior electrocatalytic activity towards water oxidation with overpotential of 270 mV at 10 mA/cm2 with low Tafel slope of 61 mV/dec. The 3D NiCo‐LDH network exhibits excellent structural stability for 36 hours in alkaline media. After testing for stability test, the NiCo‐LDH catalyst maintains its hierarchical 3D network with insignificant degradation in the catalytic activity.

Flexible Textile-based Electrode Materials for Supercapacitors

Abstract In this work, a flexible textile-based electrode material is developed. The vertical array of Co-Ni layered double hydroxide (Co-Ni LDH) nanosheets are successfully assembled on the conductive graphene/cotton composite fabrics (G/CF) using a chemical deposition method. Taking advantages of the highly conductive, porous nature of G/CF and high specific capacitance of Co-Ni LDH, the Co-Ni(OH)2 layered double hydroxide/graphene/cotton composite fabrics (Co-Ni LDH/G/CF) as electrode materials show good flexibility and high electrochemical performances. The specific capacitance of the Co-Ni LDH/G/CF electrode material is determined to be 578 F g-1 at a scan rate of 5 mV s-1. It is believed that the Co-Ni LDH electrode material may have a promising application in the development of flexible energy storage devices.

Scalable nanohybrids of graphitic carbon nitride and layered NiCo hydroxide for high supercapacitive performance.

The limited number of edge nitrogen atoms and low intrinsic electrical conductivity hinder the supercapacitive energy storage applications of the nitrogen-rich graphitic carbon nitride (g-C3N4). In this study, a novel graphitic carbon nitride/NiCo-layered double hydroxide (CNLDH), a two-dimensional nanohybrid, is prepared by a simple hydrothermal synthesis. The homogeneous interpolation of g-C3N4 nanosheets into NiCo LDH stacked nanosheets effectively increases the overall performances of the g-C3N4/NiCo LDH nanohybrid. The improved morphology of the nanohybrid electrode upon the addition of g-C3N4 to the NiCo LDH yields a specific capacity of 183.43 mA h g−1 in 6 M KOH at 1 A g−1, higher than those of bare g-C3N4 (20.89 mA h g−1) and NiCo LDH (95.92 mA h g−1) electrodes. The excellent supercapacitive performance of the CNLDH nanohybrid is complemented by its low internal resistance, excellent rate capability, and large cycling lifetime. Furthermore, the hybrid supercapacitor is assembled using CNLDH 0.1 as a positive electrode and activated carbon (AC) as a negative electrode. The hybrid supercapacitor device of CNLDH 0.1//AC shows the maximum specific capacity of 37.44 mA h g−1 at 1 A g−1 with remarkable energy density, power density and good cycling performance. This confirms that the CNLDH 0.1 nanohybrid is an excellent electrode material for supercapacitor applications.

Identifying the active site of ultrathin NiCo LDH as an efficient peroxidase mimic with superior substrate affinity for sensitive detection of hydrogen peroxide.

Nanozymes have been extensively investigated to imitate protein enzymes in biomimetic chemistry and the identification of the active site is believed to be the pre-requisite before one can effectively regulate their activity. Herein, ultrathin NiCo LDH nanosheets are synthesized via a fast co-precipitation at room temperature and can be stably dispersed in water without any additives of surfactants or organic solvents. By tuning the ratio between Ni and Co in LDH nanosheets, the activity is tuned and their peroxidase-like activity is determined by Co sites that show higher affinity to both 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) due to the strong Lewis acidity of Co3+ and the low redox potential of Co3+/Co2+. Together with their small crystallite size, ultra-thin thickness and tunable composition, NiCo LDH is used as a nanozyme for highly sensitive colorimetric detection of H2O2 and the limit of detection (LOD) reaches 0.48 μM.

A High-Performance Three-Dimensional Hierarchical Structure MOF-Derived NiCo LDH Nanosheets for Non-Enzymatic Glucose Detection

Constructing a reasonable electrode material structure is significant for the sensitivity and selectivity of glucose detection. Herein, in this paper, the three-dimensional (3D) hierarchically layered double hydroxides (CC@CCH MOF LDH) is prepared by using carbon cloth (CC) as the conductive base, cobalt carbonate nanorod (CCH) as the guiding template and metal organic framework (MOF) as the sacrifice template. This unique 3D hierarchical structure facilitates the rapid transfer of ions and the reversible redox reaction. Moreover, the electrochemical tests confirm that the material has excellent electrocatalytic oxidation activity in alkaline solution. The amperometric detection results reveal that CC@CCH MOF LDH electrode material possesses better selectivity, higher sensitivity (4310 μA·mM−1·cm−2), fast amperometric response (<6 s), wide linear range (0.001-2 mM) and low detection limit (110 nM) under the optimal conditions, which is expected to be a high performance enzyme-free glucose sensor.

Binder–free of NiCo–layered double hydroxides on Ni–coated textile for wearable and flexible supercapacitors

Recently, the combination of nickel (Ni) and cobalt (Co) binary hydroxides have been regarded as a promising class of materials due to their excellent redox reversibility and relatively high capacity. In this work, we demonstrate Ni and Co layered double hydroxides (NiCo–LDHs) on Ni–coated textile for wearable supercapacitor (SC) applications. Ni–coated textile was used as flexible current collector and NiCo–LDH nanosheets were deposited on textile as a pseudocapacitive materials. The electrochemical performances of NiCo–LDHs have been evaluated and optimized by varying the mole ratio of Ni and Co via hydrothermal process. The NiCo–LDH electrodes with Ni:Co ratio of 3:7 has the maximum specific capacitance, which is attributed to the CoOOH by improving the conductivity and enlarged interlayer spacing with intercalation of NO3−. Moreover, solid–state NiCo–LDH SC exhibits a maximum volumetric energy density of 1.25 mWh cm−3 at a power density of 47.4 mW cm−3.

Hierarchical design of hollow Co-Ni LDH nanocages strung by MnO2 nanowire with enhanced pseudocapacitive properties

Core-sheath hierarchical-architectured materials have attracted much attention due to their extensive application in energy storage devices. However, as to multi-dimensional hierarchical core-sheath architectures, relative study has rarely been reported. In this work, a unique sugar gourd-like architecture is designed for the first time with hollow Co-Ni LDH nanocages uniformly strung by MnO2 nanowire (MnO2@Co-Ni LDH). Meanwhile, its forming mechanism is also systematically studied. Beneficial from this unique architecture, the designed MnO2@Co-Ni LDH possesses highly micro-structural integrity, abundant electrochemical-active sites and developed 3D diffusion path for electrolyte ions. When evaluated as positive electrode for pseudocapacitor, this material exhibits large specific capacitance of 1436 F g−1 at a current density of 1 A g−1, excellent rate capability (e.g., 1080 F g−1 at 20 A g−1) and high cycling stability (96.1% retention after 10,000 cycles). To assess practical functionality, a hybrid supercapacitor based on MnO2@Co-Ni LDH and active carbon nanoparticle is fabricated, which exhibits a high energy density of 40.9 Wh kg−1 along with remarkable long-term cyclic stability (81.8% retention after 20,000 cycles), demonstrating its potential application in the feld of energy storage devices. More importantly, the novel structural design can be easily extended to the synthesis of other functional materials for widespread applications.

Highly efficient removal of Cd(II) ions by composite of GO and layered double hydroxide composite

Herein, we report a novel nanocomposite (graphene oxide/Ni-Co LDH) via a simple and effective chemical precipitation route. First, the GO nanosheets were synthesized by Marcano method, and then, Ni-Co LDH sheets were deposited on the surface of GO by chemical precipitation. The synthesized nanocomposite was characterized by field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy and x-ray diffraction measurements. The prepared nanocomposite was investigated as an adsorbent for cadmium (II) ions removal from aqueous solutions. Batch studies have been done for obtaining optimal experimental conditions for maximizing metal sorption on the nanocomposite. The nanocomposite shows highest adsorption capacity toward Cd(II) in aqueous solution (126.58 mg g−1). The influence of experimental parameters like time of contact between adsorbent and adsorbate, pH, adsorbent dosage, initial heavy metal concentration and temperature on the removal efficiency of Cd(II) ions was extensively investigated. Kinetic and isotherm parameters of adsorption of Cd(II) were also evaluated. The pH = 7 was chosen as an optimal pH for study of the Cd(II) removal from aqueous solutions. Langmuir isotherm and pseudo-second-order kinetic models were fitted well with experimental data of Cd(II) removal. The reusability of nanocomposite exhibited reasonable values. However, the current nanocomposite could be used as a new adsorbate for adsorption of Cd(II) from contaminant water sources.

Unique NiFe NiCoO2 hollow polyhedron as bifunctional electrocatalysts for water splitting

Abstract It is of significance to design of stable and cost-effective electrocatalyst for water splitting with high efficiency in an alkaline medium. The major obstacles for practical application of water splitting devices are lack of high-efficiency and low-cost electrocatalysts with low overpotential for both HER and OER. In this paper, we report a NiFe alloy decorated NiCoO2 hollow polyhedron (denoted as NiFe NiCoO2) by using [NiFe(CN)6]− intercalated NiCo LDH as precursor. As evidenced by the electrochemical active surface area, the resultant NiFe NiCoO2 composite shows unique hollow nanostructure, which can not only provide abundant mass transport channels, but also increase the contact area of the NiFe NiCoO2 material with the electrolyte. The overpotential (η) demand is 286 mV for OER and 102 mV for HER at the current density of 10 mA/cm2 in an alkaline medium of 1 M KOH for the NiFe/NiCoO2 composite. This work provides a new pathway for preparation of the highly efficient bifunctional electrocatalysts for water splitting.

Hierarchical NiCo LDH–rGO/Ni Foam Composite as Electrode Material for High-Performance Supercapacitors

In this study, a bulk composite material symbolized as NiCo LDH–rGO/Ni F was developed by a solvothermal process for the first time. This material was fabricated through simultaneous growth of nickel–cobalt layered double hydroxide (NiCo LDH) and reduced graphene oxide (rGO) on nickel foam. This bulk composite can be used directly as a binder-free electrode for supercapacitors (SCs). The physicochemical properties of this composite were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The electrochemical properties of the composite were measured by the cyclic voltammetry and galvanostatic charge–discharge. The results show that this composite had a hierarchical structure and exhibited a significantly enhanced specific capacitance of up to 3383 F/g at 1 A/g. The asymmetric SC using this composite as a positive electrode had a high energy density of 40.54 Wh/kg at the power density of 206.5 W/kg and good cycling stability. Owing to the synergies between the metal oxides and the rGO, the preparation method of in situ growth and its hierarchical structure, this bulk composite displayed excellent electrochemical performance and had a promising application as an efficient electrode for high-performance SCs.

Cotton yarns modified with three-dimensional metallic Ni conductive network and pseudocapacitive Co-Ni layered double hydroxide nanosheet array as electrode materials for flexible yarn supercapacitors

A novel cotton/Ni/Co-Ni layered double hydroxide (CT/Ni/Co-Ni LDH) hybrid yarn electrode material is prepared by constructing a three-dimensional (3D) metallic Ni conductive network on the cotton fiber surface for rapid electron transportation and subsequently in situ growing Co-Ni LDH nanosheet array layers with high electroactive surface area for faradic reactions. The 3D porous electrode structure facilitates the effective electrolyte ion diffusion. The obtained yarn electrode material shows a high areal capacitance of 1.26 F/cm2 (121571.1 C/cm2) at a scan rate of 5 mV/s, as well as a stable electrochemical performance under various mechanical deformations. An all-solid-state yarn supercapacitor device is further assembled based on the obtained yarn electrode materials, which exhibits a high energy density of 9.3 μWh/cm2 at a power density of 43.99 μW/cm2.

A rational method to kinetically control the rate-determining step to explore efficient electrocatalysts for the oxygen evolution reaction

A novel, rational, and efficient way to explore high-performance electrocatalysts was developed by controlling the reaction kinetics of the rate-determining step (RDS). Density functional theory (DFT) calculations demonstrate that the RDS for the oxygen evolution reaction driven by transition metal hydroxides/oxides, i.e., surface adsorption of OH−/OOH• species, can be significantly promoted by increasing the electrophilicity of electrocatalysts via hybridization with electron-withdrawing inorganic nanosheets. As predicted by DFT calculation, the hybridization of Ni–Fe-layered double hydroxide (LDH)/Ni–Co-LDH, with RuO2 nanosheets (1.0 wt%) leads to significant lowering of the overpotentials to 207/276 mV at 10 mA cm−2, i.e., one of the smallest overpotentials for LDH-based materials, with the increase in the current density. The necessity of a very small amount of RuO2 nanosheets (1.0 wt%) to optimize the electrocatalyst activity highlights the remarkably high efficiency of the RuO2 addition. The present study underscores the importance of kinetic control of the RDS via hybridization with electron-withdrawing species for exploring novel efficient electrocatalysts.

Interlaced Ni-Co LDH nanosheets wrapped Co9S8 nanotube with hierarchical structure toward high performance supercapacitors

High electrochemical performance of supercapacitor electrodes largely rely on the smart design of nanoarchitectures with scrupulous combination of different active materials. We present a facile method for the multicomponent design of hierarchical Co9S8 hollow nanotubes (CS NTs) wrapped with Ni-Co layered double hydroxides nanosheets (Ni-Co LDH NSs) core-shell high-performance supercapacitors. The CS NTs serve as an ideal backbone with pentagonal cross-section to enhance the conductivity for acting as a “superhighway” for electron transport, whereas the Ni-Co LDH NSs with high electrochemical activity electrodeposited on the surface of CS NTs provide the electroactive sites and enhance the structural stability for faradaic reaction. The CS NTs@Ni-Co LDH NSs hierarchical electrode presents a high specific capacitance of 1020 C g−1 and high cycling stability of 90.4% after 10,000 cycles. Moreover, an asymmetric supercapacitor (ASC) was assembled with CS NTs@Ni-Co LDH NSs as the anode and active carbon as cathode. The as-fabricated ASC shows high energy density of 50 Wh kg−1 and exhibit superior cyclic stability of 86.4% retention over 5000 cycles, suggesting this electrode is promising for efficient electrochemical capacitors.

Preparation of one dimensional silver nanowire/nickel-cobalt layered double hydroxide and its electrocatalysis of glucose

A novel silver nanowire/nickel–cobalt layered double hydroxide (AgNW/NiCo LDH) nanocomposite was successfully synthesized, after which a glucose sensor was fabricated. AgNW was synthesized by ethylene glycol as reductant in presence of Fe3+, and NiCo LDH grafted vertically along the 1D AgNW by slow hydrolysis of urea. The morphology and composition of AgNW/NiCo LDH were characterized by Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical investigation showed that the AgNW/NiCo LDH/GCE exhibited excellent electrocatalytic ability to glucose oxidation, with a linear range from 0.002 mM to 6 mM at a low applied potential of 0.4 V (vs. SCE) and a low detection limit of 0.66 μM at the signal-to-noise ratio of 3. It is expected that the AgNW/NiCo LDH nanocomposites appear to be a promising catalyst for non-enzymatic glucose sensor.

Electrochemical measurements of 1D/2D/3DNi-Co bi-phase mesoporous nanohybrids synthesized using free-template hydrothermal method

In this study, a facile and low cost free-template hydrothermal precipitation method was used to synthesize mesoporous Ni-Co based bimetallic carbonates (CO3)2- and/or hydroxides (OH)−micro/nanostructures with different morphologies (1D, 2D and 3D) based on variant stoichiometric compositions. The effect of the growth temperature, synthesis time as well as the Ni/Co-precursors ratio on the physico-chemical properties and faradic electrochemical behavior of these products was investigated. The as-obtained bi-phase nanohybrids were characterized extensively structurally and morphologically. The textural analysis results confirmed the presence of mesoporous products with a BET-SSA ∼50 m2 g−1 (0.52 cm3 g−1 pore volume) for the 3D urchin-like structure and a BET-SSA ∼ 47.14 m2 g−1 (0.31 cm3 g−1 pore volume) was obtained for the 2D nanoflakes structure.The electrochemical measurements performed in a 6.0 MKOH aqueous electrolyte depicted excellent electrochemical performance ascribed to the optimized composition of Ni-Co LDH (or α-Ni(OH)2) with Co2(OH)3Cl and their unique hierarchical mesoporous nanoflake and urchin-like architectures. In addition, an exceptionally notable specific capacitances (capacities) of 1700 F g−1 (161 mAh.g−1) and 1379 F g−1 (192 mAh.g−1) were obtained for both structures at 5 mV s−1 scan rate (0.5 A g−1 gravimetric current density) respectively. These are much better than mono - hydroxides synthesized in same conditions with 351 F g−1 (90 mAh.g−1) for Ni and 216 F g−1 (21.5 mAh.g−1) for Co. A good cyclic stability of ∼98% after 2000 charge-discharge cycles at 30 A g−1 was recorded depicting their potential as suitable materials for energy storage devices.

High performance all-solid-state flexible supercapacitor for wearable storage device application

Flexible power packs combining a flexible photovoltaic part with a wearable all-solid-state supercapacitor as the self-sustaining energy system to power wearable device have attracted great interest due to the increasing demands for green energy and the tendency for multi-functionalization in electronics industry. To meet this energy requirement, we report an asymmetric all-solid-state supercapacitor, then integrate with commercial flexible solar cells to develop a self-sustaining power pack. In view of comfort for wearable electronics, cotton-textile radiation-proof clothes commonly used for pregnant woman cloth (PWC) are selected as the flexible substrate to construct wearable energy storage devices, which have the properties of flexible, green, renewable, breathable and excellent conductivity. Experimental tests demonstrate that the wearable asymmetric supercapacitors with high power density and relatively large energy density, fast charge/discharge capability, light-weight, excellent reliability and flexibility can enable the solar energy captured from the environment to afford a continuous and stable output of electric power and diminish the solar energy fluctuations. The supercapacitor is assembled with the Co–Ni layered double hydroxides (Co-Ni LDH) nanosheets as the positive electrode and the FeOOH as the negative electrode. Furthermore, the fabricated self-sustaining power pack as the energy source can continuously power the press sensor for monitoring the human physiological signals regardless of the sunlight fluctuation, demonstrating its potential usage in future wearable and portable electronic devices.

Nickel-cobalt layered double hydroxide ultrathin nanosheets coated on reduced graphene oxide nonosheets/nickel foam for high performance asymmetric supercapacitors

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDS), Brunauer, Emmett and Teller (BET) and electrochemical techniques such as voltammetry (CV), galvanostatic charge-discharge curves (GCD) and electrochemical impedance spectroscopy (EIS). The resulting electrode which prepared in the presence of CTAB afforded extremely high specific capacitance of 2133.3 F g−1 at a current density of 4 A g−1. FE-SEM, TEM and EDS mapping results showed that Ni-Co LDH nanosheets uniformly covered the surface of rGO/NF in the presence of CTAB, and is closely packed and thinner in thickness compared with the sample prepared in similar way without using surfactant. Such new thin and dense morphology facilitates electrolyte ions diffusion through the prepared electrode. A good cycling stability was obtained for the electrode in alkaline media. EIS measurements showed low values of internal resistance (Rs) and charge transfer resistance (Rct), indicating that the prepared nanocomposite is a promising candidate for supercapacitor applications. The asymmetric supercapacitor (ASC) based on the Ni-Co LDH/CTAB/rGO/NF as a positive electrode and rGO/NF as a negative electrode was assembled and it exhibited a Cs of 71.4 F g−1 at a current density of 2 A/g and correspondingly energy density of as high as 68 Wh kg−1.

Electrodeposited Ni[sbnd]Co layered double hydroxides on titanium carbide as a binder-free electrode for supercapacitors

We report the synthesized mixture of MXene and NiCo LDH on nickel foam by an electrodeposition technique. The specific capacitance of the mixture attained 983.6 F g−1 at a discharge current of 2 A g−1, which is greater than that of pure MXene. Compared to NiCo LDH, the sample created through electrodeposition provided a better rate capability of 983.6 F g−1 at 2 A g−1 and 536.6 F g−1 at 50 A g−1 and cycling stability with 76% retention after 5000 cycles at 30 A g−1. Moreover, a solid-state asymmetric supercapacitor with MXene-LDH as the positive electrode and multi-walled carbon nanotube coated on the nickel foam as the negative electrode delivers high energy density (36.70 Wh kg−1 at the power density of 1.44 kW kg−1), which outperforms the other devices reported previously.

Facile Synthesis of Ni-Co LDH Nanocages with Improved Electrocatalytic Activity for Water Oxidation Reaction

Facile Synthesis of Ni-Co LDH Nanocages with Improved Electrocatalytic Activity for Water Oxidation Reaction