Sensitivity Enhancement in Nickel Hydroxide/3D‐Graphene as Enzymeless Glucose Detection

A nickel hydroxide (Ni(OH)₂)/3D‐graphene composite is used as monolithic free‐standing electrode for enzymeless electrochemical detection of glucose. Ni(OH)₂ nanoflakes are synthesized by using a simple solution growth procedure on 3D‐graphene foam which was grown by chemical vapor deposition (CVD). The pore structure of 3D‐graphene allows easy access to glucose with high surface area, which leads to glucose detection with an ultrahigh sensitivity of 3.49 mA mM^?1 cm^?2 and a significant lower detection limit up to 24 nM. Cyclic voltammetry (CV) and potentionstatic mode is used for non‐enzymatic glucose sensing. The impedance and effective surface area have been studied well. The high sensitivity, low detection limit and simple configuration of Ni(OH)₂/three dimensional (3D)‐graphene composite electrodes can evoke its industrial application in glucose sensing devices.     

Facile In Situ Synthesis of Hierarchical Porous Ni/Ni(OH)2 Hybrid Sponges with Excellent Electrochemical Energy‐Storage Performances for Supercapacitors

Herein, we report the in situ growth of single‐crystalline Ni(OH)₂ nanoflakes on a Ni support by using facile hydrothermal processes. The as‐prepared Ni/Ni(OH)₂ sponges were well‐characterized by using X‐ray diffraction (XRD), SEM, TEM, and X‐ray photoelectron spectroscopy (XPS) techniques. The results revealed that the nickel‐skeleton‐supported Ni(OH)₂ rope‐like aggregates were composed of numerous intercrossed single‐crystal Ni(OH)₂ flake‐like units. The Ni/Ni(OH)₂ hybrid sponges served as electrodes and displayed ultrahigh specific capacitance (SC=3247 F g^?1) and excellent rate‐capability performance, likely owing to fast electron and ion transport, sufficient Faradic redox reaction, and robust structural integrity of the Ni/Ni(OH)₂ hybrid electrode. These results support the promising application of Ni(OH)₂ nanoflakes as advanced pseudocapacitor materials.     

无模板剂液相合成Ni(OH)2花状微球

采用一种简单的无模板剂液相合成方法制备了Ni(OH)2花状微球. 该Ni(OH)2花状微球由几十个相互连接的纳米片组成, 为α-Ni(OH)2和β-Ni(OH)2的混合晶型. 当溶液的其它条件固定时, Ni(OH)2花状微球的微观形貌随Ni(Ⅱ)浓度的变化而显著变化. 当溶液中Ni(Ⅱ)浓度为0.03 mol/L时, 花状微球粒径分布较均匀, 平均粒径约为2 μm, 微球由花瓣长度约为400 nm、厚度约为60 nm的纳米片花瓣组成. 通过观察反应过程中Ni(OH)2花状微球的微观形貌的变化, 提出了Ni(OH)2花状微球的纳米团聚-表面生长-表面溶解的形成机制.     

Three-dimensional roselike α-Ni(OH)2 assembled from nanosheet building blocks for non-enzymatic glucose detection

Glucose detection plays very important roles in diagnostics and management of diabetes. The search for novel catalytic materials with appropriate architectures is the key step in the fabrication of highly sensitive glucose sensors. In this work, α-Ni(OH)₂ roselike structures (Ni(OH)₂-RS) assembled from nanosheet building blocks were successfully synthesized by a hydrothermal method through the hydrolysis of nickel chloride in the mixed solvents of water and ethanol with the assistance of polyethylene glycol (PEG). The structure and morphology of the roselike α-Ni(OH)₂ were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and N₂ adsorption–desorption isotherm measurement. TEM and FE-SEM images showed that the synthesized Ni(OH)₂ was roselike and the size of the leaf-shaped nanosheet was about 5 nm in thickness, which leads to larger active surface areas and faster electron transfer for the detection of glucose. Compared with the bare GCE and bulk Ni(OH)₂/GCE, the Ni(OH)₂-RS/GCE had higher catalytic activity toward the oxidation of glucose. Under the optimal conditions, the Ni(OH)₂-RS/GCE offers a variety of merits, such as a wide linear response window for glucose concentrations ranging from 0.87 μM to 10.53 mM, short response time (3 s), a lower detection limit of 0.08 μM (S/N = 3), as well as long term stability and repeatability.     

Formation of β-nickel hydroxide plate-like structures under mild conditions and their optical properties

Nanostructural β-nickel hydroxide (β-Ni(OH)₂) plates were prepared using the microwave–hydrothermal (MH) method at a low temperature and short reaction times. An ammonia solution was employed as the coordinating agent, which reacts with [Ni(H₂O)₆]²⁺ to control the growth of β-Ni(OH)₂ nuclei. A trigonal β-Ni(OH)₂ single phase was observed by X-ray diffraction (XRD) analyses, and the crystal cell was constructed with structural parameters and atomic coordinates obtained from Rietveld refinement. Field emission scanning electron microscopy (FE-SEM) images revealed that the samples consisted of hexagonal-shaped nanoplates with a different particle size distribution. Broad absorption bands assigned as transitions of Ni²⁺ in oxygen octahedral sites were revealed by UV–vis spectra. Photoluminescence (PL) properties observed with a maximum peak centered in the blue-green region were attributed to different defects, which were produced during the nucleation process. We present a growth process scheme of the β-Ni(OH)₂ nanoplates.     

阳极氧化/GCD新工艺法制备镍基超级电容器薄膜电极

采用磷酸阳极氧化法在金属镍表面形成阳极氧化复合膜,在1 mol·L^-1氢氧化钾溶液中进行大电流密度恒流充放电(GCD)处理, 使基体表面形成一层多孔纳米花瓣状膜. 采用扫描电镜(SEM), X射线光电子能谱(XPS), X射线衍射(XRD)仪, 对膜的形貌、组成和结构进行了表征, 使用电化学工作站、电池寿命测试仪对该膜的电容特性进行了测试. 结果表明, 所制氧化膜由三维多孔纳米花瓣状的NiO、α-Ni(OH)₂和β-Ni(OH)₂构成, 该膜具有优异的电容特性, 其在电流密度为6.7 A·g^-1时,比电容量达1509 F·g^-1, 而当电流密度为66.7 A·g^-1时,比电容量为1120 F·g^-1 (为6.7A·g^-1时的74%).在电流密度为66.7 A·g^-1时, 经过2000次循环测试后比电容量基本保持不变.     

Exfoliated nickel hydroxide nanosheets for urea electrolysis

Two-dimensional nickel hydroxide nanosheets were synthesized by exfoliating surfactant intercalated layered nickel hydroxides and developed as electrocatalysts for urea electro-oxidation. The electro-oxidation of urea on Ni(OH)₂ nanosheet modified electrodes shows a decrease of 100 mV in overpotential and an enhancement in current density, which reaches ca.154 mA cm^{− 2} mg^{− 1}, by a factor of ca. 170 compared to bulk Ni(OH)₂ powder modified electrodes. The Ni(OH)₂ nanosheets have promising applications in urea-rich wastewater remediation, hydrogen production, electrochemical sensors, and fuel cells due to their ability to promote the urea electrolysis reaction.     

Nickel(II) compounds of a tri-amine mono-imine macrocycle: Preparations and structures of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II) compounds

Reduction of one imine function of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)nickel(II) with 1 molar proportion of NaBH₄ produces as the major product the tri-amine-mono-imine macrocyclic cation (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II), Ni(tm)]²⁺. Pairs of isomeric singlet ground state perchlorate and tetrachlorozincate salts of [Ni(tm)]²⁺ were prepared and the structures determined for the 1RS,8SR,11SR,12RS (labeled as β) and 1RS,8RS,11RS,12SR (labeled as α) tetrachlorozincate salts. Triplet ground state trans-β-[Ni(tm)(NCS)₂] and catena-trans-{β-Ni(tm)-NC-Ni(CN)₂-CN-}_n·2nH₂O have the macrocycle in planar coordination and α-[{Ni(tm)}₂(C₂O₄)](ClO₄)₂ has the macrocycle folded. With pentane-2,4-dione the compounds [β-Ni(tm)]·[α-Ni(tm)(acac)](ClO₄)₃ and [Ni(teta)]·[α-Ni(tm)(acac)](ClO₄)₃ (teta = C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with both square-planar and octahedral Ni(II) cations were prepared and the latter was structurally characterized. Isomerisation in solution of metastable α-[Ni(tm)]²⁺ to stable β-[Ni(tm)]²⁺ is extremely slow, even in base.     

Electrodeposition of three-dimensional Ni(OH)<Subscript>2</Subscript> nanoflakes on partially crystallized activated carbon for high-performance supercapacitors

Three-dimensional Ni(OH)₂ nanoflakes were prepared via a facile and cost-effective electrodeposition method using commercial activated carbon (AC) as substrate. Nitric acid treatment (NT) and partial crystallization (PC) by metal nickel catalysis were applied for AC. The effects of the oxygen-containing functional groups and the degree of crystallization on the electrochemical performance of the electrode were investigated. The resulting Ni(OH)₂/PC–NT–AC/nickel foam electrode exhibits distinct performance with a specific capacitance of 2971 F/g (scaled to the mass of active Ni(OH)₂) at a current density of 6 A/g. A high capacitance of 1919 F/g was still achieved even at 40 A/g, which is much higher than Ni(OH)₂/AC/nickel foam electrode and Ni(OH)₂/NT–AC/nickel foam electrode. The excellent performance of Ni(OH)₂/PC–NT–AC/nickel foam electrode can be attributed to the presence of large surface area and highly conductive PC–NT–AC network on nickel foam. This study presents an effective method to improve the dispersion and rate capability of Ni(OH)₂ nanostructure electrodes.     

Infrared study of magnesium–nickel hydroxide solid solutions

The IR spectra of the co-precipitated solid solutions Mg_xNi_1−x(OH)₂ were studied in the 4000–40 cm⁻¹ region. The spectra as a whole resemble those of Mg(OH)₂ and β-Ni(OH)₂, while certain differences are noted when compared with the spectra of the mechanically mixed samples Mg(OH)₂+β-Ni(OH)₂. Such a behavior may imply formations of mono-phase solid solutions which have a brucite-like crystal structure. The composition-dependent band shifts were observed for the fundamentals and this tendency is discussed in terms of polarization of the OH bond and partial covalency of the MO bonds. The gradual changes in band position of Mg_xNi_1−x(OH)₂ (1.00≥x≥0.00) were used to assign the IR active lattice modes of the solid solutions and to review the assignment of β-Ni(OH)₂.     

Electrochemical preparation of α-Ni(OH)2 ultrafine nanoparticles for high-performance supercapacitors

Well-dispersed nanoparticles of nickel hydroxide were prepared via a simple electrochemical method. Electrodeposition experiments were performed from 0.005 M Ni(NO₃)₂ bath at a constant current density of 0.1 mA cm^?2 on the steel cathode for 1 h. Recording the potential values during the deposition process revealed that the reduction of water has major role in the base electrogeneration at the applied conditions. The obtained deposit was characterized by the X-ray diffraction (XRD), infrared (IR), differential scanning calorimeter–thermogravimetric analysis, carbon–nitrogen–hydrogen (CHN), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The CHN, XRD, and IR analyses showed that the obtained deposit has α phase of Ni(OH)₂ with intercalated nitrate ions in its structure. Morphological characterization by SEM and TEM revealed that the prepared α-Ni(OH)₂ is composed of well-dispersed ultrafine particles with the size of about 5 nm. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry and galvanostatic charge–discharge tests. The electrochemical measurements showed an excellent supercapacitive behavior of the prepared α-Ni(OH)₂ nanoparticles. It was also observed that the α-Ni(OH)₂ ultrafine particles have better electrochemical characteristic and supercapacitive behavior than β-Ni(OH)₂ ultrafine nanoparticles, including less positive charging potential, lower E _a???E _c value, better reversibility, higher E _OER???E _a, higher utilization of active material, higher proton diffusion coefficient, greater discharge capacity, and better cyclability. These results make the α-Ni(OH)₂ nanoparticles as an excellent candidate for the supercapacitor materials.     

Nickel Hydroxide and Intercalated Graphene with Ionic Liquid Nanocomposite‐modified Electrode for Sensing of Glucose

A novel non‐enzymatic glucose sensor based on nickel hydroxide and intercalated graphene with ionic liquid (G‐IL) nanocomposite modified glass carbon electrode was fabricated. Scanning electron microscope, Fourier transform infrared spectra and energy dispersive X‐ray spectroscopy of the nanocomposite confirmed the morphology and ingredient of Ni(OH)₂ as well as G‐IL. Moreover, experimental results of cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry indicated the sensing properties of Ni(OH)₂ at Ni(OH)₂/G‐IL modified electrode towards the typical electrocatalytic oxidation process of glucose at 0.43 V in 0.10 M NaOH. The current response was linearly related to glucose concentration in a range from 0.5 to 500 μM with a detection limit of 0.2 μM (S/N = 3) and sensitivity of 647.8 μA mM^?1 cm^?2. The response time of the sensor to glucose was less than 2 s. This work may be expected to develop an excellent electrochemical sensing platform of G‐IL as a catalysis carrier.     

Nickel Hydroxide Nanoparticles on Screen‐printed Electrodes as an Impedimetric Non‐enzymatic Glucose Sensor

In this study, the electrodeposition of nickel hydroxide nanoparticles onto a screen‐printed electrode (Ni(OH)₂/SPE) is described. Ni(OH)₂/SPE is proposed as an alternative non‐enzymatic glucose sensor based on Electrochemical Impedance Spectroscopy (EIS) measurements.The SPEs were modified by the cathodic electrodeposition of nickel, from a solution containing 0.010 M Ni(NO₃)₂ and 1 M NH₄Cl, at −1.3 V for 60 seconds. The SEM images show a uniform distribution of nickel spherical nanoparticles, with 60 nm average particle size. However, such morphology is not observed when the electrodeposition occurs in the absence of NH₄Cl. The electrochemical properties of the sensor were carefully evaluated by Cyclic Voltammetry. Ni(OH)₂/SPE shows a remarkable electrocatalytic behavior towards the oxidation of glucose in 0.1 M KOH. EIS measurements were carried out for Ni(OH)₂/SPE and a single‐frequency impedance method is proposed as transduction principle for glucose determination. The analysis of each parameter of complex impedance was performed. The best linear response was obtained for the module of impedance (|Z|) in the range of 0–2 mM of glucose at 0.1 Hz (R²=0.992) with a slope of 0.137 KΩ⁻¹⋅mM⁻¹ of glucose. Finally, Ni(OH)₂/SPE was utilized for quantification of glucose in blood samples.     

Characterisation of redox states of Ni(La)-hydroxide films prepared via the sol-gel route by ex situ IR spectroscopy

Ni(La)-hydroxide films were prepared from aqueous colloidal solutions containing nickel sulfate and lanthanum acetate in the molar ratio 10:1. Two types of film were made by heating for 15 and 60?min at 300?°C. Thermogravimetry (TG) and X-ray diffraction (XRD) reveal that both films consist of NiO (bunsenite 40%) nanoparticles (particle size?～30?Å), the remainder being amorphous. IR spectroscopy showed that the amorphous phase comprised the α(II)-Ni(OH)₂ phase incorporating SO₄ ^2?, carboxylate and water species. Cyclic voltammetry (CV) in a 0.1?M LiOH electrolyte combined with in situ UV-VIS spectroscopy revealed that the colouring/bleaching changes, as a function of applied potential, differed considerably for the two types of film. Ex situ IR spectroelectrochemical measurements at near-grazing incidence angle conditions using P-polarised light (NGIA IR) were performed for films heated for 60?min in 0.1?M LiOH and 0.1?M tetramethylammonium hydroxide (TMAH) electrolytes and cycled 1402 and 1802 times. During the oxidation/reduction cycles the α(II)-Ni(OH)₂ phase transforms to the γ(III)-NiOOH phase, while the β(II)-Ni(OH)₂ did not develop. This explains the high cycling stability of Ni(La)-hydroxide films. The incorporation of TMA⁺ ions was observed from the ν(CH₃) stretching band intensities in the IR spectra of cycled films.     

Ball-milling processing of nanocrystalline nickel hydroxide and its effects in pasted nickel electrodes for rechargeable nickel batteries

Nanocrystalline Ni(OH)₂ powder synthesized by a chemical precipitation method was processed using the planetary ball milling (PBM), and the physical properties of both the ball-milled and unmilled Ni(OH)₂ were characterized by scanning electron microscopy (SEM), specific surface area, particle size distribution, and X-ray diffraction. It was found that the PBM processing could significantly break up the agglomeration, uniformize the particle size distribution, increase the surface area, decrease the crystallite size, and reduce the crystallinity of nanocrystalline β-Ni(OH)₂, which were advantageous to the improvement of the electrochemical activity of Ni(OH)₂. The ball-milled nanocrystalline (BMN) Ni(OH)₂ was then used to alter the microstructure of pasted nickel electrodes and improve the distribution of the active material in the porous electrode substrate. Electrochemical performances of pasted nickel electrodes with a mixture of BMN and spherical Ni(OH)₂ as the active material were investigated, and were compared with those of pure spherical Ni(OH)₂ electrodes. Charge/discharge tests showed that BMN Ni(OH)₂ addition could enhance the charging efficiency, specific discharge capacity, discharge voltage, and high-rate capability of pasted nickel electrodes. This performance improvement could be attributed to a more compact electrode microstructure, better reaction reversibility, and lower electrochemical impedance, as indicated by SEM, cyclic voltammetry, and electrochemical impedance spectroscopy. Thus, it was an effective method to modify the microstructure and improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of BMN Ni(OH)₂ to spherical Ni(OH)₂ as the active material.     

Spectroscopic study of nickel(II) hydroxide surface modifications induced by a small iron(III) addition

Comparative Auger electron spectroscopic data on the surface composition and depth profiling for -Ni(OH)₂ and Ni(OH)₂ coprecipitated with iron(III) (3 at.%) are given showing a non-uniform distribution of the latter. They are considered together with their structural characteristics obtained using Fourier transform infrared spectroscopy (both samples) and Mössbauer spectroscopy (Fe-containing sample). The results obtained provide an explanation for the specific behaviour of the Fe(III)-doped nickel(II) hydroxide in heterogeneous processes (adsorption, electrocatalysis).     

Surfactant effect on electrochemical-induced synthesis of α-Ni(OH)2

Nickel hydroxide films were electrosynthesized in the presence of different diluted surfactant solutions by galvanostatic electroprecipitation. Lamellar α-Ni(OH)₂ films are obtained using cationic surfactant cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS), and also neutral surfactant Tween® 80. The films were structurally and morphologically characterized by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy, and electrochemically by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The results evidenced that SDS remains intercalated between the lamellae of α-Ni(OH)₂. Albeit the presence of CTAB and Tween® 80, it was noticed in FTIR spectra that the surfactants did not intercalate. The morphology was affected by the presence of different surfactants. All studied surfactants displaced the oxidation potential (E _O) of Ni²⁺/Ni³⁺ process to less positive values. Also, the presence of surfactants improved the electrode charge efficiency and the charge response for the same number of moles of nickel ions deposited. The ratio of the charge and frequency change is 4.4 times bigger for films deposited with SDS when compared with pure α-Ni(OH)₂ films.     

Preparation of Ni/poly(1,5-diaminonaphthalene)-modified carbon paste electrode; application in electrocatalytic oxidation of formaldehyde for fuel cells

This paper deals with electrochemical oxidation of formaldehyde in alkaline solution with a new electrocatalytic system composed of carbon paste electrode coated with poly(1,5-diaminonaphthalene) (P-1,5-DAN) film containing incorporated Ni(II)/Ni(III) redox ions. The modifier layer of (P-1,5-DAN-Ni)(OH)₂ at the electrode surface acts as a catalyst for the oxidation of formaldehyde in 0.1-M NaOH solution. Cyclic voltammetric and chronoamperometric experiments showed that the formaldehyde can be oxidized at the surface of Ni/P-1,5-DAN-modified carbon paste electrode. In cyclic voltammetry studies, the peak current of the oxidation of nickel hydroxide in the presence of formaldehyde increases and is followed by a decrease in the corresponding cathodic current. The rate constant (k) for the chemical reaction between the formaldehyde and nickel hydroxide has been evaluated by chronoamperometry method. This polymeric-modified electrode can oxidize the formaldehyde with high current density (over 7 mA cm⁻²). Thus, it can be a candidate as an anode for fuel cell applications.     

Electrochemical Quartz Crystal Impedance Study of Glucose Oxidation on a Nickel Hydroxide Modified Au Electrode in Alkaline Solution

The electrochemical quartz crystal impedance (EQCI) technique has been applied to investigate glucose oxidation on bare and Ni(OH)₂‐modified Au electrodes in 0.2 mol L^?1 KOH aqueous solution. The EQCI responses suggest different contributions of H⁺‐release and OH^?‐incorporation reactions of the Ni(OH)₂‐film redox process in 0.2 mol L^?1 aqueous KOH at different potentials. Glucose adsorption on the Ni(OH)₂‐modified Au electrode was studied. A mechanism for potential cyclic redox process of glucose at Ni(OH)₂‐modified Au electrode is suggested, mainly based on a comparative EQCI analysis with direct glucose oxidation on bare gold and glucose ad‐/desorption on Ni(OH)₂ film.     

Controllable synthesis of NiC2O4·2H2O nanorods precursor and applications in the synthesis of nickel-based nanostructures

A controllable synthesis of NiC₂O₄·2H₂O nanorods precursor was obtained via the microemulsion-mediated solvothermal method and a further synthesis of β-Ni(OH)₂ nanorods, nickel oxide (NiO) sub-microtubes, Ni nanospheres and flower-like nickel complexes nanostructures by using the precursor. The morphologies and crystalline structures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and the X-ray powder diffraction (XRD). The morphologies and sizes of the precursors can be readily tuned by adjusting experimental parameters of the reverse microemulsion system. The synthesized β-Ni(OH)₂ nanorods composed of fine nanosheets shown excellent electrochemical performance as an electrode material in rechargeable battery systems.