Direct electrocatalytic reduction of hydrogen peroxide at a glassy carbon electrode modified with polypyrrole nanowires and platinum hollow nanospheres

A nonenzymatic sensor for hydrogen peroxide has been fabricated by dispersing platinum hollow nanospheres onto polypyrrole (PPy) nanowires to form a PPy-Pt hollow sphere nanocomposite on a glassy carbon electrode. The materials were characterized by transmission electron microscopy and scanning electron microscopy. The process and the sensor were characterized by electrochemical impedance spectroscopy, cyclic voltammetry, and chrono-amperometry and revealed that the electrode has a large electroactive surface area and small resistance to electron transfer. The linear range for the determination of hydrogen peroxide is from 3.5 µM to 9.9 mM, the detection limit is 1.2 µM (S/N?=?3), and the response time is 3 s. The electrode exhibited good stability and excellent repeatability.     

NiO@CuO@Cu bilayered electrode: two-step electrochemical synthesis supercapacitor properties

Present work deals with a two-step synthesis and electrochemical properties of nickel oxide @copper oxide@copper (NiO@CuO@Cu) bilayered electrode. In the first step, anodization (40 V for 25 min) of Cu foil has been carried out for forming Cu-hydroxide@Cu which when annealed at 300 °C for 1 h produces CuO@Cu. In the second step, Ni-hydroxide is deposited onto CuO@Cu by applying current density of 0.03 A/cm² for 3 min which when re-annealed at 300 °C for 1 h gives out NiO@CuO@Cu bilayered electrode. Obtained NiO@CuO@Cu bilayered electrode demonstrates separate CuO and NiO phases. The electrochemical properties have obtained using cyclic voltammetry, galvonostatic charge-discharge, and Nyquist plot measurements that reveal an importance of NiO@CuO@Cu as a potential electrode material in the electrochemical supercapacitor application with 58.14, 51.25, and 4.73 F g^?1 values in 0.5 M, NaOH, KOH, and Na₂SO₄ electrolytes, respectively, measured at 2 mVs^?1 scan rate.     

Electrochemical sensing and simultaneous determination of ascorbic acid,dopamine and uric acid at nickel nanoparticles/poly (1,2-diaminoanthraquinone) modified electrode

A highly sensitive sensor based on Ni nanoparticles/poly (1,2-diaminoanthraquinone) modified electrode was fabricated at glassy carbon (GC) electrode (Ni/PDAAQ@GC ME) using cyclic voltammetry technique. The incorporation of nickel (II) ions nanoparticles (Ni NPs) followed by anodic polarization process was achieved. Surface morphologies of both PDAAQ@GC ME and Ni/PDAAQ@GC MEs were studied by scanning electron microscope. Ni/PDAAQ@GC ME was tested for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) by square wave voltammetry technique. The ME showed excellent electrocatalytic activity toward electrooxidation of these biomolecules in their single, binary and ternary systems in alkaline 0.1 M NaOH solutions. Experiment revealed that the low detection limits (LOD) for AA, DA and UA were 0.11, 0.072 and 1.2 µM in single system, respectively, and 0.069, 0.29 and 0.12 µM in ternary system, respectively.     

NiO/CNTs derived from metal-organic frameworks as superior anode material for lithium-ion batteries

In this work, porous NiO microspheres interconnected by carbon nanotubes (NiO/CNTs) were successfully fabricated by the pyrolysis of nickel metal-organic framework precursors with CNTs and evaluated as anode materials for lithium-ion batteries (LIBs). The structures, morphologies, and electrochemical performances of the samples were characterized by X-ray diffraction, N₂ adsorption-desorption, field emission scanning electron microscopy, cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results show that the introduction of CNTs can improve the lithium-ion storage performance of NiO/CNT composites. Especially, NiO/CNTs-10 exhibits the highest reversible capacity of 812 mAh g^?1 at 100 mA g^?1 after 100 cycles. Even cycled at 2 A g^?1, it still maintains a stable capacity of 502 mAh g^?1 after 300 cycles. The excellent electrochemical performance of NiO/CNT composites should be attributed to the formation of 3D conductive network structure with porous NiO microspheres linked by CNTs, which benefits the electron transfer ability and the buffering of the volume expansion during the cycling process.     

Flower-like NiO microspheres prepared by facile method as supercapacitor electrodes

Hierarchical flower-like NiO microsphere was successfully synthesized by a simple one-step template-free hydrothermal process, using l-lysine as precipitator and nickel sulfate as nickel source. The as-synthesized materials were characterized by X-ray diffraction, field emission scanning electron microscope, high-resolution transmission electron microscope, and the electrochemical workstation. The electrochemical results show that the flower-like NiO microspheres exhibit specific capacitance as large as 324 F?g^?1 at the current density of 2 A?g^?1 and the specific capacitance retention can maintain 83 % after 1,000 cycles at the current density of 20 A?g^?1 in 6 M KOH.     

Surfactant-intercalated smectite modified electrode: sensitive electrochemical detection of methyl orange dye

This work describes the use of organosmectite modified electrode to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for the determination of methyl orange (MO) dye in natural water. Organosmectites were prepared by intercalation of hexadecyltrimethylammonium cations at various ratios into the interlayer of smectite. The synthesised organosmectites were characterised by various physicochemical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. An amperometric sensor based on organosmectite as electrode modifier for MO sensing purposes was then evaluated by means of clay-film modified electrode using square wave voltammetry (SWV). The electrochemical procedure for MO analysis by stripping voltammetry involves two successive steps: accumulation of MO at open circuit conditions followed by a voltammetric detection in a same medium by the SWV technique. The peak current obtained (after 5 min preconcentration of 15 µmol L^?1 MO solution) on a glassy carbon electrode coated by a thin film of the modified clay was more than 2.5 times higher than that exhibited by the same substrate covered by a film of the pristine clay. Under optimised conditions, a linear calibration curve for MO was obtained in the concentration range from 0.1 to 1.6 µmol L^?1, leading to a detection limit of 4 × 10^?8 mol L^?1 (signal-to-noise ratio equal to 3). The interfering effect of various inorganic and organic ions likely to influence the stripping determination of the MO was also examined. To further validate application of this sensor, the proposed method was successfully used to the determination of MO in natural water with satisfactory results.     

Electrochemical detection of selenium using glassy carbon electrode modified with reduced graphene oxide

In this work, a simple experimental procedure was reported for the electroanalytical determination of selenium (IV) using reduced graphene oxide (rGO) to modify glassy carbon electrode (GCE). The rGO was obtained by reduction of graphene oxide obtained via Hummer’s method. The synthesised rGO was characterised using X-ray diffraction, Raman spectroscopy, scanning electron microscope (SEM), energy-dispersive spectroscopy and transmission Electron microscopy (TEM). GCE was modified with rGO and the electrochemical properties of the bare and modified electrode were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The results obtained showed that the modified electrode exhibited more excellent electrochemical properties than the bare GCE. The optimum conditions for detection of selenium in water using square wave anodic stripping voltammetry were as follows: deposition potential ?500 mV, pH 1, pre-concentration time of 240 s and 0.1 M nitric acid was used as supporting electrolyte. The linear regression equation obtained was I (µA) = 0.8432C + 9.2359 and the detection limit was calculated to be 0.85 μg L^?1. However, Cu(II) and Cd(II) are the two cations that interfered in the analysis of selenium in water.

The sensor was also applied for real sample water analysis and the result obtained was affirmed with inductively coupled plasma optical emission spectroscopic method. It is believed that our proposed sensor hold promise for practical application.     

Prussian Blue/Reduced Graphene Oxide Composite for the Amperometric Determination of Dopamine and Hydrogen Peroxide

Prussian blue has significant application for the construction of electrochemical biosensors. In this work, Prussian blue-reduced graphene oxide modified glass carbon electrodes were successfully fabricated using electrochemical deposition. The high surface area of graphene oxide enhanced the deposition of Prussian blue and the resulting electrocatalytic activity. Infrared spectroscopy and scanning electron microscopy showed that the relatively porous Prussian blue was on the surface of reduced graphene oxide. Cyclic voltammetry showed that Prussian blue-coated reduced graphene oxide composite films improved electron transfer compared to Prussian blue films. The Prussian blue-reduced graphene oxide composite film provided higher response for the reduction of hydrogen peroxide and the oxidation of dopamine compared with the Prussian blue film due to synergistic effects between the reduced graphene oxide and Prussian blue particles. The sensitivity of the electrode was 0.1617 µA µM^?1 cm^?2. The linear dynamic range extended from 0.5 µM to 0.7 mM dopamine with a limit of detection equal to 125 nM. This work provided a versatile strategy for the design and construction of sensitive amperometric sensors with robust electrocatalytic behavior.     

Hierarchical nanocomposites of polyaniline scales coated on graphene oxide sheets for enhanced supercapacitors

The homogeneous polyaniline–graphene oxide (PANI-GO) nanocomposites were facilely assembled with a redox system in which cumene hydroperoxide (CHP) and iron dichloride (FeCl₂) acted as oxidant and reductant, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that PANI scales coated uniformly on the surface of GO sheets owing to the synergistic effect between the PANI and GO. The obtained PANI-GO nanocomposites exhibited improved electrochemical performance as an electrode material for supercapacitors compared with the pure PANI. The specific capacitance of the PANI-GO nanocomposites was high up to 308.3 F g^?1, much higher than that of the pure PANI with specific capacitance of 150 F g^?1 at a current density of 1 A g^?1 in 2 M H₂SO₄ electrolyte. The Raman and XPS results illustrated that enhanced electrochemical performance might be attributed to the π-π conjugation between the PANI and GO sheets.     

Electrodeposition of Ag nanoparticles on graphenized pencil lead electrode as a sensitive and low-cost sensor for iodate determination

In this study, a simple, sensitive and low-cost iodate electrochemical sensor based on graphenized pencil lead electrode (GPLE) modified with Ag nanoparticles (AgNPs) was presented. The GPLE was simply prepared via electrochemical exfoliation of pencil lead electrode (PLE) by applying an optimized potential in acidic media. Afterward, silver nanoparticles were electrochemically deposited on the surface of GPLE using chronoamperometry technique. The fabricated electrode was carefully characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) techniques. Electrochemical behavior and also the electrocatalytic performance of the modified electrode toward the reduction of iodate were studied in details using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The fabricated sensor responds efficiently to iodate over the concentration range of 0.05 to 75 mM with a detection limit of 0.017 mM and sensitivity of 0.26 µA µM^?1 cm^?2. Remarkably enhanced electrocatalytic performance of the modified electrode was ascribed to the synergistic effect of graphene-like nanostructures with high surface to volume ratio, excellent conductivity and also the excessive electrocatalytic behavior of silver nanoparticles. The modified electrode was successfully employed for the determination of iodate in table and sea salt samples.     

Electrochemical exfoliation and in situ carboxylic functionalization of graphite in non-fluoro ionic liquid for supercapacitor application

Simultaneous electrochemical generation and functionalization of nano-sized graphite from graphite had been carried out in a non-fluoroanion-based ionic liquid, namely, triethylmethylammonium methylsulfate (TEMAMS) containing water and acetonitrile (AN) in different weight ratios. The oxygen-based functional groups attached with the exfoliated material had been identified using Fourier transform infrared spectroscopy (FTIR), and morphological changes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A symmetrical supercapacitor was fabricated using the exfoliated nano-sized graphite, and the influence of surface functionalities on its performance was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge–discharge cycles (CC). The highest specific capacitance (C _sp) value of 140 F g^?1 at 0.25 A g^?1 was obtained in 1.0 M H₂SO₄, followed by aqueous TEMAMS (125 F g^?1), TEMAMS/acetonitrile (115 F g^?1), and TEMAMS (106 F g^?1) at 0.10 A g^?1.     

An electrochemical sensor for sensitive determination of nitrites based on Ag-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-graphene oxide magnetic nanocomposites

A functional Ag-Fe₃O₄-grapheme oxide magnetic nanocomposite was synthesized and used to prepare a nitrite sensor. Morphology and composition of the nanocomposites were characterized by a transmission electron microscope, UV-VIS spectroscopy, X-ray diffraction, and Fourier transform infrared spectra. Electrochemical investigation indicated that the nanocomposites possess excellent electrochemical oxidation ability towards nitrites. The sensor exhibited two linear ranges: one from 0.5 µM to 0.72 mM with a correlation coefficient of 0.996 and sensitivity of 1996 µA mM^?1 cm^?2; the other from 0.72 mM to 8.15 mM with a correlation coefficient of 0.998 and sensitivity of 426 µAmM^?1 cm^?2. The limit of detection of this sensing system was 0.17 µM at the signal-to-noise ratio of 3. Additionally, the sensor exhibited long-term stability, good reproducibility, and anti-interference.     

Synthesis of micro- and mesoporous carbon spheres for supercapacitor electrode

Micro- and mesoporous carbon spheres (MMCSs) are synthesized by the polymerization of colloidal silica-entrapped resorcinol/formaldehyde in the presence of ammonia as catalyst, followed by carbonization, sodium hydroxide (NaOH) etching to remove silica template, and potassium hydroxide (KOH) activation. The morphology and microstructure are characterized by scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption. The results show that a typical sample (denoted as MMCS-3) unites the characteristics of regular spherical shape (uniform diameters of 500 nm), high specific surface area (1,620 m² g^?1), large pore volume (1.037 cm³ g^?1), and combined micropores and mesopores (11.0 nm), which endows MMCS-3 good electrochemical performance. MMCS-3 as supercapacitor electrode shows a specific capacitance of 314 F g^?1 under a current density of 0.5 A g^?1 and low internal resistance of 0.2 Ω in 6 M KOH aqueous solution. The electrochemical capacitance still retains 198 F g^?1 at a high current density of 10 A g^?1. After 500 cycle numbers of galvanostatic charge/discharge at 0.5 A g^?1, MMCS-3 electrode still remains the specific capacitance of 301 F g^?1 with the retention of 96 %. This study highlights the potential of well-designed MMCSs as electrodes for widespread supercapacitor applications.     

Electrochemical performance of Yb-doped LiFePO4/C composites as cathode materials for lithium-ion batteries

LiFePO₄/C and LiYb_0.02Fe_0.98PO₄/C composite cathode materials were synthesized by simple solution technique. The samples were characterized by X-ray diffraction, scanning electron microscope, and thermogravimetric–differential thermal analysis. Their electrochemical properties were investigated by cyclic voltammetry, four-point probe conductivity measurements, and galvanostatic charge and discharge tests. The carbon-coated and Yb³⁺-doped LiFePO4 sample exhibited an enhanced electronic conductivity of 1.9 × 10^?3 Scm^?1, and a specific discharge capacity of 146 mAhg^?1 at 0.1 C. The results suggest that the improvement of the electrochemical performance can be attributed to the ytterbium doping, which facilitates the phase transformation between triphylite and heterosite during cycling, and the conductivity improvement by carbon coating.     

Linen fiber template-assisted preparation of TiO2 nanotubes: palladium nanoparticle coating and electrochemical applications

TiO₂ nanotubes were fabricated from TiF₄ precursors within the pore channels of the linen fiber templates, resulting in crystalline fabricated titanate nanotubes (f-TNTs) upon removal by calcination at 500–600 °C. The f-TNTs were formed by the aggregation of TiO₂ nanoparticles (NPs) with a diameter of 80 nm; the wall thickness and size of the f-TNTs can be controlled by adjusting the concentration of the TiF₄ precursor, time, temperature, and the size of the linen fibers respectively. After that, palladium (Pd⁽⁰⁾) NPs were coated on the surface of the f-TNTs (Pd/f-TNTs) by the chemical reduction method, using NaBH₄ as a reducing agent. The size of the Pd⁽⁰⁾ NPs is about 10–13 nm. The Pd/f-TNT nanocomposite is systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. The Pd/f-TNT nanocomposite-modified glassy carbon electrodes exhibited excellent electrocatalytic activity as well as amperometric determination of hydrazine, ascorbic acid, and dopamine; these electrochemical applications were carried out by cyclic voltammetry.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

Hydrothermally synthesized Ni(OH)<Subscript>2</Subscript>@Zn(OH)<Subscript>2</Subscript> composite with enhanced electrochemical performance for supercapacitors

Two kinds of electrode materials Ni(OH)₂ and Ni(OH)₂@Zn(OH)₂ composite are fabricated on nickel foam. Electrochemical experiments indicate Ni(OH)₂@Zn(OH)₂ composite deserves further study due to high specific capacitance and good cycle stability, so that it can achieve energy storage and conversion as much as possible. When the hydrothermal time is different, the electrochemical performance of the sample is also different. Accurately, samples can obtain better electrochemical performance at 15 h, and the maximum specific capacitance of Ni(OH)₂@Zn(OH)₂ is 7.87 F cm^?2 compared to Ni(OH)₂ (0.61 F cm^?2) at 5 mA cm^?2. Even at 50 mA cm^?2, specific capacitance is 5.24 F cm^?2 and rate capability is 66.6%. Furthermore, Ni(OH)₂@Zn(OH)₂-15 h loses 19.8% after 1000 cycles, revealing the composite has an outstanding stable cycle. These properties also indicate Ni(OH)₂@Zn(OH)₂-15 h is a promising electrode material.     

Fabrication,characterization of polyaniline intercalated NiO nanocomposites and application in the development of non-enzymatic glucose biosensor

Determination of glucose plays very important part in diagnostics and management of diabetes. Nowadays, determination of glucose is necessary in human health. In order to develop the glucose biosensor, polymer modified catalytic composites were fabricated and used to detect glucose molecules. In this work, NiO nanostructure metal oxide (NMO) was fabricated via thermal decomposition method and polyaniline (wt% = 2, 4 and 6) assisted nanocomposites (NiO/PANI) were also prepared. The morphology and structure of synthesized nanocomposites were characterized by UV–visible diffusion reflectance spectroscopy (UV–vis-DRS), Fourier transform- infra red spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption-desorption isotherm measurement. The modified NiO/6%PANI/GCE had higher catalytic activity toward the oxidation of glucose than NiO/GCE, PANI/GCE, NiO/2%PANI/GCE and NiO/4%PANI/GCE. This is due to the larger surface area of NiO/6%PANI nanocomposites provide a ploform for faster electron transfer to the detection of glucose. The constructed glucose biosensor have been exhibited a high sensitivity of 606.13 µA mM⁻¹ cm⁻², lowest detection limit of 0.19 µM, high selectivity, stability, simplicity and low cost for the quick detection of glucose in real sample as well.     

Thionine-functionalized graphene oxide,new electrocatalyst for determination of nitrite

In this work, thionine (Th) was assembled on the surface of graphene oxide as an electron transfer mediator using diazonium reaction (Th–GO). Then, Th–GO was characterized by different methods such as scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Afterward, Th–GO was used for the modification of carbon paste electrode. Several electrochemical methods including cyclic voltammetry, differential pulse voltammetry, and hydrodynamic amperometry were used to investigate the behavior of the modified electrode. Then, the role of the modified electrode for oxidation of nitrite has been studied. For this purpose, the effect of critical experimental parameters including step potential and pulse amplitude (in differential pulse voltammetry technique), applied potential, the rotating speed of the disk (in amperometry technique), and the solution pH was investigated. Under the optimized conditions, the currents were found to be linear with the nitrite concentration in the range 0.05–33.0 and 0.5–800 µmol L^?1 with detection limits of 0.02 and 0.2 µmol L^?1 using differential pulse voltammetry and hydrodynamic amperometry, respectively. The introduced modified electrode showed good repeatability (RSD% = 3.2) and reproducibility (RSD% = 4.7). This electrochemical sensor was exerted successfully for the determination of nitrite and nitrate in real samples including water and wastewater samples.     

Highly sensitive uric acid biosensor based on individual zinc oxide micro/nanowires

We describe the use of individual zinc oxide (ZnO) micro/nanowires in an electrochemical biosensor for uric acid. The wires were synthesized by chemical vapor deposition and possess uniform morphology and high crystallinity as revealed by scanning electron microscopy, X-ray diffraction, and photoluminescence studies. The enzyme uricase was then immobilized on the surface of the ZnO micro/nanowires by physical adsorption, and this was proven by Raman spectroscopy and fluorescence microscopy. The resulting uric acid biosensor undergoes fast electron transfer between the active site of the enzyme and the surface of the electrode. It displays high sensitivity (89.74 μA cm^?2 mM^?1) and a wide linear analytical range (between 0.1 mM and 0.59 mM concentrations of uric acid). This study also demonstrates the potential of the use of individual ZnO micro/nanowires for the construction of highly sensitive nano-sized biosensors.