Porous Ni/NiO nanohybrids for electrochemical catalytic glucose oxidation

The remarkable development of nanotechnology and nanoscience has greatly promoted the vigorous development of the field of nanomaterials. This study explores a porous cuboid Ni/NiO composite nanomaterial obtained by calcining NiC_2O_4·2H_2O under a N_2 environment. The composite affords direct electrochemical activity and good electrocatalytic properties. Compared to uncalcined precursor, the porous Ni/Ni O obtained after calcination exhibited higher catalytic activity for glucose oxidation with higher sensitivity. Moreover, because of its regular cube structure the as-synthesized Ni/Ni O exhibited improved electrochemical stability. Such porous Ni/Ni O nanocubes represent promising glucose catalyst with high sensitivity and selectivity, improved stability and fast amperometric response.     

Improving biomass-derived carbon with cobalt/cobalt oxide doping for oxygen reduction reaction

Journal of Solid State Electrochemistry - Biomass-derived carbons from cypress leave, vegetable sponge, and pine needle were successfully prepared. They present three dimensional honeycomb...     

黑磷夹层氧化钴纳米片构筑电催化水氧化的仿生通道

不论在自然光合作用系统中,还是在人工能量转换系统如电解水制氢、二氧化碳还原、电化学固氮和金属空气电池中,析氧反应(OER)均是一个非常重要的半反应.OER具有多电子、多质子的特性,反应过程复杂且动力学缓慢.在自然界水氧化过程中,光合系统Ⅱ中的氨基酸残基构筑了专门的质子转移通道和电子转移通道,通过质子耦合电子转移来高效输...     

Synthesis,characterizations, and electrochemical studies of ZnO/reduced graphene oxide nanohybrids for supercapacitor application

Herein the present article reports the fabrication of ZnO/reduced graphene oxide (ZnG) nanohybrid following a reduction-based process using a non-hazardous material, i.e., ascorbic acid. The morphology, structure, and bonding in the nanohybrid were analyzed using different techniques. Atomic force microscopy and scanning electron microscopy images show spherical particles of ZnO distributed over reduced graphene oxide (rGO). The X-ray diffraction analysis gives calculated values of crystallite size for ZnO as 15.62 nm. The successful incorporation of ZnO nanoparticles into rGO was confirmed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. The electrochemical studies were performed using an electrolyte (0.5 M H₂SO₄). The calculated value of specific capacitance for the nanohybrid was 345 Fg^-1, which was found to be almost double as compared to that of rGO, which is having a value of only 190.5 Fg^-1 at the same scan rate. The nanohybrid also showed excellent capacitance retention after 1,000 cycles.     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

The effect of aluminium oxide on the reduction of cobalt oxide and thermostabillity of cobalt and cobalt oxide

During precipitation and calcination at 200°C nanocrystalline Co₃O₄ was obtained with average size crystallites of 13 nm and a well developed specific surface area of 44 m² g^?1. A small addition of a structural promoter, e.g. Al₂O₃, increases the specific surface area of the cobalt oxide (54 m² g^?1) and decreases the average size of crystallites (7 nm). Al₂O₃ inhibits the reduction process of Co₃O₄ by hydrogen. Reduction of cobalt oxide with aluminium oxide addition runs by equilibrium state at all the respective temperatures. The apparent activation energy of the recrystallization process of the nanocrystalline cobalt promoted by the aluminium oxide is 85 kJ mol^?1. Aluminium oxide improves the thermostability of both cobalt oxide and the cobalt obtained as a result of oxide phase reduction.      

CeOx-supported monodispersed MoO3 clusters for high-efficiency electrochemical nitrogen reduction under ambient condition

Developing efficient and low-cost electrocatalysts is essential for the electroreduction of N₂ to NH₃.Here,highly monodispersed MoO₃ clusters loaded on a coral-like CeO_xcompound with abundant oxygen vacancies are successfully prepared by an impregnation-reduction method.The MoO₃ clusters with small sizes of 2.6±0.5 nm are induced and anchored by the oxygen vacancies of CeO_x,resulting in excellent nitrogen reduction reaction(NRR)performance.Additionally,the synergistic effects between MoO₃ and CeO_xlead to a further improvement of the electrochemical performance.The as-prepared MoO₃-CeO_xcatalyst shows an NH₃ yield rate of 32.2 μg h^-1 mg^-1 cat and a faradaic efficiency of 7.04%at-0.75 V(vs.reversible hydrogen electrode)in 0.01 M Dulbecco’s Phosphate Buffered Saline.Moreover,it displays decent electrochemical stability over 30,000 s.Besides,the electrochemical NRR mechanism for MoO₃-CeO_xis investigated by in-situ Fourier transform infrared spectroscopy.N-H stretching,H-N-H bending,and N-N stretching are detected during the reaction,suggesting that an associative pathway is followed.This work provides an approach to designing and synthesizing potential electrocatalysts for NRR.     

Calculated phase diagrams for the electrochemical oxidation and reduction of water over Pt(111)

Ab initio density functional theory is used to calculate the electrochemical phase diagram for the oxidation and reduction of water over the Pt(111) surface. Three different schemes proposed in the literature are used to calculate the potential-dependent free energy of hydrogen, water, hydroxyl, and oxygen species adsorbed to the surface. Despite the different foundations for the models and their different complexity, they can be directly related to one another through a systematic Taylor series expansion of the Nernst equation. The simplest model, which includes the potential only as a shift in the chemical potential of the electrons, accounts very well for the thermochemical features determining the phase-diagram.     

Chemical and electrochemical oxidation and reduction of dithizone

A non-aqueous electrochemical study of dithizone, H₂Dz, 1, is compared with the chemical oxidation and reduction profile of this versatile ligand. Chemical oxidation of 1 by I₂ initially leads to an isolatable disulfide-bridged species, (HDz)₂, 2₂, but ultimately monomeric dehydrodithizone, Dz, 3, is formed. Electrochemically, in CH₂Cl₂/0.1 mol dm⁻³ [N(ⁿBu)₄][B(C₆F₅)₄], two oxidation processes are observed for 1. Evidence of the electrochemical formation of the dimer 2₂ was found, but on a CV timescale the fully oxidized species, 2_2oxidized, did not convert to the chemically stable species 3. Regeneration of 1 during an irreversible electrochemical reduction of the electrochemically generated fully oxidized species, 2_2oxidized, was detected. Two further one-electron electrochemical irreversible reduction steps were also identified to ultimately generate H₃Dz⁻, 8, one of the synthetic precursors to 1. In contrast, resolution and identification of the electron transfer steps of 1 in both dimethylsulfoxide, DMSO, or in CH₂Cl₂/0.1 mol dm⁻³ [N(ⁿBu)₄][PF₆] were hampered by solvation and ion paring of [PF₆]⁻ especially with the oxidized species of 1. A metathesis of water-soluble potassium dithizonate, KHDz, 4b, led to lipophilic [N(ⁿBu)₄][HDz], 4c.     

Kinetics of p-xylene oxidation catalyzed by cobalt oxide

Kinetics of p-xylene oxidation in an aqueous system catalyzed by cobalt oxide have been studied at 140 °C under oxygen. The reaction is second order in p-xylene and first order in cobalt oxide concentration. The rate constant and product distribution are very close to those found for homogeneous catalytic reactions. Based on these findings, a reaction scheme describing the influence of oxide catalyst is formulated. - , , 140° C . - . , . , .     

Design of Fe-MOF-bpdc deposited with cobalt oxide (CoOx) nanoparticles for enhanced visible-light-promoted water oxidation reaction

Research on Chemical Intermediates - This work spotlights the facile method to deposit cobalt oxide (CoOx) nanoparticles as a cocatalyst on Fe-MOF-bpdc to enhance its photocatalytic activity for...     

Enhanced activity of gold-supported cobalt oxide for the electrochemical evolution of oxygen

Scanning electron microscopy, linear sweep voltammetry, chronoamperometry, and in situ surface-enhanced Raman spectroscopy were used to investigate the electrochemical oxygen evolution reaction (OER) occurring on cobalt oxide films deposited on Au and other metal substrates. All experiments were carried out in 0.1 M KOH. A remarkable finding is that the turnover frequency for the OER exhibited by ～0.4 ML of cobalt oxide deposited on Au is 40 times higher than that of bulk cobalt oxide. The activity of small amounts of cobalt oxide deposited on Pt, Pd, Cu, and Co decreased monotonically in the order Au > Pt > Pd > Cu > Co, paralleling the decreasing electronegativity of the substrate metal. Another notable finding is that the OER turnover frequency for ～0.4 ML of cobalt oxide deposited on Au is nearly three times higher than that for bulk Ir. Raman spectroscopy revealed that the as-deposited cobalt oxide is present as Co(3)O(4) but undergoes progressive oxidation to CoO(OH) with increasing anodic potential. The higher OER activity of cobalt oxide deposited on Au is attributed to an increase in fraction of the Co sites present as Co(IV) cations, a state of cobalt believed to be essential for OER to occur. A hypothesis for how Co(IV) cations contribute to OER is proposed and discussed.     

Nitrogen-doped Co3O4 nanowires enable high-efficiency electrochemical oxidation of 5-hydroxymethylfurfural

Developing highly efficient and cost-effective catalysts for electrochemically oxidizing biomass-derived 5-hydroxymethylfurfural（HMF） into value-added 2,5-furandicarboxylic acid（FDCA） is of great importance.Herein, we report a controllable nitrogen doping strategy to significantly improve the catalytic activity of Co₃O₄ nanowires for highly selective electro-oxidation of HMF into FDCA. The nitrogen doping leads to the generation of defects including nitrogen dopants and oxy...     

Simple chemical route for nanorod-like cobalt oxide films for electrochemical energy storage applications

We used a simple chemical synthesis route to deposit nanorod-like cobalt oxide thin films on different substrates such as stainless steel (ss), indium tin oxide (ITO), and microscopic glass slides. The morphology of the films show that the films were uniformly spread having a nanorod-like structure with the length of the nanorods shortened on ss substrates. The electrochemical properties of the films deposited at different time intervals were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The film deposited after 20 cycles on ss gave the highest specific capacity of 67.6 mAh g^?1 and volumetric capacity of 123 mAh cm^?3 at a scan rate 5 mV s^?1 in comparison to 62.0 mAh g^?1 and 113 mAh cm^?3 obtained, respectively, for its counterpart on ITO. The film electrode deposited after 20 cycles on ITO gave the best rate capability and excellent cyclability with no depreciation after 2000 charge–discharge cycles.     

Influence of addition of cobalt oxide on microstructure and electrochemical capacitive performance of nickel oxide

Ni–Co oxide nanocomposite was prepared by thermal decomposition of the precursor obtained via a new method—coordination homogeneous coprecipitation method. The synthesized sample was characterized physically by X-ray diffraction, scanning electron microcopy, energy dispersive spectrum, transmission electron microscope, and Brunauer–Emmett–Teller surface area measurement, respectively. Electrochemical characterization of Ni–Co oxide electrode was examined by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance measurements in 6-mol L⁻¹ KOH aqueous solution electrolyte. The results indicated that the addition of cobalt oxide not only changed the morphology of NiO but also enhance its electrochemical capacitance value. A specific capacitance value of 306 F g⁻¹ of Ni–Co oxide nanocomposite with n _Co = 0.5 (n _Co is the mole fraction of Co with respect to the sum of Co and Ni) was measured at the current density of 0.2 A g⁻¹, nearly 1.5 times greater than that of pure NiO electrode. Lower resistance and better rate capability can also be observed.     

Preparation of DNA-silver nanohybrids in multilayer nanoreactors by in situ electrochemical reduction, characterization, and application

Novel nanocomposite films containing DNA-silver nanohybrids have been successfully fabricated by combined use of the layer-by-layer self-assembly technique and an in situ electrochemical reduction method with the DNA-Ag+ complex as one of the building blocks. UV-vis absorption spectroscopy was employed to monitor the buildup of the multilayer films, which suggested a progressive deposition with almost an equal amount of the DNA-Ag+ complex in each cycle. The following electrochemical reduction of silver resulted in the formation of metal nanoparticles in the film, which was evidenced by the evolution of the intense plasmon absorption band originating from silver. Scanning electron microscopy indicated that the particles formed in the multilayer films possessed good monodispersity and stability, thanks to the surrounding polymers. X-ray photoelectron spectroscopy further confirmed the presence of the main components (such as DNA and metallic silver) of the nanocomposite films. In addition, we show that the size of the metal nanoparticles and the optical property of the film could be readily tuned by manipulating the assembly conditions. Furthermore, the feasibility of the as-prepared nanocomposite films functioning as a surface-enhanced Raman scattering active substrate for sensing purposes was investigated, and the results showed great enhancement of the Raman signal of two probe molecules, Rhodamine 6G and 4-aminothiophenol.     

In situ XRD study of nanocrystalline cobalt oxide reduction

The reduction of nanocrystalline cobalt oxide samples (single-phase and supported on γ-Al₂O₃) was studied using in situ X-ray diffraction (XRD) analysis. The atomic structures of single-phase and supported Co₃O₄ samples were refined, and the occurrence of cationic vacancies was demonstrated. A set of methods (XRD, temperature-programmed reduction, and differential dissolution) was used to find that the reduction of supported and unsupported model cobalt oxide was considerably different. The single-phase sample was reduced in undiluted hydrogen to cobalt metal with a hexagonal closely packed structure. The reduction of the supported sample (unlike the single-phase sample) occurred through the formation of a crystalline CoO phase to the formation of cobalt metal with a face-centered cubic structure. Interaction of cobalt oxide with the γ-Al₂O₃ support, which hinders the reduction to cobalt metal, was detected.     

Electrochemical reduction of graphene oxide and its electrochemical capacitive performance

A convenient method for the production of graphene is developed using the electrochemical reduction of graphite oxide (GO) in solution without assembling it onto the electrode. The samples were examined by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results show that the number of oxygen functional groups can be significantly decreased. The electrochemical capacitance of the prepared graphene after 8 h of reduction is 158.5 F g^?1 at 0.5 A g^?1, much higher than that of GO and carbon nanotubes. The mechanism for this reaction is also proposed in this paper.     

Synthesis and separation of mellitic acid and graphite oxide colloid through electrochemical oxidation of graphite in deionized water

Electrochemical oxidation of graphite anode in deionized water at galvanostatic mode is investigated. It is found that mellitic acid and graphite oxide colloid (>20 nm) are coexisted as main products, as identified by XRD and TEM, FTIR and XPS. They can be separated successfully through several procedures. A few amounts of graphene and graphene rolls are also appeared as co-products.