Controllable reduction of NiCoO2@NiCo core-shell nanospheres on CNTs for high-performance electrochemical energy storage

The performances of energy storage devices are strongly dependent on the electrode materials. Owing to the high theoretical capacity, NiCoO₂ is a promising transition metal oxide for supercapacitors. Despite many efforts have been devoted, it still lacks of effective methods to overcome its shortcomings such as low conductivity and poor stability, in order to achieve its theoretical capacity. Herein, utilizing the thermal reducibility of trisodium citrate and its hydrolyzate, a series of NiCoO₂@NiCo/CNT ternary composites in which NiCoO₂@NiCo core-shell nanospheres deposited on CNT surface with adjustable metal contents are synthesized. Benefiting from the enhanced synergistic effect of both metallic core and CNTs, the optimized composite exhibits an extremely high specific capacitance (2660 F g^-1 at 1 A g^-1, the effective specific capacitance of the loaded metal oxide is 4199 F g^-1, close to the theoretical value), an excellent rate performance and stability, when the metal content is about 37%. After depolarized calculation, the energy storage mechanism of the composite is reasonably analyzed. By controlling the contents of hexamethylenetetramine, trisodium citrate and CNTs in the reactant, the roles of them are distinguished. This study reveals an efficient novel strategy for transition metal oxides to maximize the electrochemical performances.

Facile synthesis of mesoporous nano Ni/NiO and its synergistic role as super adsorbent and photocatalyst under sunlight irradiation

Tailoring a material that has a synergistic role as an adsorbent and a photocatalyst for environmental application is an attractive field for research. This article presents a study of facile synthesis of NiO and Ni/NiO with a synergistic role as super adsorbents in the lake of light and photocatalysts under light irradiation. Nano flower-like mesoporous NiO and Ni/NiO were synthesized by the co-precipitation method. XRD, SEM, EDAX, XPS, BET, and DR/UV-Vis spectroscopy techniques were employed for samples' analysis. The point of zero surface charge of prepared samples was detected by the batch equilibrium method. The adsorption efficiency was investigated in the absence of light using aniline blue as a pollutant model dye. The synergistic effect as an adsorbent and a photocatalyst was investigated under UV and sunlight irradiation. Different parameters affecting the adsorption in the dark have been optimized. The results showed that in the absence of light, the prepared samples are super adsorbents with a maximum adsorption capacity ranging from 210 to 230 mg g-1 and a removal % ranging from 95 to 100% within 2 h. Under UV or sunlight irradiation, the adsorbent/photocatalyst attained a dye removal % of 99.8% within 30 min. The adsorption data matched the pseudo-second-order model, and the equilibrium adsorption data showed compatibility with Langmuir model. The findings of experiments revealed that the adsorption is spontaneous, exothermic, and results in less entropy. Under sunlight irradiation, the dye removal efficiency increased by 19% in the case of Ni/NiO hybrid; it showed a removal efficiency of 99.5% within 30 min under sunlight irradiation versus 80% after 120 min in the dark.

Simultaneous removal of organic and inorganic pollutants from water by Ni/NiO/SnO2 nanoparticles

Herein, we report a facile synthesis of Ni/NiO/SnO₂ hybrids where the core-shell-type Ni/NiO nanoparticle is decorated with the SnO₂ nanoparticle to make a heterojunction and their potential evaluation for simultaneous removal of organic and inorganic pollutants. The metallic nickel core of the nanoparticle helps to separate easily from water magnetically and restricts the possible secondary contamination. The formation of semiconductor-semiconductor heterojunction enhances the photocatalytic activity to degrade the organic pollutants. The nanomaterial was characterized using microscopic, spectroscopic, and BET analyses. Results indicated an efficient degradation of ~ 94% of crystal violet in 40 min. An adsorption capacity of ~ 530 mg g^-1 and ~ 650 mg g^-1 of cadmium and lead ions, respectively, was found for single-component adsorption experiments, and ~ 520 mg g^-1 and ~ 720 mg g^-1 of cadmium and lead ions, respectively, were found for multi-component experiments. This observation suggested that the lead and cadmium ion adsorption process is affected by the synergistic and antagonistic effects, respectively. However, no significant change in the photocatalytic activity was observed for multi-component experiments. Results indicated that the process followed the Langmuir isotherm and pseudo-second-order kinetics irrespective of the number of pollutants present. An excellent adsorption capacity of metal ions and photodegradation capability of organic dye in multi-component solution, and possible reusability of the nanoparticle, make the Ni/NiO/SnO₂ a potential material for simultaneous removal of organic and inorganic pollutants.

A series of POM-based compounds by tuning coordination groups and spacers of ligands: electrocatalytic, capacitive and photoelectrocatalytic properties

A series of POM-based compounds can be used as amperometric detectors for NO2− and Cr(vi). They also have capacitive properties and can effect the high-efficiency photoelectrocatalytic degradation of organic dyes.

Rapid photocatalytic degradation of cationic organic dyes using Li-doped Ni/NiO nanocomposites and their electrochemical performance

This work reports novel bi-functional Li-doped Ni/NiO nanocomposites as potential candidates for energy storage and water treatment applications.

Nickel-Graphene Nanoplatelet Deposited on Carbon Fiber as Binder-Free Electrode for Electrochemical Supercapacitor Application

A binder-free process for the electrode preparation for supercapacitor application was suggested by drop casting graphene nanoplatelets on a carbon fiber (GnP@CF) followed by electrodeposition of Ni nanoparticles (NPs). The microstructure of the electrode showed that Ni was homogeneously distributed over the surface of the GnP@CF. XRD analysis confirmed the cubic structure of metallic Ni NPs. The Ni-GnP@CF electrode showed excellent pseudocapacitive behavior in alkaline solution by exhibiting a specific capacitance of 480 F/g at 1.0 A/g, while it was 375 F/g for Ni@CF. The low value of series resistance of Ni-GnP@CF (1 Ω) was attributed to the high capacitance. The enhanced capacitance of the electrode could be correlated to the highly nanoporous structure of the composite material, synergetic effect of the electrical double layer charge-storage properties of graphene, and the pseudocapacitive nature of Ni NPs.

Nickel(II) Nanoparticles Immobilized on EDTA-Modified Fe3O4@SiO2 Nanospheres as Efficient and Recyclable Catalysts for Ligand-Free Suzuki-Miyaura Coupling of Aryl Carbamates and Sulfamates

A highly efficient and air-, thermal-, and moisture-stable nickel-based catalyst with excellent magnetic properties supported on silica-coated magnetic Fe₃O₄ nanoparticles was successfully synthesized. It was well characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, dynamic light scattering (DLS), X-ray photoelectron spectroscopy, vibration sample magnetometry, energy-dispersive X-ray analysis, inductively coupled plasma analysis, and nitrogen adsorption-desorption isotherm analysis. The Suzuki-Miyaura coupling reaction between aryl carbamates and/or sulfamates with arylboronic acids was selected to demonstrate the catalytic activity and efficiency of the as-prepared magnetic nanocatalyst. Using the mentioned heterogeneous nanocatalyst in such reactions generated corresponding products in good to excellent yields in which the catalyst could easily be recovered from the reaction mixture with an external magnetic field to reuse directly for the next several cycles without significant loss of its activity.

Oxide-Carbon Nanofibrous Composite Support for a Highly Active and Stable Polymer Electrolyte Membrane Fuel-Cell Catalyst

Well-designed electronic configurations and structural properties of electrocatalyst alter the activity, stability, and mass transport for enhanced catalytic reactions. We introduce a nanofibrous oxide-carbon composite by an in situ method of carbon nanofiber (CNF) growth by highly dispersed Ni nanoparticles that are exsoluted from a NiTiO₃ surface. The nanofibrous feature has a 3D web structure with improved mass-transfer properties at the electrode. In addition, the design of the CNF/TiO₂ support allows for complex properties for excellent stability and activity from the TiO₂ oxide support and high electric conductivity through the connected CNF, respectively. Developed CNF/TiO₂-Pt nanofibrous catalyst displays exemplary oxygen-reduction reaction (ORR) activity with significant improvement of the electrochemical surface area. Moreover, exceptional resistance to carbon corrosion and Pt dissolution is proven by durability-test protocols based on the Department of Energy. These results are well-reflected to the single-cell tests with even-better performance at the kinetic zone compared to the commercial Pt/C under different operation conditions. CNF/TiO₂-Pt displays an enhanced active state due to the strong synergetic interactions, which decrease the Pt d-band vacancy by electron transfer from the oxide-carbon support. A distinct reaction mechanism is also proposed and eventually demonstrates a promising example of an ORR electrocatalyst design.

Synthesis, characterization and photocatalytic activity of mixed-metal oxides derived from NiCoFe ternary layered double hydroxides

Ternary NiCoFe mixed-metal oxides have demonstrated higher photoelectrocatalytic activity in degrading methylene blue (MB).