A facile hydrothermal synthesis of graphene porous NiO nanocomposite and its application in electrochemical capacitors

Thermophysical Investigation of Multiform NiO Nanowalls@carbon Foam/1-Octadecanol Composite Phase Change Materials for Thermal Management

Multiform NiO nanowalls with a high specific surface area were constructed in situ on carbon foam (CF) to construct NiO@CF/OD composite phase change materials (CPCMs). The synthesis mechanism, microstructures, thermal management capability, and photothermal conversion of NiO@CF/OD CPCMs were systematically studied. Additionally, the collaborative enhancement effects of CF and multiform NiO nanowalls on the thermal properties of OD PCMs were also investigated. NiO@CF not only maintains the porous 3D network structure of CF, but also effectively prevents the aggregation of NiO nanosheets. The chemical structures of NiO@CF/OD CPCMs were analyzed using XRD and FTIR spectroscopy. When combined with CF and NiO nanosheets, OD has high compatibility with NiO@CF. The thermal conductivity of NiO@CF/OD-L CPCMs was 1.12 W/m·K, which is 366.7% higher than that of OD. The improvement in thermal conductivity of CPCMs was theoretically analyzed according to the Debye model. NiO@CF/OD-L CPCMs have a photothermal conversion efficiency up to 77.6%. This article provided a theoretical basis for the optimal design and performance prediction of thermal storage materials and systems.

The Microwave Facile Synthesis of NiOx@graphene Nanocomposites for Application in Supercapacitors: Insights into the Formation and Storage Mechanisms

Recently, the strategy of combining carbon-based materials with metal oxides to enhance the electrochemical performance of electrodes has been a topic of great interest, but research focusing on the growth and charge storage mechanisms of such hybrid electrodes has rarely been conducted. In this work, a simple, reproducible, low-cost, and fast microwave heating method was used to synthesize NiOx@graphene nanocomposites. NiOx@graphene nanocomposites were used as a model system for exploring the growth and charge storage mechanisms of the hybrid electrode materials due to their simple preparation process, good stability, low cost, and high specific capacitance. The effects of reaction conditions (the type of metal precursor and feeding ratio between the nickel precursor and graphene) on the formation mechanism of the electrodes were examined, and it was demonstrated that the microstructure and morphology of the electrode materials were metal precursor-dependent, which was directly related to the electrochemical performance of the electrodes. Our work provides a new affordable approach to the synthesis of, and experimental support for designing, hybrid electrode architectures with a high electrochemical performance for next-generation energy storage devices.

Wrinkled Flower-Like rGO intercalated with Ni(OH)2 and MnO2 as High-Performing Supercapacitor Electrode

This study reports a simple one-step hydrothermal method for the preparation of a Ni(OH)₂ and MnO₂ intercalated rGO nanostructure as a potential supercapacitor electrode material. Having highly amorphous rGO layers with turbostratic and integrated wrinkled flower-like morphology, the as-prepared electrode material showed a high specific capacitance of 420 F g^-1 and an energy density of 14.58 Wh kg^-1 with 0.5 M Na₂SO₄ as the electrolyte in a symmetric two-electrode. With the successful intercalation of the γ-MnO₂ and α-Ni(OH)₂ in between the surface of the as-prepared rGO layers, the interlayer distance of the rGO nanosheets expanded to 0.87 nm. The synergistic effect of γ-MnO₂, α-Ni(OH)₂, and rGO exhibited the satisfying high cyclic stability with a capacitance retention of 82% even after 10 000 cycles. Thus, the as-prepared Ni(OH)₂ and MnO₂ intercalated rGO ternary hybrid is expected to contribute to the fabrication of a real-time high-performing supercapacitor device.

Augmented biohydrogen production from rice mill wastewater through nano-metal oxides assisted dark fermentation

This study highlights biohydrogen production enrichment through NiO and CoO nanoparticles (NPs) inclusion to dark fermentation of rice mill wastewater using Clostridium beijerinckii DSM 791. NiO (~26 nm) and CoO (~50 nm) NPs were intrinsically prepared via facile hydrothermal method with polyhedral morphology and high purity. Dosage dependency studies revealed the maximum biohydrogen production characteristics for 1.5 mg/L concentration of both NPs. Biohydrogen yield was improved by 2.09 and 1.9 folds higher for optimum dosage of NiO and CoO respectively, compared to control run without NPs. Co-metabolites analysis confirmed the biohydrogen production through acetate and butyrate pathways. Maximum COD reduction efficiencies of 77.6% and 69.5% were observed for NiO and CoO inclusions respectively, which were higher than control run (57.5%). Gompertz kinetic model fitted well with experimental data of NPs assisted fermentation. Thus, NiO and CoO inclusions to wastewater fermentation seems to be a promising technique for augmented biohydrogen production.

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.

Synthesized and Photocatalytic Mechanism of the NiO Supported YMnO3 Nanoparticles for Photocatalytic Degradation of the Methyl Orange Dye

The YMnO3, NiO, and NiO/YMnO3 nanocomposites are successfully prepared by a polyacrylamide gel method and a simple two phase recombination route. The phase structure, surface morphology, optical, magnetic and electrochemical properties and photocatalytic activity of as-prepared samples were measured by X-ray diffraction (XRD), Scanning electron microscope (SEM), UV-visible spectrophotometer, superconducting quantum interference device (SQUID), electrochemical workstation and 721 spectrophotometer. Phase structure analysis indicate that the YMnO3, NiO, and NiO/YMnO3 nanocomposites has good crystallization and no other impurities. The NiO supported YMnO3 composites improved the surface morphology, optical, magnetic and electrochemical properties and photocatalytic activity of YMnO3 nanoparticles significantly. Photocatalytic experiment analysis indicate that the NiO supported YMnO3 composites exhibits highest photocatalytic activity for degradation of the methyl red dye with dye concentration of 25 mg/L. The excellent photocatalytic activity for the NiO supported YMnO3 composites can be ascribed to the fast interfacial charge transfer, high effective charge separation and the ⋅OH radicals.

Ni(OH)2-decorated nitrogen doped MWCNT nanosheets as an efficient electrode for high performance supercapacitors

In this study, nickel hydroxide nanoparticles (NPs) decorated with nitrogen doped multiwalled carbon nanotubes (N-MWCNT) hybrid composite was synthesized by thermal reduction process in the presence of cetyl ammonium bromide (CTAB) and urea. The as-synthesized Ni(OH)₂@N-MWCNT hybrid composite was characterized by FTIR, Raman, XRD, BET, BJH and FE-TEM analyses. These prepared porous carbon hybrid composite materials possessed high specific surface area and sheet like morphology useful for active electrode materials. The maximum specific capacitance of Ni(OH)₂@N-MWCNT hybrid nanocomposite in the two electrode system showed 350 Fg⁻¹ at 0.5 A/g,energy density ~43.75 Wkg⁻¹ and corresponds to power density 1500 W kg⁻¹ with excellent capacity retention after 5000 cycles. The results suggest that the prepared two-dimensional hybrid composite is a promising electrode material for electrochemical energy storage applications.

2D nanoporous Ni(OH)2 film as an electrode material for high-performance energy storage devices

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique. The nanostructured Ni(OH)₂ film was flexible and translucent, and could be directly compressed on a current collector. Owing to the uniform well-defined morphology and stable structure, the Ni(OH)₂ film binder-free electrode displayed a high specific capacity, exceptional rate capability, and admirable cycle life. The specific capacitance was 453.6 mA h g⁻¹ (1633 F g⁻¹) at 0.5 A g⁻¹. The assembled Ni(OH)₂//activated carbon (AC) asymmetric supercapacitor (ASC) device had an energy density of 58.7 W h kg⁻¹ at a power density of 400 W kg⁻¹. These prominent electrochemical properties of Ni(OH)₂ were attributed to the high electrical conductivity, high surface area, and unique porous architecture. Free tailoring, binder-free, and direct pressing were the most significant achievements of the Ni(OH)₂ film in the development of high-performance energy storage devices.

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique.

Effective reduced graphene oxide sheets/hierarchical flower-like NiO composites for methanol sensing under high humidity

We report the methanol sensing performance of reduced graphene oxide/hierarchical flower-like NiO under 90% of relative humidity and relatively low-temperature.

Synthesis of graphene-transition metal oxide hybrid nanoparticles and their application in various fields

Single layer graphite, known as graphene, is an important material because of its unique two-dimensional structure, high conductivity, excellent electron mobility and high surface area. To explore the more prospective properties of graphene, graphene hybrids have been synthesised, where graphene has been integrated with other important nanoparticles (NPs). These graphene-NP hybrid structures are particularly interesting because after hybridisation they not only display the individual properties of graphene and the NPs, but also they exhibit further synergistic properties. Reduced graphene oxide (rGO), a graphene-like material, can be easily prepared by reduction of graphene oxide (GO) and therefore offers the possibility to fabricate a large variety of graphene-transition metal oxide (TMO) NP hybrids. These hybrid materials are promising alternatives to reduce the drawbacks of using only TMO NPs in various applications, such as anode materials in lithium ion batteries (LIBs), sensors, photocatalysts, removal of organic pollutants, etc. Recent studies have shown that a single graphene sheet (GS) has extraordinary electronic transport properties. One possible route to connecting those properties for application in electronics would be to prepare graphene-wrapped TMO NPs. In this critical review, we discuss the development of graphene-TMO hybrids with the detailed account of their synthesis. In addition, attention is given to the wide range of applications. This review covers the details of graphene-TMO hybrid materials and ends with a summary where an outlook on future perspectives to improve the properties of the hybrid materials in view of applications are outlined.

Self-assembling Ni(OH)2/α-Fe2O3 composites for pseudocapacitors with excellent electrochemical performance

Novel two-dimensional (2D) nanostructured Ni(OH)₂ nanosheet/α-Fe₂O₃ nanoplate composites (NFCs) were successfully synthesized by a simple two-step solvothermal method where the proportion of α-Fe₂O₃ nanoplates was found to be controllable. These composites achieved excellent performance in aqueous electrolyte due to the synergistic effect between Ni(OH)₂ nanosheets and α-Fe₂O₃ nanoplates, such as high specific capacitance and long-term cycle stability. The obtained NFC8 possessed a maximum mass specific capacitance of 1745.33F g^-1 at a current density of 2 A g^-1, and with 84.28% retention after 3000 cycles galvanostatic charge/discharge at a high current density of 20 A g^-1. The above results show that these novel 2D nanostructured Ni(OH)₂/α-Fe₂O₃ composites are promising electrode materials for pseudocapacitors.

A nanocrystalline structured NiO/MnO2@nitrogen-doped graphene oxide hybrid nanocomposite for high performance supercapacitors

A nanocrystalline NiO@MnO₂/NGO hybrid composite electrode showed specific capacitance of 1490 Fg⁻¹ at a current density of 0.5 Ag⁻¹ and retains 98% up to 2000 cycles indicating its good cyclic stability.

A high performance supercapacitor based on decoration of MoS2/reduced graphene oxide with NiO nanoparticles

GO and MoS₂ solution in combination with NiO nanoparticles present a high performance supercapacitor and excellent cycling stability.

Nanocrystalline LaOx/NiO composite as high performance electrodes for supercapacitors

Nanocrystalline LaO_x/NiO composite electrodes were synthesized via two types of facile cathodic electrodeposition methods onto nickel foam followed by thermal annealing without any binders.

Two-step controllable preparation of NiO nanocrystal anchored reduced graphene oxide sheets and their electrochemical performance as supercapacitors

A feasible and expandable way to prepare homogenous NiO nanocrystal coated reduced graphene oxide (rGO-NiO) for high performance supercapacitor electrodes.

2-Dimensional graphene as a route for emergence of additional dimension nanomaterials

Dimension has a different and impactful significance in the field of innovation, research and technologies. Starting from one-dimension, now, we all are moving towards 3-D visuals and try to do the things in this dimension. However, we still have some very innovative and widely applicable nanomaterials, which have tremendous potential in the form of 2-D only i.e. graphene. In this review, we have tried to incorporate the reported pathways used so far for modification of 2-D graphene sheets to make is three-dimensional. The modified graphene been applied in many fields like supercapacitors, sensors, catalysis, energy storage devices and many more. In addition, we have also incorporated the conversion of 2-D graphene to their various other dimensions like zero-, one- or three-dimensional nanostructures.

Layered NiO/reduced graphene oxide composites by heterogeneous assembly with enhanced performance as high-performance asymmetric supercapacitor cathode

Layered NiO/RGO composites by heterogeneous assembly show high energy density as an asymmetric supercapacitor.

Dense inter-particle interaction mediated spontaneous exchange bias in NiO nanoparticles

The observed spontaneous exchange bias in NiO nanoparticles is induced by the dense inter-particle interactions.

Fabrication of carbon-coated NiO supported on graphene for high performance supercapacitors

We report a feasible strategy for the synthesis of the carbon-coated NiO nanoparticles supported on graphenes and investigate their application as supercapacitor electrodes.

Microwave-assisted synthesis of void-induced graphene-wrapped nickel oxide hybrids for supercapacitor applications

A simple and fast microwave irradiation technique has been used to synthesize void-induced with graphene-wrapped nickel oxide (VGWN) hybrids. The VGWN hybrid material provides long term cyclic stability and excellent electrochemical performance.

Solid State Flexible Asymmetric Supercapacitor Based on Carbon Fiber Supported Hierarchical Co(OH)xCO3 and Ni(OH)2

Conducting flexible carbon fiber (CF) cloth was used as a substrate for the hydrothermal growth of nickel hydroxide (Ni(OH)2) and cobalt hydroxy carbonate [Co(OH)xCO3] with unique hierarchical flowery architecture and then was used as a flexible supercapacitor electrode. In a three-electrode configuration in 6 M KOH aqueous electrolyte, the CF-Ni(OH)2 and CF-Co(OH)xCO3 electrode showed the maximum specific capacitance of 789 F/g and 550 F/g, respectively, at 2A/g current accompanied by outstanding cycle stability by retaining 99.9% and 99.5% specific capacitance over 1500 consecutive charge-discharge cycles at 5 A/g. However, the low cell voltage (0.4 V) restricted the respective specific energy to 4.38 and 3.05 Wh/kg at a specific power of 100 W/kg. To overcome the issue, two solid state flexible asymmetric supercapacitors were fabricated using the CF-Ni(OH)2 and CF-Co(OH)xCO3 as the anode and sonochemically deposited CNT over carbon fiber as the cathode material in PVA-KOH gel electrolyte. The as-fabricated flexible supercapacitors CF-Ni(OH)2//CF-CNT and CF-Co(OH)xCO3//CF-CNT were able to deliver high specific energy of 41.1 and 33.48 Wh/kg, respectively, at high specific power of 1.4 kW/kg accompanied by excellent cycle stability (retaining 98% and 97.6% specific capacitance, respectively, over 3000 charge-discharge cycle at 5 A/g).

Electrochemical energy-storage performances of nickel oxide films prepared by a sparking method

The sparking method is a practical and effective preparation technique for porous nickel oxide films, suitable for energy-storage applications.

Synthesis of shape-controlled NiO–graphene nanocomposites with enhanced supercapacitive properties

The flowerlike and polyhedral NiO–graphene composites show high supercapacitive performances which were synthesized using a facile hydrothermal method.

Porous nickel oxide nanotube arrays supported on carbon fiber paper: synergistic effect on pseudocapacitive behavior

Hierarchically nanostructured NiO nanotube arrays supported on carbon fiber paper (CFP) are synthesized via a simple ZnO-template method and utilized as supercapacitor electrodes.

Self-assembled flower-like ZnCo2O4hierarchical superstructures for high capacity supercapacitors

Self-assembled ZnCo₂O₄nanosheets were synthesized by a one-step hydrothermal method and their electrochemical supercapacitor properties were investigated in 2 M aqueous KOH solution.

NiO/nanoporous graphene composites with excellent supercapacitive performance produced by atomic layer deposition

Nickel oxide (NiO) is a promising electrode material for supercapacitors because of its low cost and high theoretical specific capacitance of 2573 F g(-1). However, the low electronic conductivity and poor cycling stability of NiO limit its practical applications. To overcome these limitations, an efficient atomic layer deposition (ALD) method is demonstrated here for the fabrication of NiO/nanoporous graphene (NG) composites as electrode materials for supercapacitors. ALD allows uniform deposition of NiO nanoparticles with controlled sizes on the surface of NG, thus offering a novel route to design NiO/NG composites for supercapacitor applications with high surface areas and greatly improved electrical conductivity and cycle stability. Electrochemical measurements reveal that the NiO/NG composites obtained by ALD exhibited excellent specific capacitance of up to ∼ 1005.8 F g(-1) per mass of the composite electrode (the specific capacitance value is up to ∼ 1897.1 F g(-1) based on the active mass of NiO), and stable performance after 1500 cycles. Furthermore, electrochemical performance of the NiO/NG composites is found to strongly depend on the size of NiO nanoparticles.