The development of efficient energy storage devices with high capacity and excellent stability is a demanding necessary to
satisfy future societal and environmental needs. A hybrid material composed of low defect density graphene-supported Ni(OH)2 sheets has been fabricated via a soft chemistry route and investigated as an advanced electrochemical pseudocapacitor material.
The low defect density graphene effectively prevents the restacking of Ni(OH)2 nanosheets as well as boosting the conductivity of the hybrid electrodes, giving a dramatic rise in capacity performance
of the overall system. Moreover, graphene simultaneously acts as both nucleation center and template for the in situ growth
of smooth and large scale Ni(OH)2 nanosheets. By virtue of the unique two-dimensional nanostructure of graphene, the as-obtained Ni(OH)2 sheets are closely protected by graphene, effectively suppressing their microstructural degradation during the charge and
discharge processes, enabling an enhancement in cycling capability. Electrochemical measurements demonstrated that the specific
capacitance of the as-obtained composite is high as 1162.7 F/g at a scan rate of 5 mV/s and 1087.9 F/g at a current density
of 1.5 A/g. In addition, there was no marked decrease in capacitance at a current density of 10·A/g after 2000 cycles, suggesting
excellent long-term cycling stability.
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The growth of a Ni(OH)2 coating on conductive carbon substrates is an efficient way to address issues related to their poor conductivity in electrochemical capacitor applications. However, the direct growth of nickel hydroxide coatings on a carbon substrate is challenging, because the surfaces of these systems are not compatible and a preoxidation treatment of the conductive carbon substrate is usually required. Herein, we present a facile preoxidation-free approach to fabricate a uniform Ni(OH)2 coating on carbon nanosheets (CNs) by an ion-exchange reaction to achieve the in situ transformation of a MgO/C composite to a Ni(OH)2/C one. The obtained Ni(OH)2/CNs hybrids possess nanosheet morphology, a large surface area (278 m2/g), and homogeneous elemental distributions. When employed as supercapacitors in a three-electrode configuration, the Ni(OH)2/CNs hybrid achieves a large capacitance of 2,218 F/g at a current density of 1.0 A/g. Moreover, asymmetric supercapacitors fabricated with the Ni(OH)2/CNs hybrid exhibit superior supercapacitive performances, with a large capacity of 198 F/g, and high energy density of 56.7 Wh/kg at a power density of 4.0 kW/kg. They show excellent cycling stability with 93% capacity retention after 10,000 cycles, making the Ni(OH)2/CNs hybrid a promising candidate for practical applications in supercapacitor devices.
Exploring earth-abundant and highly efficient electrocatalysts is critical for further development of water electrolyzer systems. Integrating bifunctional catalytically active sites into one multi-component might greatly improve the overall water-splitting performance. In this work, amorphous NiO nanosheets coupled with ultrafine Ni and MoO3 nanoparticles (MoO3/Ni–NiO), which contains two heterostructures (i.e., Ni–NiO and MoO3–NiO), is fabricated via a novel sequential electrodeposition strategy. The as-synthesized MoO3/Ni–NiO composite exhibits superior electrocatalytic properties, affording low overpotentials of 62 mV at 10 mA cm−2 and 347 mV at 100 mA cm−2 for catalyzing the hydrogen and the oxygen evolution reaction (HER/OER), respectively. Moreover, the MoO3/Ni–NiO hybrid enables the overall alkaline water-splitting at a low cell voltage of 1.55 V to achieve 10 mA cm−2 with outstanding catalytic durability, significantly outperforming the noble-metal catalysts and many materials previously reported. Experimental and theoretical investigations collectively demonstrate the generated Ni–NiO and MoO3–NiO heterostructures significantly reduce the energetic barrier and act as catalytically active centers for selective HER and OER, synergistically accelerating the overall water-splitting process. This work helps to fundamentally understand the heterostructure-dependent mechanism, providing guidance for the rational design and oriented construction of hybrid nanomaterials for diverse catalytic processes. 相似文献
Supercapacitors operating in aqueous solutions are low cost energy storage devices with high cycling stability and fast charging
and discharging capabilities, but generally suffer from low energy densities. Here, we grow Ni(OH)2 nanoplates and RuO2 nanoparticles on high quality graphene sheets in order to maximize the specific capacitances of these materials. We then
pair up a Ni(OH)2/graphene electrode with a RuO2/graphene electrode to afford a high performance asymmetrical supercapacitor with high energy and power density operating
in aqueous solutions at a voltage of ∼1.5 V. The asymmetrical supercapacitor exhibits significantly higher energy densities
than symmetrical RuO2-RuO2 supercapacitors or asymmetrical supercapacitors based on either RuO2-carbon or Ni(OH)2-carbon electrode pairs. A high energy density of ∼48 W·h/kg at a power density of ∼0.23 kW/kg, and a high power density of
∼21 kW/kg at an energy density of ∼14 W·h/kg have been achieved with our Ni(OH)2/graphene and RuO2/graphene asymmetrical supercapacitor. Thus, pairing up metal-oxide/graphene and metal-hydroxide/graphene hybrid materials
for asymmetrical supercapacitors represents a new approach to high performance energy storage.
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We report the first example of a practical and efficient template-free strategy for synthesizing ordered mesoporous NiO/poly(sodium-4-styrene
sulfonate) (PSS) functionalized carbon nanotubes (FCNTs) composites by calcining a Ni(OH)2/FCNTs precursor prepared by refluxing an alkaline solution of Ni(NH3)x2+ and FCNTs at 97 °C for 1 h. The morphology and structure were characterized by X-ray diffraction, scanning electron microscopy,
and transmission electron microscopy. Thermal decomposition of the precursor results in the formation of ordered mesoporous
NiO/FCNTs composite (ca. 48 wt% NiO) with large specific surface area. Due to its enhanced electronic conductivity and hierarchical
(meso- and macro-) porosity, composite simultaneously meets the three requirements for energy storage in electrochemical capacitors
at high rate, namely, good electron conductivity, highly accessibleelectrochemical surface areas owing to the existence of
mesopores, and efficient mass transport from the macropores. Electrochemical data demonstrated that the ordered mesoporous
NiO/FCNTs composite is capable of delivering a specific capacitance (SC) of 526 F/g at 1 A/g and a SC of 439 F/g even at 6
A/g, and show a degradation of only ca. 6% in SC after 2000 continuous charge/discharge cycles.
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NiO/YSZ composite powders, with various NiO contents, have been prepared by the urea hydrolysis method. The crystallization behavior and microstructure of composite powders has been studied in detail, using differential scanning calorimetry analysis, X-ray diffraction, and transmission electron microscope. The results indicated that the actual NiO content of the NiO/YSZ powders largely deviated from the nominal value, and finally reached a saturated value. The NiO addition would retard the crystallization of NiO/YSZ composite. When the calcination temperature was increased, the NiO crystallites first precipitated at around 500 °C, and then the YSZ phase presented at about 600 °C. The calcined powders consist of NiO/YSZ nanocomposite particles, which are comprised of nano-sized NiO and YSZ crystals. In addition, with the aid of H2 plasma treatment, it is easier to distinguish the Ni and YSZ phases of Ni/YSZ cermets after sintering and subsequent reduction. This could reveal that such Ni/YSZ cermets exhibited a uniform microstructure that has fine Ni particles homogeneously dispersed within the YSZ matrix. As the NiO content was increased, the size and density number of the Ni phase within an YSZ matrix was increased. 相似文献
Carbon nano-onion (CNO) and Ni(OH)2 or NiO composites were prepared by chemical loading of Ni(OH)2 on the carbon surface. The samples were characterized by transmission electron microscopic (TEM) and scanning electron microscopic (SEM) methods, powder X-ray diffraction (XRD) technique and by differential-thermogravimetric analyses (TGA-DTG). The porosity properties were characterized by using nitrogen gas adsorption analyses. Pristine inorganic samples of NiO and Ni(OH)2 revealed different morphologies and porous characteristics when compared to those of the CNO composites, which showed unique electrochemical properties. The electrochemical performance of the CNO/Ni(OH)2 or CNO/NiO composites is largely affected by the mass, the morphology, the crystal phases of the inorganic component and the distribution of the Ni(OH)2/NiO phase. The CNO composites were used as materials for hybrid charge-storage devices. 相似文献
