Nanofoaming to Boost the Electrochemical Performance of Ni@Ni(OH)2 Nanowires for Ultrahigh Volumetric Supercapacitors

Microwave Construction of NiSb/NiTe Composites on Ni-Foam for High-Performance Supercapacitors

In this paper, NiSb/NiTe/Ni composites were smoothly developed via the microwave method for supercapacitors. The synthesis of NiSb/NiTe crystals was revealed by X-ray photoelectron spectroscopy and X-ray diffraction. The analytic results of scanning electron microscopy and energy dispersive spectroscopy uncover the microscopic morphology as well as the constituent elements of the composites. Self-supported NiSb/NiTe is a supercapacitor cathode that combines high capacitance with excellent cycling stability. The obtained composite electrode displayed remarkable electrochemical properties, presenting a special capacitance of 1870 F g-1 (1 A g-1) and 81.5% of the original capacity through 30,000 times (10 A g-1) of the charging/discharging process. Further, an asymmetric supercapacitor was prepared employing NiSb/NiTe as a cathode and activated carbon as an anode. NiSb/NiTe//AC exhibited a high energy density of 224.6 uW h cm-2 with a power density of 750 μW cm-2 and provided a favorable cycling stability of 83% after 10,000 cycles.

Synergistic redox enhancement: silver phosphate augmentation for optimizing magnesium copper phosphate in efficient energy storage devices and oxygen evolution reaction

The implementation of battery-like electrode materials with complicated hollow structures, large surface areas, and excellent redox properties is an attractive strategy to improve the performance of hybrid supercapacitors. The efficiency of a supercapattery is determined by its energy density, rate capabilities, and electrode reliability. In this study, a magnesium copper phosphate nanocomposite (MgCuPO4) was synthesized using a hydrothermal technique, and silver phosphate (Ag3PO4) was decorated on its surface using a sonochemical technique. Morphological analyses demonstrated that Ag3PO4 was closely bound to the surface of amorphous MgCuPO4. The MgCuPO4 nanocomposite electrode showed a 1138 C g-1 capacity at 2 A g-1 with considerably improved capacity retention of 59% at 3.2 A g-1. The increased capacity retention was due to the fast movement of electrons and the presence of an excess of active sites for the diffusion of ions from the porous Ag3PO4 surface. The MgCuPO4-Ag3PO4//AC supercapattery showed 49.4 W h kg-1 energy density at 550 W kg-1 power density and outstanding capacity retention (92% after 5000 cycles). The experimental findings for the oxygen evolution reaction reveal that the initial increase in potential required for MgCuPO4-Ag3PO4 is 142 mV, indicating a clear Tafel slope of 49 mV dec-1.

Engineering CoP Alloy Foil to a Well-Designed Integrated Electrode Toward High-Performance Electrochemical Energy Storage

Nanostructured integrated electrodes with binder-free design show great potential to solve the ever-growing problems faced by currently commercial lithium-ion batteries such as insufficient power and energy densities. However, there are still many challenging problems limiting practical application of this emerging technology, in particular complex manufacturing process, high fabrication cost, and low loading mass of active material. Different from existing fabrication strategies, here using a CoP alloy foil as a precursor  a simple neutral salt solution-mediated electrochemical dealloying method to well address the above issues is demonstrated. The resultant freestanding mesoporous np-Co(OH)_x /Co₂ P product possesses not only active compositions of high specific capacity and large electrode packing density (>3.0 g cm^-3 ) to meet practical capacity requirements, high-conductivity and well-developed nanoporous framework to achieve simultaneously fast ion and electron transfer, but also interconnected ligaments and suitable free space to ensure strong structural stability. Its comprehensively excellent electrochemical energy storage (EES) performances in both lithium/sodium-ion batteries and lithium-ion capacitors can further illustrate the effectiveness of the integrated electrode preparation strategy, such as remarkable reversible specific capacities/capacitances, dominated pseudo-capacitive EES mechanism, and ultra-long cycling life. This study provides new insights into preparation and design of high-performance integrated electrodes for practical applications.

Engineering Interlaced Architecture of Pristine Graphene Anchored with 2-Amino-8-Naphthol 6-Sulfonic Acids for Printed Hybrid Micro-Supercapacitors with High Electrochemical Capability

All-printed flexible micro-supercapacitors (MSCs) based on two-dimensional (2D) nanomaterials with in-plane interdigital configurations are regarded as promising miniaturized power source units, but they chronically suffer from self-aggregation and inadequate matching of electrode materials, thus resulting in inefficient electrolyte ions intercalation. Herein, an innovative multicomponent interlaced architecture essentially consisting of 2-amino-8-naphthol 6-sulfonic acid (ANS)-anchored pristine graphene and highly conductive multiwalled carbon nanotubes is reported. The assembled and optimized Gr@ANS electrodes offer sufficient absorption/desorption and redox-active sites, delivering a high areal capacitance of 33.7 mF/cm² for screen-printed MSCs. Particularly, the well-modified Gr@ANS/CNTs-interlaced complex structure effectively prevents the usual restacking of the delaminated Gr@ANS nanosheets and maximizes ion accessibility in electrodes. Ascribed to the optimized electron-transferring kinetics, the achieved Gr@ANS/CNTs MSCs exhibit excellent capacitance (40.2 mF/cm² and 18.8 F/cm³), simultaneously significantly increasing the rate capability of Gr@ANS MSCs (from 3.9 to 60.0%). Arising from the multicomponent synergism, the all-solid-state MSCs exhibit outstanding bending stability and cycling performance (73.8% after 10 000 charge/discharge cycles). The new charge reservoir engineering evidenced in graphene-based micro-supercapacitors would serve as a stepping stone toward the scalable manufacture of hybrid energy storage micro-devices.

Rational Regulation of Crystalline/Amorphous Microprisms-Nanochannels Based on Molecular Sieve (VSB-5) for Electrochemical Overall Water Splitting

Rational regulation of the composition and structure of electrocatalysts is crucial to the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a new electrocatalyst of nickel phosphate microprism (VSB/NiPO) is developed via a simple solvothermal reaction. The microprism is mainly composed of Versailles-Santa Barbara-5 (VSB-5, molecular sieve) with unique nanochannels, which contribute to accelerating mass transfer and exposing more active sites, thus displaying excellent HER activity. Subsequently, the crystallinity and electronic structure of the framework are modulated by incorporating Fe with the combination of calcination and impregnation. The nanochannels are converted to the amorphous arrangement, and the Ni centers are regulated to the higher valence. The resultant Fe-VSB/NiPO-500 exhibits a low OER overpotential of 227 mV at 50 mA cm^-2 . Interestingly, an integrated electrolyzer assembled by VSB/NiPO(-) and Fe-VSB/NiPO-500(+) performs well for overall water splitting, which requires only 1.487 V to achieve 10 mA cm^-2 , and remains stable at 100 mA cm^-2 over 100 h. This finding opens a new avenue for developing VSB-5 in the field of electrocatalysis.

Defect-Engineered NiCo-S Composite as a Bifunctional Electrode for High-Performance Supercapacitor and Electrocatalysis

Defect engineering is a reasonable solution to improve the surface properties and electronic structure of nanomaterials. However, how to introduce dual defects into nanomaterials by a simple way is still facing challenge. Herein, we propose a facile two-step solvothermal method to introduce Fe dopants and S vacancies into metal-organic framework-derived bimetallic nickel cobalt sulfide composites (NiCo-S). The as-prepared Fe-doped NiCo-S (Fe-NiCo-S) possesses improved charge storage kinetics and activities as electrode material for supercapacitors and the oxygen evolution reaction (OER). The obtained Fe-NiCo-S nanosheet has a high specific capacitance (2779.6 F g^-1 at 1 A g^-1) and excellent rate performance (1627.2 F g^-1 at 10 A g^-1). A hybrid supercapacitor device made of Fe-NiCo-S as the positive electrode and reduced graphene oxide (rGO) as the negative electrode presents a high energy density of 56.0 Wh kg^-1 at a power density of 847.1 W kg^-1 and excellent cycling stability (capacity retention of 96.5% after 10,000 cycles at 10 A g^-1). Additionally, the Fe-NiCo-S composite modified by Fe doping and S vacancy has an ultralow oxygen evolution overpotential of 247 mV at 10 mA cm^-2. Based on the density functional theory (DFT) calculation, defects cause more electrons to appear near the Fermi level, which is conducive to electron transfer in electrochemical processes. Our work provides a rational strategy for facilely introducing dual defects into metal sulfides and may provide a novel idea to prepare electrode materials for energy storage and energy conversion application.

Core-shell NiSe/Ni(OH)2with NiSe nanorods and Ni(OH)2nanosheets as battery-type electrode for hybrid supercapacitors

Novel core-shell nanostructure electrodes benefit from the excellent properties of their constituent materials, as well as the synergy between them. However, it is challenging to fabricate such structures efficiently. In this study, NiSe nanorods were fabricated using Ni foam as the conductive substrate and reactant via a one-step hydrothermal process, and Ni(OH)₂nanosheets were coated on the surface of the nanorods via one-step electrodeposition. The effect of the structure and morphology on the properties of the material was explored using scanning electron microscopy, x-ray diffraction, and electrochemical technology. The obtained core-shell NiSe/Ni(OH)₂exhibited an areal capacity of 1.89 mAh cm^-2at a current density of 5 mA cm^-2. The assembled NiSe/Ni(OH)₂//AC hybrid supercapacitor exhibited excellent energy and power densities, indicating that NiSe/Ni(OH)₂has great potential for use as a battery-type electrode in energy storage systems.

The Application of Metal-Organic Frameworks and Their Derivatives for Supercapacitors

Supercapacitors (SCs), one of the most popular types of energy-storage devices, present lots of advantages, such as large power density and fast charge/discharge capability. Being the promising SCs electrode materials, metal-organic frameworks (MOFs) and their derivatives have gained ever-increasing attention due to their large specific surface area, controllable porous structure and rich diversity. Herein, the recent development of MOFs-based materials and their application in SCs as the electrode are reviewed and summarized. The preparation method, the morphology of the materials and the electrical performance of various MOFs and their derivatives (such as carbon, metal oxide/hydroxide and metal sulfide) are briefly discussed. Most of recent works concentrate on Ni-, Co- and Mn-MOFs and their composites/derivatives. Conclusions and our outlook for the researches are also given, which would be a valuable guideline for the rational design of MOFs materials for SCs in the near future.

Metal–organic framework templated fabrication of Cu7S4@Ni(OH)2 core–shell nanoarrays for high-performance supercapacitors

Core–cell Cu₇S₄@Ni(OH)₂ nanorod arrays were fabricated by using metal–organic frameworks as templates, and showed high specific capacitance, superior rate capacity and excellent cycling stability for supercapacitors.

Achieving Rich Mixed-Valence Polysulfide/Carbon Nanotube Films toward Ultrahigh Volume Energy Density and Largely Deformable Pseudocapacitors

In this work, new insights into dependence of electrochemical performance enhancement on transition metals' rich mixed valence and their atomic ratio as well as redox active polysulfides are proposed. Especially, the influence of atomic ratio is further demonstrated by both experiments and density functional theoretical calculation where increasing Co/S leads to the enlargement of both interatom distance and hole diameter in a Mn_xCo_yS_z cell. We rationally designed and prepared novel flexible electrodes of a rich mixed-valence polysulfide Mn_xCo_yS_z/carbon nanotube film (CNTF) through acid activation of a dense CNTF into a hydrogel-like conductive matrix, growth of the Mn_xCo_y(CO₃)_0.5OH precursor on each CNT, and controlled sulfidation. Nanostructure control allows us to obtain fast electron/ion transfer and increased availability of active sites/interfaces. The optimal MnCo₉S₁₀/CNTF shows a specific capacitance reaching 450 F cm^-3 at 10 mA cm^-2, much higher than reported values for CNT-based electrodes. Also, it exhibits remarkable cycling stability with only 1.6% capacity loss after 10 000 cycles at a high current density of 80 mA cm^-2. An all-solid-state asymmetric supercapacitor (ASC) applying MnCo₉S₁₀/CNTF delivers an exceptionally high volumetric energy density of 67 mW h cm^-3 (at 10 W cm^-3). Particularly, integrated electric sources with adjustable output voltages can be obtained by connecting several ASCs in series, and there are no structural failure and capacity loss during repeated large-angle twisting and vigorous hammering. This work provides a general route to energy storage devices with ultrahigh volumetric energy density and outstanding reliability for wearable electronics.

Synthesis of Ag/NiO Honeycomb Structured Nanoarrays as the Electrode Material for High Performance Asymmetric Supercapacitor Devices

Metallic silver nickel oxide honeycomb nanoarrays were synthesized via a surfactant-assisted hydrothermal route. The crystal structure of the Ag/NiO nanoarrays was confirmed by X-ray diffraction. X-ray photoelectron spectroscopy confirmed the valance state of the nickel, oxygen, and metallic silver. The morphological studies and energy dispersive X-ray spectroscopy revealed the honeycomb structured nanoarrays and the elemental distribution of the prepared sample, respectively. The three-electrode measurements showed that the Ag/NiO nanoarray is a suitable electrode material for supercapacitor applications, which delivers the maximum specific capacity of 824 C g^-1 at a specific current of 2.5 A g^-1. An Ag/NiO positive electrode-based asymmetric device was fabricated and tested. The asymmetric device yielded a high specific cell capacity of 204 C g^-1 at a specific current of 2.5 A g^-1 as well as a maximum energy density of 63.75 W h kg^-1 at a power density of 2812.5 W kg^-1. These results are comparable to those of (NiMH) metal hydride batteries.

Engineering PPy decorated MnCo2O4 urchins for quasi-solid-state hybrid capacitors

In this work, three dimensional PPy decorated MnCo₂O₄ urchins on Ni foam are fabricated via a hydrothermal strategy and an electro-polymerization process.

Asymmetric pseudo-capacitors based on dendrite-like MnO2 nanostructures

Dendrite-like MnO₂ nanostructures grown on carbon cloth are successfully prepared by a facile one-step route.

S. V, C. S. PK, Kandaiah S. Anodic fabrication of nanostructured CuxS and CuNiSx thin films and their hydrogen evolution activities in acidic electrolytes

The electrochemical anodization method is advantageous for direct growth of highly ordered and large surface area hybrid nanostructures.

A Ni(OH)2 nanopetals network for high-performance supercapacitors synthesized by immersing Ni nanofoam in water

Developing a facile and environmentally friendly approach to the synthesis of nanostructured Ni(OH)₂ electrodes for high-performance supercapacitor applications is a great challenge. In this work, we report an extremely simple route to prepare a Ni(OH)₂ nanopetals network by immersing Ni nanofoam in water. A binder-free composite electrode, consisting of Ni(OH)₂ nanopetals network, Ni nanofoam interlayer and Ni-based metallic glass matrix (Ni(OH)₂/Ni-NF/MG) with sandwich structure and good flexibility, was designed and finally achieved. Microstructure and morphology of the Ni(OH)₂ nanopetals were characterized. It is found that the Ni(OH)₂ nanopetals interweave with each other and grow vertically on the surface of Ni nanofoam to form an "ion reservoir", which facilitates the ion diffusion in the electrode reaction. Electrochemical measurements show that the Ni(OH)₂/Ni-NF/MG electrode, after immersion in water for seven days, reveals a high volumetric capacitance of 966.4 F/cm³ at a current density of 0.5 A/cm³. The electrode immersed for five days exhibits an excellent cycling stability (83.7% of the initial capacity after 3000 cycles at a current density of 1 A/cm³). Furthermore, symmetric supercapacitor (SC) devices were assembled using ribbons immersed for seven days and showed a maximum volumetric energy density of ca. 32.7 mWh/cm³ at a power density of 0.8 W/cm³, and of 13.7 mWh/cm³ when the power density was increased to 2 W/cm³. The fully charged SC devices could light up a red LED. The work provides a new idea for the synthesis of nanostructured Ni(OH)₂ by a simple approach and ultra-low cost, which largely extends the prospect of commercial application in flexible or wearable devices.

In situ coating nickel organic complexes on free-standing nickel wire films for volumetric-energy-dense supercapacitors

A self-free-standing core-sheath structured hybrid membrane electrodes based on nickel and nickel based metal-organic complexes (Ni@Ni-OC) was designed and constructed for high volumetric supercapacitors. The self-standing Ni@Ni-OC film electrode had a high volumetric specific capacity of 1225.5 C cm^-3 at 0.3 A cm^-3 and an excellent rate capability. Moreover, when countered with graphene-carbon nanotube (G-CNT) film electrode, the as-assembled Ni@Ni-OC//G-CNT hybrid supercapacitor device delivered an extraordinary volumetric capacitance of 85 F cm^-3 at 0.5 A cm^-3 and an outstanding energy density of 33.8 at 483 mW cm^-3. Furthermore, the hybrid supercapacitor showed no capacitance loss after 10 000 cycles at 2 A cm^-3, indicating its excellent cycle stability. These fascinating performances can be ascribed to its unique core-sheath structure that high capacity nano-porous nickel based metal-organic complexes (Ni-OC) in situ coated on highly conductive Ni wires. The impressive results presented here may pave the way to construct s self-standing membrane electrode for applications in high volumetric-performance energy storage.

Hierarchical core-shell structures of P-Ni(OH)2 rods@MnO2 nanosheets as high-performance cathode materials for asymmetric supercapacitors

The hierarchical porous structure with phosphorus-doped Ni(OH)₂ (P-Ni(OH)₂) rods as the core and MnO₂ nanosheets as the shell is fabricated directly by growth on a three-dimensional (3D) flexible Ni foam (NF) via a two-step hydrothermal process. As a binder-free electrode material, this unique hybrid structure exhibits excellent electrochemical properties, including an ultrahigh areal capacitance of 5.75 F cm^-2 at a current density of 2 mA cm^-2 and great cyclic stability without capacitance loss at a current density of 20 mA cm^-2 after 10 000 cycles. Moreover, an all-solid-state asymmetric supercapacitor (AAS) based on a P-Ni(OH)₂@MnO₂ hybrid structure on Ni foam as the cathode and activated carbon (AC) as the anode is successfully assembled to enhance value the electrochemical properties. The AAS device also shows excellent electrochemical properties including a large potential window of 0∼1.6 V, an areal capacitance is 911.3 mF cm^-2 at a current density of 1 mA cm^-2 and long-term cycling performance. Meanwhile, the AAS device also delivers a high energy density of 0.324 mW h cm^-2 at a power density of 0.8 mW cm^-2; and can easily light colorful light-emitting diode (LED) lights, suggesting that 3D P-Ni(OH)₂@MnO₂ hybrid composite has promising potential for practical use in high-performance supercapacitors.

Mechanically stable ternary heterogeneous electrodes for energy storage and conversion

Recently, solid asymmetric supercapacitor (ASC) has been deemed as an emerging portable power storage or backup device for harvesting natural resources. Here we rationally engineered a hierarchical, mechanically stable heterostructured FeCo@NiCo layered double hydroxide (LDH) with superior capacitive performance by a simple two-step electrodeposition route for energy storage and conversion. In situ scanning electron microscope (SEM) nanoindentation and electrochemical tests demonstrated the mechanical robustness and good conductivity of FeCo-LDH. This serves as a reliable backbone for supporting the NiCo-LDH nanosheets. When employed as the positive electrode in the solid ASC, the assembly presents high energy density of 36.6 W h kg^-1 at a corresponding power density of 783 W kg^-1 and durable cycling stability (87.3% after 5000 cycles) as well as robust mechanical stability without obvious capacitance fading when subjected to bending deformation. To demonstrate its promising capability for practical energy storage applications, the ASC has been employed as a portable energy source to power a commercially available digital watch, mini motor car, or household lamp bulb as well as an energy storage reservoir, coupled with a wind energy harvester to power patterned light-emitting diodes (LEDs).

Pseudocapacitive-battery-like behavior of cobalt manganese nickel sulfide (CoMnNiS) nanosheets grown on Ni-foam by electrodeposition for realizing high capacity

Hierarchical interconnected nanosheets (HIN) of cobalt manganese nickel sulfide (CoMnNiS) were synthesized on Ni foam by a simple and economical electrodeposition technique for energy storage application. Sulfonated thin nanosheets of Co, Mn and Ni provide stability of chemical activity, surface functionalization and surface reactivity to the electrode. The fabricated electrode shows a specific capacity of 257.4 mA h g⁻¹ (at 2.5 A g⁻¹), measured by galvanostatic charging–discharging (GCD). Both diffusion and capacitive mechanisms in the sulfide layer contribute to the high electrical conductivity. Asymmetric devices CoMnNiS/NiCuO and CoMnNiS/CNT (CNT = carbon nanotubes) were fabricated, providing a maximum operating voltage of 1.7 V and 1 V, specific capacity of 20.8 and 50.8 mA h g⁻¹, and energy density of 8.4 and 6.3 W h kg⁻¹ corresponding to a power density of 985 and 211 W kg⁻¹, respectively, at a current density of 0.5 and 0.63 A g⁻¹. These results demonstrate a novel material for application in energy storage devices as an electrode.

Hierarchical interconnected nanosheets (HIN) of cobalt manganese nickel sulfide (CoMnNiS) were synthesized on Ni foam by a simple and economical electrodeposition technique for energy storage application.

Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni3 S2 Nanowire Films for High-Performance Supercapacitors

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni₃ S₂ core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni₃ S₂ nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730 C cm^-3 at 0.25 A cm^-3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni₃ S₂ core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni₃ S₂ as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm^-3 (based on the total volume of both electrodes) at 0.5 A cm^-3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm^-3 , which is much larger than those of thin-film lithium batteries (1-10 mWh cm^-3 ). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.

In situ cathodic activation of V-incorporated NixSy nanowires for enhanced hydrogen evolution

In situ cathodic activation (ISCA) of V-incorporated Ni_xS_y nanowires supported on nickel foam (VS/Ni_xS_y/NF) can be realized in an alkaline hydrogen evolution reaction (HER) process, which provides not only clearly enhanced activity but also ultrahigh stability for HER. The ISCA process is continuous linear sweep voltammetry (LSV) on VS/Ni_xS_y/NF as a cathodic electrode with gradually enhanced HER activity. The activated VS/Ni_xS_y/NF (A-VS/Ni_xS_y/NF) demonstrates enhanced HER activity with an overpotential of 125 mV to drive 10 mA cm^-2, which is much lower than that of other samples. It may be predicted that the ISCA-derived amorphous VOOH film covering on A-VS/Ni_xS_y/NF accelerates the HER process, and NiOOH may protect active sites from decaying, leading to excellent activity and structural stability. However, for single metal sulfides, the ISCA process of nickel or vanadium sulfides is not available, implying that the synergistic effect between Ni and V of VS/Ni_xS_y/NF may be the key to drive ISCA in alkaline HER. In addition, its ultra-high stability confirms that the stable active sites and nanostructures of A-VS/Ni_xS_y/NF are derived from ISCA. Therefore, the ISCA of V-incorporated transition metal sulfides in the alkaline HER process may be a facile and promising method to obtain efficient electrocatalysts.

Formation of g-C3N4@Ni(OH)2 Honeycomb Nanostructure and Asymmetric Supercapacitor with High Energy and Power Density

Nickel hydroxide (Ni(OH)₂) has been regarded as a potential next-generation electrode material for supercapacitor owing to its attractive high theoretical capacitance. However, practical application of Ni(OH)₂ is hindered by its lower cycling life. To overcome the inherent defects, herein we demonstrate a unique interconnected honeycomb structure of g-C₃N₄ and Ni(OH)₂ synthesized by an environmentally friendly one-step method. In this work, g-C₃N₄ has excellent chemical stability and supports a perpendicular charge-transporting direction in charge-discharge process, facilitating electron transportation along that direction. The as-prepared composite exhibits higher specific capacities (1768.7 F g^-1 at 7 A g^-1 and 2667 F g^-1 at 3 mV s^-1, respectively) compared to Ni(OH)₂ aggregations (968.9 F g^-1 at 7 A g^-1) and g-C₃N₄ (416.5 F g^-1 at 7 A g^-1), as well as better cycling performance (∼84% retentions after 4000 cycles). As asymmetric supercapacitor, g-C₃N₄@Ni(OH)₂//graphene exhibits high capacitance (51 F g^-1) and long cycle life (72% retentions after 8000 cycles). Moreover, high energy density of 43.1 Wh kg^-1 and power density of 9126 W kg^-1 has been achieved. This attractive performance reveals that g-C₃N₄@Ni(OH)₂ with honeycomb architecture could find potential application as an electrode material for high-performance supercapacitors.

Ni(OH)2 nanosheets grown on porous hybrid g-C3N4/RGO network as high performance supercapacitor electrode

A porous hybrid g-C₃N₄/RGO (CNRG) material has been fabricated through a facile hydrothermal process with the help of glucose molecules, and serves as an efficient immobilization substrate to support ultrathin Ni(OH)₂ nanosheets under an easy precipitation process. It was found that the g-C₃N₄ flakes can uniformly coat on both sides of the RGO, forming sandwich-type composites with a hierarchical structure. It is worth noting that the introduction of the g-C₃N₄ can effectively achieve the high dispersion and avoid the agglomeration of the nickel hydroxide, and significantly enhance the synthetically capacitive performance. Owning to this unique combination and structure, the CNRG/Ni(OH)₂ composite possesses large surface area with suitable pore size distribution, which can effectively accommodate the electrolyte ions migration and accelerate efficient electron transport. When used as electrode for supercapacitor, the hybrid material exhibits high supercapacitive performance, such as an admirable specific capacitance (1785 F/g at a current density of 2 A/g), desirable rate stability (retain 910 F/g at 20 A/g) and favorable cycling durability (maintaining 71.3% capacity after 5000 cycles at 3 A/g). Such desirable properties signify that the CNRG/Ni(OH)₂ composites can be a promising electrode material in the application of the supercapacitor.

Two-dimensional NiO nanosheets with enhanced room temperature NO2sensing performance via Al doping

Defects caused by Al³⁺doping significantly affect the gas-sensing properties of NiO nanosheets.