Nickel molybdate nanorods supported on three-dimensional, porous nickel film coated on copper wire as an advanced binder-free electrode for flexible wire-type asymmetric micro-supercapacitors with enhanced electrochemical performances

Ni,S co-doped Cu dendrites decorated with core-shell architecture assisted by MOF and Fe0.92Co0.08S nanoflakes on nanocellulose/graphene fibers for fabrication of flexible wire-type micro-supercapacitor

One-dimensional micro-supercapacitors (1D micro-SCs) have been regarded as an efficient energy storage system to fulfill the ever-growing need for miniaturized electronics. Designing multi-dimensional nanoarchitectures on fibrous microelectrodes is an effective strategy to build a high-performance 1D micro-SC. In this work, Ni,S-doped Cu was firstly prepared on Cu wire as a micro-sized 1D current collector through Cu electrodeposition using a H2 bubble template and then co-doped with nickel and sulfur. Benefiting from the high electrical/thermal conductivity of Cu, and the highly electroactive sites of Ni and S as well as the 3D porous architecture, the deposited Ni,S-doped Cu provided a platform for growing active substances. Thereafter, cobalt carbonate hydroxide (CoCH) pine-like nanoneedle integrated ZIF-67 polyhedrons were synthesized on a foam-like skeleton and converted into NiMoCo-layered triple hydroxide (LTH)/Ni,S-doped Cu shish-kebab type nanoarrays by applying a hydrothermal method. Finally, Ni2Mo3N-CoN/Ni,S-doped Cu was prepared via nitridation. The potent interactions and synergy between components realized a well-organized hybrid nanoarchitecture consisting of dodecahedrons decorated on needle-like arrays within a 3D framework with rich redox properties, rapid ion/electron transfer dynamics and high electroactivity. In comparison to the LTH obtained from the electrodeposition method (without the ZIF-67 precursor) and that derived from leaf-like ZIF-Co, this modified microfiber exhibited a high charge storage capacity of 1.5 mA h cm-2 (149.9 mA h cm-3 and 0.187 mA h cm-1) at 4 mA cm-2 and possesses an excellent durability of 98.4% after 5000 cycles. Additionally, FeCoS nanoflakes were electrodeposited using carbon fiber coated with an rGO-nanocellulose hydrogel (GNCH) and employed as a negative 1D microelectrode, which delivered a high specific capacitance of 1223 mF cm-2 (83 F cm-3, 232.4 mF cm-1) at 4 mA cm-2 with a superior cyclic lifespan. Ultimately, the assembled 1D flexible micro-device (Ni2Mo3N-CoN/Ni,S-doped Cu@CW//FeCoS/GNCH@CF) yielded an energy density of 7.2 mW h cm-3 at a power density of 294 mW cm-3 and outstanding cycling stability in PVA/KOH electrolyte and preserved the capacitive performance under various bending states. This research highlights that assembled 1D micro-SCs have a high potency for next-generation portable/wearable energy-supply microelectronics.

Heterogeneous Ni-Co phosphide/phosphate with a specific hollow sea-urchin-like structure for high-performance hybrid supercapacitor and alkaline zinc-metal battery applications

Constructing well-defined nanostructures consisting of the multiple components with distinctive features are a promising but challenging strategy to develop advanced electroactive materials for energy storage applications. Herein, heterogeneous Ni-Co phosphide/phosphate with a specific hollow sea-urchin-like structure has been synthesized as advanced electroactive materials for both hybrid supercapacitor (HSC) and alkaline zinc-metal battery (AZB) applications. The heterogeneous Ni-Co phosphide/phosphate combines the merits of improved electrolyte interfacial property from the specific hollow sea-urchin-like structure, high electron-conductivity of phosphide, and better ion adsorption and solid diffusion property of phosphate. As a result, the Ni-Co phosphide/phosphate achieves a high capacity to 180.7 mA h g^-1 at 1 A g^-1, excellent rate capability of 51% capacity retention when the specific current increases by 50 times, and stable cycling stability of 85% capacity retention when cycled for 1000 cycles. Ex situ test was conducted to investigate the formation mechanism for the hollow and sea-urchin-like structure, which can be ascribed to the anion exchange reaction between pre-formed hydroxide and CO₃^2- ions. When used to assemble HSCs with reduced graphene oxide (RGO), the HSCs exhibit a high specific energy of 49.4 W h kg^-1, an ultrahigh specific power to 11.7 kW kg^-1, and an eminent cycling stability over 10,000 cycles. Meanwhile, Ni₂Co-P/PO_x-based AZB also achieves both high-energy and high-power performance with the specific energy of 308.0 W h kg^-1 at 828.4 W kg^-1 and 117.4 W h kg^-1 at 30.8 kW kg^-1. These results above suggest that heterogeneous Ni-Co phosphide/phosphate has great potential to be used as a candidate for both HSC and AZB applications.

Nickel cobaltite nanowire arrays grown on nitrogen-doped carbon nanotube fiber fabric for high-performance flexible supercapacitors

Flexible supercapacitors have received considerable attention for their potential application in flexible electronics, but usually suffer from relatively low energy density. Developing flexible electrodes with high capacitance and constructing asymmetric supercapacitors with large potential window has been considered as the most effective approach to achieve high energy density. Here, a flexible electrode with nickel cobaltite (NiCo₂O₄) nanowire arrays on nitrogen (N)-doped carbon nanotube fiber fabric (denoted as CNTFF and NCNTFF, respectively) was designed and fabricated through a facile hydrothermal growth and heat treatment process. The obtained NCNTFF-NiCo₂O₄ delivered a high capacitance of 2430.5 mF cm^-2 at 2 mA cm^-2, a good rate capability of 62.1 % capacitance retention even at 100 mA cm^-2 and a stable cycling performance of 85.2 % capacitance retention after 10,000 cycles. Moreover, the asymmetric supercapacitor constructed with NCNTFF-NiCo₂O₄ as positive electrode and activated CNTFF as negative electrode exhibited a combination of high capacitance (883.6 mF cm^-2 at 2 mA cm^-2), high energy density (241 μW h cm^-2) and high power density (80175.1 μW cm^-2). This device also had a long cycle life after 10,000 cycles and good mechanical flexibility under bending conditions. Our work provides a new perspective on constructing high-performance flexible supercapacitors for flexible electronics.

Surface Engineering of Ni wires and Rapid Growth Strategy of Ni-MOF Synergistically Contribute to High-Performance Fiber-Shaped Aqueous Battery

The fiber-shaped aqueous battery (FSAB) has the advantages of flexibility, portability and safety making it promising for energy storage applications. In particular, FSABs based on metal wire current collectors with good electrical conductivity can provide excellent energy storage properties. However, the low adhesion caused by the smooth surface of the metal wire and the unavailability of many electrochemically active materials for use in FSAB is holding back their development. Herein, a substrate is effectively constructed for the strongly applicable growth of the active material via a Ni wire etching strategy. In addition, core-shell structured nanorod arrays consisting of NiCo₂ O₄ and Ni-metal-organic frameworks (MOFs) are constructed, where Ni-MOF can be obtained rapidly via β-Ni(OH)₂ intermediates. The NCO/NM-15 electrode obtained by structural regulation exhibits high capacity and outstanding cycling stability. De calculations further demonstrate that the formation of NiCo₂ O₄ and Ni-MOF heterostructures results in a significant increase in the Fermi level leading to more active internal electrons, which facilitates electron transfer in electrochemical reactions. An assembled FSAB device can provide an energy density of 158.33 µWh cm^-2 and the devices can provide power for a calculator and an electronic watch screen, demonstrating a wide application prospect in the field of energy storage.

Interfacially coupled thin sheet-like NiO/NiMoO4 nanocomposites synthesized by a simple reflux method for excellent electrochemical performance

Herein, hierarchical sheet-like assemblies of interfacially coupled NiO/NiMoO₄ (NNMO) nanocomposites are prepared by a simple and cost-effective one-step aqueous reflux method followed by post-thermal treatment. The reaction time is optimized for a high precursor yield and the homogeneity of the final product. The fabricated electrodes with varying amounts of active material and conducting carbon show better electrochemical activity for 50 : 50 weight ratio combinations as extrinsic pseudocapacitors. The optimized NNMO-3 electrode (obtained from the Ni-Mo hydroxide precursor during the 10 h reaction time) exhibits superior performance among all the tested nanocomposite electrodes like a high specific capacity of 649.8 C g^-1 (1624.5 F g^-1) and 73.5% retention of capacity after 2200 cycles at a specific current of 1.0 A g^-1 along with satisfactory rate capability (42.5% retention after a ten-times increment in specific current), which may be attributed to the abundant electroactive sites due to the high bulk as well as electrochemically active surface area, mesoporous structure, and synergistic coupling between the optimum compositions of NiO and NiMoO₄ within the sheet-like networks. Moreover, an aqueous asymmetric supercapacitor is assembled by employing NNMO-3 and activated carbon as the positive and negative electrodes, respectively, and exhibits a maximum specific capacity of 216.2 C g^-1 (144.1 F g^-1), specific energy of 45.0 W h kg^-1 at a specific power of 750.0 W kg^-1, promising rate capability of 58.5%, and good cycling stability with 86.2% capacitive retention after 2500 charge-discharge cycles. Based on the overall performance, we can infer that the NNMO-3 nanocomposite may be a promising electrode material for high-performance supercapacitor applications.

Hydrangea-like NiMoO4-Ag/rGO as Battery-type electrode for hybrid supercapacitors with superior stability

It is a great challenge to design electrode materials with good stability and high specific capacitance for supercapacitors. Herein, a three-dimensional (3D) hydrangea-like NiMoO₄ micro-architecture with Ag nanoparticles anchored on the surface has been designed by adding EDTA-2Na, which was assembled with reduced graphene oxide (rGO) and named as NiMoO₄-Ag/rGO composite. Benefiting from the synergetic contributions of structural and componential properties, NiMoO₄-Ag/rGO composite exhibits a high specific capacitance of 566.4 C g^-1 at 1 A g^-1, and great cycling performance with 90.5% capacitance retention after 1000 cycles at 10 A g^-1. The NiMoO₄-Ag/rGO electrode shows an enhanced cycling stability due to the two-dimensional towards two-dimensional (2D-2D) interface coupling between rGO and NiMoO₄ nanosheets, and the stable 3D hydrangea-like micro-architecture. Moreover, NiMoO₄-Ag/rGO with 5-15 nm pore structure and enhanced conductivity exhibits improved charge transfer and ions diffusion. Besides, NiMoO₄-Ag/rGO//AC capacitor displays an outstanding energy density of 40.98 Wh kg^-1 at 800 kW kg^-1, and an excellent cycling performance with 73.3% capacitance retention at 10 A g^-1 after 8000 cycles. The synthesis of NiMoO₄-Ag/rGO composite can provide an effective strategy to solve the poor electrochemical stability and slow electron/ion transfer of NiMoO₄ material as supercapacitors electrode.

NiMoO4 nanorods photocatalytic activity comparison under UV and visible light

Waste water remediation is the ongoing hot research topic that can reduce the water scarcity all over the world. By reducing the pollutants in the waste water drawn from industries and other sources will be more useful for domestic purposes. To reduce the rate of pollutants in water may also help in improving the aquatic environment and decreases other side effects. Efficient and cost effective catalysts were in search for both dye degradation and water remediation treatment applications. NiMoO₄ nanorods were prepared by employing co-precipitation method with different stirrer time (2 h, 4 h and 6 h). The formation of NiMoO₄ was substantiated employing X-ray diffractometer analysis (XRD). Vibrational and rotational property of the samples was analyzed by FT-IR spectra and Raman spectra. The optical property was further confirmed by UV-vis spectral studies. Morphological analysis studies revealed growth of nanorods with 6 h stirrer time. The photocatalytic behavior of the obtained product was carried out under both UV light (364 nm) and visible light irradiation. The samples subjected to visible light environment showed better efficiency on degrading the methylene blue (MB) dye. The efficiency obtained under UV irradiation were 20%, 31%, 33%, 41% and efficiency obtained in visible light irradiation were 27%, 42%, 46%, 55% with respect to bare methylene blue (MB), MB with NiMoO₄ (2 h), MB with NiMoO₄ (4 h), MB with NiMoO₄ (6 h) catalyst added. NiMoO₄ sample with 6 h stirrer time and fine nanorods growth will be the good candidate for future use.

NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor

In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.

Mesoporous Carbon Microfibers for Electroactive Materials Derived from Lignocellulose Nanofibrils

The growing adoption of biobased materials for electronic, energy conversion, and storage devices has relied on high-grade or refined cellulosic compositions. Herein, lignocellulose nanofibrils (LCNF), obtained from simple mechanical fibrillation of wood, are proposed as a source of continuous carbon microfibers obtained by wet spinning followed by single-step carbonization at 900 °C. The high lignin content of LCNF (∼28% based on dry mass), similar to that of the original wood, allowed the synthesis of carbon microfibers with a high carbon yield (29%) and electrical conductivity (66 S cm^-1). The incorporation of anionic cellulose nanofibrils (TOCNF) enhanced the spinnability and the porous morphology of the carbon microfibers, making them suitable platforms for electrochemical double layer capacitance (EDLC). The increased loading of LCNF in the spinning dope resulted in carbon microfibers of enhanced carbon yield and conductivity. Meanwhile, TOCNF influenced the pore evolution and specific surface area after carbonization, which significantly improved the electrochemical double layer capacitance. When the carbon microfibers were directly applied as fiber-shaped supercapacitors (25 F cm^-3), they displayed a remarkably long-term electrochemical stability (>93% of the initial capacitance after 10 000 cycles). Solid-state symmetric fiber supercapacitors were assembled using a PVA/H₂SO₄ gel electrolyte and resulted in an energy and power density of 0.25 mW h cm^-3 and 65.1 mW cm^-3, respectively. Overall, the results indicate a green and facile route to convert wood into carbon microfibers suitable for integration in wearables and energy storage devices and for potential applications in the field of bioelectronics.

Transition metal sulfide-laminated copper wire for flexible hybrid supercapacitor

The CV profiles of transition metal sulphide electrodes on a Cu-wire (a), and (b) capacitive (light to dark: blue and red) and diffusion-controlled (dark: blue and red) contributions of the hybrid Cu@CoS/NiCo₂S₄ and Cu@ZnCo₂S₄ electrodes.