Facile One-Step Microwave-Assisted Method to Synthesize Nickel Selenide Nanosheets for High-Performance Hybrid Supercapacitor

The Preparation of N, P-Doped NiSe Nanorod Electrode Materials on Nickel Foam Using the Microwave Method for High-Performance Supercapacitors

Transition metal selenides have the leading position in the field of energy storage and conversion due to their high theoretical capacity, good electrical conductivity, and cycling stability. Nickel is widely used for the construction of positive electrodes in devices due to its good conductivity, variable valence state, and ideal redox activity. NiSe materials have high internal resistance and are prone to volume change during charging and discharging, thus affecting the practical application of this electrode material, and the reported NiSe materials have not achieved a more desirable capacity value. Therefore, in this study, N, P-NiSe nanoelectrode materials were prepared using nickel foam as the nickel source and hexachlorocyclotriphonitrile as the nitrogen and phosphorus dopant using an efficient, energy-saving, and simple microwave method. It was also characterised by XRD and XPS to confirm the successful preparation of N, P-NiSe materials. In addition, the material yielded a high capacitance value (3184 F g-1) and good cycling stability (72% of the initial capacitance value was retained after 4000 cycles) in electrochemical tests. To demonstrate its excellent suitability for practical applications, an asymmetric supercapacitor was assembled using N, P-NiSe as the anode and activated carbon as the cathode. At an operating voltage of 1.6 V, the device achieved an energy density of 289.06 Wh kg-1 and a power density of 799.26 W kg-1 and retained 80% of its initial capacity after 20,000 cycles.

Unveiling the redox electrochemical kinetics of interconnected wrinkled microspheres of binary Cu2-xSe/Ni1-xSe as battery-type electrode for advanced supercapatteries

Developing a rational design of nanoarchitechtures with excellent electrochemical behaviors is an ultimate and unique strategy to enhance the redox electrokinetics of battery-type electrode materials. Herein, we demonstrate a hierarchical composite comprising interconnected wrinkled micro-solid sphere (ICWMS)-like binary copper selenide/nickel selenide over nickel foam (Cu2-xSe/Ni1-xSe/NF) prepared via a wet chemical synthetic protocol and utilized as an effective positrode for improved supercapaterry performance. The binary Cu2-xSe/Ni1-xSe/NF electrode considerably improved the electroactive surface area and facilitated ultrafast redox electrochemistry in an alkaline electrolyte medium. Remarkably, the binary Cu2-xSe/Ni1-xSe/NF electrode afforded the highest specific capacity of 368 ± 1C/g at 1 A/g greater than that of pristine single selenide electrodes (Cu2Se and NiSe) in a three-electrode setup which might be attributed to its large surface area, synergism between Ni and Cu, and specific morphology. Moreover, a coin cell supercapattery with the binary Cu2-xSe/Ni1-xSe/NF positrode and a porous activated carbon-on-nickel-foam negatrode was constructed, which exhibited excellent energy-storage characteristics in terms of capacity (87.5 ± 1 mAh/g), specific energy (39.3 Wh kg-1), specific power (450 W kg-1), and capacity retention (91.8 %). This simple fabrication approach of hierarchically designed Cu2-xSe/Ni1-xSe/NF paves the way for utilizing it as the promising positrode for high-performance supercapattery.

Ultra-High Cycling Stability of 3D Flower-like Ce(COOH)3 for Supercapacitor Electrode via a Facile and Scalable Strategy

An electrode material with high performance, long durability, and low cost for supercapacitors has long been desired in academia and industry. Among all the factors that affect the electrochemical performance and cycling stability of electrode materials, the morphology and intrinsic structure characteristics are the most important. In this study, a novel 3D flower-like Ce(COOH)3 electrode material was designed by taking advantage of the Ce3+ and -COOH groups and fabricated by a one-pot microwave-assisted method. The morphology and structure characteristics of the sample were examined by SEM, EDS, TEM, XRD, FT-IR, XPS, N2 adsorption/desorption techniques, and the electrochemical behaviors were investigated in a three-electrode configuration. The Ce(COOH)3 electrode presents an excellent specific capacitance of 140 F g-1 at 1 A g-1, higher than many other previously reported Ce-based electrodes. In addition, it delivers high rate capability that retains 60% of its initial capacitance when the current density is magnified 20 times. Dramatically, the Ce(COOH)3 electrode exhibits an ultra-high cycling stability with capacitance retention of 107.9% after 60,000 cycles, which is the highest durability among reported Ce-organic compound electrodes to the best of our knowledge. The excellent electrochemical performance is ascribed to its intrinsic crystal structure and unique morphology. This work indicates that the 3D flower-like Ce(COOH)3 has significant potential for supercapacitor applications and the facile and scalable synthesis strategy can be extended to produce other metal-organic composite electrodes.

Green Synthesis of NiFe2O4 Nano-Spinel Oxide-Decorated Carbon Nanotubes for Efficient Capacitive Performance-Effect of Electrolyte Concentration

Energy storage applications received great attention due to environmental aspects. A green method was used to prepare a composite of nickel-iron-based spinel oxide nanoparticle@CNT. The prepared materials were characterized by different analytical methods like X-ray diffraction, X-ray photon spectroscopy (XPS), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM). The synergistic effect between nickel-iron oxide and carbon nanotubes was characterized using different electrochemical methods like cyclic voltammetry (CV), galvanostatic charging/discharging (GCD), and electrochemical impedance spectroscopy (EIS). The capacitances of the pristine NiFe2O4 and NiFe2O4@CNT were studied in different electrolyte concentrations. The effect of OH- concentrations was studied for modified and non-modified surfaces. Furthermore, the specific capacitance was estimated for pristine and modified NiFe2O4 at a wide current range (5 to 17 A g-1). Thus, the durability of different surfaces after 2000 cycles was studied, and the capacitance retention was estimated as 78.8 and 90.1% for pristine and modified NiFe2O4. On the other hand, the capacitance rate capability was observed as 65.1% (5 to 17 A g-1) and 62.4% (5 to 17 A g-1) for NiFe2O4 and NiFe2O4@CNT electrodes.

Phase-Dependent Energy Storage Performance of the NixSey Polymorphs for Supercapacitor-Battery Hybrid Devices

Transition-metal chalcogenides have emerged as a promising class of materials for energy storage applications due to their earth abundance, high theoretical capacity, and high electrical conductivity. Herein, we introduce a facile and one-pot electrodeposition method to prepare high-performance nickel selenide Ni_xSe_y (0.5 ≤ x/y ≤ 1.5) nanostructures (specific capacity = 180.3 mA h g^-1 at 1 A g^-1). The as-synthesized nickel selenide (NS) nanostructure is however converted to other polymorphs of nickel selenide including orthorhombic NiSe₂, trigonal Ni₃Se₂, hexagonal NiSe, and orthorhombic Ni₆Se₅ over cycling. Interestingly, NiSe₂ and Ni₃Se₂ polymorphs that display a more metallic character and superior energy storage performance are the predominant phases after a few hundred cycles. We fabricated a hybrid device using activated carbon (AC) as a supercapacitor-type negative electrode and NS as a high-rate battery-type positive electrode (AC||NS). This hybrid device provides a high specific energy of 71 W h kg^-1, an excellent specific power of up to 31 400 W kg^-1, and exceptional cycling stability (80% retention of the initial capacity after 20 000 cycles). The higher energy storage performance of the device is a result of the development of high-performance NiSe₂ and Ni₃Se₂ polymorphs. Moreover, the reduction of the critical dimension of the NS particles to the nanoscale partially induces an extrinsic pseudocapacitive behavior that improves the rate capability and durability of the device. We also explored the origin of the superior energy storage performance of the NS polymorphs using density functional theory calculations in terms of the computed density of states around the Fermi level, electrical conductivity, and quantum capacitance that follows the trend NiSe₂ > Ni₃Se₂ > NiSe > Ni₆Se₅. The present study thus provides an appealing approach for tailoring the phase composition of NS as an alternative to the commonly used templated synthesis methods.

Intumescent flame retardants inspired template-assistant synthesis of N/P dual-doped three-dimensional porous carbons for high-performance supercapacitors

Heteroatom-doped three-dimensional (3D) porous carbons possess great potential as promising electrodes for high-performance supercapacitors. Inspired by the inherent features of intumescent flame retardants (IFRs) with universal availability, rich heteroatoms and easy thermal-carbonization to form porous carbons, herein we proposed a self-assembling and template self-activation strategy to produce N/P dual-doped 3D porous carbons by nano-CaCO₃ template-assistant carbonization of IFRs. The IFRs-derived carbon exhibited large specific surface area, well-balanced hierarchical porosity, high N/P contents and interconnected 3D skeleton. Benefitting from these predominant characteristics on structure and composition, the assembled supercapacitive electrodes exhibited outstanding electrochemical performances. In three-electrode 6 M KOH system, it delivered high specific capacitances of 407 F g^-1 at 0.5 A g^-1, and good rate capability of 61.2% capacitance retention at 20 A g^-1. In two-electrode organic EMIMBF₄/PC system, its displayed high energy density of 62.8 Wh kg^-1 at a power density of 748.4 W kg^-1, meanwhile it had excellent cycling stability with 84.7% capacitance retention after 10,000 cycles. To our best knowledge, it is the first example to synthesize porous carbon from IFRs precursor. Thus, the current work paved a novel and low-cost way for the production of high-valued carbon material, and expanded its application for high-performance energy storage devices.

CuCoNi–S anchored CoMoO4/MoO3 forming core–shell structure for high-performance asymmetric supercapacitors

CoMoO4/MoO3@CuCoNi–S is prepared by hydrothermal and electrodeposition methods. It offers promising supercapacitor properties.

Microwave heating followed by a solvothermal method to synthesize nickel–cobalt selenide/rGO for high-performance supercapacitors

Efficient microwave heating followed by a solvothermal method is used to synthesize (Ni0.85Se)3(Co0.85Se)/rGO nanorods with an ultrahigh specific capacitance of 2009 F g−1 at a current density of 2 A g−1.