Facile Growth of Caterpillar-like NiCo2S4 Nanocrystal Arrays on Nickle Foam for High-Performance Supercapacitors

Synthesis of urchin-like NiCo2S4 electrode materials based on a two-step hydrothermal method for high-capacitance supercapacitors

Transition metal sulfides have been considered as promising electrode materials for future super-capacitors due to their spinel structures and environmentally friendly properties. Among these materials, NiCo2S4 compounds exhibit high theoretical specific capacity but poor cycling performance. To address this issue, we synthesize several NiCo2S4 urchin balls. The NCS-1.5 nanospheres demonstrate a specific capacitance of 1352.2 F g-1 at a current density of 1 A g-1, and maintain high specific capacity after 10 000 charge-discharge cycles. An asymmetric capacitor assembled with the NCS-1.5 sample as the cathode and activated carbon as the anode achieve an energy density of 45.5 W h kg-1 at 2025 W kg-1. The urchin-like nanospheres also facilitate the combination with other materials, providing potential insights for the synthesis of supercapacitor electrode materials.

Hierarchically Developed Ni(OH)2@MgCo2O4 Nanosheet Composites for Boosting Supercapacitor Performance

MgCo₂O₄ nanomaterial is thought to be a promising candidate for renewable energy storage and conversions. Nevertheless, the poor stability performances and small specific areas of transition-metal oxides remain a challenge for supercapacitor (SC) device applications. In this study, sheet-like Ni(OH)₂@MgCo₂O₄ composites were hierarchically developed on nickel foam (NF) using the facile hydrothermal process with calcination technology, under carbonization reactions. The combination of the carbon-amorphous layer and porous Ni(OH)₂ nanoparticles was anticipated to enhance the stability performances and energy kinetics. The Ni(OH)₂@MgCo₂O₄ nanosheet composite achieved a superior specific capacitance of 1287 F g^-1 at a current value of 1 A g^-1, which is higher than that of pure Ni(OH)₂ nanoparticles and MgCo₂O₄ nanoflake samples. At a current density of 5 A g^-1, the Ni(OH)₂@MgCo₂O₄ nanosheet composite delivered an outstanding cycling stability of 85.6%, which it retained over 3500 long cycles with an excellent rate of capacity of 74.5% at 20 A g^-1. These outcomes indicate that such a Ni(OH)₂@MgCo₂O₄ nanosheet composite is a good contender as a novel battery-type electrode material for high-performance SCs.

MOF-Derived Ultrathin NiCo-S Nanosheet Hybrid Array Electrodes Prepared on Nickel Foam for High-Performance Supercapacitors

At present, binary bimetallic sulfides are widely studied in supercapacitors due to their high conductivity and excellent specific capacitance (SC). In this article, NiCo-S nanostructured hybrid electrode materials were prepared on nickel foam (NF) by using a binary metal-organic skeleton as the sacrificial template via a two-step hydrothermal method. Comparative analysis was carried out with Ni-S and Co-S in situ on NF to verify the excellent electrochemical performance of bimetallic sulfide as an electrode material for supercapacitors. NiCo-S/NF exhibited an SC of 2081 F∙g^-1 at 1 A∙g^-1, significantly superior to Ni-S/NF (1520.8 F∙g^-1 at 1 A∙g^-1) and Co-S/NF (1427 F∙g^-1 at 1 A∙g^-1). In addition, the material demonstrated better rate performance and cycle stability, with a specific capacity retention rate of 58% at 10 A∙g^-1 than at 1 A∙g^-1, and 75.7% of capacity was retained after 5000 cycles. The hybrid supercapacitor assembled by NiCo-S//AC exhibited a high energy density of 25.58 Wh∙kg^-1 at a power density of 400 W∙kg^-1.

Design strategy for high-performance bifunctional electrode materials with heterogeneous structures formed by hydrothermal sulfur etching

The synthesis of efficient, stable, and green multifunctional electrode materials is a long-standing challenge for modern society in the field of energy storage and conversion. To this end, we successfully synthesized five bimetallic precursor materials with excellent performance by hydrothermal reaction with the assistance of a high concentration of polyvinylpyrrolidone (PVP), and then, sulfide etched the lamellar precursor materials among them to obtain the one-dimensional heterostructured samples. Benefiting from the synergistic effect of the bimetal and the continuous electron/ion transport structure, the samples displayed excellent bifunctional activity in supercapacitor and oxygen evolution reaction (OER). Regarding supercapacitors, the exceptional performance of 2817.2 F g^-1 at 1 A g^-1 was demonstrated, while the asymmetric supercapacitors made showed an extraordinary energy density of 150.2 Wh kg^-1 at a power density of 618.5 W kg^-1 and outstanding cycling performance (94.74% capacity retention after 20,000 cycles at 10 A g^-1). Simultaneously, a wearable flexible electrode that can be wrapped around a finger was coated on a carbon cloth and was found to light up a 0.5-m-long strip of light. Moreover, it exhibited an ultralow oxygen reduction overpotential of 249 mV at 10 mA cm^-2. Hence, our work provides a facile strategy to modulate the synthesis of heterogeneous structured sulfides with a continuous electron/ion transport pathway, which possesses excellent oxygen reduction electrocatalytic performance while meeting superior supercapacitor performance. Such work provides an effective approach for the construction of multifunctional electrochemical energy materials.

Amorphous Mo-doped NiS0.5 Se0.5 Nanosheets@Crystalline NiS0.5 Se0.5 Nanorods for High Current-density Electrocatalytic Water Splitting in Neutral Media

It is vitally important to develop highly active, robust and low-cost transition metal-based electrocatalysts for overall water splitting in neutral solution especially at large current density. In this work, amorphous Mo-doped NiS_0.5 Se_0.5 nanosheets@crystalline NiS_0.5 Se_0.5 nanorods (Am-Mo-NiS_0.5 Se_0.5 ) was synthesized using a facil one-step strategy. In phosphate buffer saline solution, the Am-Mo-NiS_0.5 Se_0.5 shows tiny overpotentials of 48 and 209 mV for hydrogen evolution reaction (HER), 238 and 514 mV for oxygen evolution reaction (OER) at 10 and 1000 mA cm^-2 , respectively. Moreover, Am-Mo-NiS_0.5 Se_0.5 delivers excellent stability for at least 300 h without obvious degradation. Theoretical calculations revealed that the Ni sites in the defect-rich amorphous structure of Am-Mo-NiS_0.5 Se_0.5 owns higher electron state density and strengthened the binding energy of H₂ O, which will optimize H adsorption/desorption energy barriers and reduce the adsorption energy of OER determining step.

Sulfur Nanoparticle-Decorated Nickel Cobalt Sulfide Hetero-Nanostructures with Enhanced Energy Storage for High-Performance Supercapacitors

Transition-metal sulfides exaggerate higher theoretical capacities and were considered a type of prospective nanomaterials for energy storage; their inherent weaker conductivities and lower electrochemical active sites limited the commercial applications of the electrodes. The sheet-like nickel cobalt sulfide nanoparticles with richer sulfur vacancies were fabricated by a two-step hydrothermal technique. The sheet-like nanoparticles self-combination by ultrathin nanoparticles brought active electrodes entirely contacted with the electrolytes, benefiting ion diffusion and charges/discharges. Nevertheless, defect engineers of sulfur vacancy at the atomic level raise the intrinsic conductivities and improve the active sites for energy storage functions. As a result, the gained sulfur-deficient NiCo2S4 nanosheets consist of good specific capacitances of 971 F g-1 at 2 A g-1 and an excellent cycle span, retaining 88.7% of the initial capacitance over 3500 cyclings. Moreover, the values of capacitance results exhibited that the fulfilling characteristic of the sample was a combination of the hydrothermal procedure and the surface capacitances behavior. This novel investigation proposes a new perspective to importantly improve the electrochemical performances of the electrode by the absolute engineering of defects and morphologies in the supercapacitor field.

Electro-Chemical Degradation of Norfloxacin Using a PbO2-NF Anode Prepared by the Electrodeposition of PbO2 onto the Substrate of Nickel Foam

A novel three-dimensional network nickel foam/PbO2 combination electrode (PbO2-NF) with high electrochemical degradation efficiency to norfloxacin was successfully fabricated through the electrodeposition of PbO2 on the substrate of nickel foam. The characterization of an PbO2-NF electrode, including surface morphology, elemental components, electrochemical performance, and stability was performed. In electrochemical oxidation tests, the removal efficiency of norfloxacin (initial concentration for 50 mg/L) on PbO2-NF reached 88.64% within 60 min of electrolysis, whereas that of pure nickel foam was only 30%. In the presence of PbO2-NF, the optimum current density, solution pH, electrode spacing for norfloxacin degradation were 30 mA/cm2, 11, and 3 cm, respectively. The electric energy consumption for 80% norfloxacin was approximately 5 Wh/L. Therefore, these results provide a new anode to improve the removal of norfloxacin in the wastewater with high efficiency and low energy consumption.

Animal- and Human-Inspired Nanostructures as Supercapacitor Electrode Materials: A Review

Human civilization has been relentlessly inspired by the nurturing lessons; nature is teaching us. From birds to airplanes and bullet trains, nature gave us a lot of perspective in aiding the progress and development of countless industries, inventions, transportation, and many more. Not only that nature inspired us in such technological advances but also, nature stimulated the advancement of micro- and nanostructures. Nature-inspired nanoarchitectures have been considered a favorable structure in electrode materials for a wide range of applications. It offers various positive attributes, especially in energy storage applications, such as the formation of hierarchical two-dimensional and three-dimensional interconnected networked structures that benefit the electrodes in terms of high surface area, high porosity and rich surface textural features, and eventually, delivering high capacity and outstanding overall material stability. In this review, we comprehensively assessed and compiled the recent advances in various nature-inspired based on animal- and human-inspired nanostructures used for supercapacitors. This comprehensive review will help researchers to accommodate nature-inspired nanostructures in industrializing energy storage and many other applications.

Construction of NiCoZnS materials with controllable morphology for high-performance supercapacitors

A facile two-step hydrothermal approach with post-sulfurization treatment was put forward to construct the mixed transition metal sulfide (NiCoZnS) with a high electrochemical performance. The different morphologies of NiCoZnS materials were successfully fabricated by adjusted the Ni/Co molar ratio of the NiCoZn(OH)F precursor. Moreover, thein situphase transformation from the NiCoZn(OH)F phase to Zn_0.76Co_0.24S and NiCo₂S₄phases and lattice defects via the S^2-ion-exchange were determined by x-ray diffractometer, transmission electron microscopy and x-ray photoelectron spectroscopy techniques, which improved electric conductivity and interfacial active sites of the NiCoZnS, and so promoted the reaction kinetics. Significantly, the urchin-like NiCoZnS_1/1prepared at the Ni/Co molar ratio of 1.0 exhibited promising electrochemical performances with high capacitance and excellent cycling stability. Furthermore, the asymmetric device (NiCoZnS//AC) using NiCoZnS_1/1as the positive electrode had excellent supercapacitor performances with an energy density of 57.8 Wh·kg^-1at a power density of 750 W·kg^-1as well as a long cycle life (79.2% capacity retention after 10 000 cycles), indicating the potential application in high-performance supercapacitors.

Fe doped NiS nanosheet arrays grown on carbon fiber paper for a highly efficient electrocatalytic oxygen evolution reaction

Developing efficient and low-cost non-noble metal catalysts for the oxygen evolution reaction (OER) is important for hydrogen production through water electrolysis. Herein, Fe doped NiS nanosheets directly grown on conductive carbon fiber paper (Fe-NiS@CFP) were fabricated through a two-step hydrothermal process. The microstructure, interface and electronic states of the prepared sample were modulated by Fe doping, exhibiting small internal and interface charge-transfer resistance. Benefiting from these factors, Fe-NiS@CFP shows superior electrocatalytic performance with an overpotential of 275 mV at 100 mA cm^-2 and maintains the activity for at least 50 h as a working electrode for the OER. This work may provide insights into the design and fabrication of non-noble metal sulfide electrocatalysts.

Wood-Derived, Conductivity and Hierarchical Pore Integrated Thick Electrode Enabling High Areal/Volumetric Energy Density for Hybrid Capacitors

For the proliferation of the supercapacitor technology, it is essential to attain superior areal and volumetric performance. Nevertheless, maintaining stable areal/volumetric capacitance and rate capability, especially for thick electrodes, remains a fundamental challenge. Here, for the first time, a rationally designed porous monolithic electrode is reported with high thickness of 800 µm (46.74 mg cm^-2 , with high areal mass loading of NiCo₂ S₄ 6.9 mg cm^-2 ) in which redox-active Ag nanoparticles and NiCo₂ S₄ nanosheets are sequentially decorated on highly conductive wood-derived carbon (WC) substrates. The hierarchically assembled WC@Ag@NiCo₂ S₄ electrode exhibits outstanding areal capacitance of 6.09 F cm^-2 and long-term stability of 84.5% up to 10 000 cycles, as well as exceptional rate capability at 50 mA cm^-2 . The asymmetric cell with an anode of WC@Ag and a cathode of WC@Ag@NiCo₂ S₄ delivers areal/volumetric energy density of 0.59 mWh cm^-2 /3.93 mWh cm^-3 , which is much-improved performance compared to those of most reported thick electrodes at the same scale. Theoretical calculations verify that the enhanced performance could be attributed to the decreased adsorption energy of OH^- and the down-shifted d-band of Ag atoms, which can accelerate the electron transport and ion transfer.

Core-shell coaxially structured NiCo2S4@TiO2nanorod arrays as advanced electrode for solid-state asymmetric supercapacitors

An integrated electrode of core-shell coaxially structured NiCo₂S₄@TiO₂nanorod arrays/carbon cloth (NiCo₂S₄@TiO₂@CC) have been fabricated, via a two-step hydrothermal method. Comprehensive structural and compositional analyzes are performed to understand the effects of the NiCo₂S₄shell on the TiO₂core. Such core-shell arrays structure can significantly provide abundant electroactive sites for redox reactions, convenient ion transport paths, and favorable structure stability. The NiCo₂S₄@TiO₂@CC electrode represents a splendid specific capacitance (650 F g^-1at 1 A g^-1) and enhanced cycling stability (capacitance retention of 97% over 10 000 cycles at 5 A g^-1). Additionally, the assembled NiCo₂S₄@TiO₂@CC//CNT@CC solid-state asymmetric supercapacitors exhibit a maximal energy density of 0.6 mWh cm^-3at 32.4 W cm^-3, and topping cycling stability (85% capacitance retention after 5000 cycles at 5 mA cm^-2). The results demonstrate that the well-designed NiCo₂S₄@TiO₂@CC presented in this work are applicable for the development of electrode materials in energy storage devices.

Iron Doped in the Subsurface of CuS Nanosheets by Interionic Redox: Highly Efficient Electrocatalysts toward the Oxygen Evolution Reaction

Modifying the electronic structure of electrocatalysts by metal doping is favorable to their electrocatalytic activity. Herein, by a facile one-pot redox process of Fe(III) and Cu(I), Fe(II) was successfully doped into the subsurface of CuS nanosheets (NSs) for the first time to obtain a novel electrocatalyst (Fe_sub-CuS NSs) that possesses not only subtle lattice defects but also an atomic-level coupled nanointerface, greatly enhancing the oxygen evolution reaction (OER) performances. Meanwhile, Fe(II) and Fe(III) coexisting in Fe_sub-CuS nanosheets are favorable to OER through valence regulation. As expected, by simultaneously controlling the abovementioned three factors to optimize Fe_sub-CuS nanosheets, they display a lower overpotential of 252 mV at a current density of 20 mA cm^-2 for OER, better than 389 mV for pristine CuS nanosheets. This discovery furnishes low-cost and efficient Cu-based electrocatalysts by metal doping. Density functional theory (DFT) calculations further verify that Fe_sub-CuS(100) is thermodynamically stable and is more active for OER. This research provides a strategy for the atomic-scale engineering of nanocatalysts and also sheds light on the design of novel and efficient electrocatalysts.

Enhancing bifunctional catalytic activity of cobalt-nickel sulfide spinel nanocatalysts through transition metal doping and its application in secondary zinc-air batteries

Developing large-scale and high-performance OER (oxygen evolution reaction) and ORR (oxygen reduction reaction) catalysts have been a challenge for commercializing secondary zinc-air batteries. In this work, transition metal-doped cobalt-nickel sulfide spinels are directly produced via a continuous hydrothermal flow synthesis (CHFS) approach. The nanosized cobalt-nickel sulfides are doped with Ag, Fe, Mn, Cr, V, and Ti and evaluated as bifunctional OER and ORR catalyst for Zn-air battery application. Among the doped spinel catalysts, Mn-doped cobalt-nickel sulfides (Ni1.29Co1.49Mn0.22S4) exhibit the most promising OER and ORR performance, showing an ORR onset potential of 0.9 V vs. RHE and an OER overpotential of 348 mV measured at 10 mA cm-2, which is attributed to their high surface area, electronic structure of the dopant species, and the synergistic coupling of the dopant species with the active host cations. The dopant ions primarily alter the host cation composition, with the Mn(iii) cation linked to the introduction of active sites by its favourable electronic structure. A power density of 75 mW cm-2 is achieved at a current density of 140 mA cm-2 for the zinc-air battery using the manganese-doped catalyst, a 12% improvement over the undoped cobalt-nickel sulfide and superior to that of the battery with a commercial RuO2 catalyst.

Design of nickel cobalt molybdate regulated by boronizing for high-performance supercapacitor applications

Nickel-cobalt-based molybdates have been intensively investigated because of their high theoretical specific capacitance and multifarious oxidation states. Here, we have successfully synthesized hierarchical structures (Ni₃B/Ni(BO₂)₂@Ni_xCo_yMoO₄) by boronizing Ni_xCo_yMoO₄ nanosheets on flexible carbon cloth substrates. Benefitting from the synergistic effect among Ni₃B, Ni(BO₂)₂ and Ni_xCo_yMoO₄ in hybrid architectures, the electrode material possesses higher capacity of 394.7 mA h g^-1 at 1 A g^-1 and a good rate performance (309.5 mA h g^-1 maintained at 20 A g^-1). Then, a hybrid supercapacitor assembled with Ni₃B/Ni(BO₂)₂@Ni_xCo_yMoO₄ and activated carbon as the positive and the negative electrode, displays a high specific capacitance of 370.7 F g^-1 at 1 A g^-1 (210 F g^-1 at 10 A g^-1), a high voltage of 1.7 V, and a high energy density of 131.8 W h kg^-1 at the power density of 800 W kg^-1 (still 74.7 W h kg^-1 maintained at 8000 W kg^-1). This study widens the research scope of boronizing pseudocapacitance materials and reveals a high application potential of Ni₃B/Ni(BO₂)₂@Ni_xCo_yMoO₄ for energy storage devices in the future.

Hybrid structured CoNi2S4/Ni3S2 nanowires with multifunctional performance for hybrid capacitor electrodes and overall water splitting

Rational design of electrode materials plays a significant role in potential applications such as energy storage and conversion. In this work, CoNi₂S₄/Ni₃S₂ nanowires grown on Ni foam were synthesized through a facile hydrothermal approach, revealing a large capacitance of 997.2 F g⁻¹ and cycling stability with 80.3% capacitance retention after 5000 cycles. The device was prepared using CoNi₂S₄/Ni₃S₂//AC as the positive electrode and active carbon as the negative electrode, and delivered an energy density of 0.4 mW h cm⁻³ at a power density of 3.99 mW cm⁻³ and an excellent cycle life with 79.2% capacitance retention after 10 000 cycles. In addition, the hybrid CoNi₂S₄/Ni₃S₂ nanowires demonstrate excellent OER performance with low overpotential of 360 mV at 30 mA cm⁻² and overpotential of 173.8 mV at −10 mA cm⁻² for the HER, a cell voltage of 1.43 V, and excellent cycle stability.

Rational design of electrode materials plays a significant role in potential applications such as energy storage and conversion.

Fabrication of dual-hollow heterostructure of Ni2CoS4 sphere and nanotubes as advanced electrode for high-performance flexible all-solid-state supercapacitors

High-energy-density and flexible supercapacitors have shown numerous application potential in modern portable electronics. However, the relatively low specific capacity, poor rate retentions, and limited durability have hindered their implement. Herein, a novel hierarchical dual-hollow electrode, composed of a hollow Ni₂CoS₄ sphere and outer hollow Ni₂CoS₄ nanotubes (Ni₂CoS₄HS-HTs), is elaborately constructed. The Ni₂CoS₄HS-HT-5 exhibits a high specific capacity of 817.5 C g^-1 at a current density of 1 A g^-1 with remarkable rate retention of 75.3% at 50 A g^-1. In an all-solid-state asymmetric supercapacitor of Ni₂CoS₄HS-HT-5//CAC, a high capacitance of 1511.5 mF cm^-2 at 5 mA cm^-2 is obtained with an exceptional energy density of 13.6 mWh cm^-3 at a power density of 92.6 mW cm^-3. In addition, the capacity retention reaches 96% over 2000 cycles at 20 mA cm^-3, implying the outstanding durability. The flexibility and mechanical stability are demonstrated by the intact electrochemical performances under different bending angles. As a proof-of-concept, two Ni₂CoS₄HS-HT-5//CACs in series could successfully illuminate 31 LED indicators for more than 8 mins. These fascinating electrochemical performances benefit from the novel electrode structure and depict great potential for modern energy storage applications.

Multidimensional structure of CoNi2S4 materials: structural regulation promoted electrochemical performance in a supercapacitor

Multidimensional architectures of CoNi2S4 electrode materials are rationally designed by engineering the surface structure toward that of high-performance supercapacitors. The fabrication of a special morphology is highly dependent on the synergistic effect between the guidance of Co-Ni precursor arrays and a subsequent sulfidation process. The unparalleled CoNi2S4 electrode materials (NS-3) deliver a significantly enhanced specific capacitance (3784.6 F g-1 at 3 A g-1), accompanied by an extraordinary rate capability (2932.3 F g-1 at 20 A g-1) and excellent cycling life. The outstanding supercapacitor performance stated above stems from the advantages of a multidimensional structure generated by crosslinking 2D microsheets/1D nanowires/2D ultrathin nanosheets; this structure supplies additional efficient active sites and a large contact area at the electrode-electrolyte interface, providing faster transport kinetics for electrons and ions. For practical applications, asymmetric devices based on an NS-3 positive electrode and active carbon negative electrode exhibit a high energy density of 38.5 W h kg-1 accompanied by a power density of 374.9 W kg-1 (22 W h kg-1 at 7615.4 W kg-1). The above results indicate that the design of multidimensional Co-Ni-S materials is an effective strategy to achieve a high-performance supercapacitor.

Fabrication of a Hierarchical Ni(OH)2 @Ni3 S2 /Ni Foam Electrode from a Prussian Blue Analogue-Based Composite with Enhanced Electrochemical Capacitive and Electrocatalytic Properties

Developing high-efficiency, cost-effective, and durable electrodes is significant for electrochemical capacitors and electrocatalysis. Herein, a 3D bifunctional electrode consisting of nickel hydroxide nanosheets@nickel sulfide nanocubes arrays on Ni foam (Ni(OH)₂ @Ni₃ S₂ /NF) obtained from a Prussian blue analogue-based precursor is reported. The 3D higher-order porous structure and synergistic effect of different compositions endow the electrode with large specific surface area, facile ion/electron transport path, and improved conductivity. As a result, the Ni(OH)₂ @Ni₃ S₂ /NF electrode exhibits a high specific capacity of 211 mA h g^-1 at a current density of 1 A g^-1 and 73 % capacity retention after 5000 cycles at 5 A g^-1 . Moreover, the Ni(OH)₂ @Ni₃ S₂ /NF electrode has superior electrocatalytic activity for the hydrogen evolution reaction with low overpotentials of 140 and 210 mV at current densities of 10 and 100 mA cm^-2 , respectively. The synthetic strategy for the unique higher-order porous structure can be extended to fabricate other composite materials for energy storage and conversion.

Bifunctionally active nanosized spinel cobalt nickel sulfides for sustainable secondary zinc–air batteries: examining the effects of compositional tuning on OER and ORR activity

Nanosized cobalt nickel sulfides were prepared via a continuous hydrothermal method and evaluated as electrocatalysts, with the catalytic activity being linked to the cationic composition.

The ultralong cycle life of solid flexible asymmetric supercapacitors based on nickel vanadium sulfide nanospheres

The nickel vanadium sulfide electrodes shows an capacitance of 697.4 C g⁻¹ at current density of 1A g⁻¹. The flexible ACS Ni–V–S–2//rGO gives rise to a remarkable cyclic stability with 100% capacitance retention over 7000 charge–discharge cycles.

Comparative electrochemical energy storage performance of cobalt sulfide and cobalt oxide nanosheets: experimental and theoretical insights from density functional theory simulations

We have investigated the origin of enhanced energy storage performance of Co₃S₄ as compared to Co₃O₄ both by supported experimental and density functional theory investigations.

NiCo2S4 Nanotrees Directly Grown on the Nickel NP-Doped Reduced Graphene Oxides for Efficient Supercapacitors

In this work, we report a feasible fabrication of NiCo₂S₄ nanotree-like structures grown from the Ni nanoparticle (NP)-doped reduced graphene oxides (Ni-rGO) by a simple hydrothermal method. It is found that the presence of Ni NPs on the surface of the rGOs initiates growth of the NiCo₂S₄ nanotree flocks with enhanced interfacial compatibility, providing excellent cyclic stability and rate performance. The resulting NiCo₂S₄/Ni-rGO nanocomposites exhibit a superior rate performance, demonstrating 91.6% capacity retention even after 10,000 cycles of charge/discharge tests.

Formation of needle-like porous CoNi2S4-MnOOH for high performance hybrid supercapacitors with high energy density

Seeking for suitable electrode materials and designing rational porous structures are great challenges for developing high performance supercapacitors. Herein, needle-like porous CoNi₂S₄-MnOOH (denoted as NCS-MO) were prepared via a simple two steps solvothermal method and used as battery-type electrode of supercapacitor for the first time. Owing to the multiple oxidation states of needle-like porous NCS-MO and the inherent porous structure, the electrode delivers outstanding electrochemical capacitive properties with a high gravimetric specific capacitance of 1267.7 F g^-1 at the scan rate of 1 mV s^-1. To further assess the practical electrochemical performances, we assembled a hybrid supercapacitor using the as-synthesized porous NCS-MO as cathode and active carbon as anode. The device exhibits excellent performance with a high energy density of 47.1 Wh kg^-1 at the power density of 998 W kg^-1 in an extended voltage range of 1.6 V and outstanding cycling stability. These results demonstrate that the needle-like porous NCS-MO could be promising potential electrode material for high performance supercapacitor.

An Integrated Approach Toward Renewable Energy Storage Using Rechargeable Ag@Ni0.67 Co0.33 S-Based Hybrid Supercapacitors

Self-powered charging systems in conjunction with renewable energy conversion and storage devices have attracted promising attention in recent years. In this work, a prolific approach to design a wind/solar-powered rechargeable high-energy density pouch-type hybrid supercapacitor (HSC) is proposed. The pouch-type HSC is fabricated by engineering nature-inspired nanosliver (nano-Ag) decorated Ni_0.67 Co_0.33 S forest-like nanostructures on Ni foam (nano-Ag@NCS FNs/Ni foam) as a battery-type electrode and porous activated carbon as a capacitive-type electrode. Initially, the core-shell-like NCS FNs/Ni foam is prepared via a single-step wet-chemical method, followed by a light-induced growth of nano-Ag onto it for enhancing the conductivity of the composite. Utilizing the synergistic effects of forest-like nano-Ag@NCS FNs/Ni foam as a composite electrode, the fabricated device shows a maximum capacitance of 1104.14 mF cm^-2 at a current density of 5 mA cm^-2 and it stores superior energy and power densities of 0.36 mWh cm^-2 and 27.22 mW cm^-2 , respectively along with good cycling stability, which are higher than most of previous reports. The high-energy storage capability of HSCs is further connected to wind fans and solar cells to harvest renewable energy. The wind/solar charged HSCs can effectively operate various electronic devices for a long time, enlightening its potency for the development of sustainable energy systems.

Ionic Liquid-Controlled Growth of NiCo2 S4 3D Hierarchical Hollow Nanoarrow Arrays on Ni Foam for Superior Performance Binder Free Hybrid Supercapacitors

A significant development in the design of a NiCo₂ S₄ 3D hierarchical hollow nanoarrow arrays (HNA)-based supercapacitor binder free electrode assembled by 1D hollow nanoneedles and 2D nanosheets on a Ni foam collector through controlling ionic liquid 1-octyl-3-methylimidazolium chloride ([OMIm]Cl) concentration is reported. The unique NiCo₂ S₄ -HNA electrode acquires high specific capacity (1297 C g^-1 at 1 A g^-1 , 2.59 C cm^-2 at 2 mA cm^-2 ), excellent rate capability (maintaining 73.0% at 20 A g^-1 ), and long operational life (maintaining 92.4% after 10 000 cycles at 5 A g^-1 ), which are superior to those for 1D hollow nanoneedle arrays (HNN) and 2D porous nanoflake arrays (PNF). The outstanding electrochemical performance is attributed to the novel 3D structure with large specific surface, hollow cores, high porosity as well as stable architecture. In addition, a hybrid supercapacitor applying 3D NiCo₂ S₄ -HNA as the positive electrode and active carbon as the negative electrode exhibits a high energy density of 42.5 Wh kg^-1 at a power density of 2684.2 W kg^-1 in an operating voltage of 1.6 V. Robust cycling stability is also expressed with 84.9% retention after repeating 10 000 cycles at 5 A g^-1 , implying their great potential in superior-performance supercapacitors.

Facile one-pot synthesis of NiCo2Se4-rGO on Ni foam for high performance hybrid supercapacitors

A facile, innovative synthesis for the fabrication of NiCo₂Se₄-rGO on a Ni foam nanocomposite via a simple hydrothermal reaction is proposed. The as-prepared NiCo₂Se₄-rGO@Ni foam electrode was tested through pxrd, TEM, SEM, and EDS to characterize the morphology and the purity of the material. The bimetallic electrode exhibited outstanding electrochemical performance with a high specific capacitance of 2038.55 F g⁻¹ at 1 A g⁻¹. NiCo₂Se₄-rGO@Ni foam exhibits an extensive cycling stability after 1000 cycles by retaining 90% of its initial capacity. A superior energy density of 67.01 W h kg⁻¹ along with a high power density of 903.61 W kg⁻¹ further proved the high performance of this electrode towards hybrid supercapacitors. The excellent electrochemical performance of NiCo₂Se₄-rGO@Ni foam can be explained through the high electrocatalytic activity of NiCo₂Se₄ in combination with reduced graphene oxide which increases conductivity and surface area of the electrode. This study proved that NiCo₂Se₄-rGO@Ni foam can be utilized as a high energy density-high power density electrode in energy storage applications.

A hybrid supercapacitor comprising a NiCo₂Se₄-rGO composite has been fabricated on Ni foam and shows high energy and power density and superior flexibility.

Anion Exchange of Ni-Co Layered Double Hydroxide (LDH) Nanoarrays for a High-Capacitance Supercapacitor Electrode: A Comparison of Alkali Anion Exchange and Sulfuration

A facile and new anion exchange process is presented, which involves the conversion of NiCo-CO₃ layered double hydroxide (LDH) nanosheet arrays in an alkaline solution. The anion exchange between CO₃ ^2- and OH^- results in the construction of a reservoir for OH^- anions, and the decoration of thin nanoflakes on the surface of nanosheets effectively enlarges the surface area of NiCo LDH nanoarrays. The capacitance of the as-soaked NiCo LDH nanoarrays electrode increases from 1.78 F cm^-2 (684 F g^-1 ) to 6.22 F cm^-2 (2391 F g^-1 ) at 2 mA cm^-2 after soaking for 12 h. Moreover, the soaked NiCo-OH LDH electrode exhibits an enhanced rate capacity, high coulombic efficiency, and good cycling stability compared with the Ni-Co-S nanosheet electrode synthesized through a hydrothermal sulfuration process. The as-assembled all-solid-state NiCo LDH//active carbon asymmetric supercapacitor shows a maximum energy density of 83.4 W h kg^-1 at a power density of 1066 W kg^-1 .