Hierarchical Nanosheet-Built CoNi2S4 Nanotubes Coupled with Carbon-Encapsulated Carbon Nanotubes@Fe2O3 Composites toward High-Performance Aqueous Hybrid Supercapacitor Devices

Reduced graphene oxide-wrapped ZnS-SnS2 heterojunction bimetallic hollow cubic boxes as high-magnification and long lifespan supercapacitor anode materials

Metal sulfides have attracted extensive attention due to their excellent electrochemical performance. However, issues such as poor conductivity and severe volume expansion during charge and discharge processes affect the applications of sulfides as electrode materials. Here, a combination of coprecipitation and high-temperature sulfidation methods are employed to synthesize a ZnS-SnS2 composite with a hollow cubic structure, which is further composited with reduced graphene oxide (RGO) to form ZnS-SnS2 hollow cubic boxes encapsulated in a conductive framework of reduced graphene oxide (RGO) (denoted as ZnS-SnS2@RGO) for electrode materials. The hollow structure effectively alleviates the pulverization of ZnS-SnS2@RGO caused by volume expansion during charge and discharge processes. The heterogeneous structure formed by ZnS and SnS2 effectively reduces the electron transfer resistance of the material. The use of RGO wrapping enhances the conductivity of the ZnS-SnS2 hollow cubic boxes, and RGO's dispersion effect on the ZnS-SnS2 cubes improves particle agglomeration, further mitigating volume expansion of the material. These results indicate the outstanding electrochemical performance of heterostructural ZnS-SnS2 hollow cubic electrodes encapsulated with reduced graphene oxide as a conductive framework. The fabrication process provides a novel approach for addressing volume expansion and poor conductivity issues in other pseudocapacitive materials.

Tailoring the phase composition of carbon-coated nickel sulfides to achieve a high specific capacitance

As significant transition metal sulfides, nickel sulfides integrated with carbon were successfully synthesized in the presence of polyethylenimine and glutaraldehyde with a solvothermal route at 180 °C followed by carbonization. Glutaraldehyde prevented complete sulfur loss and allowed the formation of a mixed phase of nickel sulfide. The electrochemical performances of pure NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes were tested by a series of measurements. The specific capacitances obtained from GCD analysis were 698, 1160, 1484, and 908 F g-1 at 1 A g-1 for NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes, respectively. The results implied that the NiS2/NiS@C1 electrode possessed the highest specific capacitances and this study can be a good reference for the preparation of other hybrid metal sulfides as pseudocapacitive electrode materials.

All Si3 N4 Nanowires Membrane Based High-Performance Flexible Solid-State Asymmetric Supercapacitor

Recently, much attention has been drawn in the development of flexible energy storage devices due to the increasing demands for flexible/portable electronic devices with high energy density, low weight, and good flexibility. Herein, vertically oriented graphene nanosheets (VGNs) are in situ fabricated on the surface of free-standing and flexible Si₃ N₄ nanowires (NWs) membrane by plasma-enhanced chemical vapor deposition (PECVD), which are directly used as flexible nanoscale conductive substrates. NiCo₂ O₄ hollow nanospheres (HSs) and FeOOH amorphous nanorods (NRs) are finally prepared on Si₃ N_4NWs @VGNs, which are served as the positive and negative electrodes, respectively. Profiting from the structural merits, the synthesized Si₃ N_4NWs @VGNs@NiCo₂ O_4HSs and Si₃ N_4NWs @VGNs@FeOOH_NRs membrane electrodes exhibit remarkable electrochemical performance. Using Si₃ N_4NWs membrane as the separator, the assembled all Si₃ N_4NWs membrane-based flexible solid-state asymmetric supercapacitor (ASC) with a wide operating potential window of 1.8 V yields the outstanding energy density of 96.3 Wh kg^-1 , excellent cycling performance (91.7% after 6000 cycles), and good mechanical flexibility. More importantly, this work provides a rational design strategy for the preparation of flexible electrode materials and broadens the applications of Si₃ N_4NWs in the field of energy storage.

Hollow 3D Frame Structure Modified with NiCo2 S4 Nanosheets and Spinous Fe2 O3 Nanowires as Electrode Materials for High-Performance All-Solid-State Asymmetric Supercapacitors

Supercapacitors have attracted tremendous research interest, since they are expected to achieve battery-level energy density, while having a long calendar life and short charging time. Herein, a novel asymmetric supercapacitor has been successfully assembled from NiCo₂ S₄ nanosheets and spinous Fe₂ O₃ nanowire modified hollow melamine foam decorated with polypyrrole as positive and negative electrodes, respectively. Owing to the well-designed nanostructure and suitable matching of electrode materials, the assembled asymmetric supercapacitor (ASC) exhibits an extended operation voltage window of 1.6 V with an energy density of 20.1 Wh kg^-1 at a power density of 159.4 kW kg^-1 . Moreover, the ASC shows stable cycling stability, with 81.3 % retention after 4000 cycles and a low internal resistance of 1.03 Ω. Additionally, a 2.5 V light-emitting diode indicator can be lit up by three ASCs connected in series; this provides evidence of the practical application potential of the assembled energy-storage system. The excellent electrochemical performances should be credited to the significant enhancement of the specific surface area, charge transport, and mechanical stability resulting from the unique 3D morphology.

Electronegativity principles in metal oxides based supercapacitors

To meet growing demands for energy consumptions in modern society, it is necessary to develop different energy sources. Renewable energy such as wind and solar sources are intermittent, therefore, energy storage devices become more and more important to store energy for use when no wind or no light. Supercapacitors play a key role in energy storage, mainly due to their high power density and long cycling life. However, supercapacitors are facing the obstacle of low energy density, one of the most intensive approaches is to rationally design new electrode materials. In this review, we focus on metal oxides-based materials and present an electronegativity criterion for the design and appropriate selection of new electrode chemical compositions. Metal elements with proper electronegativity scale have the potential to transfer electron for energy storage. Suitable positive and negative electrodes matching can enhance many properties of supercapacitors, which may overcome many related obstacles. Furthermore, electronegativity scale may also help people to find novel metal oxides based supercapacitors.

Formation of graphene-wrapped multi-shelled NiGa2O4 hollow spheres and graphene-wrapped yolk-shell NiFe2O4 hollow spheres derived from metal-organic frameworks for high-performance hybrid supercapacitors

To construct a supercapacitor (SC) with considerable performance, synthesis of an electrode material with a highly porous structure is necessary. Herein, an efficient metal-organic framework (MOF)-derived procedure is offered to construct a graphene wrapped multi-shelled NiGa2O4 hollow sphere (GW-MSNGOHS) positive electrode material and a graphene-wrapped yolk-shell NiFe2O4 hollow sphere (GW-YS-NFOHS) negative electrode material with a highly porous nature in SCs. The GW-MSNGOHS and GW-YS-NFOHS electrodes exhibit excellent capacities (∼411.25 mA h g-1 and 254.25 mA h g-1, respectively, at 1 A g-1), reasonable rate performances (75.85%, and 62.7%, respectively), and outstanding cyclability (98.9% and 90.9%, respectively). Benefiting from the reasonably engineered negative and positive electrodes, the fabricated asymmetric device (GW-MSNGOHS//GW-YS-NFOHS) can show an excellent energy density (ED) of 118.97 W h kg-1 at a power density (PD) of 1702 W kg-1, an exceptional robustness of 92.1%, and an excellent capacity (Cs) of 140.2 mA g-1.

Construction of a continuously layered structure of h-BN nanosheets in the liquid phase via sonication-induced gelation to achieve low friction and wear

Herein, to endow h-BN nanosheets with gelling ability, a diurea compound was decorated on the h-BN nanosheets via designed adsorption and in situ reaction processes. The prepared h-BN-based gelator, BTO, exhibited excellent dispersibility in non-polar liquid media, and the gelation of BTO dispersions could be readily triggered by ultrasonic treatments. The sol-gel transformation of the system was found to be highly reversible by stirring and sonication. Based on the investigation on the self-assembly behavior of BTO nanosheets in the liquid phase, it was proposed that a continuous and layered structure formed by BTO during sonication was the key factor for the gelling properties of these nanosheets. The viscoelasticity of the sonication-induced gel was studied using a rheometer. Tribological evaluations show that the prepared h-BN nanogel exhibits outstanding lubricating performances, and more importantly, it has been proved that the gel state of the h-BN nanosheets provides superior and more reliable lubricating performances than the corresponding dispersion state under certain conditions; this can be ascribed to the formation of a continuous and uniform structure of modified h-BN nanosheets during gelation. Thus, this study not only clarifies the key role of the assembly structure in the tribological performances of 2D nanomaterials, but also demonstrates the potential of gelation in improving the macroscopic friction reduction and wear resistance of 2D nanomaterials.

High electroactive material loading on a carbon nanotube/carbon nanofiber as an advanced free-standing electrode for asymmetric supercapacitors

3D hierarchical nanocomposites always lead to excellent electrochemical properties.

Mesoporous nickel cobalt manganese sulfide yolk–shell hollow spheres for high-performance electrochemical energy storage

Mesoporous Ni–Co–Mn sulfide yolk–shell hollow spheres have been prepared via a self-template route and show excellent electrochemical performance in supercapacitors.