Transition-Metal Oxides Anchored on Nitrogen-Enriched Carbon Ribbons for High-Performance Pseudocapacitors

Sea Urchin-Like NiCo-LDH Hollow Spheres Anchored on 3D Graphene Aerogel for High-Performance Supercapacitors

To enhance the inherent poor conductivity and low cycling stability of dimetallic layered double hydroxides (LDHs) materials, designing a synergistic effect between EDLC capacitors and pseudocapacitors is an efficient strategy. In this paper, we utilized a solvothermal technique employing Co-glycerate as a precursor to prepare sea urchin-like NiCo-LDH hollow spheres anchored on a 3D graphene aerogel. The unique morphology of these hollow microspheres significantly expand the specific surface area and exposes more active sites, while reducing the volume changes of materials during long-term charging and discharging processes. The 3D graphene aerogel serves as a conductive skeleton, improving the material's electrical conductivity and buffering high current. The sea urchin-like NiCo-LDH hollow spheres anchored on 3D graphene aerogel (H-NiCo-LDH@GA) has a specific surface area of 51 m2 g-1 and the ID/IG value is 1.02. The H-NiCo-LDH@GA demonstrate a significant specific capacitance of 236.8 mAh g-1 at 1 A g-1, with a remarkable capacity retention rate of 63.1 % even at 20 A g-1. Even after 8000 cycles at 10 A g-1, the capacity retention still remains at 96.3 %, presenting excellent cycling stability.

Carbon Transition-metal Oxide Electrodes: Understanding the Role of Surface Engineering for High Energy Density Supercapacitors

Supercapacitors store electrical energy by ion adsorption at the interface of the electrode-electrolyte (electric double layer capacitance, EDLC) or through faradaic process involving direct transfer of electrons via oxidation/reduction reactions at one electrode to the other (pseudocapacitance). The present minireview describes the recent developments and progress of carbon-transition metal oxides (C-TMO) hybrid materials that show great promise as an efficient electrode towards supercapacitors among various material types. The review describes the synthetic methods and electrode preparation techniques along with the changes in the physical and chemical properties of each component in the hybrid materials. The critical factors in deriving both EDLC and pseudocapacitance storage mechanisms are also identified in the hope of pointing to the successful hybrid design principles. For example, a robust carbon-metal oxide interaction was identified as most important in facilitating the charge transfer process and activating high energy storage mechanism, and thus methodologies to establish a strong carbon-metal oxide contact are discussed. Finally, this article concludes with suggestions for the future development of the fabrication of high-performance C-TMO hybrid supercapacitor electrodes.

CoNi2S4 nanosheets on nitrogen-doped carbon foam as binder-free and flexible electrodes for high-performance asymmetric supercapacitors

Flexible electrode materials show many advantages and hold great prospects for energy storage application. But, the synthesis processes of these kind of materials are always complicated, are low in efficiency and high in cost. Here, we propose a facile and cost-effective two-step synthesis strategy of a flexible electrode by growing ultrathin and vertical CoNi₂S₄ nanosheets on nitrogen-doped carbon foam (CoNi₂S₄ NSs@NCF). The NCF is obtained by direct carbonization of the melamine foam. When evaluated as binder-free electrode material for supercapacitor in three-electrode system, the CoNi₂S₄ NSs@NCF exhibits an excellent specific capacitance of 1576.8 F g^-1 and a superior cycling stability (91.5% capacitance retention at the 5000th cycle). Then, an asymmetrical supercapacitor was fabricated using the as-synthesized material as the positive electrode and activated carbon as the negative electrode, which delivers a high energy density of 42.8 Wh kg^-1 at a power density of 399.7 W kg^-1, remarkable rate capability and satisfactory cycling stability (85.3% capacitance retention at the 5000th cycle). In brief, our work offers a low-cost and facile approach to prepare promising flexible electrode materials for high-performance supercapacitors.

Co(OH)F nanorods@K x MnO2 nanosheet core-shell structured arrays for pseudocapacitor application

In this work, Co(OH)F nanorods@K x MnO2 nanosheet core-shell nanostructure was assembled on Ni foam by a facile hydrothermal method and incorporated with an electrodeposition process. Benefiting from their core-shell nanostructure and heterogeneous nanocomposites, the arrays present high areal capacitance up to 1046 mF cm-2 at 1 mA cm-2 and display a remarkable specific capacitance retention of 118% after 3000 cycles. When the current density increases to 10 mA cm-2, the capacitance is 821 mF cm-2 displaying a good rate capability. The excellent electrochemical properties allow them to be used as a promising electrode material for pseudocapacitors and display wide application potential in the field of electrochemical capacitors.

Tribochemical Behaviors of Onion-like Carbon Films as High-Performance Solid Lubricants with Variable Interfacial Nanostructures

Onion-like carbon (OLC), spherical nanoparticles consisting of carbon shells, is capable of providing exceptional lubrication effects. Nevertheless, the underlying mechanism, especially the tribo-induced evolution of interfacial nanostructures and their correlation with the friction states, is not clear. In this work, OLC films with a thickness of ∼1 μm were synthesized by electrophoretic deposition on the mirror-polished stainless steel. The lubricity was evaluated by tailoring the sliding aspects including applied normal load, contact time, and counterface materials. It is found that the friction reduction level is highly dependent on the material transfer and transformation of the OLC surface and the physicochemical nature of the as-formed tribolayer in the contact areas. The subsurface of the OLC film always undergoes a deep amorphization transformation upon sliding. It is interesting to note that the tribolayer formed on the bare steel ball is mainly composed of highly ordered graphene-like nanoflakes derived from the sliding-induced degradation of OLC nanospheres. In comparison, the nanospherical carbon structure can be retained in the topmost subsurface of the tribolayer formed on the ceramic Si₃N₄ ball. Such a nanosphere-/amorphization-coupled interface is capable of providing a robust lubrication state under high contact stresses. The findings identify a new lubrication mechanism for the spherical carbon nanostructure, rendering them effective solid lubricants.

Construction of NiCo2O4 nanosheet-decorated leaf-like Co3O4 nanoarrays from metal–organic framework for high-performance hybrid supercapacitors

Leaf-like Co₃O₄@NiCo₂O₄ nanoarrays with an excellent energy storage performance was designed by a MOF-guided strategy.

Supercapacitive performance of TiO2 boosted by a unique porous TiO2/Ti network and activated Ti3+

Excellent supercapacitive performance is achieved by constructing a 3D porous TiO₂/Ti network structure and introducing an activated Ti³⁺/Ti⁴⁺ redox couple.