Hierarchical self-supported Ni(OH)2@Ni12P5 for supercapacitor electrodes with ultra-high area ratio capacitance

Design and fabrication of MoO42--intercalated LDH nanosheets coated on Co9S8 nanotubes with enhanced cycling stability for high-performance supercapacitors

Transition metal sulfides are promising electrode materials for supercapacitors due to their excellent electrochemical performance and high conductivity. Unfortunately, the low rate performance and poor cycling stability limited their progress towards commercial applications. Herein, the core-shell structure of MoO42--intercalated LDHs coated on Co9S8 nanotubes was rationally designed and prepared to improve their electrochemical performance and cycling stability by adjusting the composition of LDHs. Compared to NiMo-LDH@Co9S8 and CoMo-LDH@Co9S8, the optimized NiCoMo-LDH@Co9S8 electrode exhibits excellent areal specific capacitance (11 F cm-2 at 3 mA cm-2) and excellent cycling stability (94.4% after 5000 cycles). In addition, asymmetric supercapacitor devices were assembled with NiCoMo-LDH@Co9S8 and activated carbon (AC), which delivered a high energy density of 0.94 mWh cm-2, at a power density of 1.70 mW cm-2, and good cycling stability (89.4% after 5000 cycles). These results indicate that the introduction of MoO42- can enhance the synergistic effect of multiple metals and the synthesized NiCoMo-LDH@Co9S8 core-shell composite has great potential in the development of high-performance electrode materials for supercapacitors.

High-mass-loading cobalt iron phosphide@nickel vanadium layered double hydroxide heterogeneous nanosheet arrays for hybrid supercapacitors

Designing multidimensional heterostructures on flexible substrates is an efficient approach to resolve the low energy density of supercapacitors. Herein, a three-dimensional (3D) porous cobalt iron phosphide (CoFeP)@nickel vanadium-layered double hydroxide (NiV-LDH) heterostructure has been prepared anchored on carbon cloth (CC) substrate. In this nanoarchitecture, NiV-LDH nanosheets are densely wrapped on the surface of CoFeP nanosheets, which forms a hierarchically porous framework with an enlarged surface area and accessible pore channels. Benefiting from the strong interaction and synergistic effect between CoFeP and NiV-LDH, the well-defined heterostructure can realize simultaneously rich redox active sites, rapid reaction dynamics, and good structural stability. Thus, the binder-free CoFeP@NiV-LDH electrode with a high mass loading of 6.47 mg cm-2 displays a significantly increased specific capacity of 903.1C g-1 (2.35C cm-2) at 1 A g-1 and enhanced rate capability when compared to pristine CoFeP and NiV-LDH. Additionally, the assembled hybrid supercapacitor (HSC) yields an energy density of 77.9 Wh kg-1/0.98 Wh cm-2 and excellent long-term stability. This research proposes a rational route for designing heterogeneous micro-/nanoarchitectures with commercial-level mass loading for the practical application of high-energy-density supercapacitors.

Mushroom-like cobalt nickle metaphosphate@nickel diselenide core-shell nanorods for asymmetric supercapacitors

Although transition metal metaphosphates (TMPOs) display special physical/chemical features and high theoretical capacities, their applications for supercapacitors (SCs) are still restricted by their low energy densities and inferior cycling stability. Herein, a novel strategy has been proposed to address these issues through in situ construction of cobalt nickle metaphosphate (Co_0.2Ni_0.8(PO₃)₂)@nickel diselenide (NiSe₂) core-shell heterostructure on carbon paper (CP) as a self-supporting flexible electrode for SCs. Particularly, this unique mushroom-like porous nanoarchitecture assembled by one-dimensional (1D) Co_0.2Ni_0.8(PO₃)₂ nanorods and zero-dimensional (0D) NiSe₂ nanospheres can expose abundant active sites and afford multi-dimensional channels, which favors rapid electron ions/electron transfer, accelerates the reaction kinetics, and alleviates volume changes during charging/discharging processes. Profiting from its well-aligned 1D/0D nanostructure and strong synergistic effect between Co_0.2Ni_0.8(PO₃)₂ and NiSe₂, the Co_0.2Ni_0.8(PO₃)₂@NiSe₂/CP electrode delivers a specific capacity of 219.4 mAh/g/0.414 mAh cm^-2 at 1 A/g and good cycling stability with capacity retention of 90.7% after 5000 cycles, outperforming many previously reported TMPO-based electrodes in literature. Impressively, an asymmetric supercapacitor (ASC) device assembled with Co_0.2Ni_0.8(PO₃)₂@NiSe₂ as cathode and porous carbon as anode achieves an energy density of 69.2 Wh kg^-1 at 736.0 W kg^-1 and maintains a capacity retention of 97.6% after 20,000 charge-discharge cycles. This work provides an efficient approach to design multi-dimensional hybrid nanomaterials for high-performance SCs.

CNTs support 2D NiMOF nanosheets for asymmetric supercapacitors with high energy density

The NiMOF/CNTs composite with NiMOF nanosheets grows along the CNTs is synthesized with a one-step solvothermal method, and the NiMOF/CNTs//AC asymmetric supercapacitors provide a high energy density of 113.8 Wh kg−1 at 800.0 W kg−1.