Ni-Co sulfide hollow nanoboxes with enhanced lattice interfaces for high performance hybrid supercapacitors

Multi-layered heterogeneous interfaces created in Co0.85Se@Ni3S4/NF to enhance supercapacitor performances by multi-step alternating electrodeposition

Heterogeneous interface construction is of far-reaching significance to optimize the electrochemical performance of electrodes. Herein, a multi-step alternating electrochemical deposition (MAED) method is proposed to alternately deposit Co0.85Se and Ni3S4 nanosheets on a nickel foam (NF), forming a special alternate layer-by-layer structure with multi-layered heterogeneous interfaces. The creation of the multi-layered heterogeneous interfaces provides a large interfacial area for redox reactions with optimum interstitials facilitating ion diffusion, thus greatly improving the electrochemical energy storage efficiency. With the increase in the layer number, the material exhibits increasingly better energy storage performance, and 8L-Co0.85Se@Ni3S4/NF exhibits the highest specific capacitances of 2508 F g-1 and 1558 F g-1 at a scan rate of 2 mV s-1 and a current density of 1 A g-1. The 8L-Co0.85Se@Ni3S4/NF//polypyrrole (PPy)/NF asymmetric supercapacitor provides a maximum operation potential window of 1.55 V and energy densities of 76.98 and 35.74 W h kg-1 when the power densities are 775.0 and 15 500 W kg-1, respectively, superior to most of the related materials reported. Through MAED, the deposited phase and the layer number can be accurately controlled, thus providing an efficient strategy for interface construction so as to increase the electrochemical activity of the energy storage materials.

Hollow Ni3S4@Co3S4 with core-satellite nanostructure derived from metal-organic framework (MOF)-on-MOF hybrids as an electrode material for supercapacitors

Metal-organic frameworks (MOFs) have found wide applications in the field of supercapacitors due to their highly controllable porous structure, big specific surface area, and abundant chemical functional groups. MOF-on-MOF hybrids not only enhance the composition of MOFs (such as ligands and/or metal centers) but also provide greater structural diversity. By utilizing MOFs as precursors for preparing sulfides, the unique characteristics and inherent structure of MOFs are preserved but their conductivity and capacitance are enhanced. This study successfully synthesized hollow-structured Ni3S4@Co3S4 derived from an Ni-MOF@ZIF-67 hybrid structure, where the Ni-MOF serves as the core and ZIF-67 as the satellite. The Ni3S4@Co3S4 electrode demonstrated a specific capacity as high as 747.3 C g-1 at 1 A g-1, and it could still maintain 77% of its initial capacity at 10 A g-1. Furthermore, the assembled Ni3S4@Co3S4//AC hybrid supercapacitor (HSC) device achieved a maximum energy density of 30.8 W h kg-1 when the power density was 750 W kg-1. The device exhibited remarkable cycling durability, retaining 85.4% of its initial capacitance after 5000 cycles. Therefore, the derived functional materials based on MOF-on-MOF provide a more scalable and promising approach for the preparation of efficient electrode materials.

Phosphorization Engineering on a MOF-Derived Metal Phosphide Heterostructure (Cu/Cu3P@NC) as an Electrode for Enhanced Supercapacitor Performance

A highly conductive and rationally constructed metal-organic framework (MOF)-derived metal phosphide with a carbonaceous nanostructure is a meticulous architecture toward the development of electrode materials for energy storage devices. Herein, we report a facile strategy to design and construct a new three-dimensional (3D) Cu-MOF via a solvent diffusion method at ambient temperature, which was authenticated by a single-crystal X-ray diffraction study, revealing a novel topology of (2,4,7)-connected three-nodal net named smm4. Nevertheless, the poor conductivity of pristine MOFs is a major bottleneck hindering their capacitance. To overcome this, we demonstrated an MOF-derived Cu3P/Cu@NC heterostructure via low-temperature phosphorization of Cu-MOF. The electronic and ionic diffusion kinetics in Cu3P/Cu@NC were improved due to the synergistic effects of the heterostructure. The as-prepared Cu3P/Cu@NC heterostructure electrode delivers a specific capacity of 540 C g-1 at 1 A g-1 with outstanding rate performance (190 C g-1 at 20 A g-1) and cycle stability (91% capacity retention after 10,000 cycles). Moreover, the assembled asymmetric solid-state supercapacitor (ASC) achieved a high energy density/power density of 45.5 Wh kg-1/7.98 kW kg-1 with a wide operating voltage (1.6 V). Long-term stable capacity retention (87.2%) was accomplished after 5000 cycles. These robust electrochemical performances suggest that the Cu3P/Cu@NC heterostructure is a suitable electrode material for supercapacitor applications.