Zeolitic Imidazolate Framework-Derived Co3S4@NiFe-LDH Core-Shell Heterostructure as Efficient Bifunctional Electrocatalyst for Water Splitting

The development of stable and efficient bifunctional electrocatalysts is of utmost importance for overall water splitting. This study introduces Co3S4@NiFe-LDH core-shell heterostructure prepared via an electrodeposition of ultrathin NiFe-LDH nanosheet on zeolitic imidazolium framework-derived Co3S4 nanosheet arrays. The bifunctional Co3S4@NiFe-LDH/NF exhibits impressive catalytic performance and long-term stability for both the OER and HER with low overpotentials of 100 mA cm-2 at 235 mV and 10 mA cm-2 at 95 mV in 1 M KOH, respectively. The assembled cell with Co3S4@NiFe-LDH/NF as both cathode and anode shows voltages of 1.595 and 1.666 V at current densities of 10 and 20 mA cm-2, respectively, as well as ultralong stability over 500 h. DFT calculations expose a robust electron interaction at the heterogeneous interface of the Co3S4@NiFe-LDH/NF core-shell structure. This interaction promotes electron transfer from NiFe-LDH to Co3S4 and reduces the energy barriers for OER intermediates, thereby enhancing electrocatalytic activity. This research contributes novel insights toward the promising materials for electrochemical water splitting through the construction of heterojunction interfaces.

Amorphous Co-Mo-S nanospheres fabricated via room-temperature vulcanization for asymmetric supercapacitors

Ternary metal sulfides employed in supercapacitors exhibit better electrochemical performances than their counterpart oxides due to their superior conductivity. However, the insertion/extraction of electrolyte ions can lead to a significant volume change in electrode materials, which can result in poor cycling stability. Herein, novel amorphous Co-Mo-S nanospheres were fabricated through a facile room-temperature vulcanization method. It involves the conversion of crystalline CoMoO4 by reacting it with Na2S at room temperature. In addition to the conversion of the crystalline state into an amorphous structure with more grain boundaries, which is beneficial for the transport of electron/ion and can accommodate the volume change generated by the insertion/extraction of electrolyte ions, the production of more pores led to an increased specific surface area. The electrochemical results indicate that the as-prepared amorphous Co-Mo-S nanospheres had a specific capacitance of up to 2049.7F/g@1 A/g together with good rate capability. The amorphous Co-Mo-S nanospheres can be used as the cathode of supercapacitors and assembled with an activated carbon anode into an asymmetric supercapacitor possessing a satisfactory energy density of 47.6 Wh kg-1@1012.9 W kg-1. One of the prominent features exhibited by this asymmetric device is its remarkable cyclic stability, with a capacitance retention of 107% after 10,000 cycles.

Cyclodextrin-supported Co(OH)2 Clusters as Electrocatalysts for Efficient and Selective H2 O2 Synthesis

Co-based material catalysts have shown attractive application prospects in the 2 e- oxygen reduction reaction (ORR). However, for the industrial synthesis of H2 O2 , there is still lack of Co-based catalysts with high production yield rate. Here, novel cyclodextrin-supported Co(OH)2 cluster catalysts were prepared via a mild and facile method. The catalyst exhibited remarkable H2 O2 selectivity (94.2 % ~ 98.2 %), good stability (99 % activity retention after 35 h), and ultra-high H2 O2 production yield rate (5.58 mol gcatalyst -1 h-1 in the H-type electrolytic cell), demonstrating its promising industrial application potential. Density functional theory (DFT) reveals that the cyclodextrin-mediated Co(OH)2 electronic structure optimizes the adsorption of OOH* intermediates and significantly enhances the activation energy barrier for dissociation, leading to the high reactivity and selectivity for the 2 e- ORR. This work offers a valuable and practical strategy to design Co-based electrocatalysts for H2 O2 production.

Zeolitic Imidazolate Framework-Derived Zn/Co-S@Ni(OH)2 Nanoarrays with Excellent Energy Storage and Electrocatalytic Performance

The design and development of high-performance electrochemical electrode materials are crucial for energy storage and conversion systems. This work reports a facile preparation of a self-supported Zn/Co-S@Ni(OH)2 array electrode in which a Zn/Co-S nanosheet is derived from a leaf-like zeolitic imidazolate framework (Zn/Co-ZIF-L). The core-shell structure provides multiple benefits such as enhanced electrical conductivity, an abundance of exposed active sites, and strong electronic interactions between Zn/Co-S and ultra-thin Ni(OH)2 nanosheets, facilitating faster charge transfer. Consequently, Zn/Co-S@Ni(OH)2 demonstrates remarkable electrochemical characteristics as an electrode material for supercapacitors with an area capacitance of 12.9 F cm-2 at a current density of 2 mA cm-2 in 2 M KOH. The assembled asymmetric supercapacitor device achieves a high energy density of 0.95 mW h cm-2, while showing excellent longevity with a retention of 90.9% over 5000 cycles. Additionally, the Zn/Co-S@Ni(OH)2 arrays demonstrate significant oxygen evolution reaction activity with an overpotential of 242 mV at 10 mA cm-2 in 1 M KOH and significant stability for more than 100 h. This work provides a valuable approach for synthesizing bifunctional electrode materials for both energy storage and electrocatalysis applications.

Cooperative effect of bimetallic MOF-derived CoNi(OH)2@NiCo2S4nanocomposite electrocatalysts with boosted oxygen evolution activity

Highly efficient and inexpensive electrocatalysts for oxygen evolution reaction (OER) are extensively studied for water splitting. Herein, a unique bimetallic nanocomposite CoNi(OH)₂@NiCo₂S₄nanosheet arrays derived from metal-organic-frameworks (MOFs, CoNi-ZIF) is simply fabricated on Ni foam, endowing large specific surface area and outstanding electrical conductivity. Compared with their single-metallic counterparts, the bimetallic composite displays dramatically low overpotential and small Tafel slope as well as outstanding catalytic stability. The overpoptential at 20 mA cm^-2for CoNi(OH)₂@NiCo₂S₄is only 230 mV in comparison with Ni(OH)₂@Ni₃S₂(266 mV), Co(OH)₂@Co₃S₄(294 mV) and RuO₂(η = 302 mV). First-principle calculations based on density functional theory (DFT) are carried out and reveal that the introduction of Ni in Co(OH)₂helps lowered the energy difference of ΔG_OOH*-ΔG_O*, and thereby boosting the OER reactivity. This study provides an effective approach for the rational construction of low-cost metal hybrids.

MOF-derived hierarchical core-shell hollow Co3S4@NiCo2O4 nanosheet arrays for asymmetric supercapacitors

Transition metal sulfides (TMSs) have been widely explored as electrode materials for supercapacitors (SCs). Nevertheless, the application of single TMS is limited due to its lattice expansion and dissolution in...

Heterostructured Co-NTC@Co3S4 as an anode material for asymmetric pseudocapacitors

Herein, a composite structure of ZIF-67@Co-NTC was synthesized and it was partially vulcanized to form layer-like Co3S4 nanosheets to finally successfully synthesize a composite heterostructure of Co-NTC@Co3S4.

Recent advances in metal-organic framework-based electrode materials for supercapacitors

Exploring porous electrode materials with designed micro/nano-structures is an effective way to realize high-performance supercapacitors (SCs). A metal-organic framework (MOF) is a porous crystalline material with a periodic structure formed by coordination of metal ions/clusters and organic ligands. Due to the excellent properties (e.g., large specific surface area, high porosity and tailorable structure), MOFs have been widely used in diverse applications. This Frontier article highlights the recent progress in the synthesis of MOF-based micro/nano-structured electrode materials including pristine MOFs, MOF composites and MOF derivatives, and their application in SCs. Furthermore, the challenges of MOF-based electrode materials and possible solutions are also discussed.

Porous 3,4-di(3,5-dicarboxyphenyl)phthalate-based Cd2+ coordination polymer and its potential applications

Porous coordination polymers with organic aminium as one of the guest species possess a potential application in dye adsorption and white-light material manufacture. Polycarboxylic acid with multiple COOH substituents tends to form this type of porous material (with metal ion). Here the solvothermal self-assembly between Cd²⁺ and a hexacarboxylic acid creates such a porous material [(CH₃)₂NH₂]₆[Cd₃(L)₂]·5DMF·3H₂O (H₆L = 3,4-di(3,5-dicarboxyphenyl)phthalic acid) 1. Total potential guest accessible void volume in 3-D 1 is found to be 4327 Å³. Based on its better porous structure and stability, the ability of 1 to adsorb organic dyes is investigated. It has been proved that (i) 1 can selectively adsorb cationic dyes as Azure A (AA⁺) and/or Methylene Blue (MB⁺), rather than neutral and anionic ones; (ii) the maximum adsorption capacity is 698.2 mg·g^-1 for AA⁺ and 573.2 mg·g^-1 for MB⁺, respectively; and (iii) to the adsorption of AA⁺, it can be recycled for at least five rounds. Also, it is utilized to fabricate the while-light emitting material. Based on the blue-light emission of 1, the trace Eu³⁺ and Tb³⁺ ions are introduced into the pores of 1 successfully, obtaining a white-light emitting material Eu³⁺/Tb³⁺@1 (CIE chromaticity coordinates: (0.33, 0.32)). Meanwhile, Eu³⁺/Tb³⁺@1 is found to be a potential fluorescence photochromic material, showing a yellow-white-blue light emission. According to these investigations, the relationship between material structure and its adsorption property for dyes, the points that should be paid attention to in the construction of white-light emitting materials as well as the potential adsorption mechanism for dyes and rare earth ions are deeply discussed.

Hierarchical Ni-Co-Mn hydroxide hollow architectures as high-performance electrodes for electrochemical energy storage

In this study, hierarchical Ni-Co-Mn hydroxide hollow architectures were successfully achieved via an etching process. We first performed the synthesis of NiCoMn-glycerate solid spheres via a solvothermal route, and then NiCoMn-glycerate as the template was etched to convert into hierarchical Ni-Co-Mn hydroxide hollow architectures in the mixed solvents of water and 1-methyl-2-pyrrolidone. Hollow architectures and high surface area enabled Ni-Co-Mn hydroxide to manifest a specific capacitance of 1626 F g-1 at 3.0 A g-1, and it remained as large as 1380 F g-1 even at 3.0 A g-1. The Ni-Co-Mn hydroxide electrodes also displayed notable cycle performance with a decline of 1.6% over 5000 cycles at 12 A g-1. Moreover, an asymmetric supercapacitor assembled with this electrode exhibited an energy density of 44.4 W h kg-1 at 1650 W kg-1 and 28.5 W h kg-1 at 12 374 W kg-1. These attractive results demonstrate that hierarchical Ni-Co-Mn hydroxide hollow architectures have broad application prospects in supercapacitors.

MOF-derived ZnCo2O4@NiCo2S4@PPy core-shell nanosheets on Ni foam for high-performance supercapacitors

The ZnCo₂O₄@NiCo₂S₄@PPy core-shell nanosheets material is prepared by directly growing leaf-like ZnCo₂O₄ nanosheets derived from the metal-organic framework (MOF) on Ni foam (NiF) via chemical bath deposition and annealing methods and then combining with NiCo₂S₄ and PPy via electrodeposition methods. The special core-shell structure formed by MOF-derived ZnCo₂O₄, NiCo₂S₄ and PPy creates a bi-interface, which could significantly promote the contact between electrode and electrolyte, provide more active sites and accelerate electron/ion transfer. And the combination of these three materials also produces a strong synergistic effect, which could further improve the capacitive performance of the electrode. Therefore, the ZnCo₂O₄@NiCo₂S₄@PPy/NiF electrode exhibits the maximum areal capacitance (3.75 F cm^-2) and specific capacitance (2507.0 F g^-1) at 1 mA cm^-2 and 0.5 A g^-1, respectively. Moreover, its capacitance retention rate is still 83.2% after 5000 cycles. In addition, a coin-type hybrid supercapacitor is assembled and displays a high energy density of 44.15 Wh kg^-1 and good cycling performance.

Hierarchical core-shell 2D MOF nanosheet hybrid arrays for high-performance hybrid supercapacitors

Two-dimensional (2D) metal-organic frameworks (MOFs) with large surface area, ordered pores and ultrathin thickness have recently emerged as ideal electrode materials for supercapacitors (SCs). However, their straightforward applications are restricted by the drawbacks of self-stacking and unsatisfactory electrical conductivity. Herein, ultrathin Ni-MOF nanosheets have been grafted on zeolite imidazolate framework (ZIF-L)-derived porous Co3O4 nanosheets to form hierarchical core-shell Co3O4@Ni-MOF 2D nanosheet hybrid arrays. The porous Co3O4 "core" acts as a conductive skeleton for anchoring Ni-MOF and provides shortened ion diffusion paths. The Ni-MOF "shell" can expose large active sites. Benefiting from these merits and the synergic effects of the "core and "shell", the Co3O4@Ni-MOF/NF shows a high specific capacity (capacitance) of 225.6 mA h g-1 (1980.7 F g-1) at 1 A g-1 with decent capacitance retention (82.2% after 2000 cycles). The asymmetric two-electrode cell assembled from Co3O4@Ni-MOF/NF exhibits an energy density of 37.05 W h kg-1 at a power density of 800 W kg-1 with good long-term durability (75% capacitance retention after 10 000 cycles). Moreover, two charged cells can power a red light-emitting diode (LED) for up to 16 min, manifesting the great promise of Co3O4@Ni-MOF/NF for real energy storage devices.

Metal–organic framework derived petal-like Co3O4@CoNi2S4 hybrid on carbon cloth with enhanced performance for supercapacitors

Starting from 2D Co-based metal-organic frameworks, novel petal-like core-shell Co₃O₄@CoNi₂S₄ nanowall arrays are synthesized on carbon cloth using a facile two-step method and investigated as promising electrode materials for supercapacitors.

Fabrication of 2D/2D nanosheet heterostructures of ZIF-derived Co3S4 and g-C3N4 for asymmetric supercapacitors with superior cycling stability

Asymmetric supercapacitors with superior cycling stability are achieved by designing 2D/2D nanosheet heterostructures of ZIF-derived Co₃S₄ and g-C₃N₄.

MOF-assisted construction of a Co9S8@Ni3S2/ZnS microplate array with ultrahigh areal specific capacity for advanced supercapattery

Transition metal sulfides are important candidates of battery-type electrode materials for advanced supercapatteries due to their high electric conductivity and electrochemical activity. The Co9S8@Ni3S2/ZnS composite microplate array was prepared by a metal-organic framework-assisted strategy because the electrochemical properties of composite arrays are governed by the synergistic effects of their diverse structures and compositions. As a battery-type material, the Co9S8@Ni3S2/ZnS electrode expressed an ultrahigh areal specific capacity of 8192 C cm-2 at the current density of 2 mA cm-2, and excellent cycling stability of 79.7% capacitance retention after 4000 cycles. An assembled supercapattery device using the Co9S8@Ni3S2/ZnS microplate array as a positive electrode and active carbon as the negative electrode delivered a high energy density of 0.377 mW h cm-2 at a high power density of 1.517 mW cm-2, and outstanding retention of 95.2% after 5000 cycles. As a result, the obtained Co9S8@Ni3S2/ZnS shows potential for applications in high-performance supercapattery.

Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

The fabrication of advanced MOF-derived multicomponent NiCoP/NC marigold flowers electrode for high-performance hybrid supercapacitors.

Core–shell assembly of Co3O4@NiO-ZnO nanoarrays as battery-type electrodes for high-performance supercapatteries

Core–shell Co₃O₄@NiO-ZnO nanoarrays are fabricated by annealing metal–organic framework assisted precursors and investigated as battery-type electrode for supercapattery.