Efficient improvement in the electrochemical performance of petal-like lamellar NiMn-LDHs with affluent oxygen vacancies derived from Mn MOF-74

Supercapacitors (SCs) as a kind of novel energy storage devices have emerged to meet the urgent requirement of environmentally friendly clean energy storage equipment. However, unsatisfactory energy density and low operating voltage tremendously restrict their practical application. Herein, petal-like lamellar NiMn-layered double hydroxide (NiMn-LDH) was successfully fabricated through a simple Ni(NO3)2 etching method with Mn MOF-74 as a sacrificial template. This NiMn-LDH 3/NF electrode exhibited an improved specific capacitance of 1410.2 F g-1 at a current density of 1 A g-1 (Mn MOF-74/NF: 172.2) owing to its high redox activity, compositional flexibility and intercalating capability. Importantly, NiMn-LDH was further optimized via a facile hydroperoxide treatment to harvest NiMn-LDH (O-LDH) with abundant oxygen vacancies, exhibiting remarkable improvement in specific capacitance (990%) compared to original MOF-74 before modification. The preparation of O-LDH enriches the electrode material engineering strategy and achieves improved electrochemical performance for application in new-generation SCs.

Manganese-cobalt hydroxide nanosheets anchored on a hollow sulfur-doped bimetallic MOF for high-performance supercapacitors and the hydrogen evolution reaction in alkaline media

Nonmetallic doping and in situ growth techniques for designing electrode materials with excellent electrocatalytic activity are effective strategies to enhance the electrochemical performance. Bifunctional electrode materials for supercapacitors (SCs) and the hydrogen evolution reaction (HER) have attracted great interest due to their potential applications in green energy storage and conversion. Herein, the bimetallic MnCo LDH is anchored on a hollow sulfur (S)-doped MnCo-MOF-74 surface, forming a poplar flower-like 3D composite which is used for SCs and the HER in alkaline media. The fabricated S-MnCo-MOF-74@MnCo LDH/NF electrode exhibits a favorable specific capacitance of 1875.4 F g-1 at 1 A g-1 and steady long-term cycling performance. Moreover, the assembled HSC using S-MnCo-MOF-7@MnCo LDH/NF as the cathode material and active carbon (AC) as the anode material shows 546.4 F g-1 capacitance (1 A g-1) with a maximum energy density of 58 W h kg-1 at 14 000 W kg-1 power density. As an electrocatalyst, S-MnCo-MOF-7@MnCo LDH/NF exhibits excellent HER properties with a small Tafel slope of 128.9 mV dec-1 a low overpotential of 197 mV at 10 mA cm-2 and durable performance for 10 hours in alkaline media. The present work provides insights into understanding and designing active electrode materials for stable hydrogen evolution and high-performing supercapacitors in an alkaline environment.

Trimetallic Oxide Electrocatalyst for Enhanced Redox Activity in Zinc-Air Batteries Evaluated by In Situ Analysis

Researchers are investigating innovative composite materials for renewable energy and energy storage systems. The major goals of this studies are i) to develop a low-cost and stable trimetallic oxide catalyst and ii) to change the electrical environment of the active sites through site-selective Mo substitution. The effect of Mo on NiCoMoO4 is elucidated using both in situ X-ray absorption spectroscopy and X-ray diffraction analysis. Also, density functional theory strategies show that NiCoMoO4 has extraordinary catalytic redox activity because of the high adsorption energy of the Mo atom on the active crystal plane. Further, it is demonstrated that hierarchical nanoflower structures of NiCoMoO4 on reduced graphene oxide can be employed as a powerful bifunctional electrocatalyst for oxygen reduction/evolution reactions in alkaline solutions, providing a small overpotential difference of 0.75 V. Also, Zn-air batteries based on the developed bifunctional electrocatalyst exhibit outstanding cycling stability and a high-power density of 125.1 mW cm-2 . This work encourages the use of Zn-air batteries in practical applications and provides an interesting concept for designing a bifunctional electrocatalyst.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Metal-organic frameworks-derived layered double hydroxides: From controllable synthesis to various electrochemical energy storage/conversion applications

Over the past years, metal-organic frameworks (MOF) have been directly used as electrodes or as a precursor for MOF-derived materials in energy storage and conversion systems. In the wide range of existing MOF derivatives, MOF-derived layered double hydroxides (LDHs) are determined to be promising materials due to their unique structure and features. However, MOF-derived LDHs (MDL) materials can suffer from insufficient intrinsic conductivity and agglomeration during formation. Various techniques and approaches were designed and applied to tackle these problems, such as using ternary LDHs, ion-doping, sulphurization, phosphorylation, selenization, direct growth, and conductive substrates. All the mentioned enhancement techniques aim to create the ideal electrode materials with maximum performance. In this review, we gathered and discussed the most recent progressive advances, different synthesis methodologies, unsolved challenges, applications, and electrochemical and electrocatalytic performance of MDL materials. We hope this work will be a reliable source for future progress and synthesis of these materials.

MOF-on-MOF heterojunction-derived Co3O4-CuCo2O4 microflowers for low-temperature catalytic oxidation

Through the exchange-extended growth method (EEGM), MOF-on-MOF heteroarchitectures with distinct crystallography were produced and pyrolyzed into hybrid metal oxides. The strong exchange ability of organometallic compounds realized the component reconstruction of the MOF matrix and enhanced the interfacial forces between MOFs, showing an excellent performance in low-temperature catalytic oxidation.

Ni-soc-MOF derived carbon hollow sphere encapsulated Ni3Se4 nanocrystals for high-rate supercapacitors

Carbon hollow sphere encapsulated Ni₃Se₄ (Ni₃Se₄@CHS) nanocrystals are prepared using the Ni-soc-MOF by pyrolysis and further selenization. Ni₃Se₄@CHS exhibits a capacitance of 1720 F g^-1 at 1 A g^-1 and a capacitance retention of 97% after 6000 cycles at 5 A g^-1. Moreover, the asymmetric supercapacitor of Ni₃Se₄@CHS//AC displays a wide potential window of 1.6 V, an energy density of 45.2 W h kg^-1 at a power density of 800 W kg^-1, and excellent cycling stability (89% capacitance retention) after 5000 cycles. Overall, this work establishes a significant step to synthesize a new carbon-based material with appreciable capacitance and long cycling durability for potential applications in energy storage and beyond.

Controllable Synthesis of Ultrathin Defect-Rich LDH Nanoarrays Coupled with MOF-Derived Co-NC Microarrays for Efficient Overall Water Splitting

Water electrolysis has attracted immense research interest, nevertheless the lack of low-cost but efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions greatly hinders its commercial applications. Herein, the controllable synthesis of ultrathin defect-rich layered double hydroxide (LDH) nanoarrays assembled on metal-organic framework (MOF)-derived Co-NC microarrays for boosting overall water splitting is reported. The Co-NC microarrays can not only provide abundant nucleation sites to produce a large number of LDH nuclei for favoring the growth of ultrathin LDHs, but also help to inhibit their tendency to aggregate. Impressively, five types of ultrathin bimetallic LDH nanoarrays can be electrodeposited on the Co-NC microarrays, forming desirable nanoarray-on-macroarray architectures, which show high uniformity with thicknesses from 1.5 to 1.9 nm. As expected, the electrocatalytic performance is significantly enhanced by exploiting the respective advantages of Co-NC microarrays and ultrathin LDH nanoarrays as well as the potential synergies between them. Especially, the optimal Co-NC@Ni₂ Fe-LDH as both cathode and anode can afford the lowest cell voltage of 1.55 V at 10 mA cm^-2 , making it one of the best earth-abundant bifunctional electrocatalysts for water electrolysis. This study provides new insights into the rational design of highly-active and low-cost electrocatalysts and facilitates their promising applications in the fields of energy storage and conversion.

Multi-step electrodeposited Ni-Co-P@LDH nanocomposites for high-performance interdigital asymmetric micro-supercapacitors

The development of high-performance electrode materials and the rational design of asymmetric structures are the two main keys to fabricating micro-supercapacitors (MSCs) with high energy density. Transition metal compounds, especially nickel-cobalt phosphides and hydroxides, are promising electrode materials with excellent pseudo-capacitance. However, they are rarely used in fabricating asymmetric MSCs (AMSCs) due to the limitations of the preparation method. In this work, we constructed hierarchical Ni-Co-P@LDH nanocomposites with outstanding mass specific capacitance (1980 F g^-1 at 1 A g^-1) via a multi-step electrodeposition method, which is employed with FeOOH to fabricate an interdigital AMSC device (Ni-Co-P@LDHs//PVA-KOH//FeOOH). The as-prepared device exhibits a high working voltage (1.4 V), a large specific capacitance (24.0 mF cm^-2 at 0.14 mA cm^-2), a high energy density (6.54 μW h cm^-2 at a power density of 100 μW cm^-2) and good cycling stability (86.5% of capacitance retention after 5000 cycles). This work may provide novel methods for the synthesis of high-performance nickel-cobalt composite materials and their potential applications in interdigital AMSC devices.

Molybdenum doped induced amorphous phase in cobalt acid nickel for supercapacitor and oxygen evolution reaction

Reasonable structural design and metal-doping play significant roles in the optimization of electrochemical energy storage and conversion. Herein, in situ growth of Molybdenum-doped amorphous cobalt acid nickel nanoneedles on Ni foam (Mo-NiCo₂O₄/NF) has been successfully synthesized by a simple hydrothermal-annealing strategy. Benefiting from the unique hierarchical nanostructures and doping-optimized electronic structural configuration, the cross-link network structure of Mo-doped amorphous NiCo₂O₄ with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, the optimized Mo-doped NiCo₂O₄ samples possess a specific capacitance of 3970 mF cm^-2 at 1 mA cm^-2 and remarkable rate performance. The assembled hybrid supercapacitor obtains a maximum energy density of 35 Wh kg^-1 (420 W kg^-1) and keeps a capacitance retention of 107% after 5000 cycles. As an electrocatalyst, Mo-NiCo₂O₄/NF shows a rapid self-reconstruction process during oxygen evolution reaction (OER) that produces rich oxygen vacancies and thus exhibits remarkable long-term stability. The nanocomposites exhibit small overpotential (280 mV at 10 mA cm^-2) and Tafel slope (43 mV dec^-1). These results strongly demonstrate that both local amorphous phase and porous hierarchical structure design from Mo dopant provide superiorities for the synthesis of efficient and stable multifunctional electrode materials for energy storage and conversion.

Reduced Mo-doped NiCo2O4 with rich oxygen vacancies as advanced electrode material in supercapacitors

Reduced Mo-doped NiCo2O4 (R-Mo-NiCo2O4) was facilely prepared through a dual-defect strategy. Mo-doped NiCo layered double hydroxide (Mo-NiCo-LDH) was used as the precursor and calcined in an air atmosphere, and the...

Efficient and selective removal of Congo red by a C@Mo composite nanomaterial using a citrate-based coordination polymer as the precursor

To research the effect of structural diversity on citrate-based coordination polymers (CPs), citric acid (H4cit) was selected to combine with Cu(ii) under hydrothermal conditions. A new CP [Cu2(cit)(H2O)2] (1) was synthesized and structurally characterized. The title complex shows a 3D 2,4,6-connected topology with the point symbol of {43·63}{44·66·85}{4}. Inspired by the decomposition and functional molybdenum component, 1 was used as a catalyst precursor to synthesize a carbon-based material (C-1) and a C@Mo material (C-Mo-1) by the chemical vapor deposition (CVD) method and characterized in detail. The selective removal of a contaminant (Congo red) by complex 1, C-1 and C-Mo-1 in the aqueous phase was also comparatively investigated.

Effect of pomelo seed-derived carbon on the performance of supercapacitors

Electrochemical ultracapacitors derived from green and sustainable materials could demonstrate superior energy output and an ultra-long cycle life, which could contribute to next-generation applications. Herein, we utilize pomelo seeds, a bio-waste from pomelo, in high-energy and high-power supercapacitors by a facile low-cost pyrolysis and activation method. The as-synthesized hierarchically porous carbon is surface-engineered with a large quantity of nitrogen and sulfur heteroatoms to give a high specific capacitance of ∼845 F g-1 at 1 A g-1. An ultra-high stability of ∼93.8% even after 10 000 cycles (10 A g-1) is achieved at room temperature. Moreover, a maximum energy density of ∼85 W h kg-1 at a power density of 1.2 kW kg-1 could be achieved in 1.2 V aqueous symmetrical supercapacitors. The results provide new insights that will be of use in the development of high-performance, green supercapacitors for advanced energy storage systems.

Controllable synthesis of hydrangea-like NixSy hollow microflower all-solid-state asymmetric supercapacitor electrodes with enhanced performance by the synergistic effect of multiphase nickel

In this work, through controlling the urea content in the synthesis system, the nucleation rate of Ni_xS_y can be adjusted, and a series of Ni_xS_y with multiphase nickel and various sizes and surface morphologies can be achieved.

Construction of hierarchical layered hydroxide grown in situ on carbon tubes derived from a metal-organic framework for asymmetric supercapacitors

Electrode materials are very important for the performance of supercapacitors (SCs). Therefore, preparation of hybrid electrode materials is an effective way to develop high-performance SCs. We firstly design and prepare metal organic framework (MOF) derived carbon nanotubes as the core skeleton to support the shell of a nickel gallium layered hydroxide nanosheet (NiGa-LDH). MOF derived carbon nanomaterials have high conductivity and a large specific surface area, which can promote electron transfer and improve the agglomeration of LDH. The deposited LDH can provide high specific capacitance and the layered structure can further enhance the reaction site. The NiGa-LDH@CNT-500@CC has an excellent specific capacitance of 2580 F g-1 at 1 A g-1 and a high capacitance retention rate of 83.3% at 5 A g-1 due to the synergistic effect of two materials. The assembled NiGa-LDH@CNT-500@CC//carbon NS asymmetric supercapacitor (ASC) has an operating voltage of 1.6 V and a high energy density of 52 W h kg-1 at a power density of 952 W kg-1. Therefore, the core-shell structure composed of LDH and carbon nanomaterials provides an effective way for the design of high-performance electrodes.