A Hierarchically Porous ZIF@LDH Core-Shell Structure for High-Performance Supercapacitors

Microfluidic Synthesis of Multifunctional Micro-/Nanomaterials from Process Intensification: Structural Engineering to High Electrochemical Energy Storage

Multifunctional micro-/nanomaterials featuring functional superiority and high value-added physicochemical nature have received immense attention in electrochemical energy storage. Microfluidic synthesis has become an emergent technology for massively producing multifunctional micro-/nanomaterials with tunable microstructure and morphology due to its rapid mass/heat transfer and precise fluid controllability. In this review, the latest progresses and achievements in microfluidic-synthesized multifunctional micro-/nanomaterials are summarized via reaction process intensification, multifunctional micro-/nanostructural engineering and electrochemical energy storage applications. The reaction process intensification mechanisms of various micro-/nanomaterials, including quantum dots (QDs), metal materials, conducting polymers, metallic oxides, polyanionic compounds, metal-organic frameworks (MOFs) and two-dimensional (2D) materials, are discussed. Especially, the multifunctional structural engineering principles of as-fabricated micro-/nanomaterials, such as vertically aligned structure, heterostructure, core-shell structure, and tunable microsphere, are introduced. Subsequently, the electrochemical energy storage application of as-prepared multifunctional micro-/nanomaterials is clarified in supercapacitors, lithium-ion batteries, sodium-ion batteries, all-vanadium redox flow batteries, and dielectric capacitors. Finally, the current problems and future forecasts are illustrated.

Conductive Metal-Organic Framework Grown on the Nickel-Based Hydroxide to Realize High-Performance Electrochemical Glucose Sensing

Glucose holds significant importance in disease diagnosis as well as beverage quality monitoring. The high-efficiency electrochemical sensor plays a crucial role in the electrochemical conversion technology. Ni(OH)2 nanosheets are provided with high specific surface area and redox activity that are widely used in electrochemistry. Conductive metal-organic frameworks (cMOFs) perfectly combine the structural controllability of organic materials with the long-range ordering of inorganic materials that possess the characteristic of high electron mobility. Based on the above considerations, the combination of Ni(OH)2 and Ni-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) as an electrode modification material is designed to enhance electrochemical performance. In this work, to improve glucose detection, a sequence of Ni(OH)2@NiCo-HHTP and NiM-LDH@Ni-HHTP (M=Co2+, Mn2+, Cu2+, LDH=layered double hydroxide) are successfully synthesised by doping metals into Ni-HHTP and Ni(OH)2, respectively. As a result, NiCu-LDH@Ni-HHTP showed the best excellent glucose detection sensitivity.

The Realization of Uniform Growth of Conductive MOFs on LDHs and Their High Performance in Supercapacitors

Metal-organic frameworks (MOFs) have been widely investigated as functional materials with excellent properties. However, most MOFs are of poor electrical conductivity, which hinders their further application in electrochemical fields. Fortunately, the emergence of intrinsically conductive MOFs (c-MOFs) alleviates this problem. Layered double hydroxides (LDHs) possess Faraday redox reactivity, which is favorable to capacitors. In this paper, we combined c-MOFs with LDHs and prepared a series of NiCo-LDH@M-HHTP(-EtOH) (M=Ni or Co; HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) multilayer nanoarrays, and the effects of solvent on the morphology and energy storage properties of the materials were investigated. When NiCo-LDH@Co-HHTP-EtOH is applied as an electrode material in supercapacitors, it exhibits a capacitance of 830 F g-1 at 1 A g-1 . Furthermore, it exhibits high energy density and excellent rate performance when assembled in aqueous asymmetric supercapacitors.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

Ligand Incorporating Sequence-dependent ZIF67 Derivatives as Active Material of Supercapacitor: Competition between Ammonia Fluoride and 2-Methylimidazole

The zeolitic imidazolate framework 67 (ZIF67) derivative is a potential active material of supercapacitors (SC), owing to high specific surface area and porosity and possible formation of cobalt compounds. A novel ZIF67 derivative is synthesized using a one-step solution process with cobalt precursor 2-methylimidazole (2-Melm) and ammonia fluoride in our previous work. Due to its facile synthesis and excellent electrocapacitive behavior, it is crucial to understand the competition between ammonia fluoride and 2-Melm on forming derivatives with cobalt ions and to create more efficient ZIF67 derivatives for charge storage. In this work, several ZIF67 derivatives are designed using a one-step solution process with 2-Melm and ammonia fluoride incorporated in different sequences. The reaction durations for a single ligand and two ligands are controlled. The largest capacity of 176.33 mAh/g corresponding to the specific capacitance of 1057.99 F/g is achieved for the ZIF67 derivative electrode prepared by reacting ammonia fluoride and a cobalt precursor for 0.5 h and then incorporating 2-Melm for another 23.5 h of reaction (NM0.5). This derivative composed of highly conductive CoF₂, NiF₂, Co(OH)F, and Ni(OH)F presents high specific surface area and porosity. The relevant SC presents a maximum energy density of 19.5 Wh/kg at 430 W/kg, a capacity retention of 92%, and Coulombic efficiency of 96% in 10000 cycles.

Unprecedented Duel Role of Polyaniline for Enhanced Pseudocapacitance of Cobalt-iron Layered Double Hydroxide

Creating nanosized pores in layered materials can increase the abundant active surface area and boost potential applications of energy storage devices. Herein, a unique synthetic strategy based on the polyaniline (PANI) doped two-dimensional (2D) cobalt-iron layered double hydroxide (CoFe-LDH/P) nanomaterials are being designed, and the formation of pores at low temperature (80 °C) is developed. It is found that the optimized concentration of PANI creates the nanopores on the CoFe-LDH nanosheets among all other polymers. The well-ordered pores of CoFe-LDH/P allow the high accessibility of the redox-active sites and promote effective ion diffusion. The optimized CoFe-LDH/P2 cathode reveals a specific capacitance 1686 (1096 Cg^-1 ) and 1200 Fg^-1 (720 Cg^-1 ) at 1 and 30 Ag^-1 respectively, a high rate capability (71.2%), and a long cycle life (98% over 10000 cycles) for supercapcitor applications. Charge storage analysis suggested that the CoFe-LDH/P2 electrode displays like a capacitive-type storage mechanism (69% capacitive at 1 mVs^-1 ). Moreover, an asymmetric aqueous supercapacitor (CoFe-LDH/P2//AC) was fabricated, delivering the excellent energy density (75.9 Wh kg^-1 at 1124 W kg^-1 ) with outstanding stability (97.5%) over 10000 cycles. This work opens a new avenue for designing porous 2D materials at low temperature for aqueous energy storage devices. This article is protected by copyright. All rights reserved.

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...