Recent Advances in Pristine Iron Triad Metal-Organic Framework Cathodes for Alkali Metal-Ion Batteries.

Pristine iron triad metal-organic frameworks (MOFs), i.e., Fe-MOFs, Co-MOFs, Ni-MOFs, and heterometallic iron triad MOFs, are utilized as versatile and promising cathodes for alkali metal-ion batteries, owing to their distinctive structure characteristics, including modifiable and designable composition, multi-electron redox-active sites, exceptional porosity, and stable construction facilitating rapid ion diffusion. Notably, pristine iron triad MOFs cathodes have recently achieved significant milestones in electrochemical energy storage due to their exceptional electrochemical properties. Here, the recent advances in pristine iron triad MOFs cathodes for alkali metal-ion batteries are summarized. The redox reaction mechanisms and essential strategies to boost the electrochemical behaviors in associated electrochemical energy storage devices are also explored. Furthermore, insights into the future prospects related to pristine iron triad MOFs cathodes for lithium-ion, sodium-ion, and potassium-ion batteries are also delivered.

Vanadate-based Fe-MOFs as promising negative electrode for hybrid supercapacitor device.

In the supercapacitor field, negative electrodes are mainly concentrated in carbon-based materials, such as activated carbon, carbon nanotubes, graphene, and so forth. However, materials based on metal-organic frameworks (MOFs) as negative active components are relatively rare. Herein, a series of composite materials based on graphene oxide (GO) and vanadate-based Fe-organic frameworks have been prepared by hydrothermal method namely GO/Fe-VO4-BIPY. The deposition amount of polyoxometalate-based metal-organic frameworks (POMOFs) on the surface of graphene is adjusted by changing the content of POMOFs. Through the deposition, it can effectively reduce the accumulation between graphene, and increase the dispersion of POMOFs. As a result, the charge storage performance of the as-obtained materials is greatly improved. Among these materials, GO/Fe-VO4-BIPY-1 has the most prominent performance, with a specific capacitance of 190 F g-1at 0.5 A g-1, which is attributed to the excellent synergistic effect between the Faraday chemical reaction and electric double-layer capacitance. In comparison with pristine Fe-VO4-BIPY, GO/Fe-VO4-BIPY-1 delivers more excellent surface area and therefore exhibits abundant redox reaction sites, achieving better electrochemical performance the best. After assembly with the positive Ni(OH)2electrode, the maximum energy density of 46.84 W h kg-1at a power density of 850 W kg-1is achieved.

Exploration for cobalt/nitrogen-doped catalyst to creatinine degradation via peroxymonosulfate activation: toxicity evaluation, statistical modeling, and mechanisms study.

Developing multifunctional catalysts applied in diversiform modes via advanced oxidation processes (AOPs) is a promising and attractive approach for organic pollution degradation. Herein, a novel hollow bamboo-like structural cobalt/nitrogen-doped carbonized material (CoC/N) was employed as a catalyst for AOPs, in which CoC/N was prepared in situ through calcining a Co-based coordination polymer. When CoC/N was utilized as a peroxymonosulfate (PMS) activator, the catalyst stood out prominent activities for effective CA oxidation. Furthermore, a five-level central composite rotatable design (CCRD) model describing CA decay as a function of PMS concentration, CoC/N dosage, and solution pH value was successfully constructed and engaged to explore the optimal operating conditions. Finally, the possible degradation mechanism of CA in CoC/N-PMS system was proposed by quantum chemistry calculation and LC/MS analysis. This work shed light on the structural morphology of the catalyst and its PMS synergy degradation pathway, which promotes its applications in miscellaneous pollutant degradation. A new Co/N-doped material was used to degrade unconventionality organic pollutant creatinine (CA) for the first time, in which the scientific approaches of five-level central composite rotatable design (CCRD) model, response surface methodology (RSM) and density function theory (DFT) were employed to evaluate the material performance and CA degradation pathway. The toxicity evaluation, statistical modeling and mechanisms study have been investigated meticulously.

Carbon Nanodots Memristor: An Emerging Candidate toward Artificial Biosynapse and Human Sensory Perception System.

In the era of big data and artificial intelligence (AI), advanced data storage and processing technologies are in urgent demand. The innovative neuromorphic algorithm and hardware based on memristor devices hold a promise to break the von Neumann bottleneck. In recent years, carbon nanodots (CDs) have emerged as a new class of nano-carbon materials, which have attracted widespread attention in the applications of chemical sensors, bioimaging, and memristors. The focus of this review is to summarize the main advances of CDs-based memristors, and their state-of-the-art applications in artificial synapses, neuromorphic computing, and human sensory perception systems. The first step is to systematically introduce the synthetic methods of CDs and their derivatives, providing instructive guidance to prepare high-quality CDs with desired properties. Then, the structure-property relationship and resistive switching mechanism of CDs-based memristors are discussed in depth. The current challenges and prospects of memristor-based artificial synapses and neuromorphic computing are also presented. Moreover, this review outlines some promising application scenarios of CDs-based memristors, including neuromorphic sensors and vision, low-energy quantum computation, and human-machine collaboration.

Insight into Electrochemical Performance of Nitrogen-Doped Carbon/NiCo-Alloy Active Nanocomposites.

Nanocomposites containing Ni or Co or NiCo alloy and nitrogen-doped carbon with diverse ratios have been prepared and utilized as active elements in supercapacitors. The atomic contents of nitrogen, nickel, and cobalt have been adjusted by the supplement amount of Ni and Co salts. In virtue of the excellent surface groups and rich redox active sites, the NC/NiCo active materials exhibit superior electrochemical charge-storage performances. Among these as-prepared active electrode materials, the NC/NiCo1/1 electrode performs better than other bimetallic/carbon electrodes and pristine metal/carbon electrodes. Several characterization methods, kinetic analyses, and nitrogen-supplement strategies determine the specific reason for this phenomenon. As a result, the better performance can be ascribed to a combination of factors including the high surface area and nitrogen content, proper Co/Ni ratio, and relatively low average pore size. The NC/NiCo electrode delivers a maximum capacity of 300.5 C g-1 and superior capacity retention of 92.30% after 3000 unceasing charge-discharge cycles. After assembling it into the battery-supercapacitor hybrid device, a high energy density of 26.6 Wh kg-1 (at 412 W kg-1 ) is achieved, comparable to the recent reports. Furthermore, this device can also power four light-emitting-diode (LED) demos, suggesting the potential practicability of these N-doped carbon compositing with bimetallic materials.

Cu/CuxO@C nanocomposites as efficient electrodes for high-performance supercapacitor devices.

A novel method, reduction followed by oxidation procedure, has been developed to fabricate efficient electrodes derived from metal-organic frameworks (MOFs), which were synthesized using terephthalic acid (TP) and 1,3,5-benzenetricarboxylic acid (BTC) as organic ligands. The copper-based composites, namely Cu/CuxO@C (x = 1 and 2), were obtained through two steps: first calcining the precursors at high temperature under a nitrogen atmosphere, and then calcining in air to increase the number of porous active sites. For a more convenient description, the calcined materials are denoted as 800-TP, 900-TP, 800-BTC and 900-BTC, respectively, according to the calcination temperature and the corresponding organic ligand. Their electrochemical performances in supercapacitors (SCs) suggest that a higher calcination temperature endows the as-resultant materials with a larger specific surface area, higher carbon content, higher electrical conductivity, and better ion transport ability. For example, the 900-BTC electrode delivers a specific capacity of 400 C g-1 at a current density of 3 A g-1 under a three-electrode configuration. Even under a double-electrode system, the corresponding 900-BTC//AC device (AC represents activated carbon) also achieves superior electrochemical performance with an energy density of 24.02 W h kg-1 at a power density of 825 W kg-1 and the specific capacitance retention rate for the device is maintained at 91.7% after 3000 unceasing loops, indicating its potential for practical applications.

Nanofiber Architecture Engineering Implemented by Electrophoretic-Induced Self-Assembly Deposition Technology for Flash-Type Memristors.

Electrophoretic deposition (EPD) has been recognized as a promising large-scale film preparation technology for industrial application. Inspired by the conventional EPD method and the crystal diffusion growth strategy, we propose a modified electrophoretic-induced self-assembly deposition (EPAD) technique to control the morphologies of organic functional materials. Here, an ionic-type dye with a conjugated skeleton and strong noncovalent interactions, celestine blue (CB), is chosen as a module molecule for EPAD investigation. As expected, CB molecules can assemble into different nanostructures, dominated by applied voltage, concentration effect, and duration. Compared to a nanopillar layered packing structure formed by the traditional spin-coating method, the EPAD approach can produce a nanofiber structure under a fixed condition of 10 V/10 min. Intriguingly, a memristor device based on a pillar-like nanostructure exhibits WORM-type behavior, while a device based on nanofibers presents Flash memory performance. The assemble process and the memory mechanism are uncovered by molecular dynamics simulations and density-functional theory (DFT) calculations. This work endows the typical EPD technique with a fresh application scenario, where an in-depth study on the growth mechanism of nanofibers and the positive effect of unique morphologies on memristor performance are offered.

2D MOFs-based Materials for the Application of Water Pollutants Removing: Fundamentals and Prospects.

Water quality can have serious impacts on human health. One crucial issue of water pollution seriously affects our safety due to the continually emerging of discovered anthropogenic pollutants. The water treatment technologies are persistent improvement to adapt such new contaminants, which accelerates the evolution of materials science to explore solving the problems. Metal-organic Frameworks (MOFs) as the significant porous and multi-dimensional networks has been concerned for toxic pollutant elimination, especially probed the applications of outstanding layered 2D skeletons MOFs-based materials. The emphases of this review highlight the 2D MOFs-based materials used in water remediation and treatment strategies including adsorption and catalysis methods. Further, the prospects and challenges of 2D MOFs-based materials for water treatments applications would be surveyed meticulously for the future research and development.

Recent progress on pristine two-dimensional metal-organic frameworks as active components in supercapacitors.

Two-dimensional (2D) metal-organic frameworks (MOFs) are a new generation of 2D materials that can provide uniform active sites and unique open channels as well as excellent catalytic abilities, interesting magnetic properties, and reasonable electrical conductivities. Thus, these MOFs are uniquely qualified for use in applications in energy-related fields or portable devices because they possess fast charge and discharge ability, high power density, and ultralong cycle life factors. There has been worldwide research interest in 2D conducting MOFs, and numerous techniques and strategies have been developed to synthesize these MOFs and their derivatives. Thus, this is the opportune time to review recent research progress on the development of 2D MOFs as electrodes in supercapacitors. This review covers synthetic design strategies, electrochemical performances, and working mechanisms. We will divide these 2D MOFs into two types on the basis of their conductive aspects: 2D conductive MOFs and 2D layered MOFs (including pillar-layered MOFs and 2D nanosheets). The challenges and perspectives of 2D MOFs are also provided.

Fe-Based Coordination Polymers as Battery-Type Electrodes in Semi-Solid-State Battery-Supercapacitor Hybrid Devices.

One two-dimensional Fe-based metal-organic framework (FeSC1) and one one-dimensional coordination polymer (FeSC2) have been solvothermally prepared through the reaction among FeSO4·7H2O, the tripodal ligand 4,4',4″-s-triazine-2,4,6-triyl-tribenzoate (H3TATB), and flexible secondary building blocks p/m-bis((1H-imidazole-1-yl)methyl)benzene (bib). Given that their abundant interlayer spaces and different coordination modes, two compounds have been employed as battery-type electrodes to understand how void space and different coordination modes affect their performances in three-electrode electrochemical systems. Both materials exhibit outstanding but different electrochemical performances (including distinct capacities and charge-transfer abilities) under three-electrode configurations, where the charge storage for each electrode material is mainly dominated by the diffusion-controlled section (i ∝ v0.5) through power-law equations. Additionally, the partial phase transformations to more stable FeOOH are also detected in the long-term cycling loops. After coupling with the capacitive carbon-based electrode to assemble into the semi-solid-state battery-supercapacitor-hybrid (sss-BSH) devices, the sss-FeSC1//AC BSH device delivers excellent capacitance, superior energy and power density, and longstanding endurance as well as the potential practical property.

Fabrication of One-Dimensional Organic Nanofiber Networks via Electrophoretic Deposition for a Nonvolatile Memory Device.

Despite many advanced growth methodologies for organic nanofibers (ONFs), the lack of efficient and scalable ONF-based film preparation technologies has long been a hindrance in their practical application in organic electronic devices. Here, a typical cathode electrophoretic deposition (C-EPD) technology was developed to controllably produce ONFs and their corresponding thin films. Using the solvent effect and an external electric field force during the C-EPD process, a one-dimensional ONF network was formed, which exhibits compact molecular packing and superior optoelectronic properties in the thin-film state. Prototype sandwich-structure memory devices based on these ONF films exhibited a binary nonvolatile memory performance significantly superior than that of the bulk materials. This study provides an efficient and scalable ONF fabrication technology for high-performance electronic devices in various potential applications.

Enhancing the Performance of a Battery-Supercapacitor Hybrid Energy Device Through Narrowing the Capacitance Difference Between Two Electrodes via the Utilization of 2D MOF-Nanosheet-Derived Ni@Nitrogen-Doped-Carbon Core-Shell Rings as Both Negative and Positive Electrodes.

Narrowing the capacitance gap between the positive and negative electrodes for the enhancement of the energy densities of battery-supercapacitor hybrid (BSH) devices is urgent and very important. Herein, a new strategy to synchronously improve the positive-negative system and reduce the capacitance discrepancies between two electrodes through the utilization of the same MOF-based precursors ([Ni(ATA)2(H2O)2](H2O)3) has been proposed. Nickel/nitrogen codoped carbon (Ni@NC) materials, serving as positive electrodes, deliver battery-type behavior with the enhancement of capacities, which are even superior to those of pristine carbon-based materials with large surface areas. Meanwhile, HCl-treated Ni@NC materials (named A-Ni@NC) are employed as negative electrodes within the potential window of -1 to 0 V and exhibit higher capacitances than that of the commercial activated carbon. With Ni@NC and A-Ni@NC as positive and negative electrodes in BSH devices, the as-fabricated cells display higher capacities and energy densities, more excellent cycling stability, and far superior capacity retention in comparison with those of Ni@NC//AC cells. These results clearly confirm that our strategy is successful and effective.

Ferrocene-Based Mixed-Valence Metal-Organic Framework as an Efficient and Stable Cathode for Lithium-Ion-Based Dual-Ion Battery.

Organic anion-hosting cathodes are remarkably attractive platform candidates for lithium-ion-based dual-ion batteries (LDIBs) due to their various advantages such as variety, designable, and adjustable. Here, a new organic anion-hosting mixed-valence metal-organic framework cathode (Co2IICoIII(DFc)2(OH)3·H2O, abbreviated as Co(DFc)x) is first employed in LDIBs. With the redox reactions happening in the couples of Fe2+/Fe3+ and Co2+/Co3+, PF6- anions can be incorporated into the cathode and reversibly released into the LiPF6-based electrolyte. Meanwhile, benefiting from its unique structure and insolubility, Co(DFc)x shows a high energy density of 632 Wh kg-1 (vs lithium anode), a high operating potential of 3.63 V (vs Li+/Li), a high reversible (discharge) capacity of 170 mAh g-1 at 50 mA g-1 (the third cycle), an excellent rate performance (up to 2000 mA g-1, 5 min for one cycle), and extraordinary cycling stability (an average capacity of 74.9 mAh g-1 for 8000 cycles at 2000 mA g-1).

2D Metal-Organic Frameworks (MOFs) for High-Performance BatCap Hybrid Devices.

Two identical layered metal-organic frameworks (MOFs) (CoFRS and NiFRS) are constructed by using flexible 1,10-bis(1,2,4-triazol-1-yl)decane as pillars and 1,4-benzenedicarboxylic acid as rigid linkers. The single-crystal structure analysis indicates that the as-synthesized MOFs possess fluctuant 2D networks with large interlayer lattices. Serving as active electrode elements in supercapacitors, both MOFs deliver excellent rate capabilities, high capacities, and longstanding endurances. Moreover, the new intermediates in two electrodes before and after long-lifespan cycling are also examined, which cannot be identified as metal hydroxides in the peer reports. After assembled into battery-supercapacitor (BatCap) hybrid devices, the NiFRS//activated carbon (AC) device displays better electrochemical results in terms of gravimetric capacitance and cycling performance than CoFRS//AC devices, and a higher energy-density value of 28.7 Wh kg-1 compared to other peer references with MOFs-based electrodes. Furthermore, the possible factors to support the distinct performances are discussed and analyzed.

Porous Cobalt Metal-Organic Frameworks as Active Elements in Battery-Supercapacitor Hybrid Devices.

With the trigonal linker 4,4',4″-s-triazine-2,4,6-triyltribenzoic acid as a building block, porous cobalt metal-organic frameworks (named as PCN) have been successfully prepared and directly utilized as active materials in alkaline battery-type devices. For comparison, their carbon-supported hybrids (CNFs/PCN) have also been employed as battery-type electrodes. We found that the pristine PCN displayed a better performance than the CNFs/PCN composite electrode in electrochemical cells. To further investigate their electrochemical performances, alkaline battery-supercapacitor hybrid (BSH) devices with these materials as positive electrodes and activated carbon (AC) as the negative electrode were fabricated. The results indicate that the PCN//AC BSH devices delivered a maximum energy density of 16.0 Wh kg-1 at a power density of 749 W kg-1 within the voltage range of 0-1.5 V, which are much higher than those of CNFs/PCN//AC devices (12.4 Wh kg-1 at 753 W kg-1).

Nanostructured potassium-organic framework as an effective anode for potassium-ion batteries with a long cycle life.

Finding new organic materials to address several issues (e.g. capacity, stability, and cycle life) in organic potassium-ion batteries (OPIBs) is very important and highly desirable. Here, to directly investigate the redox reaction of organic pyridine dicarboxylate in OPIBs and to avoid the interference from the redox-active metal ions, a non-redox-metal potassium metal-organic framework (K-MOF), [C7H3KNO4]n, based on pyridine-2,6-dicarboxylic acid (H2PDA), has been successfully synthesized and applied as a promising organic anode for long-cycle life PIBs. The crystal structure of [C7H3KNO4]n was confirmed by single-crystal X-ray diffraction analysis and FT-IR spectra. Moreover, the potassium-storage mechanism of organic pyridine dicarboxylate ligand was revealed by ex situ FT-IR/XRD characterization and theoretical calculations. The as-synthesized K-MOF resulted in a unique and reversible three-step redox reaction, exhibited superior electrochemical performance with the aid of N-K/O-K coordination bonds, and showed a high average specific capacity of 115 mA h g-1 at 100 mA g-1 for 300 cycles with the capacity retention of 92%.

A self-penetrated three-dimensional zinc(II) coordination framework based on 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzoic acid and 1,3-bis[(imidazol-1-yl)methyl]benzene ligands: synthesis, structure and properties.

With the rapid development of metal-organic frameworks (MOFs), a variety of MOFs and their derivatives have been synthesized and reported in recent years. Commonly, multifunctional aromatic polycarboxylic acids and nitrogen-containing ligands are employed to construct MOFs with fascinating structures. 4,4',4''-(1,3,5-Triazine-2,4,6-triyl)tribenzoic acid (H3TATB) and the bidentate nitrogen-containing ligand 1,3-bis[(imidazol-1-yl)methyl]benzene (bib) were selected to prepare a novel ZnII-MOF under solvothermal conditions, namely poly[[tris{µ-1,3-bis[(imidazol-1-yl)methyl]benzene}bis[µ3-4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzoato]trizinc(II)] dimethylformamide disolvate trihydrate], {[Zn3(C24H12N3O6)2(C14H14N4)3]·2C3H7NO·3H2O}n (1). The structure of 1 was characterized by single-crystal X-ray diffraction, IR spectroscopy and powder X-ray diffraction. The properties of 1 were investigated by thermogravimetric and fluorescence analysis. Single-crystal X-ray diffraction shows that 1 belongs to the monoclinic space group Pc. The asymmetric unit contains three crystallographically independent ZnII centres, two 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzoate (TATB3-) anions, three complete bib ligands, one and a half free dimethylformamide molecules and three guest water molecules. Each ZnII centre is four-coordinated and displays a distorted tetrahedral coordination geometry. The ZnII centres are connected by TATB3- anions to form an angled ladder chain with large windows. Simultaneously, the bib ligands link ZnII centres to give a helical Zn-bib-Zn chain. Furthermore, adjacent ladders are bridged by Zn-bib-Zn chains to form a fascinating three-dimensional self-penetrated framework with the short Schläfli symbol 65·7·813·9·10. In addition, the luminescence properties of 1 in the solid state and the fluorescence sensing of metal ions in suspension were studied. Significantly, compound 1 shows potential application as a fluorescent sensor with sensing properties for Zr4+ and Cu2+ ions.

Two-fold interpenetrated Mn-based metal-organic frameworks (MOFs) as battery-type electrode materials for charge storage.

Two novel interpenetrated 2-fold Mn-based metal-organic frameworks (MOFs) (SC-7 and SC-8), assembled from the rigid ligand H3TATB (4,4',4''-s-triazine-2,4,6-triyl-tribenzoic acid) and Mn ions with the assistance of the flexible N-donor linker BIB (bis((1H-imidazol-1-yl)methyl)benzene) or TIPA (tris(4-imidazolylphenyl)amine), have been successfully prepared. The as-obtained MOFs show two distinct topological structures with the symbols 44·62 and (52·6)(53·6·73·82·9) due to discrepancies between the flexibilities of the bi-imidazole and tri-imidazole linkers. The electrodes based on the as-prepared bulk Mn-MOFs behave as alkaline batteries in electrochemical cells and deliver high capacities (279 and 172 mA h g-1 at 1 A g-1 for SC-7 and SC-8, respectively). Theoretical mechanism analyses indicate that the surface-controlled (k1v) process can be transformed into a diffusion-dominated (k2v1/2) process when the charging time exceeds 30 seconds in the MOF-based systems. Our research provides a new strategy to construct an increasing number of stable redox sites in MOFs for application to battery-capacitor hybrid devices.

Boosting the performance of broccoli-like Ni-triazole frameworks through a CNTs conductive-matrix.

Different approaches for the fabrication of CNT-supported Ni-triazole composites, such as room-temperature stirring and hydrothermal treatment for a distinct reaction time has been presented. As a result, various morphologies, MMOF wrapped CNTs, CNTs entangled with an MMOF and CNTs attached on an MMOF, were synthesized and investigated through electrochemical measurements. The as-synthesized CNTs/MMOF-based hybrids, especially for the CNTs/MMOF-8H structure, show a good rate capability after 20 times increase, a superior coulombic efficiency and an excellent long-term cycling stability (more than 98% retained after 2000 cycles). This enhancement can be ascribed to the introduction of the CNT conductive additives, which promote the fast charge-transfer ability of ions and electrons. Even for the other CNTs/MMOF-based composites, the overall electrochemical performances are still superior to those of pristine MMOF electrodes.

Interpenetrated and Polythreaded CoII-Organic Frameworks as a Supercapacitor Electrode Material with Ultrahigh Capacity and Excellent Energy Delivery Efficiency.

Synthesizing kinetically stable coordination polymers (CPs) through ligand functionalization can effectively improve their supercapacitive performances. Herein, we have successfully synthesized three novel and topological Co-CPs by varying the flexible N-donor ligand and inorganic anions, namely, interpenetrated [Co(HTATB)( o-bib)]·H2O, extended two-dimensional (2D) layered Co(HTATB)( m-bib)·2H2O, and three-dimensional (3D) Co(HTATB)( m-bib), where bib is the flexible N-donor bis((1 H-imidazol-1-yl)methyl)benzene linker (where o- and m- refer to ortho and meta positions, respectively) ligand and HTATB is the partial deprotonation mode from 4,4',4″- s-triazine-2,4,6-triyl-tribenzoic acid. Various Co-CPs have been directly applied in the field of supercapacitors. All these framework materials exhibit high capacitance, excellent energy delivery efficiency, and good cycling performance. For instance, the maximum specific capacitance for penetrated 3D networks is 2572 F g-1 at 2.0 A g-1, and the mean energy delivery efficiency is up to 92.7% based on the tested current densities. Compared with extensional 2D layered and 3D networks, the 3D interpenetrated and polythreaded architectures could provide more active sites and thus promote fast charging and discharging processes. Furthermore, the Li+ uptake-release abilities of the Co-based CPs are also investigated, and the initial discharge capacity value for the 3D interpenetrated structures can reach up to 1792 mA h g-1 at a current density of 50 mA g-1.