MOF-based Materials Research Articles

Structural engineering of rare earth metal-organic frameworks derivatives with high anisotropy for high-efficiency electromagnetic wave absorption

Structural engineering and component design are crucial for conceiving outstanding metal-organic frameworks (MOFs)-based electromagnetic wave (EMW) absorption materials. However, an efficient and direct clarification of the structural influences on the EMW absorption performance of MOF-based absorption materials remains highly challenging and still awaits exploration. To this end, we synthesized a new type of rare earth (RE) MOFs with hexagonal-bipyramidal, snowflake-like, and dendritic structures through facilely controlling the solvent ratios in a scalable coprecipitation approach. The MOF-derived CeO2/Co/C hybrids with the same component content inheriting the morphological structures showcased tunable dielectric property and EMW absorption performance. The dendritic MOF derivatives with the highest anisotropy achieved a superior EMW absorption performance, manifesting a minimum reflection loss value of −71.5 dB at 1.7 mm and an effective absorption bandwidth of 5.2 GHz at 1.6 mm thickness, comparable to those of the best EMW absorbers. This work not only confirmed the high potential of RE MOF derivatives for EMW absorption, but also directly and efficiently unveiled the mechanism of morphological structure on the dielectric property and EMW absorption performance for the MOF-based EMW absorption material.

Au-Based MOFs as Anodic Electrocatalysts for Direct Borohydride Fuel Cells

Researchers are exploring direct liquid fuel cells (DLFCs) as alternatives to proton-exchange membrane fuel cells because of their higher energy density and ease of storing and transporting the fuel. Direct borohydride fuel cells (DBFCs) are of particular interest as they offer a sustainable energy source with their high-power density output and the use of a highly alkaline NaBH4 medium [1]. Ensuring efficient and cost-effective catalysts for DBFCs is crucial for their commercial viability. Metal-organic frameworks (MOFs) have demonstrated significant potential as anodic electrocatalysts for BOR in DBFCs [2]. However, research should explore various modifications to MOFs, such as the incorporation of alternative metal ions or functional groups, to improve their catalytic efficiency and reduce cost. This study evaluated the performance of newly developed MOF-based electrocatalysts for DBFCs. Specifically, six MOF-based materials were synthesized and analyzed for their ability to facilitate borohydride oxidation (BOR) using cyclic voltammetry and chronoamperometry in alkaline media. MIL-101_Au@NH2 and MOF-808_Au@NH2 were found to be highly effective for BOR. The kinetic parameters for BOR with MOF-based electrocatalysts, including activation energy, reaction order, exchanged electrons, and anodic charge transfer coefficient, were determined. The activation energy for BOR was found to be 13.6 kJ mol−1 and 15.3 kJ mol−1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. The number of transferred electrons, n, was found to be 7.0 and 3.1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. This study demonstrates that MOF-based electrocatalysts can enhance DBFCs' performance, while offering insight into the potential usage of MOFs in other fuel cell technologies.[1] B. Šljukić, D.M.F. Santos, "Direct borohydride fuel cells", in: "Direct Liquid Fuel Cells: Fundamentals, Advances, and Future", 1st ed., R.G. Akay, A.B. Yurtcan (eds.), Academic Press, USA, 203-232 (2021)[2] G. Backovic, B. Šljukić, G.S. Kanberoglu, M. Yurderi, A. Bulut, M. Zahmakiran, D.M.F. Santos, Ruthenium (0) nanoparticles stabilized by the metal-organic framework as an efficient electrocatalyst for borohydride oxidation reaction, International Journal of Hydrogen Energy, 45, 27056-27066 (2020).

Amorphous Ni-Fe-Co-P-B nanosheets as efficient electrocatalyst for oxygen evolution reaction

Non-noble metal electrocatalysts with hierarchically structural design and heteroatom-doped is highly urgent for high-efficiency, low-cost electrochemical water splitting systems. Herein, this paper uses a simple and low-cost method to synthesize amorphous carbon-based Ni-Fe-Co-B-P composite material as efficient OER catalyst. Specifically, the catalytic performance can be enhanced through processes such as etching-recombination-reduction. First, we use ZIF-67 as the precursor to provide Co source and carbon source. Fe and Ni are creatively incorporated into the Co3O4 lattice as auxiliary metal atoms. Then, the above three metal oxides were simultaneously reduction with NaH2PO2 and NaBH4. Although this is the first time that MOF-based materials have been treated with P and B, the resulting samples are chemically stable. The obtained amorphous carbon-based material Ni-Fe-Co-B-P benefits from the advantages of its structure and composition, showing that the electron density is rearranged around the center of the catalytic metal atom and the energy barrier formed by the intermediate is reduced by weakening the metal-metal bond, thereby exhibiting excellent electrochemical performance. The overpotential to afford the current density of 10 mA cm-2 (268 mV) and the small Tafel slope (51.83 mV dec-1) show a predatorily competitive advantage compared with commercially available RuO2 (284 mV and 69.34 mV dec-1 respectively).

Highly Selective Extraction of U(VI) from Solutions by Metal Organic Framework-Based Nanomaterials through Sorption, Photochemistry, and Electrochemistry Strategies.

With the rapid development of nuclear technology and peaceful utilization of nuclear energy, plentiful U(VI) not only is required to be extracted from solutions for a sustainable nuclear fuel supply but also is inevitably released into the surrounding environment to result in pollution and threaten human health. Thereby, realizing selective extraction of U(VI) from aqueous solutions is crucial for U(VI) pollution control and a sustainable nuclear industry. Metal organic frameworks (MOFs) have gained multidisciplinary attention due to their excellent properties including large specific surface areas, tunable pore structures, easy functionalization, etc. This Review comprehensively summarizes the research progress of MOFs and MOF-based materials on U(VI) removal from aqueous solutions by sorption, photocatalysis, electrocatalysis, membrane separation, etc. The efficient high extraction ability is dependent on the intrinsic properties of MOFs and the techniques used. The removal properties of MOF-based materials as adsorbents, photocatalysts, and electrocatalysts for U(VI) are discussed. Information about the interaction mechanisms between U(VI) and MOF-based materials are analyzed in-depth, including experiments, theoretical calculations, and advanced spectroscopy analysis. The removal properties for U(VI) of various MOF-based materials are assessed through different techniques. Finally, a summary and perspective on the direction and challenges of MOF-based materials and various pollutant removal technologies are proposed to provide some significant information on designing and fabricating MOF-based materials for environmental pollution management.

Multi-analyte fluorescence sensing based on a post-synthetically functionalized two-dimensional Zn-MOF nanosheets featuring excited-state proton transfer process

Covalent post-synthetic modification of metal–organic frameworks (MOFs) represents an underexplored but promising avenue for allowing the addition of specific fluorescent recognition elements to produce the novel MOF-based sensory materials with multiple-analyte detection capability. Here, an excited-state proton transfer (ESPT) active sensor 2D-Zn-NS-P was designed and constructed by covalent post-synthetic incorporation of the excited-state tautomeric 2-hydroxypyridine moiety into the ultrasonically exfoliated amino-tagged 2D Zn-MOF nanosheets (2D-Zn-NS). The water-mediated ESPT process facilitates the highly accessible active sites incorporated on the surface of 2D-Zn-NS-P to specifically respond to the presence of water in common organic solvents via fluorescence turn-on behavior, and accurate quantification of trace amount of water in acetonitrile, acetone and ethanol was established using the as-synthesized nanosheet sensor with the detection sensitivity (<0.01% v/v) superior to the conventional Karl Fischer titration. Upon exposure to Fe3+ or Cr2O72−, the intense blue emission of the aqueous colloidal dispersion of 2D-Zn-NS-P was selectively quenched even in the coexistence of common inorganic interferents. The prohibition of the water-mediated ESPT process and local emission, induced by the coordination of ESPT fluorophore with Fe3+ or by Cr2O72− competitively absorbs the excitation energy, was proposed to responsible for the fluorescence turn-off sensing of the respective analytes. The present study offers the attractive prospect to develop the ESPT-based fluorescent MOF nanosheets by covalent post-synthetic modification strategy as multi-functional sensors for detection of target analytes.

Revolutionizing Energy Storage: Exploring Processing Approaches and Electrochemical Performance of Metal-Organic Frameworks (MOFs) and Their Hybrids

&lt;p&gt;The text highlights the growing need for eco-friendly energy storage and the potential of metal-organic frameworks (MOFs) to address this demand. Despite their promise, challenges in MOF-based energy storage include stability, reproducible synthesis, cost-effectiveness, and scalability. Recent progress in supercapacitor materials, particularly over the last decade, has aimed to overcome these challenges. The review focuses on the morphological characteristics and synthesis methods of MOFs used in supercapacitors to achieve improved electrochemical performance. Various types of MOFs, including monometallic, binary, and tri-metallic compositions, as well as derivatives like hybrid nanostructures, sulfides, phosphides, and carbon composites, are explored for their energy storage potential. The review emphasizes the quest for superior electrochemical performance and stability with MOF-based materials. By analyzing recent research, the review underscores the potential of MOF-based supercapacitors to meet the increasing demands for high power and energy density solutions in the field of energy storage.&lt;/p&gt;

Manganese-based MOF interconnected carbon nanotubes as a high-performance cathode for rechargeable aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) have attracted extensive attention due to their low cost, environmental friendliness, and high volumetric specific capacity. However, the design of cathode materials with high performance for ZIBs is quite limited. In this paper, a kind of manganese-based metal-organic framework/carbon nanotubes (Mn-MOF/CNT) composite is prepared as the cathode material for ZIBs via a one-pot in situ solvothermal method. Particularly, the assembled Mn-MOF/CNT//Zn battery exhibits high specific capacity (260 mAh g−1 at 50 mA g−1) and excellent capacity retention (approximately 100 %) after 900 cycles at 1000 mA g−1. This significant electrochemical performance is attributed to the high porosity and the high conductivity of Mn-MOF/CNT, as well as the Mn2+ electrolyte additive. This work renders a new sight to design high-performance MOF-based cathode materials for aqueous ZIBs.

Interface regulation of Zr-MOF/Ni2P@nickel foam as high-efficient electrocatalyst for pH-universal hydrogen evolution reaction

Currently, the development of economical and effective non-noble metal electrocatalysts is vital for advancing hydrogen evolution reaction (HER) and enabling its widespread applications. The customizable pore structure and enormous surface area of metal–organic frameworks (MOFs) have made them to become promising non-noble metal electrocatalysts for HER. However, MOFs have some challenges, including low conductivity and instability, which can result in them having high overpotentials and slow reaction kinetics in electrocatalytic processes. In this work, we present an innovative approach for synthesizing cost-effective and high-efficient Zr-MOF-derived pH-universal electrocatalysts for HER. It entails creating the interfaces of the electrocatalysts with suitable proportions of phosphide nanostructures. Zr-MOF/Ni2P@nickel foam (NF) electrodes with interface regulated by Ni2P nanostructures were successfully developed for high-efficient pH-universal HER electrocatalysts. The presence of Ni2P nanostructures with abundant active sites at the Zr-MOFs@NF interfaces boosted the electronic conductivity and local charge density of the hybrid electrocatalysts. This helped to improve their reaction kinetics and electrocatalytic activity. By optimizing the Ni2P amount, Zr-MOF/Ni2P@NF demonstrated impressive stability and superior HER activities, with a low overpotential of 149 mV (acidic electrolytes) and 143 mV (alkaline electrolytes) at 10 mA cm−2. The proven strategy in this work can be expanded to many types of MOF-based materials for wider practical applications.

Research Progress on Metal–Organic Framework-Based Electrode Materials for Supercapacitors

Supercapacitors play an important role in power systems since they are a key part of electrochemical energy storage devices. To assemble high-performance supercapacitors, it is crucial to discover and innovate high-capacitive electrode materials. Recently, metal–organic frameworks (MOFs) and their derivatives have received wide concerns as electrode materials for supercapacitors, not only because of their high pore volume and large surface area for ions and electrons insertion and transportation, but also due to the intrinsic metal active sites that possibly offer extra faradaic pseudocapacitance. Additionally, the abundant species of MOFs with various morphologies also feature advantages in enriching the structural diversity of electrodes. In this paper, we first report the latest research progress and demonstrate the feasibility of pure MOFs for directly constructing supercapacitor electrodes. Furthermore, different MOF derivatives, including porous carbons, transition metal oxides, metal hydroxides and MOF composites for supercapacitors, are summarized, and their electrochemical performances with corresponding energy storage mechanisms are presented in detail. Finally, the perspectives for MOF-based materials applied in supercapacitors are discussed, aiming to provide a guideline for further research based on these promising materials.

Hierarchical Porous Amidoximated Metal-Organic Framework for Highly Efficient Uranium Extraction.

With the rapid development of industry and technology, high-efficiency extraction of uranium from seawater is a research hotspot from the aspect of nuclear energy development. Herein, a new amidoximated metal-organic framework (UiO-66-DAMN-AO) constructed through a novel organic ligand of 2-diaminomaleonitrile-terephthalic acid (BDC-DAMN) is designed via one-step post-synthetic methods (PSM), which possess the merit of abundant multiaffinity sites, large specific surface area, and unique porous structure for efficient uranium extraction. Adopting one-step PSM can alleviate the destruction of structural stability and the reduction of the conversion rate of amidoxime groups. Meanwhile, introducing the BDC-DAMN ligand with abundant multiaffinity sites endow UiO-66-DAMN-AO with excellent adsorption ability (Qm=426.3mgg-1) and selectivity. Interestingly, the UiO-66-DAMN-AO has both micropores and mesopores, which may be attributed to the partial etching of UiO-66-DAMN-AO during the amidoximation. The presence of mesopores improves the mass transfer rate of UiO-66-DAMN-AO and provides more exposed active sites, favoring the adsorption of uranium on UiO-66-DAMN-AO. Thus, this study provides a feasible strategy for modifying metal-organic framework (MOFs) with plentiful amidoxime groups and the promising prospect for MOF-based materials to adsorb uranium from ocean.

In situ growth of MIL-101 (Fe) on waste PET plastic slices for effective arsenic removal

Converting waste Polyethylene terephthalate (PET) plastic into value-added metal–organic frameworks (MOFs) has emerged as a prospective solution to plastic upcycling. Within this work, MIL-101(Fe)@PET was fabricated via microwave method. The as-prepared MIL-101(Fe)@PET performed high removal efficiency (100 %) toward three arsenic pollutants at low concentration (1 mg/L) within 60 min. The maximum adsorption capacity of MIL-101(Fe)@PET toward 4-aminophenylarsonic acid (ASA), hydroxy-3-nitrobenzenearsonic acid (ROX) and As(V) were 320.6, 476.5, 240.0 mg g−1, respectively. Further, the household water purifiers filter was assembled adopting the as-prepared MIL-101(Fe)@PET as absorbent. MIL-101(Fe)@PET filter performed higher arsenic removal efficiency than active carbon filter and commercial filter. The adsorption behaviors of MIL-101(Fe)@PET toward arsenic was found to be fitted with pseudo-second-order kinetic models and Langmuir isotherm models. The possible adsorption mechanism was proposed. The developed strategy provides a new method in the application of MOFs-based materials and upcycling waste plastics.

A self-supporting multi-component collaborative structure for enhancing interface electron transfer in hybrid supercapacitor

Multi-component synergistic effect is a feasible strategy to boost the capacity of electrode materials. Herein, carbon nanotubes (CNTs) film supporting NiCo phosphide (NiCoP) modified metal-organic framework (MOF) is reasonably synthesised as a self-supporting electrode for high-performance supercapacitors. Benefiting from the synergistic effect of the high conductivity of the CNT film substrate, the specific surface area of Cu-MOF (HKUST-1), and the high activity of NiCoP, the charge transfer and ionic diffusion among the electrode greatly improved. The as-prepared electrode displays a remarkably enhanced specific capacitance of 1154 F g−1. In addition, the as-assembled NiCoP/HKUST-1@CNTs//activated carbon supercapacitor possesses a considerable energy density of 58.2 W h kg−1 and satisfactory cyclic performance (retaining 80.6 % capacitance over 10,000 cycles). The synthesis approach of this study provides some reference for the controllable preparation of new high-capacity MOF-based electrode materials.

Tailoring the Hydrophobic Interface of Core-Shell HKUST-1@Cu2O Nanocomposites for Efficiently Selective CO2 Electroreduction.

The electrochemical reduction of carbon dioxide (CO2) to ethylene creates a carbon-neutral approach to converting carbon dioxide into intermittent renewable electricity. Exploring efficient electrocatalysts with potentially high ethylene selectivity is extremely desirable, but still challenging. In this report, a laboratory-designed catalyst HKUST-1@Cu2O/PTFE-1 is prepared, in which the high specific surface area of the composites with improved CO2 adsorption and the abundance of active sites contribute to the increased electrocatalytic activity. Furthermore, the hydrophobic interface constructed by the hydrophobic material polytetrafluoroethylene (PTFE) effectively inhibits the occurrence of hydrogen evolution reactions, providing a significant improvement in the efficiency of CO2 electroreduction. The distinctive structures result in the remarkable hydrocarbon fuels generation with high Faraday efficiency (FE) of 67.41%, particularly for ethylene with FE of 46.08% (-1.0V vs RHE). The superior performance of the catalyst is verified by DFT calculation with lower Gibbs free energy of the intermediate interactions with improved proton migration and selectivity to emerge the polycarbon（C2+） product. In this work, a promising and effective strategy is presented to configure MOF-based materials with tailored hydrophobic interface, high adsorption selectivity and more exposed active sites for enhancing the efficiency of the electroreduction of CO2 to C2+ products with high added value.

Dye-sensitized NH2-UiO-66 anchored with copper ions for tandem visible-light-driven hydrogen evolution

Metal-organic frameworks (MOFs) have attracted exciting application prospects in photocatalytic hydrogen (H2) evolution due to the diversity of organic ligands and metal ions. However, the inappropriate conduction band position of pristine MOFs and corresponding large overpotential for H2 evolution restrict the H2 production under visible light. Herein, a dye-sensitized NH2-UiO-66 anchored with copper ions (EY-6Cu-NU-66) was synthesized by in-situ Cu anchoring followed by Eosin Y sensitization. The H2 production activity showed that EY-6Cu-NU-66 reached 3579.82 μmol·g−1·h−1 under visible light, which was four times higher than that of dye-sensitized pristine NU-66 (EY-NU-66) and 99-fold higher than that of 6Cu-NU-66 free of dye sensitization. A series of characterizations and theoretical computations indicated that photo-generated electrons first transfer from the excited Eosin Y to the lowest unoccupied molecular orbital (LUMO) of the NU-66, then further transfer to the transition CuII/CuI metal center that is formed by Cu anchored on -NH2. This tandem mechanism not only improves the visible-light absorption ability of NU-66 but also promotes its separation efficiency of photo-generated carriers, thus greatly reducing the overpotential for H2 evolution. This work provides a new strategy for visible-light-driven H2 production by dye-sensitized MOF-based materials without noble metal loading.

A ROS reservoir based on a polyoxometalate and metal-organic framework hybrid for efficient bacteria eradication and wound healing

Infections by bacteria always post significant challenges to global human health. Recent developed non-antibiotic treatment, such as using metal–organic frameworks (MOFs) to kill bacteria by generating reactive oxygen species (ROS) represents a promising strategy. However, drawbacks including low efficiencies of ROS generation and high concentrations of toxic metal ions released always exist. We have creatively designed a robust polyoxometalate (POM) and MOF hybrid (denoted as CuPOM-MOF@S) that functions as an efficient catalytic reservoir for cascaded generation of ROS (mainly ·OH) from H2O2 thus eradicating bacteria and enhancing wound healing at an administration dosage as low as 5 μg∙mL−1. The remarkable antibacterial capability surpasses those for most MOF-based materials reported thus far, which is mainly attributed to the reservation of massive catalytic copper ions, the synergistic effect regarding catalytic activity between MOFs and Keggin-type POMs as well as its bacteria-capturing ability by the coated surfactants. Its biological safety is investigated and confirmed by cell cytotoxicity and body weight assessment. This work presents a prospective strategy towards cascaded ROS generation by combining inorganic catalytic POMs with MOFs thus for multiple biomedical applications including treating bacterial infections and cancer as well as inducing biological signal responses.

Recent Progress of Metal-Organic Framework-Assisted Sensing System for Point-of-Care Antibiotics Detection in Food Industry; a Mini Review

Antibiotics (ANBs) are essential for animal health and are used for treatment, prevention, and growth promotion. However, ANB use in animals can lead to antibiotic residue in food products, which can cause various side effects. These include the transfer of ANB-resistant bacteria to humans, immunopathological effects, allergies, and even carcinogenicity. The most significant adverse effect is the transfer of ANB-resistant bacteria to humans due to the mobile properties of resistance. Therefore, timely detection is the best approach to prevent the spread of downsides of these compounds. Various methods exist for measuring ANB concentrations, such as LC-MS, high-performance liquid chromatography, capillary electrophoresis, thin-layer chromatography, and enzyme-linked immunoassay. However, complicated sample preparation processes and expensive equipment are often considered obstacles to their prevalent usage. Emerging technologies like Metal-Organic Frameworks (MOFs) offer a simpler, quicker, and more cost-effective solution for detecting veterinary drugs in animal-derived food samples. This investigation first reviews some conventional methods for ANB recognition, including microbiological, immunological, and laboratory-based procedures. Then, Sensor-based analytical methods and their advantages and disadvantages were discussed. Finally, the recent progress in ANB detection approaches using MOF-based sensors in food products was investigated. MOFs have become a topic of great interest due to their remarkable properties. These include high surface areas that can be easily modified, defined porosity, lightweight, adjustable pore sizes, ordered structures, and impressive mechanical strength. The performance of MOFs is superior to traditional chemosensory materials due to their ability to adjust properties. Various sensing systems based on MOFs have been reported, including photoelectrochemical, electrochemiluminescence, electrochemical, and quartz crystal microbalance. As discussed in this review, sensors based on MOFs have emerged as reliable alternatives for fast and routine detection in clinical and environmental analysis and food safety control. Various MOF-based materials have been used for detecting antibiotics, and their advantages and limitations have been critically evaluated for future applications in diagnosing antibiotics in food products.

Synthesis of the highly efficient catalysts CdZnS@MIL-53(Fe) and ZnS@MIL-53(Fe) and their thermally decomposed derivative for electrochemical OER activity and photodegradation of Rhodamine B dye

The development of a highly efficient catalyst for water splitting and photodegradation of organic dyes has become the focus of a considerable number of research groups. In the work described here CdZnS@MIL-53(Fe) and ZnS@MIL-53(Fe) were synthesized by the solvothermal method and subjected to thermal degradation at 520 °C in an oxidative environment to obtain CdZnS/Fe2O3 and ZnS/Fe2O3, respectively. Electrocatalytic activity for the oxygen evolution reaction is analyzed via cyclic voltammetry and linear sweep voltammetry. It was found that CdZnS@MIL-53(Fe) shows maximum catalytic activity for the oxygen evolution reaction and delivers 10 mAcm−2 current density at 95 mV overpotential as compared to MIL-53(Fe)/NF (210 mV) and ZnS@MIL-53(Fe)/NF (112 mV). Similarly, the derivative of it, CdZnS/Fe2O3, shows maximum catalytic activity for the oxygen evolution reaction and delivers 10 mAcm−2 current density at 90 mV overpotential as compared to Fe2O3 (204 mV) and ZnS/Fe2O3 (115 mV). Based on these results, it is evident that these materials are highly efficient for OER activity compared with other materials in literature. Similarly, CdZnS/Fe2O3 shows maximum photocatalytic activity for the photodegradation of Rhodamine B, up to 75% compared to CdZnS@MIL-53(Fe), which degrades up to 51% of the dye. The synthesized materials were characterized by powdered X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. Based on these results the aim is to develop more MOF-based materials and their derivatives by simple heat treatment and to implement them in different catalytic applications.

Developing New MOF-Based Hybrid Materials for Efficient Adsorptive Desulfurization of a Refractory Sulfur Compound

Developing New MOF-Based Hybrid Materials for Efficient Adsorptive Desulfurization of a Refractory Sulfur Compound

Development of hierarchical MOF-based composite phase change materials with enhanced latent heat storage for low-temperature battery thermal optimization

Most of the composite phase change materials (PCMs) based on metal-organic frameworks (MOFs) have much lower latent heat than pure PCMs due to nanoconfined effects, which limits their application in the field of battery insulation. In this work, a series of hierarchical porous carbon nanotubes (CNT)/MOF-199 were synthesized by adjusting the content of N-methyl pyrrolidone (NMP) in the solvent components, and scattered in stearic acid (SA) to obtain a novel composite PCM. The results show that there is a nearly linear relationship between the impregnation ratio, crystallization fraction and impregnation efficiency of PCMs and the mesoporous content of the supporting materials at the maximum loading rate of 70 wt%, which may provide an idea for selecting MOFs supporting materials for PCMs. The latent heat of SA/CNT/MOF-199-2 (SA/CM-2) composite PCM is 97.1/96.2 J·g−1, with a heat loss percentage of only 0.96%. Furthermore, when the lithium-ion battery is discharged 2C at −20 °C, SA/CM-2 used as insulation material can increase the discharge energy by 8.27%. Accordingly, this novel composite PCMs would be hopefully applied to thermal optimization of batteries at low temperatures.

Construction of hierarchical porous two-dimensional Zn-MOF-based heterostructures for supercapacitor applications

Recently, two-dimensional metal-organic frameworks (2D MOFs) are drawing increasing attention in energy storage area. Specially, hybrid 2D MOF-based heterostructures have greatly promoted the development of MOF-based electrode materials. However, the underutilization of both abundant active sites and high surface area causes 2D MOFs poor performance and thus restricts their practical application. Herein, to shorten the ion transport paths and enhance the ion diffusion ability, mesopores were introduced into 2D Zn-MOF sheets to construct a hierarchical porous Zn-MOF-based heterostructure. The energy-storage mechanism in the heterostructures was deeply investigated and the importance of the introduced-mesopores on enhancing the electrochemical behaviors was confirmed. With the optimized design, the obtained Meso-Zn-MOF@rGO-PBA delivered outstanding electrochemical performance, including a high capacitance (292.8 F g−1 at 0.2 A g−1), an excellent rate capacity (268.1 F g−1 at 5 A g−1) and a good cycling stability (83.2 % retention after 2000 cycles). Furthermore, the practical applicability of Meso-Zn-MOF@rGO-PBA was researched by assembling an asymmetric supercapacitor using activated carbon as the other electrode, achieving a satisfied specific capacitance of 54.9 F g−1 with an energy density of 19.5 Wh kg−1 (1 A g−1). Our observation provides a strategic design idea for high-performance supercapacitor electrode materials.