Electronic, optical and charge transport properties of Zn-porphyrin-C60 MOFs: a combined periodic and cluster modeling

Density functional theory (DFT) calculations were performed on the 5,15 meso-positions of nine porphyrin-containing MOFs; Zn2(TCPB)-(NMe2-ZnP); (H4TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene), (NMe2-ZnP = [5,15-bis[(4-pyridyl)-ethynyl]-10,20-bis-(dimethylamine) porphinato]zinc(II)) functionalized with nitrogen-, oxygen-, and sulfur-containing groups to study their effects on the electronic, optical and transport properties of the materials. The properties of these materials have also been investigated by encapsulating fullerene (C60) in their pores (C60@MOFs). The results indicate that the guest C60 in the MOF generates high photoconductivity through efficient porphyrin/fullerene donor-acceptor (D-A) interactions, which are facilitated by oxygen and sulfur functionalities. DFT calculations show that C60 interacts favorably in MOFs due to negative Eint values. Encapsulated C60 molecules modify the electronic band structure, affecting the conduction band and unoccupied states of MOFs corresponding to C60 p orbitals. TD-DFT calculations show that incorporating C60 promotes D-A interactions in MOFs, leading to charge transfer in the near-infrared and visible photoinduced electron transfer (PET) from porphyrins to C60. Nonequilibrium Green's function-based calculations for MOFs with sulfur group, with and without C60, performed using molecular junctions with Au(111)-based electrodes show increased charge transport for the doped MOF. These insights into tuning electronic/optical properties and controlling charge transfer can aid in the design of new visible/near-infrared MOF-based optoelectronic devices.

A Highly Robust and Conducting Ultramicroporous 3D Fe(II)-Based Metal-Organic Framework for Efficient Energy Storage

Exploitation of metal-organic framework (MOF) materials as active electrodes for energy storage or conversion is reasonably challenging owing to their poor robustness against various acidic/basic conditions and conventionally low electric conductivity. Keeping this in perspective, herein, a 3D ultramicroporous triazolate Fe-MOF (abbreviated as Fe-MET) is judiciously employed using cheap and commercially available starting materials. Fe-MET possesses ultra-stability against various chemical environments (pH-1 to pH-14 with varied organic solvents) and is highly electrically conductive (σ = 0.19 S m-1) in one fell swoop. By taking advantage of the properties mentioned above, Fe-MET electrodes give prominence to electrochemical capacitor (EC) performance by delivering an astounding gravimetric (304 F g-1) and areal (181 mF cm-2) capacitance at 0.5 A g-1 current density with exceptionally high cycling stability. Implementation of Fe-MET as an exclusive (by not using any conductive additives) EC electrode in solid-state energy storage devices outperforms most of the reported MOF-based EC materials and even surpasses certain porous carbon and graphene materials, showcasing superior capabilities and great promise compared to various other alternatives as energy storage materials.

Arresting dissolution of two-dimensional metal-organic frameworks enables long life in electrochemical devices

Two-dimensional conjugated metal-organic frameworks (2D cMOFs) are emerging as promising materials for electrochemical energy storage (EES). Despite considerable interest, an understanding of their electrochemical stability and the factors contributing to their degradation during cycling is largely lacking. Here we investigate three Cu-based MOFs and report that the dissolution of 2D cMOFs into electrolytes is a prevalent and significant degradation pathway. Several factors, such as the inherent solubility of ligands in electrolyte solvents and the duration of charge-discharge cycling exert a strong influence on the dissolution process. When these factors combine within a MOF, severely limited cycling stability is observed, with dissolution accounting for up to 80% of capacity degradation. Conversely, excellent cycling stability is observed when testing a Cu-MOF with a sparingly soluble ligand within an optimized potential window. Overall, these findings represent essential insights into the electrochemical stability of 2D cMOFs, offering crucial guidelines for their targeted development in EES applications.

Conjugation and Topology Engineering of 2D π-d Conjugated Metal-Organic Frameworks for Robust Potassium Organic Batteries

The evolution of two-dimensional conjugated metal-organic frameworks (2D c-MOFs) provides a significant prospect for researching the next generation of green and advanced energy storage systems (ESSs). Especially, conjugation and topology engineering serve as an irreplaceable character in adjusting the electrochemical properties of ESSs. Herein, we proposed a novel strategy using conjugation and topology engineering to demonstrate the application of 2D c-MOFs in robust potassium-ion batteries (PIBs) for the first time. By comparing 2D c-MOFs with the rhombus/kagome structure as well as three/four-arm core, the rhombus structure (sql-Cu-TBA-MOF) cathode for PIBs can display the impressive electrochemical performance, including a high specific discharge capacity of 178.4 mAh g-1 (at 0.2 A g-1) and a well long-term cycle stability of more than 9,000 (at 10.0 A g-1). Moreover, full PIBs (FPIBs) are constructed by pairing sql-Cu-TBA-MOF cathode with dipotassium terephthalate (KTP) anode, which delivers a high reversible discharge specific capacity of 146.6 mAh g-1 (at 0.1 A g-1) and great practical application prospect. These findings provide reasonable implications for the design of 2D c-MOFs from the perspective of conjugation and topology engineering for advanced energy storage systems.

Successful In Situ Growth of Conductive MOFs on 2D Cobalt-Based Compounds and Their Electrochemical Performance

Conductive metal-organic frameworks (cMOFs), as a kind of porous material, are considered to be highly promising materials in the field of electrochemistry due to their excellent conductivity. However, due to the low specific capacitance of pure cMOFs, their application in supercapacitors is limited. By virtue of the high theoretical capacity and excellent chemical stability of Co-based compounds, in this work, cMOFs' M-HHTP (M = Ni, Co, NiCo, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) are grown in situ on Co(OH)2, CoP, and Co3O4 nanosheets, resulting in a series of electroactive compounds as electrode materials used in supercapacitors. Among all of the compounds, Ni-HHTP@Co(OH)2 shows the most excellent energy storage performance and outstanding cyclic stability in the application of aqueous asymmetric supercapacitors.

A Rhombic 2D Conjugated Metal-Organic Framework as Cathode for High-Performance Sodium-Ion Battery

2D conjugated metal-organic frameworks (2D c-MOFs) have garnered significant attention as promising electroactive materials for energy storage. However, their further applications are hindered by low capacity, limited cycling life, and underutilization of the active sites. Herein, Cu-TBA (TBA = octahydroxyltetrabenzoanthracene) with large conjugation units (narrow energy gap) and a unique rhombus topology is introduced as the cathode material for sodium-ion batteries (SIBs). Notably, Cu-TBA with a rhombus topology exhibits a high specific surface area (613 m2 g-1) and metallic band structure. Additionally, Cu-TBA outperforms its hexagonal counterpart, Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxyltriphenylene), demonstrating superior reversible capacity (153.6 mAh g-1 at 50 mA g-1) and outstanding cyclability with minimal capacity decay even after 3000 cycles at 1 A g-1. This work elucidates a new strategy to enhance the electrochemical performance of 2D c-MOFs cathode materials by narrowing the energy gap of organic linkers, effectively expanding the utilization of 2D c-MOFs for SIBs.

The Utilization of Metal-Organic Frameworks and Their Derivatives Composite in Supercapacitor Electrodes

Up to now, the mainstream adoption of renewable energy has brought about substantial transformations in the electricity and energy sector. This shift has garnered considerable attention within the scientific community. Supercapacitors, known for their exceptional performance metrics like good charge/discharge capability, strong power density, as well as extended cycle longevity, have gained widespread traction across various sectors, including transportation and aviation. Metal-organic frameworks (MOFs) with unique traits including adaptable structure, highly customizable synthetic methods, and high specific surface area, have emerged as strong candidates for electrode materials. For enhancing the performance, MOFs are commonly compounded with other conducting materials to increase capacitance. This paper provides a detailed analysis of various common preparation strategies and characteristics of MOFs. It summarizes the recent application of MOFs and their derivatives as supercapacitor electrodes alongside other carbon materials, metal compounds, and conductive polymers. Additionally, the challenges encountered by MOFs in the realm of supercapacitor applications are thoroughly discussed. Compared to previous reviews, the content of this paper is more comprehensive, offering readers a deeper understanding of the diverse applications of MOFs. Furthermore, it provides valuable suggestions and guidance for future progress and development in the field of MOFs.

Metal-Organic Framework-Based Nanovaccine for Relieving Immunosuppressive Tumors via Hindering Efferocytosis of Macrophages and Promoting Pyroptosis and Cuproptosis of Cancer Cells

Current cancer vaccines face challenges due to an immunosuppressive tumor microenvironment and their limited ability to produce an effective immune response. To address the above limitations, we develop a 3-(2-spiroadamantyl)-4-methoxy-4-(3-phosphoryloxy)-phenyl-1,2-dioxetane (alkaline phosphatase substrate) and XMD8-92 (extracellular signal-regulated kinase 5 inhibitor)-codelivered copper-tetrahydroxybenzoquinone (Cu-THBQ/AX) nanosized metal-organic framework to in situ-generate therapeutic vaccination. Once inside the early endosome, the alkaline phosphatase overexpressed in the tumor cells' membrane activates the in situ type I photodynamic effect of Cu-THBQ/AX for generating •O2-, and the Cu-THBQ/AX catalyzes O2 and H2O2 to •O2- and •OH via semiquinone radical catalysis and Fenton-like reactions. This surge of ROS in early endosomes triggers caspase-3-mediated proinflammatory pyroptosis via activating phospholipase C. Meanwhile, Cu-THBQ/AX can also induce the oligomerization of dihydrolipoamide S-acetyltransferase to trigger tumor cell cuproptosis. The production of •OH could also trigger the release of XMD8-92 for effectively inhibiting the efferocytosis of macrophages to convert immunosuppressive apoptosis of cancer cells into proinflammatory secondary necrosis. The simultaneous induction of pyroptosis, cuproptosis, and secondary necrosis effectively converts the tumor microenvironment from "cold" to "hot" conditions, making it an effective antigen pool. This transformation successfully activates the antitumor immune response, inhibiting tumor growth and metastasis.

De Novo Design and Facile Synthesis of Highly Crystalline 2D Conductive Metal-Organic Frameworks: A "Rotor-Stator" Strategy

Two-dimensional conductive metal-organic frameworks (2D c-MOFs), which feature high electrical conductivity and large charge carrier mobility, hold great promise in electronics and optoelectronics. Nevertheless, the limited solubility of commonly used planar ligands inevitably brings challenges in synthesis and purification and causes laborious coordination conditions for screening. Moreover, most reported 2D c-MOFs are polycrystalline powders with relatively low crystallinity and irregular morphology, hindering the unveiling of the detailed structure-function relationship. Herein, we developed a "rotor-stator" molecular design strategy to construct 2D c-MOFs using a delicately designed nonplanar biscarbazole ligand (8OH-DCB). Benefiting from the special "rotor-stator" structure of the ligand, crystals of Cu-DCB-MOF were successfully prepared, allowing for the precise determination of their crystal structure. Interestingly, the crystals of Cu-DCB-MOF can be obtained in various organic solvents, indicating excellent solvent compatibility. The versatility of the "rotor-stator" molecular design strategy was further demonstrated by another two new ligands with a "rotor-stator" structure, and afford corresponding 2D c-MOF crystals (Cu-DCBT-MOF and Cu-DCBBT-MOF). The current work presents a facile approach toward the rational design and direct construction of highly crystalline 2D c-MOFs using nonplanar ligands.

2D Conjugated Metal-Organic Frameworks: Defined Synthesis and Tailor-Made Functions

Conspectus2D conjugated metal-organic frameworks (2D -MOFs) have emerged as a class of graphene-like materials with fully π-conjugated aromatic structures. Their unique structural characteristics provide abundant physiochemical features, including regular nanochannels, high electrical conductivity, and customizable band gaps. Recent intensive research has significantly advanced this field, yet the exploration of 2D c-MOFs with enhanced features is limited by the availability of organic linkages and topologies. Designing novel ligands is essential for the construction of new 2D c-MOFs with high crystallinity, excellent conductivity, and tailor-made functions.In this Account, we summarize our recent contributions in fine-tuning the topology of 2D c-MOFs through precise ligand design, thereby giving them fantastic structures and tailor-made functions. First, we propose the concept of replacing planar ligands by nonplanar ligands on conductive MOF skeletons. The incorporation of nonplanar ligands improves the solubility of large π-conjugated organic molecules without interfering with the interlayer π-stacking. Our investigation discovered that conjugate polycyclic aromatics-based ligands can be synthesized through in situ Scholl reactions by means of oxidative cyclodehydrogenation of a nonplanar precursor ligand during the solvothermal synthesis process. Hence, fully conjugated 2D c-MOFs can be directly synthesized from nonplanar organic ligands, simplifying and diversifying the preparation of 2D c-MOFs. Accordingly, the design flexibility of the ligands expands the topological structures and pore types. By controlling the synthesis conditions, we can successfully induce either a rhombus or a kagome topology from a nonplanar D2 symmetric ligand. Moreover, by employing a ligand engineering strategy, we incrementally increase the number of coordination functional groups on a twisted hexabenzocoronene core, resulting in the formation of three distinct symmetric hydroxyl ligands. These ligands elicit diverse target topologies and pore sizes, resulting in variances in the coordination node density on the skeletons. This, in turn, leads to differences in electron transfer abilities, ultimately causing variations in the electrical conductivity and mobility. In addition, we employ a straightforward coupling method to incorporate redox components, such as salphen and pyrazine, into nonplanar ligands, facilitating the synthesis of 2D c-MOFs with highly active centers. This strategy confers upon the resulting frameworks substantial capacity for catalysis and energy storage, offering a good platform for elucidating the structure-property relationships at the molecular level. Moreover, the well-defined synthesis of 2D c-MOFs imparts them with specific properties, particularly in the fields of electrical, electrochemical, and spintronic applications. At the end, the primary challenges facing 2D c-MOFs in achieving tailor functions and their practical applications are proposed. This account is expected to evoke new inspirations and innovative research in the field of 2D c-MOFs, especially in emerging interdisciplinary research areas.

Single-Site Nanozymes with a Highly Conjugated Coordination Structure for Antitumor Immunotherapy via Cuproptosis and Cascade-Enhanced T Lymphocyte Activity

The extracellular matrix (ECM) in the tumor microenvironment (TME) and upregulated immune checkpoints (ICs) on antitumor immune cells impede the infiltration and killing effect of T cells, creating an immunosuppressive TME. Herein, a cholesterol oxidase (CHO) and lysyl oxidase inhibitor (LOX-IN-3) co-delivery copper-dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol single-site nanozyme (Cu-DBCO/CL) was developed. The conjugated organic ligand and well-distributed Cu-O4 sites endow Cu-DBCO with unique redox capabilities, enabling it to catalyze O2 and H2O2 to ·O2- and ·OH. This surge of reactive oxygen species (ROS) leads to impaired mitochondrial function and insufficient ATP supply, impacting the function of copper-transporting ATPase-1 and causing dihydrolipoamide S-acetyltransferase oligomerization-mediated cuproptosis. Moreover, multiple ROS storms and glutathione peroxidase 4 depletion also induce lipid peroxidation and trigger ferroptosis. Simultaneously, the ROS-triggered release of LOX-IN-3 reshapes the ECM by inhibiting lysyl oxidase activity and further enhances the infiltration of cytotoxic T lymphocytes (CD8+ T cells). CHO-triggered cholesterol depletion not only increases ·OH generation but also downregulates the expression of ICs such as PD-1 and TIM-3, restoring the antitumor activity of tumor-infiltrating CD8+ T cells. Therefore, Cu-DBCO/CL exhibits efficient properties in activating a potent antitumor immune response by cascade-enhanced CD8+ T cell viability. More importantly, ECM remodeling and cholesterol depletion could suppress the metastasis and proliferation of the tumor cells. In short, this immune nanoremodeler can greatly enhance the infiltration and antitumor activity of T cells by enhancing tumor immunogenicity, remodeling ECM, and downregulating ICs, thus achieving effective inhibition of tumor growth and metastasis.

Urchin-like Ce(HCOO)3 Synthesized by a Microwave-Assisted Method and Its Application in an Asymmetric Supercapacitor

In this work, a series of urchin-like Ce(HCOO)3 nanoclusters were synthesized via a facile and scalable microwave-assisted method by varying the irradiation time, and the structure-property relationship was investigated. The optimization of the reaction time was performed based on structural characterizations and electrochemical performances, and the Ce(HCOO)3-210 s sample shows a specific capacitance as high as 132 F g-1 at a current density of 1 A g-1. This is due to the optimal mesoporous hierarchical structure and crystallinity that are beneficial to its conductivity, offering abundant Ce3+/Ce4+ active sites and facilitating the transportation of electrolyte ions. Moreover, an asymmetric supercapacitor based on Ce(HCOO)3//AC was fabricated, which delivers a maximum energy density of 14.78 Wh kg-1 and a considerably high power density of 15,168 W kg-1. After 10,000 continuous charge-discharge cycles at 3 A g-1, the ASC device retains 81.3% of its initial specific capacitance. The excellent comprehensive electrochemical performance of this urchin-like Ce(HCOO)3 offers significant promise for practical supercapacitor applications.

Synthesis of Electrical Conductive Metal-Organic Frameworks for Electrochemical Applications

Electrical conductivity is very important property of nanomaterials for using wide range of applications especially energy applications. Metal-organic frameworks (MOFs) are notorious for their low electrical conductivity and less considered for usage in pristine forms. However, the advantages of high surface area, porosity and confined catalytic active sites motivated researchers to improve the conductivity of MOFs. Therefore, 2D electrical conductive MOFs (ECMOF) have been widely synthesized by developing the effective synthetic strategies. In this article, we have summarized the recent trends in developing the 2D ECMOFs, following the summary of potential applications in the various fields with future perspectives.

Expanding the horizons of porphyrin metal-organic frameworks via catecholate coordination: exploring structural diversity, material stability and redox properties

Porphyrin based Metal-Organic Frameworks (MOFs) have generated high interest because of their unique combination of light absorption, electron transfer and guest adsorption/desorption properties. In this study, we expand the range of available MOF materials by focusing on the seldom studied porphyrin ligand H10TcatPP, functionalized with tetracatecholate coordinating groups. A systematic evaluation of its reactivity with M(iii) cations (Al, Fe, and In) led to the synthesis and isolation of three novel MOF phases. Through a comprehensive characterization approach involving single crystal and powder synchrotron X-ray diffraction (XRD) in combination with the local information gained from spectroscopic techniques, we elucidated the structural features of the solids, which are all based on different inorganic secondary building units (SBUs). All the synthesized MOFs demonstrate an accessible porosity, with one of them presenting mesopores and the highest reported surface area to date for a porphyrin catecholate MOF (>2000 m2 g-1). Eventually, the redox activity of these solids was investigated in a half-cell vs. Li with the aim of evaluating their potential as electrode positive materials for electrochemical energy storage. One of the solids displayed reversibility during cycling at a rather high potential (∼3.4 V vs. Li+/Li), confirming the interest of redox active phenolate ligands for applications involving electron transfer. Our findings expand the library of porphyrin-based MOFs and highlight the potential of phenolate ligands for advancing the field of MOFs for energy storage materials.

Metal-organic frameworks (MOFs) for energy production and gaseous fuel and electrochemical energy storage applications

The increasing energy demands in society and industrial sectors have inspired the search for alternative energy sources that are renewable and sustainable, also driving the development of clean energy storage and delivery systems. Various solid-state materials (e.g., oxides, sulphides, polymer and conductive nanomaterials, activated carbon and their composites) have been developed for energy production (water splitting-H2 production), gaseous fuel (H2 and CH4) storage and electrochemical energy storage (batteries and supercapacitors) applications. Nevertheless, the low surface area, pore volume and conductivity, and poor physical and chemical stability of the reported materials have resulted in higher requirements and challenges in the development of energy production and energy storage technologies. Thus, to overcome these issues, the development of metal-organic frameworks (MOFs) has attracted significant attention. MOFs are a class of porous materials with extremely high porosity and surface area, structural diversity, multifunctionality, and chemical and structural stability, and thus they can be used in a wide range of applications. In the present review, we precisely discuss the interesting properties of MOFs and the various methodologies for their synthesis, and also the future dependence on the valorization of solid waste for the recovery of metals and organic ligands for the synthesis of new classes of MOFs. Subsequently, the utilization of these interesting characteristics for energy production (water splitting), storage of gaseous fuels (H2 and CH4), and electrochemical storage (batteries and supercapacitors) applications are described. However, although MOFs are efficient materials with versatile uses, they still have many challenges, limiting their practical applications. Therefore, finally, we highlight the challenges associated with MOFs and show the way forward in overcoming them for the development of these highly porous materials with large-scale practical utility.

Mobile energy storage technologies for boosting carbon neutrality

Carbon neutrality calls for renewable energies, and the efficient use of renewable energies requires energy storage mediums that enable the storage of excess energy and reuse after spatiotemporal reallocation. Compared with traditional energy storage technologies, mobile energy storage technologies have the merits of low cost and high energy conversion efficiency, can be flexibly located, and cover a large range from miniature to large systems and from high energy density to high power density, although most of them still face challenges or technical bottlenecks. In this review, we provide an overview of the opportunities and challenges of these emerging energy storage technologies (including rechargeable batteries, fuel cells, and electrochemical and dielectric capacitors). Innovative materials, strategies, and technologies are highlighted. Finally, the future directions are envisioned. We hope this review will advance the development of mobile energy storage technologies and boost carbon neutrality.

Near-Infrared Light-Enhanced Generation of Hydroxyl Radical for Cancer Immunotherapy

Hydroxyl radical (• OH) as a highly oxidizing reactive oxygen species can induce immunogenic cell death (ICD) in cancer treatment. However, high-efficiency cancer immunotherapy is still a huge challenge due to the low • OH generation efficiency in the tumor microenvironment, resulting in insufficient immunogenicity and the poor immune response. Here, a near-infrared (NIR) light-enhanced • OH generation strategy is developed for cancer immunotherapy by using a copper-based metal-organic framework (Cu-DBC) nanoplatform. With this strategy, the generation efficiency of • OH under NIR irradiation is increased 7.34 times than that without NIR irradiation, which induces robust ICD and immune response, thus leading to primary tumor elimination and the inhibition of distant tumor growth and tumor lung metastasis. Experimental results show that Cu-DBC can induce • OH boosting through photothermal (PT)-enhanced Cu-catalytic Fenton-like reaction and photocatalytic electron transfer under NIR light irradiation to amplify tumor ICD for immunotherapy.

Nonporous, conducting bimetallic coordination polymers with an advantageous electronic structure for boosted faradaic capacitance

Conductive coordination polymers (c-CPs) are promising electrode materials for supercapacitors (SCs) owing to their excellent conductivity, designable structures and dense redox sites. However, despite their high intrinsic density and outstanding electrical properties, nonporous c-CPs have largely been overlooked in SCs because of their low specific surface areas and deficient ion-diffusion channels. Herein, we demonstrate that the nonporous c-CPs Ag5BHT (BHT = benzenehexathiolate) and CuAg4BHT are both battery-type capacitor materials with high specific capacitances and a large potential window. Notably, nonporous CuAg4BHT with bimetallic bis(dithiolene) units exhibits superior specific capacitance (372 F g-1 at 0.5 A g-1) and better rate capability than isostructural Ag5BHT. Structural and electrochemical studies showed that the enhanced charge transfer between different metal sites is responsible for its outstanding capacitive performance. Additionally, the assembled CuAg4BHT//AC SC device displays a favorable energy density of 17.1 W h kg-1 at a power density of 446.1 W kg-1 and an excellent cycling stability (90% capacitance retention after 5000 cycles). This work demonstrates the potential applications of such nonporous redox-active c-CPs in SCs and highlights the roles of bimetallic redox sites in capacitive performance, which hold promise for the future development of c-CP-based energy storage technologies.

Modulating the Oxygen Reduction Reaction Performance via Precisely Tuned Reactive Sites in Porphyrin-Based Covalent Organic Frameworks

Covalent organic frameworks (COFs) have emerged as promising electrocatalysts due to their controllable architectures, highly exposed molecular active sites, and ordered structures. In this study, a series of porphyrin-based COFs (TAPP-x-COF) with various transition metals (Co, Ni, Fe) were synthesized via a facile post-metallization strategy under solvothermal synthesis. The resulting porphyrin-based COFs showed oxygen reduction reaction (ORR) activity with a trend in Co > Fe > Ni. Among them, TAPP-Co-COF exhibited the best ORR activity (E_1/2 = 0.66 V and jL = 4.82 mA cm^-2) in alkaline media, which is comparable to those of Pt/C under the same conditions. Furthermore, TAPP-Co-COF was employed as a cathode in a Zn-air battery, demonstrating a high power density of 103.73 mW cm^-2 and robust cycling stability. This work presents a simple method for using COFs as a smart platform to fabricate efficient electrocatalysts.

A Cobalt-Based Metal-Organic Framework Nanosheet as the Electrode for High-Performance Asymmetric Supercapacitor

Inspired by the significant advantages of the bottom-up synthesis whose structures and functionalities can be customized by the selection of molecular components, a 2D metal-organic framework (MOF) nanosheet Co-BTB-LB has been synthesized by a liquid-liquid interface-assisted method. The as-prepared Co-BTB-LB is identified by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX) and X-ray photoelectron spectroscopy (XPS), and the sheet-like structure is verified by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). Co-BTB-LB electrode exhibits an excellent capacity of 4969.3 F g-1 at 1 A g-1 and good cycling stability with 75% capacity retention after 1000 cycles. The asymmetric supercapacitor device with Co-BTB-LB as the positive electrode shows a maximum energy density of 150.2 Wh kg-1 at a power density of 1619.2 W kg-1 and good cycling stability with a capacitance retention of 97.1% after 10000 cycles. This represents a state-of-the-art performance reported for asymmetric supercapacitor device using electroactive bottom-up metal-complex nanosheet, which will clearly lead to a significant expansion of the applicability of this type of 2D nanomaterials.

Bridging the Gap between Charge Storage Site and Transportation Pathway in Molecular-Cage-Based Flexible Electrodes

Porous materials have been widely applied for supercapacitors; however, the relationship between the electrochemical behaviors and the spatial structures has rarely been discussed before. Herein, we report a series of porous coordination cage (PCC) flexible supercapacitors with tunable three-dimensional (3D) cavities and redox centers. PCCs exhibit excellent capacitor performances with a superior molecular capacitance of 2510 F mmol^-1, high areal capacitances of 250 mF cm^-2, and unique cycle stability. The electrochemical behavior of PCCs is dictated by the size, type, and open-close state of the cavities. Both the charge binding site and the charge transportation pathway are unambiguously elucidated for PCC supercapacitors. These findings provide central theoretical support for the "structure-property relationship" for designing powerful electrode materials for flexible energy storage devices.

Design and Synthesis of Bisulfone-Linked Two-Dimensional Conjugated Microporous Polymers for CO2 Adsorption and Energy Storage

We have successfully synthesized two types of two-dimensional conjugated microporous polymers (CMPs), Py-BSU and TBN-BSU CMPs, by using the Sonogashira cross-coupling reaction of BSU-Br2 (2,8-Dibromothianthrene-5,5′,10,10′-Tetraoxide) with Py-T (1,3,6,8-Tetraethynylpyrene) and TBN-T (2,7,10,15-Tetraethynyldibenzo[g,p]chrysene), respectively. We characterized the chemical structure, morphology, physical properties, and potential applications of these materials using various analytical instruments. Both Py-BSU and TBN-BSU CMPs showed high thermal stability with thermal decomposition temperatures (Td10) up to 371 °C and char yields close to 48 wt%, as determined by thermogravimetric analysis (TGA). TBN-BSU CMPs exhibited a higher specific surface area and porosity of 391 m2 g−1 and 0.30 cm3 g−1, respectively, due to their large micropore and mesopore structure. These CMPs with extended π-conjugated frameworks and high surface areas are promising organic electroactive materials that can be used as electrode materials for supercapacitors (SCs) and gas adsorption. Our experimental results demonstrated that the TBN-BSU CMP electrode had better electrochemical characteristics with a longer discharge time course and a specific capacitance of 70 F g−1. Additionally, the electrode exhibited an excellent capacitance retention rate of 99.9% in the 2000-cycle stability test. The CO2 uptake capacity of TBN-BSU CMP and Py-BSU CMP were 1.60 and 1.45 mmol g−1, respectively, at 298 K and 1 bar. These results indicate that the BSU-based CMPs synthesized in this study have potential applications in electrical testing and CO2 capture.

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.

Largely Pseudocapacitive Two-Dimensional Conjugated Metal-Organic Framework Anodes with Lowest Unoccupied Molecular Orbital Localized in Nickel-bis(dithiolene) Linkages

Although two-dimensional conjugated metal-organic frameworks (2D c-MOFs) provide an ideal platform for precise tailoring of capacitive electrode materials, high-capacitance 2D c-MOFs for non-aqueous supercapacitors remain to be further explored. Herein, we report a novel phthalocyanine-based nickel-bis(dithiolene) (NiS₄)-linked 2D c-MOF (denoted as Ni₂[CuPcS₈]) with outstanding pseudocapacitive properties in 1 M TEABF₄/acetonitrile. Each NiS₄ linkage is disclosed to reversibly accommodate two electrons, conferring the Ni₂[CuPcS₈] electrode a two-step Faradic reaction with a record-high specific capacitance among the reported 2D c-MOFs in non-aqueous electrolytes (312 F g^-1) and remarkable cycling stability (93.5% after 10,000 cycles). Multiple analyses unveil that the unique electron-storage capability of Ni₂[CuPcS₈] originates from its localized lowest unoccupied molecular orbital (LUMO) over the nickel-bis(dithiolene) linkage, which allows the efficient delocalization of the injected electrons throughout the conjugated linkage units without inducing apparent bonding stress. The Ni₂[CuPcS₈] anode is used to demonstrate an asymmetric supercapacitor device that delivers a high operating voltage of 2.3 V, a maximum energy density of 57.4 Wh kg^-1, and ultralong stability over 5000 cycles.

Mechanochemical Access to Catechol-Derived Metal-Organic Frameworks

Mechanochemistry, a resurging synthetic approach, has been developed into an effective and controllable method to access a family of crystalline porous catechol-derived metal-organic frameworks (MOFs) for the first time. We have identified that the obtained crystalline phase is readily tunable by precursors and the addition of solvents or drying agents. The described mechanochemistry allows us to synthesize these materials in a highly sustainable manner. Thus, mechanochemistry is expected to pave a promising avenue to access a broader class of MOF materials, in addition to those based on the motifs of carboxylic acid or imidazole.

Cu(II)-Metallized Three-Layered Cu-8HQ Complex with Hierarchical Crystallite Morphologies Synthesized via Reaction-Diffusion

Self-organization of regular band patterns of the precipitate via a reaction-diffusion (RD) framework is called Liesegang phenomenon. This non-equilibrium system is emerging as an efficient method for synthesizing materials with unique morphologies that may have desired properties. The formation of continuous precipitation inside a band with poor control over the shape and size of sparingly soluble salts has been well documented. However, only a few reports on forming organic-inorganic bonds are available. In the present work, we demonstrate the formation of 2D frameworks of bis-(8-hydroxyquinoline) copper(II) in the agar gel via RD. The macroscopic particles were dumbbell-shaped, with aspect ratios ranging from 2.7 (inner bands) to 0.7 (outer bands). The particles were composed of ribbon-shaped crystallites at the microscopic level, each with three layers of parallelogram prismatic monoclinic sheets stacked over one another, which could easily be exfoliated. The powder X-ray diffraction patterns at low angles and the surface areas of the crystallites indicated the formation of metal-organic frameworks. It was observed that the sizes of the particles could be tuned by controlling the extent of diffusion using reactant concentrations. Since such heterostructures have energy storage capacity, the cyclic voltammograms of the unexfoliated and exfoliated materials showed that they fall in the pseudocapacitor category with potential application as the electrode material. The frameworks were further characterized by techniques such as optical and electron microscopy, X-ray diffraction, IR spectroscopy, and UV-visible spectrophotometry.

A three-dimensional Mn-based MOF as a high-performance supercapacitor electrode

Developing new high-performance electrode materials for improving the energy density of supercapacitors is an important task. Herein, a new three-dimensional (3D) metal-orgainc framework (MOF) [Mn(BGPD)(H₂O)₂] (Mn-BGPD; BGPD = N,N'-bis(glycinyl)pyromellitic diimide) was synthesized. When Mn-BGPD is used as the electrode material of supercapacitors, in a three-electrode setup, it shows an outstanding specific capacitance of 832.6 F g^-1 at a current density of 1 A g^-1. The asymmetrical supercapacitor of Mn-BGPD shows an attractive specific capacitance of 100 F g^-1 at 1 A g^-1, which corresponds to an excellent energy density of 35.5 W h kg^-1. Moreover, better cycling stability with a capacitance retention of 46.7% is also shown. The high electrochemical performance makes Mn-BGPD a very promising electrode material for supercapacitors.

In Silico High-Throughput Design and Prediction of Structural and Electronic Properties of Low-Dimensional Metal-Organic Frameworks

The advent of π-stacked layered metal-organic frameworks (MOFs), which offer electrical conductivity on top of permanent porosity and high surface area, opened up new horizons for designing compact MOF-based devices such as battery electrodes, supercapacitors, and spintronics. Permutation of structural building blocks, including metal nodes and organic linkers, in these electrically conductive (EC) materials, results in new systems with unprecedented and unexplored physical and chemical properties. With the ultimate goal of providing a platform for accelerated material design and discovery, here we lay the foundations for the creation of the first comprehensive database of EC-MOFs with an experimentally guided approach. The first phase of this database, coined EC-MOF/Phase-I, is composed of 1,057 bulk and monolayer structures built by all possible combinations of experimentally reported organic linkers, functional groups, and metal nodes. A high-throughput screening (HTS) workflow is constructed to implement density functional theory calculations with periodic boundary conditions to optimize the structures and calculate some of their most relevant properties. Because research and development in the area of EC-MOFs has long been suffering from the lack of appropriate initial crystal structures, all of the geometries and property data have been made available for the use of the community through an online platform that was developed during the course of this work. This database provides comprehensive physical and chemical data of EC-MOFs as well as the convenience of selecting appropriate materials for specific applications, thus accelerating the design and discovery of EC-MOF-based compact devices.

Reversible Metal and Ligand Redox Chemistry in Two-Dimensional Iron-Organic Framework for Sustainable Lithium-Ion Batteries

Metal-organic frameworks (MOFs) are emerging as attractive electrode materials for lithium-ion batteries, owing to their fascinating features of sustainable resources, tunable chemical components, flexible molecular skeletons, and renewability. However, they are faced with a limited number of redox-active sites and unstable molecular frameworks during electrochemical processes. Herein, we design a novel two-dimensional (2D) iron(III)-tetraamino-benzoquinone (Fe-TABQ) with dual redox centers of Fe cations and TABQ ligands for high-capacity and stable lithium storage. It is constructed of square-planar Fe-N₂O₂ linkages and phenylenediamine building blocks, between which the Fe-TABQ chains are connected by multiple hydrogen bonds, and then featured as an extended π-d-conjugated 2D structure. The redox chemistry of both Fe³⁺ cations and TABQ anions is revealed to render its remarkable specific capacity of 251.1 mAh g^-1. Benefiting from the intrinsic robust Fe-N(O) bonds and reinforced Li-N(O) bonds during cycling, Fe-TABQ delivers high capacity retentions over 95% after 200 cycles at various current densities. This work will enlighten more investigations for the molecular designs of advanced MOF-based electrode materials.

Approaches to Enhancing Electrical Conductivity of Pristine Metal-Organic Frameworks for Supercapacitor Applications

Metal-organic frameworks (MOFs), known as porous coordination polymers, have attracted intense interest as electrode materials for supercapacitors (SCs) owing to their advantageous features including high surface area, tunable porous structure, structural diversity, etc. However, the insulating nature of most MOFs has impeded their further electrochemical applications. A common solution for this issue is to transform pristine MOFs into more stable and conductive metal compounds/porous carbon materials through pyrolysis, which however losses the inherent merits of MOFs. To find a consummate solution, recently a surge of research devoted to improving the electrical conductivity of pristine MOFs for SCs has been carried out. In this review, the most related research work on pristine MOF-based materials is reviewed and three effective strategies (chemical structure design of conductive MOFs (c-MOFs), composite design, and binder-free structure design) which can significantly increase their conductivity and consequently the electrochemical performance in SCs are proposed. The conductivity enhancement mechanism in each approach is well analyzed. The representative research works on using pristine MOFs for SCs are also critically discussed. It is hoped that the new insights can provide guidance for developing high-performance electrode materials based on pristine MOFs with high conductivity for SCs in the future.

The Increasing Number of Electron Reservoirs in Nonporous, High-Conducting Coordination Polymers Cux BHT (x = 3, 4, and 5, BHT = Benzenehexathiol) for Improved Faradaic Capacitance

Although asymmetric supercapacitors (ASCs) can achieve high energy density, the lifespan and power density are severely suppressed due to the low conductivity of using pseudocapacitive or battery-type electrode materials. Recently, nonporous conductive coordination polymers (c-CPs) have sparked interests in supercapacitors. However, their performance is expected to be limited by the nonporous features, low specific surface area and absence of ion-diffusion channels. Here, it is demonstrated that the capacity of nonporous CPs will be significantly enhanced by maximizing the number of faradaic redox sites in their structures through a comparative investigation on three highly conductive nonporous c-CPs, Cu_x BHT(x = 3, 4, 5.5). They show excellent capacitance of 312.1 F g^-1 (374.5 C g^-1 ) (Cu₃ BHT), 186.7 F g^-1 (224.0 C g^-1 ) (Cu₄ BHT) and 89.2 F g^-1 (107.0 C g^-1 ) (Cu_5.5 BHT) at 0.5 A g^-1 in a sequence related to the number of electron storage units in structures and outstanding rate performance and cycle stability. Furthermore, the constructed Cu₃ BHT//MnO₂ ASC device exhibits capacity retention of 92% (after 1500 cycles at 3 A g^-1 ) and delivers a high energy density of 39.1 Wh kg^-1 at power density of 549.6 W kg^-1 within a large working potential window of 0-2.2 V.

Selective Center Charge Density Enables Conductive 2D Metal-Organic Frameworks with Exceptionally High Pseudocapacitance and Energy Density for Energy Storage Devices

Conductive 2D conjugated metal-organic frameworks (c-MOFs) are attractive electrode materials due to their high intrinsic electrical conductivities, large specific surface area, and abundant unsaturated bonds/functional groups. However, the 2D c-MOFs reported so far have limited charge storage capacity during electrochemical charging and discharging, and the energy density is still unsatisfactory. In this work, a strategy of selective center charge density to expand the traditional electrode materials to the electrode-electrolyte coupled system with the prototypical of 2D Co-catecholate (Co-CAT) is proposed. Electrochemical mechanism studies and density functional theory calculations reveal that dual redox sites are achieved with the quinone groups (CAT) and metal-ion linkages (Co-O) serving as the active sites of pseudocapacitive cation (Na⁺ ) and redox electrolyte species (SO₃ ^2- ). The resultant electrode delivers an exceptionally high capacity of 1160 F g^-1 at 1 A g^-1 and a special self-discharge rate (86.8% after 48 h). Moreover, the packaged asymmetric device exhibits a state-of-the-art energy density of 158 W h kg^-1 at the power density of 2000 W kg^-1 and an excellent self-discharge rate of 80.6% after 48 h. This success will provide a new perspective for the performance enhancement for the 2D-MOF-based energy storage devices.

Two-Dimensional Conjugated Metal-Organic Frameworks for Electrocatalysis: Opportunities and Challenges

A highly effective electrocatalyst is the central component of advanced electrochemical energy conversion. Recently, two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as a class of promising electrocatalysts because of their advantages including 2D layered structure with high in-plane conjugation, intrinsic electrical conductivity, permanent pores, large surface area, chemical stability, and structural diversity. In this Review, we summarize the recent advances of 2D c-MOF electrocatalysts for electrochemical energy conversion. First, we introduce the chemical design principles and synthetic strategies of the reported 2D c-MOFs, as well as the functional design for the electrocatalysis. Subsequently, we present the representative 2D c-MOF electrocatalysts in various electrochemical reactions, such as hydrogen/oxygen evolution, and reduction reactions of oxygen, carbon dioxide, and nitrogen. We highlight the strategies for the structural design and property tuning of 2D c-MOF electrocatalysts to boost the catalytic performance, and we offer our perspectives in regard to the challenges to be overcome.

Metal-hydrogen-pi-bonded organic frameworks

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.

Metal-Organic Framework Based Gas Sensors

The ever-increasing concerns over indoor/outdoor air quality, industrial gas leakage, food freshness, and medical diagnosis require miniaturized gas sensors with excellent sensitivity, selectivity, stability, low power consumption, cost-effectiveness, and long lifetime. Metal-organic frameworks (MOFs), featuring structural diversity, large specific surface area, controllable pore size/geometry, and host-guest interactions, hold great promises for fabricating various MOF-based devices for diverse applications including gas sensing. Tremendous progress has been made in the past decade on the fabrication of MOF-based sensors with elevated sensitivity and selectivity toward various analytes due to their preconcentrating and molecule-sieving effects. Although several reviews have recently summarized different aspects of this field, a comprehensive review focusing on MOF-based gas sensors is absent. In this review, the latest advance of MOF-based gas sensors relying on different transduction mechanisms, for example, chemiresistive, capacitive/impedimetric, field-effect transistor or Kelvin probe-based, mass-sensitive, and optical ones are comprehensively summarized. The latest progress for making large-area MOF films essential to the mass-production of relevant gas sensors is also included. The structural and compositional features of MOFs are intentionally correlated with the sensing performance. Challenges and opportunities for the further development and practical applications of MOF-based gas sensors are also given.

SrFeO3–δ: A Novel Fe4+↔Fe2+ Redox Mediated Pseudocapacitive Electrode in Aqueous Electrolyte

Pseudocapacitor offers both high energy and high power making them suitable for grid scale electrochemical energy storage to harness the renewable energy produced through solar, wind and tides. To overcome...

Coordination environment dependent selectivity of single-site-Cu enriched crystalline porous catalysts in CO2 reduction to CH4

The electrochemical CO₂ reduction to high-value-added chemicals is one of the most promising and challenging research in the energy conversion field. An efficient ECR catalyst based on a Cu-based conductive metal-organic framework (Cu-DBC) is dedicated to producing CH₄ with superior activity and selectivity, showing a Faradaic efficiency of CH₄ as high as ~80% and a large current density of -203 mA cm^-2 at -0.9 V vs. RHE. The further investigation based on theoretical calculations and experimental results indicates the Cu-DBC with oxygen-coordinated Cu sites exhibits higher selectivity and activity over the other two crystalline ECR catalysts with nitrogen-coordinated Cu sites due to the lower energy barriers of Cu-O₄ sites during ECR process. This work unravels the strong dependence of ECR selectivity on the Cu site coordination environment in crystalline porous catalysts, and provides a platform for constructing highly selective ECR catalysts.

Semiconductive coordination polymers with continuous π-π interactions and defined crystal structures

Two semiconductive coordination polymers based on a chelating redox-active ligand were synthesized and structurally characterized. Strong and continuous intermolecular π-π interactions are likely the reason for moderate electrical conductivity of about 10^-5 S m^-1 in these materials. The results of DFT calculations indicate that the continuous π-π stacking structure contributes to the orbital overlap and thus improves charge transport performance.

A comparative study of honeycomb-like 2D π-conjugated metal-organic framework chemiresistors: conductivity and channels

Two-dimensional (2D) π-conjugated conductive metal-organic frameworks (cMOFs, 2DπcMOF) with modulated channel sizes and a broad conductivity range have been reported in the last decade. In contrast, the corresponding comparative studies on their effects on chemiresistive sensing performances, which measure the resistive response toward external chemical stimuli, have not yet been reported. In this work, we sought to explore the structure-performance relationships of honeycomb-like 2D π-conjugated cMOF chemiresistive gas sensors with channel sizes less than 2 nm (the mass transport issue) and broad conductivity in the range from ∼10^-8 S cm^-1 to 1 S cm^-1 (the charge transport issue). As a result, we found that the cMOF with a lower conductivity facilitates the much more sensitive response toward the charge transfer of the adsorbed gases (relative increases in resistance: R = 63.5% toward 100 ppm of NH₃ for the as prepared Cu-THQ sensor with the conductivity of ∼10^-8 S cm^-1). Interestingly, the cMOF with a medium channel size (Cu-THHP-THQ) exhibited the fastest response speed in sensing, although it contains H₂en²⁺ as neutralizing counterions in the channels. From the evaluation of the pore size distribution, it is found that the overall porosity (meso- & micro-pores) of cMOFs, rather than the pore size of the honeycomb structure, would determine their sensing speed. When comparing the performance of two different morphologies of nanorods (NRs) and nanosheets (NSs), NRs showed a slower response and extended recovery time, which can be ascribed to the slower gas diffusion in the more extended 1D channel. Altogether, our results demonstrate the first systematic studies on the effect of various structural parameters on the chemiresistive sensor performance of cMOFs.

Recent Progress in Designing Thermoelectric Metal-Organic Frameworks

Thermoelectrics that enable direct heat-electricity conversion possess unique advantages for green and renewable energy revolution and have received rapidly growing attention in the past decade. Among various thermoelectric materials, metal-organic frameworks (MOFs) with intrinsic high porosity and tunable physical/chemical properties are emerging as a promising class of materials that have been demonstrated to exhibit many unique merits for thermoelectric applications. Their structural topologies and thermoelectric properties can be facilely regulated by precisely selecting and arranging metal centers and organic ligands. Besides, a large variety of guest molecules can be incorporated within their pores, giving rise to novel avenues of raising energy-conversion efficiency. This review focuses on the recent advances in designing conductive MOFs and MOF-based composites for thermoelectric applications. It first introduces the fundamental thermoelectric parameters and the underlying regulation mechanisms specifically effective for MOFs, then summarizes the related studies conducted in recent years, where the structural design strategies of tuning thermoelectric properties are demonstrated and discussed. In the final part, conclusions and perspectives with the envision of an outlook for this promising area are presented.

Effective enhancement of capacitive performance by the facile exfoliation of bulk metal-organic frameworks into 2D-functionalized nanosheets

Recently, much attention has been paid to two-dimensional MOF nanosheets (MONs) due to their widespread application in many specific areas. In this work, a simple and efficient congenerous-exfoliation strategy was developed to prepare vast and uniform few-layered Ni²⁺@Ce-MOF (Ce-MOF: {[Ce(HPIA)(PIA)(H₂O)₂]·H₂O}_n) nanosheets with a thickness of ca. 10 nm. In the exfoliation process, the synergistic action of Ni²⁺ and methanol solvents under ultrasonication plays a major role in restraining the interactions between the layers. Importantly, supercapacitor applications indicate that the exfoliated Ni²⁺@Ce-MOF nanosheet shows a remarkable improvement in the specific capacitance (921.05%) in comparison with that of the bulk Ce-MOF sample before modification.