Electrochemical oxygen reduction catalysed by Ni3(hexaiminotriphenylene)2

Metal-organic frameworks-molecularly imprinted polymers (MOF-MIP): Synthesis, properties, and applications in detection and control of microorganisms

Microbial contamination poses a significant threat to human health, food safety, and the ecological environment. Its rapid spread and potential pathogenicity create an urgent global challenge for efficient detection and control. However, existing methods have several shortcomings such as traditional techniques like culture methods and polymerase chain reaction (PCR) are time-consuming, while nanomaterials and aptamers often lack selectivity, stability, and affordability. Additionally, conventional disinfectants can be inefficient, lead to drug resistance, and harm the environment. To address these challenges, developing new materials and technologies that are efficient, sensitive, and stable is crucial for microbial detection and control. In this context, metal-organic frameworks (MOF) and molecularly imprinted polymers (MIP) have emerged as promising functional materials due to their unique structural advantages. The high porosity of MOF provides ample imprinting sites for MIP, while MIP enhance selective adsorption and inactivation of target microorganisms by MOF. This synergistic combination results in a composite material that offers a novel solution for microbial detection, significantly improving sensitivity, selectivity, antibacterial efficiency, and environmental friendliness. This paper reviews the synthesis strategies of metal-organic frameworks-molecularly imprinted polymers (MOF-MIP), highlighting their structural properties and innovative applications in microbial detection, which aim to inspire researchers in related fields. Looking ahead, future advancements in material science and biotechnology are expected to lead to widespread use of MOF-MIP composites in food safety, environmental monitoring, medical diagnosis, and public health-providing robust support against microbial pollution. By studying the collaborative mechanisms of MOF and MIP while optimizing design processes will enhance precision speed cost-effectiveness in microbial detection technology significantly contributing to human health and environmental safety.

Electrochemistry sensing of ascorbic acid based on conductive metal-organic framework (Cu3(benzenehexathiol)) nanosheets modified electrode

BACKGROUND

Bulk-type conductive metal-organic frameworks (c-MOFs) had been applied to modify the electrode and used in electrochemical sensing because of the high conductive properties. But which still suffer from low mass permeability, restricted active site exposure, and poor accessibility due to the coordination saturation at metal sites in the bulk-type c-MOF. Recent studies have demonstrated that transforming bulk-type MOFs into MOFs nanosheets (NSs) can maximize the exposure of active sites and mass transfer. However, c-MOF NSs have rarely been applied in electrochemical sensing.

RESULTS

This study presents NSs type c-MOF Cu3(benzenehexathiol) (CuBHT), synthesized using a simple sacrificial template method. CuBHT NSs were modified onto a glassy carbon electrode (GCE) to prepare CuBHT NSs/GCE, which was then applied to sense the model target ascorbic acid (AA), the system exhibits high sensitivity of 1.521 mA mM-1 cm-2 and a wide linear range of 1-789 μM, low detection limit of 0.46 μM. The sensitivity is 1.90 times higher than that of bulk-type CuBHT nanoparticles (NPs) modified GCE, which can be attributed to the CuBHT NSs having more exposed Cu sites on their surfaces. CuBHT NSs/GCE was then used to monitor AA levels in human sweat during daily activities or exercise, and the results indicated high reliability compared to the vitamin C ASA kit method.

SIGNIFICANCE

The design of c-MOF CuBHT NSs/GCE lead to better performance in terms of sensitivity and low detection limit in AA sensing compared to bulk-type nanoparticles. The AA sensing mechanism based on CuBHT was investigated, and the sensing system was demonstrated by detecting AA in sweat. This work advances both the fundamental understanding and practical applications of c-MOF NSs in AA sensing.

Catalysis-Assisted Synthesis of Two-Dimensional Conductive Metal-Organic Framework Films with Controllable Orientation

The facile preparation of two-dimensional (2D) conductive metal-organic framework (MOF) films with controllable orientation and thickness greatly facilitates the further structure-property investigation and performance optimization in their applications. Here, we report a catalysis-assisted synthesis strategy to the rapid production of oriented films of catechol-based (Cu3(HHTP)2, Zn3(HHTP)2, and Cu2TBA) and diamine-based (Ni3(HITP)2) 2D conductive MOFs with thicknesses adjustable from tens of nanometers to several micrometers. Relying on the utilization of a 0.3 nm Pt layer, which can be conveniently predecorated on a substrate surface via evaporating deposition or sputtering, as a catalyst for the aerobic oxidation of the redox-active ligands to trigger the formation of 2D conductive MOFs, this strategy is compatible with a majority of commonly used substrates and capable of producing patterned films with feature sizes ranging from micrometers to centimeters. Investigation on the growth kinetics of Cu3(HHTP)2 indicates that the preferential growth along the c-axis or in the ab-basal plane of its crystallites can be flexibly tuned by the formation reaction kinetics to guide the evolution of films with the face-on or edge-on orientation. The chemiresistive device incorporating the face-on Cu3(HHTP)2 film presents a high response (197%) and a fast respond speed (27 s) toward NH3 (30 ppm) at room temperature, which are superior not only to its edge-on counterpart (90% and 69 s, correspondingly) but also to other reported Cu3(HHTP)2-based sensors.

Optimizing active sites via chemical bonding of 2D metal-organic frameworks and MXenes for efficient hydrogen evolution reaction activity

Metal-organic frameworks (MOFs) are promising electrocatalysts due to their large surface areas and abundant metal sites, but their efficacy is limited by poor exposure of active metal atoms to the electrolyte. To address this issue, we report an innovative approach that integrates a conductive layered MXene (Ti3C2Tx) with a 2-dimensional (2D) Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2-MOF through in situ synthesis of the MOF on the MXene, maximizing the accessible exposure of active sites for electrocatalytic hydrogen evolution reaction (HER) activity. XPS analysis confirms that the MOF is chemically bonded with the MXene layers, while SEM analysis shows complete overlapping, intercalation, and surface growth of the MOF on the MXene layers. The optimized chemically bonded MOF on MXene exhibits superior electrocatalytic activity, with an overpotential of 180 mV in alkaline media-four times better than that of the pristine MOF-and an overpotential of 240 mV in acidic media, three times better than that of the pristine MOF. The enhanced electrocatalytic activity is attributed to the bond formation between Ti atoms from the MXene and N atoms from the MOF, which facilitates charge transfer and improves both the kinetics and active electrocatalytic area for the HER. This method offers a simple, pioneering approach to fabricate noble metal-free, nanostructured electrocatalysts, enhancing water electrolysis efficiency and extending applicability to other conductive MOFs.

Ligand Regulated the Coordination Environment of Cobalt-Group-MOF for Efficient Electrocatalytic Oxygen Reduction/Evolution Catalysis

In recent years, the TMN4 moieties have demonstrated significant catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in graphene, CxNy, and other carbon-based two-dimensional (2D) support materials. Modifying the coordination number and species of N atoms in the TMN4 moieties has proven to be an effective approach to regulate their catalytic activity. In this research, by incorporating different triphenylene ligands, we have successfully constructed TMA2B2 (TM = Co, Rh, Ir; A/B = N, O, S, Se) moieties with varying coordination environments within 2D metal organic frameworks (MOFs), which are linked by TM and triphenylene. These moieties serve as an effective model to elucidate the structure-property relationship of two-dimensional 2D-MOFs in OER and ORR. Our findings confirm that alterations in the coordination environment can finely tune the d-band electron distribution of the TM within the TMA2B2 unit, particularly activating the dyz and dz2 orbitals of O2, thereby influencing the interactions between TM and key intermediates. We discovered that the regulatory effect of the coordination environment is closely linked to the electronegativity of the coordinating atoms, which led us to establish reliable descriptors such as φ1 and φ2 to elucidate the impact of coordination environments on the performance of OER/ORR. This criterion can be applied to numerous other 2D-MOFs and provides an in-depth understanding of the structure-activity relationship facilitates the development of highly efficient bifunctional electrocatalysts for OER and ORR applications.

Pyrolytic Transformation of Zn-TAL Metal-Organic Framework into Hollow Zn-N-C Spheres for Improved Oxygen Reduction Reaction Catalysis

Metal-organic frameworks (MOFs) are promising precursors for creating metal-nitrogen-carbon (M-N-C) electrocatalysts with high performance, though maintaining their structure during pyrolysis is challenging. This study examines the transformation of a Zn-based MOF into an M-N-C electrocatalyst, focusing on the preservation of the carbon framework and the prevention of Zn aggregation during pyrolysis. A highly porous Zn-N-C electrocatalyst derived from Zn-TAL MOF (where TAL stands for the TalTech-UniTartu Alliance Laboratory) was synthesized via optimized pyrolysis, yielding notable electrocatalytic activity toward oxygen reduction reaction (ORR). Scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) analyses confirmed that the carbon framework preserved its integrity and remained free of Zn metal aggregates, even at elevated temperatures. Rotating disc electrode (RDE) tests in an alkaline solution showed that the optimized Zn-N-C electrocatalyst demonstrated ORR activity on par with commercial Pt/C electrocatalysts. In an anion-exchange membrane fuel cell (AEMFC), the Zn-N-C material pyrolyzed at 1000 °C exhibited a peak power density of 553 mW cm-2 at 60 °C. This work demonstrates that Zn-TAL MOF is an excellent precursor for forming hollow Zn-N-C structures, making it a promising high-performance Pt-free electrocatalyst for fuel cells.

Intramolecular Double Activation by Biligands Sharing a Single Metal Atom for Preferred Two-Electron Oxygen Reduction

It is challenging to selectively promote the two-electron oxygen reduction reaction (2e-ORR) since highly ORR-active electrocatalysts are not satisfied with 2e-ORR and are most likely to go all the way to 4e-ORR, completely reducing dioxygen to water. Recently, however, the possibility of a 2e-ORR preference over 4e-ORR was raised by extensively considering multiple ORR mechanisms and employing a potential-dependent activity measure for constructing volcano plots. Here, we realized the preferred 2e-ORR via an intramolecular double activation of the peroxide intermediate (*OOH) by allowing the intermediate to be easily desorbed before proceeding to 4e-ORR. Dioxygen was transformed to *OOH on a carbon atom of the imidazole ligand of zeolitic imidazolate framework-8 (ZIF-8). When an amine group was introduced via ligand exchange, the selectivity of 2e-ORR was enhanced by 11%. The added amine attracted the oxygen atom of *OOH via a hydrogen bond to weaken the binding strength of *OOH to the carbon active site (double activation). The amine-decorated ZIF-8 exhibited H2O2 faradaic efficiency at 98.5% at ultrahigh-rate production at 625 mg cm-2 h-1 by 1 A cm-2 in a flow cell.

Two-dimensional conjugated metal-organic frameworks for electrochemical energy conversion and storage

Effective electrocatalysts and electrodes are the core components of energy conversion and storage systems for sustainable carbon and nitrogen cycles to achieve a carbon-neutral economy. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as multifunctional materials for electrochemical applications benefiting from their similarity to graphene with remarkable conductivity, abundant active sites, devisable components, and well-defined crystalline structures. In this review, the structural design strategies to establish active components with a maximum degree through redox-active ligand assembly in 2D c-MOFs are briefly summarized. Next, recent representative examples of 2D c-MOFs applied in electrocatalysis (hydrogen/oxygen evolution and oxygen/carbon dioxide/nitrogen reduction) and energy storage systems (supercapacitors and batteries) are introduced. The synergistic effect of multiple components in 2D c-MOFs is particularly emphasized for enhanced performance in electrochemical energy conversion and storage systems. Finally, an outlook and challenges are proposed for realizing more active components, elucidating the reaction mechanism involving the derived structures, and achieving low-cost economy in practical applications.

Conductive Metal-Organic Frameworks and Their Electrocatalysis Applications

Recently, electrically conductive metal-organic frameworks (EC-MOFs) have emerged as a wealthy library of porous frameworks with unique properties, allowing their use in diverse applications of energy conversion, including electrocatalysis. In this review, the electron conduction mechanisms in EC-MOFs are examined, while their electrical conductivities are considered. There have been various strategies to enhance the conductivities of MOFs including ligand modification, the incorporation of conducting materials, and the construction of multidimensional architectures. With sufficient conductivities being established for EC-MOFs, there have been extensive pursuits in their electrocatalysis applications, such as in the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, N2 reduction reaction, and CO2 reduction reaction. In addition, computational modeling of EC-MOFs also exerts an important impact on revealing the synthesis-structure-performance relationships. Finally, the prospects and current challenges are discussed to provide guidelines for designing promising framework materials.

2D Conjugated Metal-Organic Framework-Based Composite Membranes for Nanofluidic Ionic Photoelectric Conversion

Nanofluidic photoelectric conversion system based on photo-excitable 2D materials can directly transduce light stimuli into an ion-transport-mediated electric signal, showing potential for mimicking the retina's function with a more favorable human-robot interactions. However, the current membranes suffer from low generation efficiency of charge carriers due to the mixed microstructure and limited charge transport ability caused by the large interlayer spacing and monotonous pathway. Here, a fully conjugated 2D hexaimino-substituted triphenylene-based metal-organic framework (2D-HATP-cMOF) based composite membrane with high conductivity for photoelectric conversion is presented. The extended π-d conjugation within the ab plane and the favorable transport pathway through π-π stacking of the c-MOF maximize the generation and transfer of charge carrier and greatly accelerate the ion transport. As a result, the 2D-HATP-cMOF-based composite membrane possesses ultrafast photoelectric response, superior to other reported 2D systems like graphene oxide (GO), transition metal carbides, carbonitrides and nitrides (MXene), and MoS2, which require at least 10 s. A successful ion pump phenomenon, that is active transport from low concentration to high concentration as an important way of information transmission in organisms, is realized based on the efficient photoelectric conversion capability. This work demonstrates the great promise of 2D c-MOF in ionic photoelectric conversion.

Reversible and Ultrasensitive Detection of Nitric Oxide Using a Conductive Two-Dimensional Metal-Organic Framework

This paper describes the use of a highly crystalline conductive 2D copper3(hexaiminobenzene)2 (Cu3(HIB)2) as an ultrasensitive (limit of detection of 1.8 part-per-billion), highly selective, reversible, and low power chemiresistive sensor for nitric oxide (NO) at room temperature. The Cu3(HIB)2-based sensors retain their sensing performance in the presence of humidity, and exhibit strong signal enhancement towards NO over other highly toxic reactive gases, such as NO2, H2S, SO2, NH3, CO, as well as CO2. Mechanistic investigations of the Cu3(HIB)2-NO interaction through spectroscopic analyses and density functional theory revealed that the Cu-bis(iminobenzosemiquinoid) moieties serve as the binding sites for NO sensing, while the Ni-bis(iminobenzosemiquinoid) MOF analog shows no noticeable response to NO. Overall, these findings provide a significant advance in the development of crystalline metal-bis(iminobenzosemiquinoid)-based conductive 2D MOFs as highly sensitive, selective, and reversible sensing materials for the low-power detection of toxic gases.

Interconnected Lamellar 3D Semiconductive PCP for Rechargeable Aqueous Zinc Battery Cathodes

2D electronically conductive porous coordination polymers/metal-organic frameworks (2D EC-MOFs) of M-HHTPs (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene; M = Co, Ni, Cu, etc.) have received extensive attention due to their ease of preparation, semiconductive properties, and tunability based on the choice of metal species. However, slight shifts between layers attenuate their specific surface area and stability. In this study, the metal-ion bridge strategy is newly adopted and a vanadyl counterpart of M-HHTP is synthesized with a chemical formula of (VO)3(HHTP)2, hereafter referred to as VO-HHTP. The semiconductor VO-HHTP has a vertical interconnection by octahedral VO6 chains and exhibits a relatively high specific surface area (ca. 590 m2 g-1) compared to other 2D EC-MOFs. Motivated by its redox activity and porous nature, VO-HHTP is applied as the cathode material in rechargeable aqueous zinc batteries (RAZBs). VO-HHTP demonstrates a high capacity of 240 mAh g-1 and excellent rate capability, even with a reduced amount of conductive agent, surpassing the performance of the previous EC-MOFs. Furthermore, its stable structure ensures long-term cycling stability, addressing a common issue in previous EC-MOFs. The work contributes to the development of new concepts in both the design of π-conjugated EC-MOFs and the study of cathode materials for RAZBs.

Two-Dimensional Catalysts: From Model to Reality

Two-dimensional (2D) materials have been utilized broadly in kinds of catalytic reactions due to their fully exposed active sites and special electronic structure. Compared with real catalysts, which are usually bulk or particle, 2D materials have more well-defined structures. With easily identified structure-modulated engineering, 2D materials become ideal models to figure out the catalytic structure-function relations, which is helpful for the precise design of catalysts. In this review, the unique function of 2D materials was summarized from model study to reality catalysis and application. It includes several typical 2D materials, such as graphene, transition metal dichalcogenides, metal, and metal (hydr)oxide materials. We introduced the structural characteristics of 2D materials and their advantages in model researches. It emphatically summarized how 2D materials serve as models to explore the structure-activity relationship by combining theoretical calculations and surface research. The opportunities of 2D materials and the challenges for fundamentals and applications they facing are also addressed. This review provides a reference for the design of catalyst structure and composition, and could inspire the realization of two-dimensional materials from model study to reality application in industry.

Developing porous electrocatalysts to minimize overpotential for the oxygen evolution reaction

The development of electrocatalysts for the oxygen evolution reaction (OER) is one of the most critical issues for improving the efficiency of electrochemical water-splitting, which can produce green hydrogen energy without CO2 emissions. This review outlines the advances in the precise design of inorganic- and organic-based porous electrocatalysts, which are designed by various strategies, to catalyze the OER in the electrolytic cycle for efficient water-splitting. For developing high-performance electrocatalysts with low overpotentials, it is important to design a chemical composition that optimizes binding energy for an intermediate in the OER and allows the easy access of reactants to active sites depending on the porosity of electrocatalysts. Porous structures give us the positive opportunity to increase the accessible surface of active sites and effective diffusion of targeting molecules, which is potentially one of the guidelines for developing active electrocatalysts. Further modification of the frameworks is also powerful for tailoring the function of pore surfaces and the environment of inner spaces. Designable organic molecules can also be embedded inside inorganic- and organic-based frameworks. According to chemical composition (inorganic and organic), nanostructure (crystalline and amorphous) and additional modification (metal doping and organic design) of porous electrocatalysts, the current status of resultant OER performance is surveyed with some problems that should be solved for improving the OER activity. The remarkable progress in OER electrocatalysts is also introduced for demonstrating the bifunctional hydrogen evolution reaction (HER) and for utilizing seawater.

Modification of metals and ligands in two-dimensional conjugated metal-organic frameworks for CO2 electroreduction: A combined density functional theory and machine learning study

Electrochemical carbon dioxide reduction reaction (CO2RR) is a promising technology to establish an artificial carbon cycle. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) with high electrical conductivity have great potential as catalysts. Herein, we designed a range of 2D c-MOFs with different transition metal atoms and organic ligands, TMNxO4-x-HDQ (TM = Cr∼Cu, Mo, Ru∼Ag, W∼Au; x  = 0, 2, 4; HDQ = hexadipyrazinoquinoxaline), and systematically studied their catalytic performance using density functional theory (DFT). Calculation results indicated that all of TMNxO4-x-HDQ structures possess good thermodynamic and electrochemical stability. Notably, among the examined 37 MOFs, 6 catalysts outperformed the Cu(211) surface in terms of catalytic activity and product selectivity. Specifically, NiN4-HDQ emerged as an exceptional electrocatalyst for CO production in CO2RR, yielding a remarkable low limiting potential (UL) of -0.04 V. CuN4-HDQ, NiN2O2-HDQ, and PtN2O2-HDQ also exhibited high activity for HCOOH production, with UL values of -0.27, -0.29, and -0.27 V, respectively, while MnN4-HDQ, and NiO4-HDQ mainly produced CH4 with UL values of -0.58 and -0.24 V, respectively. Furthermore, these 6 catalysts efficiently suppressed the competitive hydrogen evolution reaction. Machine learning (ML) analysis revealed that the key intrinsic factors influencing CO2RR performance of these 2D c-MOFs include electron affinity (EA), electronegativity (χ), the first ionization energy (Ie), p-band center of the coordinated N/O atom (εp), the radius of metal atom (r), and d-band center (εd). Our findings may provide valuable insights for the exploration of highly active and selective CO2RR electrocatalysts.

Strong electronic interaction enhanced electrocatalysis of copper phthalocyanine decorated Co-MOF-74 toward highly efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) have been identified as promising electrocatalysts for the oxygen evolution reaction (OER). However, most of the reported MOFs have low electrical conductivity and poor stability, and therefore addressing these problems is crucial for achieving higher electrocatalytic performance. Meanwhile, direct observations of the electrocatalytic behavior, which is of great significance to the understanding of the electrocatalytic mechanism, remain highly challenging. Here, we report on a significant electrocatalytic performance enhancement of Co-MOF-74 for the OER after decoration by copper phthalocyanine (CuPc) molecules. Co-MOF-74@CuPc, synthesized by solvothermal reactions, displays a low overpotential of 293 mV and a robust long-term stability (70 h) at 10 mA cm-2. The enhancement has been attributed to strong electronic interaction between the π-conjugated CuPc molecule and Co-MOF-74, which promotes the electron transfer, increases the electrocatalytic active surface area and regulates the electronic structure during the OER process.

Two-Dimensional (2D) Conductive Metal-Organic Framework Thin Films: The Preparation and Applications in Electrochemistry

Two-dimensional conductive MOF thin films have attracted attention due to their rich pore structure and unique electrical properties, and their applications in many fields, including batteries, sensing, supercapacitors, electrocatalysis, etc. This paper discusses several preparation methods for 2D conductive MOF thin films. And the applications of 2D conductive MOF thin films are summarized. In addition, the current challenges in the preparation of 2D conductive MOF thin films and the great potential in practical applications are discussed.

Metal-Based Oxygen Reduction Electrocatalysts for Efficient Hydrogen Peroxide Production

Hydrogen peroxide (H2O2) is a high-value chemical widely used in electronics, textiles, paper bleaching, medical disinfection, and wastewater treatment. Traditional production methods, such as the anthraquinone oxidation process and direct synthesis, require high energy consumption, and involve risks from toxic substances and explosions. Researchers are now exploring photochemical, electrochemical, and photoelectrochemical synthesis methods to reduce energy use and pollution. This review focuses on the 2-electron oxygen reduction reaction (2e- ORR) for the electrochemical synthesis of H2O2, and discusses how catalyst active sites influence O2 adsorption. Strategies to enhance H2O2 selectivity by regulating these sites are presented. Catalysts require strong O2 adsorption to initiate reactions and weak *OOH adsorption to promote H2O2 formation. The review also covers advances in single-atom catalysts (SACs), multi-metal-based catalysts, and highlights non-noble metal oxides, especially perovskite oxides, for their versatile structures and potential in 2e- ORR. The potential of localized surface plasmon resonance (LSPR) effects to enhance catalyst performance is also discussed. In conclusion, emphasis is placed on optimizing catalyst structures through theoretical and experimental methods to achieve efficient and selective H2O2 production, aiming for sustainable and commercial applications.

Solid-State Electrochemical Carbon Dioxide Capture by Conductive Metal-Organic Framework Incorporating Nickel Bis(diimine) Units

This paper presents the first implementation of electrically conductive metal-organic framework (MOF) Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) integrated with nickel bis(diimine) (Ni-BDI) units for efficient solid-state electrochemical carbon dioxide (CO2) capture. The electrochemical cell assembled using Ni3(HITP)2 as working electrodes can reversibly capture and release CO2 through potential control. A high-capacity utilization of 96% and a Faraday efficiency of 98% have been achieved. The material also exhibits excellent electrochemical stability with its capacity maintained during 50 capture-release cycles and resistance to general interferences, including O2, H2O, NO2, and SO2. Capacity utilization of up to 35% is obtained at CO2 concentrations as low as 1%. The capture of CO2 at concentrations ranging from 1% to 100% requires exceptionally low energy consumption of only 30.5-72.4 kJ mol-1. Studies combining spectroscopic experiments and computational approaches reveal that the CO2 capture and release mechanism involves reversible carbamate formation on the N atom of the Ni-BDI unit in the MOF upon its one-electron redox reaction.

Alkali-Stable Metal-Organic Frameworks with Enhanced Electroconductivity for Black-Brown Electrochromic Energy Storage Smart Window

Metal-organic frameworks (MOFs) deliver potential applications in electrochromism and energy storage. However, the poor intrinsic conductivity of MOFs in electrolytes seriously hampers the development of the above-mentioned electrochemical applications, especially in one MOF electrode. Herein, a new Ni-based MOF (denoted Ni-DPNDI) is proposed with enhanced conductivity by π-delocalized DPNDI connectors. Predictably, the obtained Ni-DPNDI MOF achieves a conductivity of up to 4.63 S∙m-1 at 300 K. Profiting from its unique electronic structure, the Ni-DPNDI MOF delivers excellent electrochromic and energy storage performance with a great optical modulation (60.8%), a fast switching speed (tc = 7.9 s and tb = 6.4 s), a moderate specific capacitance (25.3 mAh·g-1) and good cycle stability over 2000 times. Meanwhile, energy storage capacity is visual by the coloration states of Ni-DPNDI film. As a proof of the potential application, a large-area (100 cm2) electrochromic energy storage smart window is further designed and displayed. The strategy provides an interesting alternative to porous multifunctional materials for the new generation of electronic devices with diverse applications.

Selective Reduction of Nitroarenes via Noncontact Hydrogenation

In traditional hydrogenation, where H2 and substrates with unsaturated bonds are activated on the same catalyst (contact mode), competitive hydrogenation of multiple reducible groups often occurs. We employ an unbiased H-cell for selective hydrogenation of the nitro group when multiple reducible groups are present. The setup spatially separates H2 and nitroarenes into two chambers connected by a proton-exchange membrane, thus adding barriers for a Langmuir-Hinshelwood-type mechanism that is common in thermocatalytic hydrogenation. Through a unique proton/electron transfer pathway that is specific to nitro functional group reduction to hydroxylamine, side reactions like C═C, C═O, and C≡C bond hydrogenation are fully avoided. Using Pd/C for H2 activation, and CNT for selective proton/electron transfer to -NO2 groups while being inert to C≡C, C═C, and C═O hydrogenation, the system effectively eliminates the competitive hydrogenation, achieving 100% nitro-group reduction selectivity in the hydrogenation of various nitroarenes, in sharp contrast to negligible selectivity over the same catalysts in a batch reactor under contact mode. This device enables selectivity control in hydrogenation reactions, moving beyond the traditional focus on catalyst active site engineering.

Synthesis and structure of a non-van-der-Waals two-dimensional coordination polymer with superconductivity

Two-dimensional conjugated coordination polymers exhibit remarkable charge transport properties, with copper-based benzenehexathiol (Cu-BHT) being a rare superconductor. However, the atomic structure of Cu-BHT has remained unresolved, hindering a deeper understanding of the superconductivity in such materials. Here, we show the synthesis of single crystals of Cu3BHT with high crystallinity, revealing a quasi-two-dimensional kagome structure with non-van der Waals interlayer Cu-S covalent bonds. These crystals exhibit intrinsic metallic behavior, with conductivity reaching 103 S/cm at 300 K and 104 S/cm at 2 K. Notably, superconductivity in Cu3BHT crystals is observed at 0.25 K, attributed to enhanced electron-electron interactions and electron-phonon coupling in the non-van der Waals structure. The discovery of this clear correlation between atomic-level crystal structure and electrical properties provides a crucial foundation for advancing superconductor coordination polymers, with potential to revolutionize future quantum devices.

Spontaneous-Spin-Polarized 2D π-d Conjugated Frameworks Towards Enhanced Oxygen Evolution Kinetics

Alternative strategies to design sustainable-element-based electrocatalysts enhancing oxygen evolution reaction (OER) kinetics are demanded to develop affordable yet high-performance water-electrolyzers for green hydrogen production. Here, it is demonstrated that the spontaneous-spin-polarized 2D π-d conjugated framework comprising abundant elements of nickel and iron with a ratio of Ni:Fe = 1:4 with benzenehexathiol linker (BHT) can improve OER kinetics by its unique electronic property. Among the bimetallic NiFex:y-BHTs with various ratios with Ni:Fe = x:y, the NiFe1:4-BHT exhibits the highest OER activity. The NiFe1:4-BHT shows a specific current density of 140 A g-1 at the overpotential of 350 mV. This performance is one of the best activities among state-of-the-art non-precious OER electrocatalysts and even comparable to that of the platinum-group-metals of RuO2 and IrO2. The density functional theory calculations uncover that introducing Ni into the homometallic Fe-BHT (e.g., Ni:Fe = 0:1) can emerge a spontaneous-spin-polarized state. Thus, this material can achieve improved OER kinetics with spin-polarization which previously required external magnetic fields. This work shows that a rational design of 2D π-d conjugated frameworks can be a powerful strategy to synthesize promising electrocatalysts with abundant elements for a wide spectrum of next-generation energy devices.

Impact of Organic Anions on Metal Hydroxide Oxygen Evolution Catalysts

Structural metamorphosis of metal-organic frameworks (MOFs) eliciting highly active metal-hydroxide catalysts has come to the fore lately, with much promise. However, the role of organic ligands leaching into electrolytes during alkaline hydrolysis remains unclear. Here, we elucidate the influence of organic carboxylate anions on a family of Ni or NiFe-based hydroxide type catalysts during the oxygen evolution reaction. After excluding interfering variables, i.e., electrolyte purity, Ohmic loss, and electrolyte pH, the experimental results indicate that adding organic anions to the electrolyte profoundly impacts the redox potential of the Ni species versus with only a negligible effect on the oxygen evolution activities. In-depth studies demonstrate plausible reasons behind those observations and allude to far-reaching implications in controlling electrocatalysis in MOFs, mainly where compositional modularity entails fine-tuning organic anions.

Venus Flytrap-Inspired Data-Center-Free Fast-Responsive Soft Robots Enabled by 2D Ni3(HITP)2 MOF and Graphite

The rapid and responsive capabilities of soft robots in perceiving, assessing, and reacting to environmental stimuli are highly valuable. However, many existing soft robots, designed to mimic humans and other higher animals, often rely on data centers for the modulation of mechanoelectrical transduction and electromechanical actuation. This reliance significantly increases system complexity and time delays. Herein, drawing inspiration from Venus flytraps, a soft robot employing a power modulation strategy is presented for active stimulus reaction, eliminating the need for a data center. This robot achieves mechanoelectrical transduction through Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) metal-organic framework (MOF) with an ultralow time delay (256 ns) and electromechanical actuation via graphite. The Joule heating effect in graphite is effectively modulated by Ni3(HITP)2 before and after the presence of pressure, thus enabling the stimulus reaction of soft robots. As demonstrated, three soft robots are created: low-level edge tongue robots, Venus flytrap robots, and high-level nerve-center-controlled dragonfly robots. This power modulation strategy inspires designs of edge soft robots and high-level robots with a human-like effective fusion of conditioned and unconditioned reflexes.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Functionalization and Structural Evolution of Conducting Quasi-One-Dimensional Chevrel-Type Telluride Nanocrystals

Interfacing organic molecular groups with well-defined inorganic lattices, especially in low dimensions, enables synthetic routes for the rational manipulation of both their local or extended lattice structures and physical properties. While appreciably studied in two-dimensional systems, the influence of surface organic substituents on many known and emergent one-dimensional (1D) and quasi-1D (q-1D) crystals has remained underexplored. Herein, we demonstrate the surface functionalization of bulk and nanoscale Chevrel-like q-1D ionic crystals using In2Mo6Te6, a predicted q-1D Dirac semimetal, as the model phase. Using a series of alkyl ammonium (-NR4+; R = H, methyl, ethyl, butyl, and octyl) substituents with varying chain lengths, we demonstrate the systematic expansion of the intrachain c-axis direction and the contraction of the interchain a/b-axis direction with longer chain substituents. Additionally, we demonstrate the systematic expansion of the intrachain c-axis direction and the contraction of the interchain a/b-axis direction as the alkyl chain substituents become longer using a combination of powder X-ray diffraction and Raman experiments. Beyond the structural modulation that the substituted groups can impose on the lattice, we also found that the substitution of ammonium-based groups on the surface of the nanocrystals resulted in selective suspension in aqueous (NH4+-functionalized) or organic solvents (NOc4+-functionalized), imparted fluorescent character (Rhodamine B-functionalized), and modulated the electrical conductivity of the nanocrystal ensemble. Altogether, our results underscore the potential of organic-inorganic interfacing strategies to tune the structural and physical properties of rediscovered Chevrel-type q-1D ionic solids and open opportunities for the development of surface-addressable building blocks for hybrid electronic and optoelectronic devices at the nanoscale.

A Conductive 3D Dual-Metal π-d Conjugated Metal-Organic Framework Fe3(HITP)2/bpm@Co for Highly Efficient Oxygen Evolution Reaction

Although 2D π-d conjugated metal-organic frameworks (MOFs) exhibit high in-plane conductivity, the closely stacked layers result in low specific surface area and difficulty in mass transfer and diffusion. Hence, a conductive 3D MOF Fe3(HITP)2/bpm@Co (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) is reported through inserting bpm (4,4'-bipyrimidine) ligands and Co2+ into the interlayers of 2D MOF Fe3(HITP)2. Compared to 2D Fe3(HITP)2 (37.23 m2 g-1), 3D Fe3(HITP)2/bpm@Co displays a huge improvement in the specific surface area (373.82 m2 g-1). Furthermore, the combined experimental and density functional theory (DFT) theoretical calculations demonstrate the metallic behavior of Fe3(HITP)2/bpm@Co, which will benefit to the electrocatalytic activity of it. Impressively, Fe3(HITP)2/bpm@Co exhibits prominent and stable oxygen evolution reaction (OER) performance (an overpotential of 299 mV vs RHE at a current density of 10 mA cm-2 and a Tafel slope of 37.14 mV dec-1), which is superior to 2D Fe3(HITP)2 and comparable to commercial IrO2. DFT theoretical calculation reveals that the combined action of the Fe and Co sites in Fe3(HITP)2/bpm@Co is responsible for the enhanced electrocatalytic activity. This work provides an alternative approach to develop conductive 3D MOFs as efficient electrocatalysts.

High-Performance Ni3(HHTP)2 Film-Based Flexible Field-Effect Transistor Gas Sensors

Conductive metal-organic frameworks (MOFs) have received increasing attention in recent years and present high application potential as sensing elements in electronic sensors. In this study, flexible field-effect transistor (FET) sensors based on conductive MOF, i.e., Ni3(HHTP)2, have been constructed. This Ni3(HHTP)2 sensor has high sensitivity (detection limit of 56 ppb) as well as superior selectivity for NO2 detection at room temperature, which is demonstrated by accurate gas detection in a mixed gas atmosphere. Moreover, by employing six flexible substrates, i.e., polyimide (PI), tape (PET), facemask, paper cup, tablecloth, and take-out bag (textile), we successfully demonstrate the universality of the flexible sensor construction with conductive MOF as sensing film on various substrates. This study of conductive MOF-based flexible electronic sensors offers a new opportunity for a wide range of sensing applications with wearable and portable electronic devices.

Controlling Film Formation and Host-Guest Interactions to Enhance the Thermoelectric Properties of Nickel-Nitrogen-Based 2D Conjugated Coordination Polymers

2D conjugated coordination polymers (cCPs) based on square-planar transition metal-complexes (such as MO4, M(NH)4, and MS4, M = metal) are an emerging class of (semi)conducting materials that are of great interest for applications in supercapacitors, catalysis, and thermoelectrics. Finding synthetic approaches to high-performance nickel-nitrogen (Ni-N) based cCP films is a long-standing challenge. Here, a general, dynamically controlled on-surface synthesis that produces highly conductive Ni-N-based cCP films is developed and the thermoelectric properties as a function of the molecular structure and their dependence on interactions with ambient atmosphere are studied. Among the four studied cCPs with different ligand sizes hexaminobenzene- and hexaaminotriphenylene-based films exhibit record electrical conductivity (100-200 S cm-1) in this Ni-N based cCP family, which is one order of magnitude higher than previous reports, and the highest thermoelectric power factors up to 10 µW m-1 K-2 among reported 2D cCPs. The transport physics of these films is studied and it is shown that depending on the host-guest interaction with oxygen/water the majority carrier type and the value of the Seebeck coefficient can be largely regulated. The high conductivity is likely reflecting good interconnectivity between (small) ordered domains and grain boundaries supporting disordered metallic transport.

Strategies to Improve Electrical Conductivity in Metal-Organic Frameworks: A Comparative Study

Metal-organic frameworks (MOFs), formed by the combination of both inorganic and organic components, have attracted special attention for their tunable porous structures, chemical and functional diversities, and enormous applications in gas storage, catalysis, sensing, etc. Recently, electronic applications of MOFs like electrocatalysis, supercapacitors, batteries, electrochemical sensing, etc., have become a major research topic in MOF chemistry. However, the low electrical conductivity of most MOFs represents a major handicap in the development of these emerging applications. To overcome these limitations, different strategies have been developed to enhance electrical conductivity of MOFs for their implementation in electronic devices. In this review, we outline all these strategies employed to increase the electronic conduction in both intrinsically (framework-modulated) and extrinsically (guests-modulated) conducting MOFs.

How the Support Defines Properties of 2D Metal-Organic Frameworks: Fe-TCNQ on Graphene versus Au(111)

The functionality of 2D metal-organic frameworks (MOFs) is crucially dependent on the local environment of the embedded metal atoms. These atomic-scale details are best ascertained on MOFs supported on well-defined surfaces, but the interaction with the support often changes the MOF properties. We elucidate the extent of this effect by comparing the Fe-TCNQ 2D MOF on two weakly interacting supports: graphene and Au(111). We show that the Fe-TCNQ on graphene is nonplanar with iron in quasi-tetrahedral sites, but on Au(111) it is planarized by stronger van der Waals interaction. The differences in physical and electronic structures result in distinct properties of the supported 2D MOFs. The dz2 center position is shifted by 1.4 eV between Fe sites on the two supports, and dramatic differences in chemical reactivity are experimentally identified using a TCNQ probe molecule. These results outline the limitations of common on-surface approaches using metal supports and show that the intrinsic MOF properties can be partially retained on graphene.

Engineering organic polymers as emerging sustainable materials for powerful electrocatalysts

Cost-effective and high-efficiency catalysts play a central role in various sustainable electrochemical energy conversion technologies that are being developed to generate clean energy while reducing carbon emissions, such as fuel cells, metal-air batteries, water electrolyzers, and carbon dioxide conversion. In this context, a recent climax in the exploitation of advanced earth-abundant catalysts has been witnessed for diverse electrochemical reactions involved in the above mentioned sustainable pathways. In particular, polymer catalysts have garnered considerable interest and achieved substantial progress very recently, mainly owing to their pyrolysis-free synthesis, highly tunable molecular composition and microarchitecture, readily adjustable electrical conductivity, and high stability. In this review, we present a timely and comprehensive overview of the latest advances in organic polymers as emerging materials for powerful electrocatalysts. First, we present the general principles for the design of polymer catalysts in terms of catalytic activity, electrical conductivity, mass transfer, and stability. Then, the state-of-the-art engineering strategies to tailor the polymer catalysts at both molecular (i.e., heteroatom and metal atom engineering) and macromolecular (i.e., chain, topology, and composition engineering) levels are introduced. Particular attention is paid to the insightful understanding of structure-performance correlations and electrocatalytic mechanisms. The fundamentals behind these critical electrochemical reactions, including the oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, oxygen evolution reaction, and hydrogen oxidation reaction, as well as breakthroughs in polymer catalysts, are outlined as well. Finally, we further discuss the current challenges and suggest new opportunities for the rational design of advanced polymer catalysts. By presenting the progress, engineering strategies, insightful understandings, challenges, and perspectives, we hope this review can provide valuable guidelines for the future development of polymer catalysts.

A Cu2(C6O6) metal-organic framework monolayer assembled on silicon carbide grown graphene exhibiting a metallic band structure

We report the self-assembly of a monolayer metal-organic framework of Cu-benzenehexol (BHO) on a graphene/SiC substrate assisted by in situ Cu-catalyzed deprotonation reactions. The density functional theory calculations reveal that the free-standing framework is a semiconductor with a band gap of 0.485 eV. Interestingly, upon adsorption on the substrate, the Fermi level is up-shifted to the conduction band of the free-standing framework due to the n-doped graphene on SiC, while the other band structure features are largely preserved. The metallic nature corroborates the scanning tunneling microscopy images acquired near the Fermi level. This work demonstrates that the graphene substrate, which interacts weakly with the framework, can be used to tune the Fermi level of the metal-organic framework.

Atomic-level design of metalloenzyme-like active pockets in metal-organic frameworks for bioinspired catalysis

Natural metalloenzymes with astonishing reaction activity and specificity underpin essential life transformations. Nevertheless, enzymes only operate under mild conditions to keep sophisticated structures active, limiting their potential applications. Artificial metalloenzymes that recapitulate the catalytic activity of enzymes can not only circumvent the enzymatic fragility but also bring versatile functions into practice. Among them, metal-organic frameworks (MOFs) featuring diverse and site-isolated metal sites and supramolecular structures have emerged as promising candidates for metalloenzymes to move toward unparalleled properties and behaviour of enzymes. In this review, we systematically summarize the significant advances in MOF-based metalloenzyme mimics with a special emphasis on active pocket engineering at the atomic level, including primary catalytic sites and secondary coordination spheres. Then, the deep understanding of catalytic mechanisms and their advanced applications are discussed. Finally, a perspective on this emerging frontier research is provided to advance bioinspired catalysis.

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.

Review of Carbon Support Coordination Environments for Single Metal Atom Electrocatalysts (SACS)

This topical review focuses on the distinct role of carbon support coordination environment of single-atom catalysts (SACs) for electrocatalysis. The article begins with an overview of atomic coordination configurations in SACs, including a discussion of the advanced characterization techniques and simulation used for understanding the active sites. A summary of key electrocatalysis applications is then provided. These processes are oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR). The review then shifts to modulation of the metal atom-carbon coordination environments, focusing on nitrogen and other non-metal coordination through modulation at the first coordination shell and modulation in the second and higher coordination shells. Representative case studies are provided, starting with the classic four-nitrogen-coordinated single metal atom (MN4 ) based SACs. Bimetallic coordination models including homo-paired and hetero-paired active sites are also discussed, being categorized as emerging approaches. The theme of the discussions is the correlation between synthesis methods for selective doping, the carbon structure-electron configuration changes associated with the doping, the analytical techniques used to ascertain these changes, and the resultant electrocatalysis performance. Critical unanswered questions as well as promising underexplored research directions are identified.

Conductive Metal-Organic Framework Nanosheets Constructed Hierarchical Water Transport Biological Channel for High-Performance Interfacial Seawater Evaporation

Solar interfacial water evaporation shows great potential to address the global freshwater scarcity. Water evaporation being inherently energy intensive, Joule-heating assisted solar evaporation for addressing insufficient vapor under natural conditions is an ideal strategy. However, the simultaneous optimization of low evaporation enthalpy, high photothermal conversion, and excellent Joule-heating steam generation within a single material remain a rare achievement. Herein, inspired by the biological channel structures, a large-area film with hierarchical macro/microporous structures is elaborately designed by stacking the nanosheet of a conductive metal-organic framework (MOF), Ni3 (HITP)2 , on a paper substrate. By combining the above three features in one material, the water evaporation enthalpy reduces from 2455 J g-1 to 1676 J g-1 , and the photothermal conversion efficiency increases from 13.75% to 96.25%. Benefiting from the synergistic photothermal and Joule-heating effects, the evaporation rate achieves 2.60 kg m-2 h-1 under one sun plus input electrical power of 4 W, surpassing the thermodynamic limit and marking the highest reported value in MOF-based evaporators. Moreover, Ni3 (HITP)2 -paper exhibits excellent long-term stability in simulated seawater, where no salt crystallization and evaporation rate degradation are observed. This design strategy for nanosheet films with hierarchical macro/microporous channels provides inspiration for electronics, biological devices, and energy applications.

Dominant Role of Hole Transport Pathway in Achieving Record High Photoconductivity in Two-Dimensional Metal-Organic Frameworks

Metal-organic frameworks (MOFs) with mobile charges have attracted significant attention due to their potential applications in photoelectric devices, chemical resistance sensors, and catalysis. However, fundamental understanding of the charge transport pathway within the framework and the key properties that determine the performance of conductive MOFs in photoelectric devices remain underexplored. Herein, we report the mechanisms of photoinduced charge transport and electron dynamics in the conductive 2D M-HHTP (M=Cu, Zn or Cu/Zn mixed; HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) MOFs and their correlation with photoconductivity using the combination of time-resolved terahertz spectroscopy, optical transient absorption spectroscopy, X-ray transient absorption spectroscopy, and density functional theory (DFT) calculations. We identify the through-space hole transport mechanism through the interlayer sheet π-π interaction, where photoinduced hole state resides in HHTP ligand and electronic state is localized at the metal center. Moreover, the photoconductivity of the Cu-HHTP MOF is found to be 65.5 S m-1 , which represents the record high photoconductivity for porous MOF materials based on catecholate ligands.

High-Performance Electrochemical Actuator under an Ultralow Driving Voltage with a Mixed Electronic-Ionic Conductive Metal-Organic Framework

Although versatile deformation, high flexibility, and environmental friendliness of electrochemical actuators (EAs) have made them promising in bioinspired soft robots and biomedical devices, the relatively high driving voltages unfortunately impose great restrictions on their applications in low-energy and human-friendly electronics. Here, we find that the uses of a mixed electronic-ionic conductive metal-organic framework (c-MOF), i.e., Ni3(hexaiminotriphenylene)2 (Ni3(HITP)2), largely lower the driving voltage of EAs. The as-fabricated EA can work under a driving voltage as low as 0.1 V, representing the lowest value among those for the c-MOF-based EAs reported so far. The Ni3(HITP)2-based EA shows an excellent actuation performance such as a high bending strain difference of 0.48% (±0.5 V, 0.1 Hz) and long-term durability of >99% after 15,000 cycles due to the improved conductivity up to 1000 S·cm-1 and double-layer capacitance as high as 176.3 F·g-1 stemming from the mixed electronic-ionic conduction of Ni3(HITP)2.

New Insights on Designing the Next-Generation Materials for Electrochemical Synthesis of Reactive Oxidative Species Towards Efficient and Scalable Water Treatment: A Review and Perspectives

Electrochemical water remediation technologies offer several advantages and flexibility for water treatment and degradation of contaminants. These technologies generate reactive oxidative species (ROS) that degrade pollutants. For the implementation of these technologies at an industrial scale, efficient, scalable, and cost-effective in-situ ROS synthesis is necessary to degrade complex pollutant mixtures, treat large amount of contaminated water, and clean water in a reasonable amount of time and cost. These targets are directly dependent on the materials used to generate the ROS, such as electrodes and catalysts. Here, we review the key design aspects of electrocatalytic materials for efficient in-situ ROS generation. We present a mechanistic understanding of ROS generation, including their reaction pathways, and integrate this with the key design considerations of the materials and the overall electrochemical reactor/cell. This involves tunning the interfacial interactions between the electrolyte and electrode which can enhance the ROS generation rate up to ~ 40% as discussed in this review. We also summarized the current and emerging materials for water remediation cells and created a structured dataset of about 500 electrodes and 130 catalysts used for ROS generation and water treatment. A perspective on accelerating the discovery and designing of the next generation electrocatalytic materials is discussed through the application of integrated experimental and computational workflows. Overall, this article provides a comprehensive review and perspectives on designing and discovering materials for ROS synthesis, which are critical not only for successful implementation of electrochemical water remediation technologies but also for other electrochemical applications.

Air/liquid interfacial formation process of conductive metal-organic framework nanosheets

The air/liquid interface is a superior platform to create nanosheets of materials by promoting spontaneous two-dimensional growth of components. Metal-organic frameworks (MOFs)-intrinsically porous crystals-with π-conjugated triphenylene-based ligands show high electrical conductivities. Forming nanosheets of such conductive MOFs should enable their use in electronic devices. Although highly conductive MOF nanosheets have been created at the air/liquid interface, direct control of their continuity, morphology, thickness, crystallinity, and orientation directly influencing device performance remains as an issue to be addressed. Here, we present detailed insights into the formation process of electrically conductive MOF nanosheets composed of 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and Ni2+ ions (HITP-Ni-NS) at the air/liquid interface. The morphological and structural features of HITP-Ni-NS strongly depend on the standing time-the time without any external actions involved, but leaving the interface undisturbed after setting the ligand solution onto the metal-ion solution. We find that the fundamental features of HITP-Ni-NS are determined by the standing time with conductivity sensitively influenced by such pre-determined HITP-Ni-NS characteristics. These findings will lead towards the establishment of a rational strategy for creating MOF nanosheets at the air/liquid interface with desired properties, thereby accelerating their use in diverse potential applications.

Electrosynthesis of Hydrogen Peroxide Enabled by Exceptional Molecular Ni Sites in a Graphene-Supported Nickel Organic Framework

Electrosynthesis of hydrogen peroxide (H2O2) from 2e- transfer of the oxygen reduction reaction (2e--ORR) is a potential alternative to the traditional anthraquinone process. Two-dimensional (2D) metal-organic frameworks (MOFs) supported by carbon are frequently reported as promising 2e--ORR catalysts. Herein, a graphene-supported 2D MOF of Ni3(2,3,6,7,10,11-hexahydrotriphenylene)2 is synthesized through a common hydrothermal method, which exhibits high 2e--ORR performance. It is discovered that except for emerging MOFs, exceptional molecularly dispersed Ni sites coexist in the synthesis that have the same coordination sphere of the NiO4C4 moiety as the MOF. The molecular Ni sites are more catalytically active. The graphene support contains a suitable amount of residual oxygen groups, leading to the generation of those molecularly dispersed Ni sites. The oxygen groups exhibit a moderate electron-withdrawing effect at the outer sphere of Ni sites to slightly increase their oxidation state. This interaction decreases overpotentials and kinetically improves the selectivity of the 2e- reaction pathway.

Coordination polymers: a promising candidate for photo-responsive electronic device application

The design and synthesis of electrically conductive coordination polymers (CPs) are of special interest due to their applications in the fabrication of many environmentally benign emerging technologies, such as molecular wires, photovoltaic cells, light emitting diodes (LEDs), field effect transistors (FETs) and Schottky barrier diodes (SBDs). Owing to their structural flexibility, easy functionality and adjustable energy levels, CPs are promising candidates for providing a better pathway for superior charge transport. Again, the utilization of visible light as an external stimulus to control and manoeuvre the electrical properties of the CPs is exceptionally motivating for the development of many optoelectronic devices, such as photodetectors, photo-switches, photodiodes and chemiresistive sensors. The applications of such materials in devices will solve questions regarding the energy crisis and environmental concerns. This study provides an overview of the recent advances in the development of photo-responsive CPs and the possibility of their application in developing optoelectronic devices. In this regard, a thorough literature survey was performed and the studies related to the fabrication of photosensitive conducting CPs for applications in optoelectronic devices are listed.

From a Collapse-Prone, Insulating Ni-MOF-74 Analogue to Crystalline, Porous, and Electrically Conducting PEDOT@MOF Composites

Electrically conductive porous metal-organic frameworks (MOFs) show great promise in helping advance electronics and clean energy technologies. However, large porosity usually hinders long-range charge transport, an essential criterion of electrical conductivity, underscoring the need for new strategies to combine these two opposing features and realize their diverse potentials. All previous strategies to boost the conductivity of porous MOFs by introducing redox-complementary guest molecules, conducting polymers, and metal nanoparticles have led to a significant loss of frameworks' porosity and surface areas, which could be otherwise exploited to capture additional guests in electrocatalysis and chemiresistive sensing applications. Herein, we demonstrate for the first time that the in situ oxidative polymerization of preloaded 3,4-ethylenedioxythiophene (EDOT) monomers into the polyethylenedioxythiophene (PEDOT) polymer inside the hexagonal cavities of an intrinsically insulating Ni2(NDISA) MOF-74 analogue (NDISA = naphthalenediimide N,N-disalicylate), which easily collapses and becomes amorphous upon drying, simultaneously enhanced the crystallinity, porosity, and electrical conductivity of the resulting PEDOT@Ni2(NDISA) composites. At lower PEDOT loading (∼22 wt %), not only did the Brunauer-Emmett-Teller surface area of the PEDOT@Ni2(NDISA) composite (926 m2/g) more than double from that of evacuated pristine Ni2(NDISA) (387 m2/g), but also its electrical conductivity (1.1 × 10-5 S/cm) soared 105 times from that of the pristine MOF, demonstrating unprecedented dual benefits of our strategy. At higher PEDOT loading (≥33 wt %), the electrical conductivity of Ni2(NDISA)⊃PEDOT composites further increased modestly (10-4 S/cm), but their porosity dropped precipitously as large amounts of PEDOT filled up the hexagonal MOF channels. Thus, our work presents a simple new strategy to simultaneously boost the structural stability, porosity, and electrical conductivity of intrinsically insulating and collapse-prone MOFs by introducing small amounts of conducting polymers that can not only reinforce the MOF scaffolds and prevent them from collapsing but also help create a much coveted non-native property by providing charge carriers and charge transport pathways.

Electrocatalytic Microdevice Array Based on Wafer-Scale Conductive Metal-Organic Framework Thin Film for Massive Hydrogen Production

The synthesis of large-scale 2D conductive metal-organic framework films with tunable thickness is highly desirable but challenging. In this study, an Interface Confinement Self-Assembly Pulling (ICSP) method for in situ synthesis of 4-in. Ni-BHT film on the substrate surface is developed. By modulating the thickness of the confined space, the thickness of Ni-BHT films could be easily varied from 4 to 42 nm. To eliminate interference factors and evaluate the effect of film thickness on the catalytic performance of HER, an electrocatalytic microdevice based on the Ni-BHT film is designed. The effective catalytic thickness of the Ni-BHT film is found to be around 32 nm. Finally, to prepare the electrocatalytic microdevice array, over 100 000 microdevices on a 4-in. Ni-BHT film are integrated. The results show that the microdevice array has good stability and a high hydrogen production rate and could be used to produce large amounts of hydrogen. The wafer-scale 2D conductive metal-organic framework's fabrication greatly advances the practical application of microdevices for massive hydrogen production.

Terrace-Like 2D Hierarchically Porous Iron/Cobalt Metal-Organic Framework: Ambient Fast Synthesis and Efficient Oxygen Evolution Reaction Application

It is urgent to design a low-cost electrocatalyst with high activity to enhance the efficiency of oxygen evolution reaction (OER), which is limited by the slow four-electron transfer kinetics process. Nevertheless, traditional synthetic methods, including calcination and solvothermal, of the electrocatalysts are high-cost, low-yield, and energy-hogging, which limits their industrial application. Herein, an ambient fast synthetic method is developed to prepare terrace-like Fe/Co bimetal-organic framework (TFC-MOF) electrocatalyst materials in gram scale in 1 h. The method in this paper is designable based on coordination chemistry. Fe and Co ions can coordinate with the carboxyl groups on benzene-1,3,5-tricarboxylic acid (H3 BTC) to form a 2D-MOF structure. Structural characterizations, including SEM, TEM, and XRD are conducted to verify that the TFC-MOF is a terrace-like layered structure with uniform-sized mesoporous, which reduces the adsorption steric hindrance and facilitates the mass and electron transfer efficiency of OER. The TFC-MOF shows low overpotential, 255 mV at a current density of 10 mA cm-2 , and a low Tafel slope of 49.9 mV dec-1 , in an alkaline solution. This work provides a planar coordination strategy to synthesize 2D-MOF OER electrocatalyst on a large scale with low cost and low energy consumption, which will promote its practical OER applications.

Computational Prediction of Stacking Mode in Conductive Two-Dimensional Metal-Organic Frameworks: An Exploration of Chemical and Electrical Property Changes

Conductive two-dimensional metal-organic frameworks (2D MOFs) have attracted interest as they induce strong charge delocalization and improve charge carrier mobility and concentration. However, characterizing their stacking mode depends on expensive and time-consuming experimental measurements. Here, we construct a potential energy surface (PES) map database for 36 2D MOFs using density functional theory (DFT) for the experimentally synthesized and non-synthesized 2D MOFs to predict their stacking mode. The DFT PES results successfully predict the experimentally synthesized stacking mode with an accuracy of 92.9% and explain the coexistence mechanism of dual stacking modes in a single compound. Furthermore, we analyze the chemical (i.e., host-guest interaction) and electrical (i.e., electronic structure) property changes affected by stacking mode. The DFT results show that the host-guest interaction can be enhanced by the transition from AA to AB stacking, taking H2S gas as a case study. The electronic band structure calculation confirms that as AB stacking displacement increases, the in-plane charge transport pathway is reduced while the out-of-plane charge transport pathway is maintained or even increased. These results indicate that there is a trade-off between chemical and electrical properties in accordance with the stacking mode.

Conductive Lanthanide Metal-Organic Frameworks with Exceptionally High Stability

Electrically conductive metal-organic frameworks (MOFs) have been extensively studied for their potential uses in energy-related technologies and sensors. However, achieving that goal requires MOFs to be highly stable and maintain their conductivity under practical operating conditions with varying solution environments and temperatures. Herein, we have designed and synthesized a new series of {[Ln4(μ4-O)(μ3-OH)3(INA)3(GA)3](CF3SO3)(H2O)6}n (denoted as Ln4-MOFs, Ln = Gd, Tm, and Lu, INA = isonicotinic acid, GA = glycolic acid) single crystals, where electrons are found to transport along the π-π stacked aromatic carbon rings in the crystals. The Ln4-MOFs show remarkable stability, with minimal changes in conductivity under varying solution pH (1-12), temperature (373 K), and electric field as high as 800 000 V/m. This stability is achieved through the formation of strong coordination bonds between high-valent Ln(III) ions and rigid carboxylic linkers as well as hydrogen bonds that enhance the robustness of the electron transport path. The demonstrated lanthanide MOFs pave the way for the design of stable and conductive MOFs.

Unveiling the Hidden Energy Profiles of the Oxygen Evolution Reaction via Machine Learning Analyses

The oxygen evolution reaction (OER) is a crucial electrochemical process for hydrogen production in water electrolysis. However, due to the involvement of multiple proton-coupled electron transfer steps, it is challenging to identify the specific elementary reaction that limits the rate of the OER. Here we employed a machine-learning-based approach to extract the reaction pathway exhaustively from experimental data. Genetic algorithms were applied to search for thermodynamic and kinetic parameters using the current-electrochemical potential relationship of the OER. Interestingly, analysis of the datasets revealed the energy state distributions of reaction intermediates, which likely originated in the interactions among intermediates or the distribution of multiple sites. Through our exhaustive analyses, we successfully uncovered the hidden energy profiles of the OER. This approach can reveal the reaction pathway to activate for efficient hydrogen production, which facilitates the design of catalysts.