ABSTRACT From concept to realization, the integration of porous redox‐active metal–organic frameworks (MOFs) into asymmetric electrochemical capacitors for the assembly of electrochemical capacitor‐diodes (CAPodes) is reported. CAPodes are innovative electrochemical capacitor analogues of diodes, designed for unidirectional charge storage and logic gate applications. The novel devices deliberately utilize two distinct electroactive metal–organic frameworks with characteristic redox potentials acting as positively or negatively polarizable electrode materials, respectively. The first proof‐of‐concept devices presented here make use of the Chichibabin‐like diradicaloid formation upon oxidation of the N,N,N',N' ‐benzidinetetrabenzoate linker in DUT‐65/66 and N,N,N',N' ‐(1,4‐phenylenebis‐(azanetriyl))‐tetrabenzoate in DUT‐232/233 at high oxidation potentials as a positively polarizable electrode material paired with the highly reversible two‐step reduction in Zn(ndi) (ndi 2 − = 1,4‐bis[(3,5‐dimethyl)‐pyrazolate‐4‐yl]naphthalene‐diimide). The novel porous MOF‐CAPode achieves a remarkable figure of merit with rectification ratios (RR) up to RR I = 23 and RR II = 94% at 10 mV s −1 . The new MOF‐based CAPodes operate efficiently in “AND” and “OR” logic gates, demonstrating logic operation under varying input voltages up to 3.0 V and frequencies of up to 40 mHz.

This study describes a novel experimental apparatus for monitoring electrochemical reactions by in situ NMR spectroscopy. A unique cylindrical 3D-printed electrochemical cell, incorporating a reference electrode, was developed to enable electrochemical measurements through exact potential control. The performance of the novel cell is demonstrated by monitoring ethanol electrooxidation, an important process in fuel cell technology. Ethanol electrooxidation reaction utilizing the UiO-66/Pt/Vulcan XC 72R catalyst was monitored for more than 70 h, providing significant insights into catalyst efficiency, deterioration, and reactivation. This novel methodology fosters the potential of in situ electrochemical investigations, thus widening the applicability in electrocatalysis research.

Herein, we report a novel and green synthetic approach for pyrazolate-based metal-organic frameworks (MOFs) as demonstrated by the three prominent examples of this material class: [Ni(bdp)]n and two supramolecular isomers [Zn(bdp)]n and BUT-58 (H2bdp = 1,4-bis(1H-pyrazol-4-yl)benzene). The replacement of dimethylformamide (DMF) with a dynamic solvent system (DSS) - a reactive mixture of 1-butanol and acetic acid - in the synthesis allows us to avoid toxic chemicals, as well as precisely control the crystal size and morphology of the products. Unlike DMF, which decomposes into lower-value byproducts during synthesis, DSS produces a value-added ester (butyl acetate). Furthermore, a sustainable washing procedure fully eliminates the need for DMF, while ensuring a high-porosity product. Improved material crystallinity leads to a more pronounced breathing behavior during nitrogen physisorption. Moreover, flexibility modulation through crystal size engineering becomes within reach. Due to the accessibility to highly crystalline materials, single-crystal X-ray diffraction on the pristine crystals could be performed to elucidate the preferred adsorption sites in the studied frameworks.

Herein we report a novel and green synthetic approach for pyrazolate-based metal-organic frameworks (MOFs) as demonstrated by the three prominent examples of this material class: [Ni(bdp)]n, and two supramolecular isomers [Zn(bdp)]n and BUT-58 (H2bdp = 1,4-bis(1H- pyrazol-4-yl)benzene). Replacement of dimethylformamide (DMF) by a reactive mixture of 1-butanol and acetic acid enables to avoid toxic chemicals, as well as precise control over the crystal sizes and shapes of the products. Improved crystallinity consequently leads to a more pronounced breathing behavior during nitrogen physisorption. Moreover, flexibility modulation through crystal size engineering becomes within reach. Due to the accessibility to highly crystalline materials, single-crystal X-ray diffraction on the pristine crystals could be performed to elucidate the preferred adsorption sites in the studied frameworks.

The valorisation of glycerol using renewable electricity is recognised as an effective and attractive approach for producing high-value compounds from biomass byproducts. 2D conjugated metal–organic frameworks (2D c-MOFs) have emerged as promising electrocatalysts due to their tunable structures, high electronic conductivity, and efficient utilisation of well-defined active centres. In this study, we report the first systematic investigation of 2D c-MOFs containing Ni-X 4 (X = O or N) moieties for the glycerol oxidation reaction (GOR), examining key factors influencing both electrocatalytic activity and selectivity. In situ 13 C electrochemical nuclear magnetic resonance and Raman spectroscopies provide insights into the GOR mechanism and confirm that Ni–O 4 sites are the primary active centres. Theoretical calculations further reveal that [Ni 3 (HHTQ) 2 ] n (HHTQ = 2,3,7,8,12,13-hexahydroxytricycloquinazoline) exhibits superior GOR activity due to strong adsorption of reaction intermediates and weak interlayer interactions. This work highlights the potential of 2D c-MOFs as highly efficient GOR catalysts, paving the way for the rational design of advanced electrocatalysts and contributing to the development of sustainable energy conversion and storage technologies.

For the first time a printable, miniaturized and gate-controlled electrochemical capacitor-diode (G-CAPode) is presented. The heart of the device consists of a recently developed asymmetric electrical double-layer capacitor system based on selective, size-depended ion adsorption. Due to the introduction of a sieving carbon with ultramicroporous pores (d = 0.69 nm) as one electrode material an effective blocking of ions with sizes below the pore size of the carbon can be achieved, leading to a unidirectional charging comparable to a diode (CAPode). This “working capacitor” (W-Cap) was further expanded by introducing a third (“gate”) electrode enabling a control of current and voltage output of the W-Cap depending on the applied gate bias between gate electrode and counter electrode of the W-Cap resembling transistor features. By varying the gate bias voltage, the potentials and therefore the working window of the W-Cap electrodes are shifted to more positive or negative potentials, leading to an increase or decrease of the G-CAPode capacitance. The printed G-CAPode was tested as switchable device analogous to an I-MOS varactor for the adjustable filtering of AC signals in a high-pass filter and band-pass filter application. This investigation opens the possibility to couple capacitive (energy storage), diodic (current rectification) and transistor (voltage-controlled switching) characteristics in one device and also addresses its process integration via 3D printing.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7 nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor.

A commercial catalyst (Pt/Vulcan XC 72R) was transformed into a selective electrocatalyst for alcohol oxidation by functionalization of Pt particles with membrane-like metal-organic framework (MOF) coatings of UiO-66 and UiO-66-NO2 materials. The electrochemical performance of the MOF-coated electrocatalysts was evaluated using cyclic voltammetric studies in alkaline electrolyte for various alcohols (methanol, ethanol, n-propanol, and n-butanol). The coating modulates the catalytic selectivity, depending on the surface polarity of the MOF material favoring the oxidation of more hydrophilic or more hydrophobic molecules. The adsorption state of alcohols in MOFs was investigated at the molecular level by solid-state NMR experiments. C-13 MAS NMR spectroscopy was applied to UiO-66 and UiO-66-NO2 loaded with aqueous solutions of isotope-enriched alcohols. To quantitatively detect C-13 MAS NMR spectra, single pulse (SP) excitation was used. Cross-polarization was applied to investigate the CP buildup behavior of alcohols in MOFs at different contact times in order to characterize the adsorption state, i.e., the mobility of alcohols in the pores. H-1-C-13 HETCOR spectra were measured to further characterize the adsorption complexes of alcohols in UiO-66. The experiments demonstrated that the electrocatalytic selectivity originates from the differences in the adsorption strength of primary alcohols in the pores of the MOFs.

The high degree of corrosivity and reactivity of bromine, which is released from various sources, poses a serious threat to the environment. Moreover, its coexistence with iodine forming an equilibrium compound, iodine monobromide (IBr) necessitates the selective capture of bromine from halogen mixtures. The electrophilicity of halogens to π-electron rich structures enabled us to strategically design a covalent organic framework for halogen capture, featuring a defined pore environment with localized sorption sites. The higher capture capacity of bromine (4.6 g g-1) over iodine by ~41 % shows its potential in selective capture. Spectroscopic results uncovering the preferential interaction sites are supported by theoretical investigations. The alkyne bridge is a core functionality promoting the selectivity in capture by synergistic physisorption, rationalized by the higher orbital overlap of bromine due to its smaller atomic size as well as reversible chemical interactions. The slip stacking in the structure has further promoted this phenomenon by creating clusters of molecular interaction sites with bromine intercalated between the layers. The inclusion of unsaturated moieties, i.e. triple bonds and the complementary pore geometry offer a promising design strategy for the construction of porous materials for halogen capture.

Die hohe Korrosivität und Reaktivität von Brom, welches aus verschiedenen Quellen freigesetzt wird, stellt eine ernsthafte Gefahr für die Umwelt dar. Darüber hinaus erfordert seine Koexistenz mit Iod und die daraus resultierende Gleichgewichtsverbindung Iodmonobromid (IBr) die selektive Abtrennung von Brom aus Halogengemischen. Die Elektrophilie von Halogenen gegenüber π‐elektronenreichen Strukturen ermöglichte uns die strategische Entwicklung einer kovalent organischen Gerüstverbindung für die Halogenaufnahme, die eine definierte Porenumgebung mit lokalisierten Sorptionsstellen aufweist. Die um ~41 % höhere Aufnahmekapazität von Brom (4,6 g g −1 ) gegenüber Iod zeigt das Potenzial für die selektive Aufnahme. Die spektroskopischen Ergebnisse, welche die bevorzugten Wechselwirkungsstellen aufzeigen, werden durch theoretische Untersuchungen gestützt. Die Alkin‐Brücke ist eine Kernfunktionalität, die die Selektivität bei der Aufnahme durch synergistische Physisorption fördert, was durch die höhere Orbitalüberlappung von Brom aufgrund seiner geringeren atomaren Größe, sowie durch reversible chemische Wechselwirkungen begründet ist. Das sogenannte „slip stacking“ in der Struktur hat dieses Phänomen weiter gefördert, indem Cluster molekularer Interaktionsstellen mit zwischen den Schichten eingelagertem Brom geschaffen wurden. Die Einführung ungesättigter Einheiten, d. h. Dreifachbindungen, und die komplementäre Porengeometrie bieten eine vielversprechende Designstrategie für die Konstruktion poröser Materialien für die Halogenaufnahme.

The development of tailor-made electrochromic (EC) materials requires a large variety of available substances with properties that precisely match the task. Since the inception of electrochromic metal-organic frameworks (MOFs), the field relies only on a limited set of building blocks, providing the desired electrochromic effect. Herein, we demonstrate for the first time the implementation of a Piccard-type system (N,N,N',N'-benzidinetetrabenzoate) into Zr-MOFs to obtain electrochromic materials. With fast switching rates, high contrast ratio, long-life stability, and exceptional chemical and physical stability, the novel material is on par with inorganic EC material. The new EC system exhibits an ultrahigh contrast from the bleaching state, with transmittance in the visible region >53%, to the colored state with a transmittance of ca. 3%. The 5 μm thick film attained up to 90% of the coloring in 12.5 s and exhibited high electrochemical reversibility. Moreover, the conformational lability of the electrochromic ligand chosen is locked via the topology design of the framework, which is not attainable in the solution. Locked conformations of the redox active linker in distinct polymorphous frameworks (DUT-65 and DUT-66) feature different redox characteristics and opens the door to the overarching control of the oxidation pathway in the Piccard-type systems.

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing Li-storage mechanism, which can be considered as a lithium-organosulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox-mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organosulfide interactions. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery.

Recent developments in the field of covalent organic frameworks (COFs) describe the issue of processability. The precise tunability of delamination of such structures to obtain few layered nanosheets by synthetic control has been ventured in this study. Covalent anchoring of a series of linear and branched alkoxy side chains to the backbone of layered covalent organic frameworks was used to achieve this. To support the hypothesis, powder X-ray diffraction studies accompanied by computational modeling revealed that the elongation of side chains increases the interlayer distances of the COFs. This led to a successful study of the solvent-assisted exfoliation by atomic force microscopy techniques to obtain nanosheets with heights less than 2 nm, representing stacks of 4-5 layers. Dispersions of the functionalized COF nanosheets are stable for several hours. Furthermore, the surface properties are drastically changed, rendering the materials hydrophobic, with contact angles reaching up to 142 degrees and complete blockage of the pore space toward water vapor. As a proof of concept, the sheets are processable and could be integrated into separators for lithium-ion batteries.

The rational design and preparation of conductive metal-organic frameworks (MOFs) are alluring and challenging pathways to develop active catalysts toward electrocatalytic glucose oxidation. The hybridization of conductive MOFs with carbon nanotubes (CNTs) in the form of a composite can greatly improve the electrocatalytic performance. Herein, a facile one-step synthetic strategy is utilized to fabricate a Ni3(HHTP)2/CNT (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) composite for nonenzymatic detection of glucose in an alkaline solution. The Ni3(HHTP)2/CNT composite, as an electrochemical glucose sensor material, exhibits superior electrocatalytic activity toward glucose oxidation with a wide detection range of up to 3.9 mM, a low detection limit of 4.1 μM (signal/noise = 3), a fast amperometric response time of <2 s, and a high sensitivity of 4774 μA mM-1 cm-2, surpassing the performance of some recently reported nonenzymatic transition-metal-based glucose sensors. In addition, the composite sensor also shows outstanding selectivity, robust long-term electrochemical stability, favorable anti-interference properties, and good reproducibility. This work displays the effectiveness of enhancing the electrocatalytic performance toward glucose detection by combing conductive MOFs with CNTs, thereby opening up an applicable and encouraging approach for the design of advanced nonenzymatic glucose sensors.

Several metal-organic frameworks (MOFs) excel in harvesting water from the air or as heat pumps as they show a steep increase in water uptake at 10-30 % relative humidity (RH%). A precise understanding of which structural characteristics govern such behavior is lacking. Herein, CAU-10-H and CAU-10-CH3 are studied with H, CH3 corresponding to the functions grafted to the organic linker. CAU-10-H shows a steep water uptake ≈18 RH% of interest for water harvesting, yet the subtle replacement of H by CH3 in the organic linker drastically changes the water adsorption behavior to less steep water uptake at much higher humidity values. The materials' structural deformation and water ordering during adsorption with in situ sum-frequency generation, in situ X-ray diffraction, and molecular simulations are unraveled. In CAU-10-H, an energetically favorable water cluster is formed in the hydrophobic pore, tethered via H-bonds to the framework μOH groups, while for CAU-10-CH3, such a favorable cluster cannot form. By relating the findings to the features of water adsorption isotherms of a series of MOFs, it is concluded that favorable water adsorption occurs when sites of intermediate hydrophilicity are present in a hydrophobic structure, and the formation of energetically favorable water clusters is possible.

Redox‐active covalent organic frameworks (COFs) store charges but possess inadequate electronic conductivity. Their capacitive action works by storing H+ ions in an acidic electrolyte and is typically confined to a small voltage window (0–1 V). Increasing this window means higher energy and power density, but this risks COF stability. Advantageously, COF's large pores allow the storage of polarizable bulky ions under a wider voltage thus reaching higher energy density. Here, a COF–electrode–electrolyte system operating at a high voltage regime without any conducting carbon or redox active oxides is presented. Conducting polypyrrole (Ppy) chains are synthesized within a polyimide COF to gain electronic conductivity (≈10 000‐fold). A carbon‐free quasi‐solid‐state capacitor assembled using this composite showcases high pseudo‐capacitance (358 mF cm−2@1 mA cm−2) in an aqueous gel electrolyte. The synergy among the redox‐active polyimide COF, polypyrrole and organic electrolytes allows a wide‐voltage window (0–2.5 V) leading to high energy (145 μWh cm−2) and power densities (4509 μW cm−2). Amalgamating the polyimide‐COF and the polypyrrole as one material minimizes the charge and mass transport resistances. Computation and experiments reveal that even a partial translation of the modules/monomers intrinsic electronics to the COF imparts excellent electrochemical activity. The findings unveil COF‐confined polymers as carbon‐free energy storage materials.

Isoreticular chemically stable two-dimensional imine covalent organic frameworks (COFs), further denoted as DUT-175 and DUT-176, are obtained in a reaction of 4,4'-bis(9H-carbazol-9-yl)biphenyl tetraaldehyde with phenyldiamine and benzidine. The crystal structures, solved and refined from the powder X-ray diffraction data and confirmed by high-resolution transmission electron microscopy, indicate AA-stacked layer structures. Both structures feature distorted hexagonal channel pores, assuring remarkable porosity (SBET = 1071 m2 g-1 for DUT-175 and SBET = 1062 m2 g-1 for DUT-176), as confirmed by adsorption of gases and vapors. The complex conjugated π system of the COFs involves electron-rich carbazole building units, which in combination with the imine groups allow reversible pH-dependent protonation of the frameworks, accompanied by charge transfer and shift of the absorption bands in the UV-vis spectrum. The sigmoidal shape of the water vapor adsorption and desorption isotherms with a steep adsorption step at p/p0 = 0.4-0.6 in combination with excellent stability over dozens of adsorption and desorption cycles ranks these COFs among the best materials for indoor humidity control applications.

Alcohol adsorption by metal-organic frameworks (ZIF-8 and ZIF-11) in aqueous solutions is investigated including alcohol mixtures. Solid-state 13C NMR spectroscopy is demonstrated to be well-suited for such liquid-phase adsorption studies at the molecular level. Adsorption-induced immobilization could be visualized. Finally, an unexpected phase transition of ZIF-11 was discovered.