Construction of efficient Pb(II) carboxylate catalysts for the oxygen and hydrogen evolution reactions

The development of cost-effective and efficient electrocatalysts can solve the problems associated with the production of energy via water-splitting reactions. In this work, we have focused on two lead-based coordination polymers (CPs), namely, {[Pb2(TPBN)(HBTC)2]2·2.5H2O}n (CP1) and {[Pb2(TPBN)(NDC)2]·H2O}n (CP2), that were synthesized by self-assembly method at room temperature in good yields. The two-dimensional structures of CP1 and CP2 were determined by single-crystal X-ray diffraction studies. Their phase purity and thermal stability were confirmed by powder X-ray diffraction and TGA analysis, respectively. In addition to this, Hirshfeld surface analysis of CP1 and CP2 revealed the key differences in their intermolecular interactions. Both CP1 and CP2 were employed for HER and OER. It has been found that the change in the carboxylate from BTC to NDC resulted in better electrocatalytic activity towards water-splitting reactions. This may be attributed to the presence of more π character in NDC compared to BTC, which makes the electron flow much easier for HER process. CP1 and CP2 showed overpotential values of -0.58 V and -0.55 V, respectively, in 1 M H2SO4 to reach a 10 mA cm-2 current density with Tafel slopes of 31 mV dec-1 and 25 mV dec-1, respectively. For the OER process, CP1 and CP2 exhibited overpotentials of 590 mV and 470 mV, respectively, in 1 M KOH at a current density of 50 mA cm-2 with Tafel slope values of 81 mV dec-1 and 56 mV dec-1, respectively. Turnover frequency (TOF) values of CP1 and CP2 were 1.05 s-1 and 3.21 s-1 for OER and 1.97 s-1 and 9.65 s-1 for HER, respectively. These results indicate that both CPs can act as highly efficient electrocatalysts for clean energy production.

Oxidation of Ni(H2O)6@MoO3 to Ni2O3/MoO3 Composites by Aerial Annealing: Electrocatalytic Hydrogen Evolution

Molybdenum trioxide (α-MoO3) is a promising and inexpensive alternative to platinum group metals (PGMs), for electrocatalytic hydrogen evolution reaction (HER). However, to make it a viable candidate for electrocatalytic systems, we must address the hurdles associated with its inferior electrical conductivity and lack of active sites. Unlike Mo-based compounds such as MoS₂ and MoSe₂, which possess catalytically active edges, α-MoO₃ lacks inherent active sites for HER. Previous studies have employed various strategies to activate MoO₃ for HER, yet its activation in near-neutral conditions remain largely unexplored. In this study, a previously known α-MoO3 intercalating {Ni(H2O)6}2+, [MoVI 2O6(CH3COO){NiII(H2O)6}0.5] ⋅ H2O (Ni(H2O)6@MoO3) is prepared via a simple and scalable room-temperature aqueous synthesis. In the subsequent aerial thermal annealing process at 300, 400 and 500 °C, Ni(H2O)6@MoO3 acts as a self-sacrificial template, yielding mixed metal oxide composites of nickel and molybdenum (named as MoO3-300, MoO3-400 and MoO3-500). The HR-TEM and XPS analyses confirm the formation of the Ni2O3 phase alongside the orthorhombic α-MoO3. The annealing temperature plays a key role in the crystallinity, phase, morphology, and electrocatalytic performance of the resulting composites. The composite formed at 400 °C (MoO3-400) shows the best electrocatalytic performance among them, showcasing a fivefold enhancement in the HER current density as compared to that shown by commercially available α-MoO3 in mildly acidic acetate buffer. The enhanced performance towards HER by MoO3-400 could be attributed to the nanostructured morphology attained via thermal treatment, which provides greater access to the surface sites and the synergistic interaction between the nickel oxide phases and MoO₃ structure, enabling an intermediate pH HER activity rarely reported for molybdenum oxide materials.

Hybrid organic monolithic column containing MIL-68(Al) for the separation of small molecules by capillary HPLC

A hybrid organic monolithic column made of poly(lauryl methacrylate-co-1,6-hexanediol dimethacrylate) and the metal-organic framework MIL-68(Al) was prepared for the first time. The column was used in capillary liquid chromatography, both in isocratic and gradient elution modes. Separation performance towards small molecules of different chemical nature (polycyclic aromatic hydrocarbons, alkylbenzenes, phenols, etc.) was studied. Monte Carlo simulations were made to both select the proper precursors to obtain empty metal-organic framework micropores in the monolithic polymer and also, to analyze the potential free access of the studied analytes into the micropores (necessary to improve mass transfer and column efficiency). The hereby synthesized metal-organic framework microcrystals allowed obtaining homogeneous hybrid monolithic columns. Adding of MIL-68(Al) (1030 m2 g-1 BET specific surface area) increased the surface area from 3.9 m2 g-1 for the parent monolith to 18.2 m2 g-1 for the hybrid column containing 8 mg mL-1 of the microcrystals. Chromatographic performance of this new column was evaluated by studying retention factors, resolution, and plate counts at room temperature. Different compounds, not completely resolved in the parent monolith, were partially or completely separated after metal-organic framework addition. Using the monolithic column with only 2 mg mL-1 of MIL-68(Al), five alkylbenzenes were completely separated with very symmetrical peak shapes, resolution factors up to 3.60 and plate counts of 4300 plates m-1 for n-hexylbenzene. This value is higher than those obtained by other authors who used organic monolithic columns with embedded metal-organic frameworks to perform separations at room temperature. Additionally, nine polycyclic aromatic hydrocarbons were partially or completely resolved in gradient elution mode. The hybrid monolithic columns exhibited very good intra-day (%RSD=1.9), inter-day (%RSD=2.6), and column-to-column (%RSD=4.3) reproducibility values. Easy and fast column preparation, and versatility to efficiently separate several compounds of different chemical nature in isocratic and gradient mode, makes this new hybrid column a very good option for the analysis of small molecules in capillary (or nano) HPLC.

Rational Design of Improved Ru Containing Fe-Based Metal-Organic Framework (MOF) Photoanode for Artificial Photosynthesis

Metal-Organic Frameworks (MOFs) recently emerged as a new platform for the realization of integrated devices for artificial photosynthesis. However, there remain few demonstrations of rational tuning of such devices for improved performance. Here, a fast molecular water oxidation catalyst working via water nucleophilic attack is integrated into the MOF MIL-142, wherein Fe3O nodes absorb visible light, leading to charge separation. Materials are characterized by a range of structural and spectroscopic techniques. New, [Ru(tpy)(Qc)(H2O)]+ (tpy = 2,2':6',2″-terpyridine and Qc = 8-quinolinecarboxylate)-doped Fe MIL-142 achieved a high photocurrent (1.6 × 10-3 A·cm-2) in photo-electrocatalytic water splitting at pH = 1. Unassisted photocatalytic H2 evolution is also reported with Pt as the co-catalyst (4.8 µmol g-1 min-1). The high activity of this new system enables hydrogen gas capture from an easy-to-manufacture, scaled-up prototype utilizing MOF deposited on FTO glass as a photoanode. These findings provide insights for the development of MOF-based light-driven water-splitting assemblies utilizing a minimal amount of precious metals and Fe-based photosensitizers.

Evaluation of Ce-MOFs as Photoanode Materials for the Water Oxidation Reaction: The Effect of Doping with [Ru(bpy)(dcbpy)(H2O)2]2+ Catalyst

Artificial photosynthesis stands out as a highly effective method for harnessing sunlight to produce clean and renewable energy. The light-absorbing properties, chemical stability, and high redox activity of Ce-based metal-organic frameworks (MOFs) make them attractive materials for visible-light-driven water splitting. Currently, Ce-based MOFs remain a relatively underexplored system for photocatalytic water oxidation in acidic media. In this study, we synthesized a Ce-MOF with different linkers (1,4-benzenedicarboxylic acid, tetrafluoroterephthalic acid, 2-nitroterephthalic acid, 2,2'-bipyridine-5,5'-dicarboxylic acid, and 4,4'-biphenyldicarboxylic acid), which exhibit light-absorbing capability. Ce-based MOFs doped with [Ru(bpy)(dcbpy)(H2O)2]2+ (MOF-1 and MOF-2) water oxidation catalyst showed an enhanced photoelectrocatalytic current of ∼10-4 A·cm-2 at pH = 1, which is comparable with the [Ru(bpy)(dcbpy)(H2O)2]2+-doped MIL-126 Fe-based MOF. We also demonstrated the long-term durability of Ru-doped Ce-MOFs for photoelectrocatalytic water oxidation under acidic conditions. The as-synthesized MOFs were analyzed with powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), UV-visible diffuse reflectance spectroscopy, scanning electron microscopy (SEM), and electric conductivity measurements. This study contributes to the development of cost-effective materials for sustainable photocatalytic water splitting processes.

Enhanced Electrochemical Hydrogenation of Benzaldehyde to Benzyl Alcohol on Pd@Ni-MOF by Modifying the Adsorption Configuration

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal-organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm-2 h-1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency.

From Simple Palladium(II) Monomers to 2D Heterometallic Sodium-Palladium(II) Coordination Networks with 2-Halonicotinates

The 2D heterometallic sodium-palladium(II) coordination polymers with 2-halonicotinates [2-chloropyridine-3-carboxylate (2-chloronicotinate), 2-Clnic- and 2-bromopyridine-3-carboxylate (2-bromonicotinate), 2-Brnic-], {[Na2(H2O)2(μ-H2O)4PdCl2(μ-2-Clnic-N:O')2]}n (1), and {[Na2(H2O)2(μ-H2O)4PdBr2(μ-2-Brnic-N:O')2]·2H2O}n (2) were prepared in aqueous solutions under the presence of NaHCO3, while palladium(II) monomers with the neutral 2-chloronicotinic and 2-bromonicotinic acid ligands, [PdCl2(2-ClnicH-N)2]·2DMF (3) and [PdCl2(2-BrnicH-N)2]·2DMF (4), were prepared in DMF/water mixtures (DMF = N,N'-dimethylformamide). The zigzag chains of water-bridged sodium ions are in turn bridged by [PdCl2(2-Clnic)2]2- moieties in 1 or by [PdBr2(2-Brnic)2]2- moieties in 2, leading to the formation of the infinite 2D coordination networks of 1 or 2. The DFT calculations showed the halosubstituents type (Cl vs Br) does not have an influence on the formation of either trans or cis isomers. The trans isomers were found in all reported compounds; being more stable for about 10 to 15 kJ mol-1. The 2D coordination networks 1 and 2 are more stabilized by the formation of Na-Ocarboxylate bonds, comparing to the stabilization of palladium(II) monomers 3 and 4 by hydrogen-bonding with DMF molecules. The difference in DFT calculated energy stabilization for 1 and 2 is ascribed to the type of halosubstituents and to the presence/absence of lattice water molecules in 1 and 2. The compounds show no antibacterial activity toward reference strains of Escherichia coli and Staphylococcus aureus bacteria and no antiproliferative activity toward bladder (T24) and lung (A549) cancer cell lines.

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH

A sole inorganic framework material [Li(H2O)4][{CuI(H2O)1.5} {CuII(H2O)3}2{WVI12O36(OH)6}]·N2·H2S·3H2O (1) consisting of a hydroxylated polyoxometalate (POM) anion, {WVI12O36(OH)6}6-, a mixed-valent Cu(II)- and Cu(I)-aqua cationic complex species, [{CuI(H2O)1.5}{CuII(H2O)3}2]5+, a Li(I)-aqua complex cation, and three solvent molecules, has been synthesized and structurally characterized. During its synthesis, the POM cluster anion gets functionalized with six hydroxyl groups, i.e., six WVI-OH groups per cluster unit. Moreover, structural and spectral analyses have shown the presence of H2S and N2 molecules in the concerned crystal lattice, formed from "sulfate-reducing ammonium oxidation (SRAO)". Compound 1 functions as a bifunctional electrocatalyst exhibiting oxygen evolution reaction (OER) by water oxidation and hydrogen evolution reaction (HER) by water reduction at the neutral pH. We could identify that the hydroxylated POM anion and copper-aqua complex cations are the functional sites for HER and OER, respectively. The overpotential, required to achieve a current density of 1 mA/cm2 in the case of HER (water reduction), is found to be 443 mV with a Faradaic efficiency of 84% and a turnover frequency of 4.66 s-1. In the case of OER (water oxidation), the overpotential needed to achieve a current density of 1 mA/cm2 is obtained to be 418 mV with a Faradaic efficiency of 80% and turnover frequency of 2.81 s-1. Diverse electrochemical controlled experiments have been performed to conclude that the title POM-based material functions as a true bifunctional catalyst for electrocatalytic HER as well as OER at the neutral pH without catalyst reconstruction.

Chiral "doped" MOFs: an electrochemical and theoretical integrated study

This work reports on the electrochemical behaviour of Fe and Zn based metal-organic framework (MOF) compounds, which are "doped" with chiral molecules, namely: cysteine and camphor sulfonic acid. Their electrochemical behaviour was thoroughly investigated via "solid-state" electrochemical measurements, exploiting an "ad hoc" tailored experimental set-up: a paste obtained by carefully mixing the MOF with graphite powder is deposited on a glassy carbon (GC) surface. The latter serves as the working electrode (WE) in cyclic voltammetry (CV) measurements. Infrared (IR), X-ray diffraction (XRD) and absorbance (UV-Vis) techniques are exploited for a further characterization of the MOFs' structural and electronic properties. The experimental results are then compared with DFT based quantum mechanical calculations. The electronic and structural properties of the MOFs synthesized in this study depend mainly on the type of metal center, and to a minor extent on the chemical nature of the dopant.

Molecular Catalysis of Energy Relevance in Metal-Organic Frameworks: From Higher Coordination Sphere to System Effects

The modularity and synthetic flexibility of metal-organic frameworks (MOFs) have provoked analogies with enzymes, and even the term MOFzymes has been coined. In this review, we focus on molecular catalysis of energy relevance in MOFs, more specifically water oxidation, oxygen and carbon dioxide reduction, as well as hydrogen evolution in context of the MOF-enzyme analogy. Similar to enzymes, catalyst encapsulation in MOFs leads to structural stabilization under turnover conditions, while catalyst motifs that are synthetically out of reach in a homogeneous solution phase may be attainable as secondary building units in MOFs. Exploring the unique synthetic possibilities in MOFs, specific groups in the second and third coordination sphere around the catalytic active site have been incorporated to facilitate catalysis. A key difference between enzymes and MOFs is the fact that active site concentrations in the latter are often considerably higher, leading to charge and mass transport limitations in MOFs that are more severe than those in enzymes. High catalyst concentrations also put a limit on the distance between catalysts, and thus the available space for higher coordination sphere engineering. As transport is important for MOF-borne catalysis, a system perspective is chosen to highlight concepts that address the issue. A detailed section on transport and light-driven reactivity sets the stage for a concise review of the currently available literature on utilizing principles from Nature and system design for the preparation of catalytic MOF-based materials.

Metal-Organic Framework Materials in Perovskite Solar Cells: Recent Advancements and Perspectives

Organic-inorganic hybrid perovskite solar cells (PSCs) are among the most promising candidates for the next generation of photovoltaic devices because of the significant increase in their power conversion efficiency (PCE) from less than 10% to 25.7% in past decade. The metal-organic framework (MOF) materials owing to their unique properties, such as large specific surface area, abundant binding sites, adjustable nanostructures, and synergistic effects, are used as additives or functional layers to enhance the device performance and long-term stability of PSCs. This review focuses on the recent advancements in the applications of MOFs as/in different functional layers of PSCs. The photovoltaic performance, impact, and advantages of MOF materials integrated into the perovskite absorber, electron transport layer, hole transport layer, and interfacial layer are reviewed. In addition, the applicability of MOFs to mitigate leakage of Pb²⁺ from halide perovskites and corresponding devices is discussed. This review concludes with the perspectives on further research directions for employing MOFs in PSCs.

Synthesis of 3D Cadmium(II)-Carboxylate Framework Having Potential for Co-Catalyst Free CO2 Fixation to Cyclic Carbonates

Metal-organic frameworks (MOFs) are porous coordination polymers with interesting structural frameworks, properties, and a wide range of applications. A novel 3D cadmium(II)-carboxylate framework, CdMOF ([Cd2(L)(DMF)(H2O)2]n), was synthesized by the solvothermal method using a tetracarboxylic bridging linker having amide functional moieties. The CdMOF crystal structure exists in the form of a 3D layer structure. Based on the single-crystal X-ray diffraction studies, the supramolecular assembly of CdMOF is explored by Hirshfeld surface analysis. The voids and cavities analysis is performed to check the strength of the crystal packing in CdMOF. The CdMOF followed a multistage thermal degradation pattern in which the solvent molecules escaped around 200 °C and the structural framework remained stable till 230 °C. The main structural framework collapsed (>60 wt.%) into organic volatiles between 400–550 °C. The SEM morphology analyses revealed uniform wedge-shaped rectangular blocks with dimensions of 25–100 μm. The catalytic activity of CdMOF for the solvent and cocatalyst-free cycloaddition of CO2 into epichlorohydrin was successful with 100% selectivity. The current results revealed that this 3D CdMOF is more active than the previously reported CdMOFs and, more interestingly, without using a co-catalyst. The catalyst was easily recovered and reused, having the same performance.

Barrel-Shaped-Polyoxometalates Exhibiting Electrocatalytic Water Reduction at Neutral pH: A Synergy Effect

Two copper-based barrel-shaped polyoxometalates (POMs), namely, [{H₃O}₄{Na₆(H₂O)₂₂}][{Cu^I (H₂O)₃}₂{Cu^II (H₂O)}₃{B-α-Bi^IIIW^VI₉O₃₃}₂]·7H₂O (NaCu-POM) and Li₄[{NH₄}₂{H₃O}₃{Li(H₂O)₅}][{Cu^II(SH)}{(Cu^IICu^I_1.5)(B-α-Bi^IIIW^VI₉O₃₃)}₂]·9H₂O (LiCu-POM) have been synthesized and structurally characterized. The single-crystal X-ray diffraction analyses of NaCu-POM and LiCu-POM reveal the presence of penta- and hexa-nuclear copper wheels per formula units, respectively; these copper wheels are sandwiched between two lacunary Keggin anions {B-α-Bi^IIIW^VI₉O₃₃}^9- (BiW₉) to form the barrel-shaped title POM compounds. In both the compounds NaCu-POM and LiCu-POM, the mixed-valent copper centers are present in their respective penta- and hexa-nuclear copper wheels, established by X-ray photoelectron spectroscopy (XPS) as well as by bond valence sum (BVS) calculations. Compound LiCu-POM additionally shows the presence of a sulfhydryl ligand (SH^-), coordinated to one of the copper centers of its {Cu₆}-wheel, that is expected to be generated from the in situ reduction of sulfate anion present in the concerned reaction mixture (lithium-ion in ammonia solution may be the reducing agent). Interestingly, the title compounds, NaCu-POM and LiCu-POM exhibit an efficient electrocatalytic hydrogen evolution reaction (HER) by reducing water at neutral pH. Detailed electrochemical studies including controlled experiments indicate that the active sites for this electrocatalysis are the W(VI) centers of the title compounds, not the copper centers. However, a relevant tri-lacunary Keggin cluster anion {P^VW^VI₉O₃₃}^7- (devoid of copper ion) does not show comparable HER as shown by the title compounds. The intra-cluster cooperative interactions of the mixed-valent copper centers (Cu^II/Cu^I) with the tungsten centers (W⁶⁺) make the overall system electrocatalytically active toward water reduction to molecular hydrogen at neutral pH. High Faradaic efficiencies (89 and 92%) and turnover frequencies (1.598 s^-1 and 1.117 s^-1) make the title compounds NaCu-POM and LiCu-POM efficient catalysts toward electrochemical water reduction to molecular hydrogen.

Design and Synthesis of Lead(II)-Based Electrocatalysts for Oxygen Evolution Reaction

A well-organized worldwide effort in providing remedies to sustainable clean energy generation and storage has focused on the strategic design and development of stable and efficient earth-abundant metal (Fe, Co, Ni, Pb, etc.)-based electrocatalysts for the oxygen evolution reaction (OER). Unfortunately, examples of Pb-based catalysts for such a process are rare. In this work, based on the dual-linker strategy, we have designed and synthesized two new two-dimensional (2D) coordination polymers of Pb with the hcb topology, [Pb₂(tpbn)(adc)₂]·4H₂O·0.5CH₃OH}_n (CP1) and {[Pb₂(tpbn)(fum)₂]·7H₂O}_n (CP2), in excellent yields by the room-temperature self-assembly of Pb(OAc)₂, tpbn, and H₂adc or H₂fum (where tpbn = N,N',N‴,N‴'-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane, H₂adc = acetylene dicarboxylic acid, and H₂fum = fumaric acid). In addition to determining their X-ray single crystal structures, the phase purity and thermal stability were established by powder X-ray diffraction and thermogravimetric analysis, respectively. Furthermore, these were also characterized by the microscopic techniques (SEM/EDX and TEM/HRTEM). For their conductive and highly stable nature in alkaline medium, both CP1 and CP2 were tested for their suitability in the OER process. Interestingly, with a subtle change from adc in CP1 to fumarate in CP2 as the dicarboxylate linker, the latter performed much better than the former and displayed an excellent electrochemical stability in basic medium. Remarkably, CP2 has one of the lowest Tafel values (35 mV dec^-1) and a low overpotential value (140 mV vs RHE) in 0.5 M KOH compared to those reported for any materials. Such a comparative study with CP1 and CP2, which are the simplest CPs and made with green-chemistry protocols for an easy making in large quantities, provides an outlook to developing the next-generation Pb-based electrocatalysts.

Systematic Influence of Electronic Modification of Ligands on the Catalytic Rate of Water Oxidation by a Single-Site Ru-Based Catalyst

Catalytic water oxidation is an important process for the development of clean energy solutions and energy storage. Despite the significant number of reports on active catalysts, systematic control of the catalytic activity remains elusive. In this study, descriptors are explored that can be correlated with catalytic activity. [Ru(tpy)(pic)₂ (H₂ O)](NO₃ )₂ and [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ (where tpy=2,2' : 6',2"-terpyridine, EtO-tpy=4'-(ethoxy)-2,2':6',2"-terpyridine, pic=4-picoline) are synthesized and characterized by NMR, UV/Vis, EPR, resonance Raman, and X-ray absorption spectroscopy, and electrochemical analysis. Addition of the ethoxy group increases the catalytic activity in chemically driven and photocatalytic water oxidation. Thus, the effect of the electron-donating group known for the [Ru(tpy)(bpy)(H₂ O)]²⁺ family is transferable to architectures with a tpy ligand trans to the Ru-oxo unit. Under catalytic conditions, [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ displays new spectroscopic signals tentatively assigned to a peroxo intermediate. Reaction pathways were analyzed by using DFT calculations. [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ is found to be one of the most active catalysts functioning by a water nucleophilic attack mechanism.

Electron-Conductive Metal-Organic Framework, Fe(dhbq)(dhbq = 2,5-Dihydroxy-1,4-benzoquinone): Coexistence of Microporosity and Solid-State Redox Activity

Redox-active metal-organic frameworks (MOFs) have great potential for use as cathode materials in lithium-ion batteries (LIBs) with large capacities because the organic ligands can undergo multiple-electron redox processes. However, most MOFs are electrical insulators, limiting their application as electrode materials. Here, we report an electron-conductive MOF with a 2,5-dihydroxy-1,4-benzoquinone (dhbq) ligand, Fe(dhbq). This compound had an electrical conductivity of 5 × 10^-6 S cm^-1 at room temperature due to d-π interactions between the Fe ion and the ligand and the permanent microporosity. Fe(dhbq) had an initial discharge capacity of 264 mA h g^-1, corresponding to the two-electron redox process of dhbq.

A Highly-Efficient Oxygen Evolution Electrocatalyst Derived from a Metal-Organic Framework and Ketjenblack Carbon Material

The composite of the metal-organic framework (MOF) Ni(Fe)-MOF-74 and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the in-situ MOF synthesis in a one-step solvothermal reaction. The composite material features a remarkable electrochemical oxygen evolution reaction (OER) performance where the overpotential at 10 mA/cm2 and the current density at 1.7 VRHE are recorded as 0.274 VRHE and 650 mA/cm2 , respectively, in 1 mol/L KOH. In particular, the activation of nickel-iron clusters from the MOF under an applied anodic bias steadily boosts the OER performance. Although Ni(Fe)-MOF-74 goes through some structural modification during the electrochemical measurements, the stabilized and optimized composite material shows excellent OER performance. This simple strategy to design highly-efficient electrocatalysts, utilizing readily available precursors and carbon materials, will leverage the use of diverse metal-organic complexes into electrode fabrication with a high energy conversion efficiency.

Assembly of a Metal-Organic Framework (MOF) Membrane on a Solid Electrocatalyst: Introducing Molecular-Level Control Over Heterogeneous CO2 Reduction

Electrochemically active Metal‐Organic Frameworks (MOFs) have been progressively recognized for their use in solar fuel production schemes. Typically, they are utilized as platforms for heterogeneous tethering of exceptionally large concentration of molecular electrocatalysts onto electrodes. Yet so far, the potential influence of their extraordinary chemical modularity on electrocatalysis has been overlooked. Herein, we demonstrate that, when assembled on a solid Ag CO₂ reduction electrocatalyst, a non‐catalytic UiO‐66 MOF acts as a porous membrane that systematically tunes the active site's immediate chemical environment, leading to a drastic enhancement of electrocatalytic activity and selectivity. Electrochemical analysis shows that the MOF membrane improves catalytic performance through physical and electrostatic regulation of reactants delivery towards the catalytic sites. The MOF also stabilizes catalytic intermediates via modulation of active site's secondary coordination sphere. This concept can be expanded to a wide range of proton‐coupled electrochemical reactions, providing new means for precise, molecular‐level manipulation of heterogeneous solar fuels systems.

Defects as catalytic sites for the oxygen evolution reaction in Earth-abundant MOF-74 revealed by DFT

The oxygen evolution reaction (OER) is the bottleneck of hydrogen production via water splitting and understanding electrocatalysts at atomic level becomes paramount to enhance the efficiency of this process.

Synthesis of a palladium based MOF via an effective post-synthetic modification approach and its catalytic activity towards Heck type coupling reactions

The complete exchange of metal nodes in a MOF with the Pd(ii) ions was done without losing the structural integrity. The new MOF turned out to be an excellent catalyst for the C–C bond formation via un-reacted cleavage C–N bond of arylhydrazines.

Heterometallic coordination polymers as heterogeneous electrocatalysts

Heterometallic coordination polymers have been rapidly developed as heterogeneous electrocatalysts. This review highlights the synthesis strategies of these polymers and the relationships between structures and electrocatalytic performances.