Regulated Second-sphere Coordination in Amorphous Metal-organic Framework for Efficient CO2 Fixation.

Amorphous metal-organic framework (MOF) materials have drawn extensive interest in the design of high-performance electrocatalysts for use in the electrochemical oxygen evolution reaction. However, there are limitations to the utilization of amorphous MOFs due to their low electrical conductivity and unsatisfactory stability. Herein, a novel amorphous-crystalline (AC) heterostructure is successfully constructed by synthesizing a crystalline metal sulfide (MS)-embedded amorphous Ni0.67Fe0.33-MOF, namely an MS/Ni0.67Fe0.33-MOF. It exhibits excellent catalytic performance (a low overpotential of 248 mV at 10 mA cm-2 with a small Tafel slope of 50 mV decade-1), durability, and stability (only 8% degradation of the current density at a constant voltage after 24 h). This work thus sheds light on the engineering of highly efficient catalysts with AC heterointerfaces for optimizing water-splitting systems.

Rare-earth layered hydroxides with intercalated tetrasulfonated porphyrins and corresponding to the chemical formula Ln2(OH)4.7(Por)0.33·2H2O (Ln = Eu(3+), Tb(3+); Por = 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and PdTPPS) have been prepared to investigate their photophysical properties. A slight variation of the synthetic procedure led to the metal-organic framework (MOF) assembled from a distorted octahedral oxometalate clusters [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+). These secondary building units (SBUs) are linked together by six distorted porphyrin units. During activation, the original SBU loses not only water molecules from the coordination sphere but also the central μ6-O atom. The loss of the central atom results in the distortion of the octahedral [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+) SBU into a trigonal antiprismatic [Eu6(μ3-OH)8(H2O)2](10+) SBU with two μ3-OH groups nearly in plane with the europium atoms and the reduction of pores to approximately 2 × 3 Å. As a result, the MOF has no accessible porosity. This transformation was thoroughly characterized by means of single-crystal X-ray crystallographic analysis of both phases. Solid-state photophysical investigations suggest that the MOF material is fluorescent; however, in contrast to the prepared layered hydroxides, the as-prepared MOF is an effective sensitizer of singlet oxygen, O2((1)Δg), with a relatively long lifetime of 23 ± 1 μs. The transition is also accompanied by variation in photophysical properties of the coordinated TPPS. The alteration of the fluorescence properties and of the O2((1)Δg) lifetime presents an opportunity for preparation of MOFs with oxygen-sensing ability or with oxidation potential toward organic molecules by O2((1)Δg).

Amorphous metal–organic frameworks (aMOFs) are emerging as complementary alternatives to crystalline MOFs (cMOFs) in several electrochemical energy applications; however, their preparation typically involves harsh conditions and intricate compositions and structures. In this work, we synthesized coordinately saturated crystalline metal–organic frameworks, known as Ni-cMOF and NiCo-cMOFn (n = 1, 2, 3, and 4), which were successfully amorphized under physical force and alkaline conditions. Interestingly, the amorphized samples maintained the compositional integrity of the parent crystalline framework and exhibited nanocrystalline characteristics at the nanodomain scale. These cMOFs possess a coordinately saturated and exposed 2D sheet-like architecture of secondary building unit Ni3(μ3-O) which bestowed them with excellent catalytic properties. Real-time overall seawater splitting was conducted using the amorphized samples (aMOFs) and showed an excellent performance with oxygen selectivity and stability over 24 h at 340 mA, which is the highest compared to other amorphous MOF-based systems and the first using seawater to the best of our knowledge. We envision that this direct amorphization approach will enable the production of a new generation of amorphous MOFs as effective materials for electrocatalytic applications.

The increasing levels of atmospheric carbon dioxide caused by anthropogenic emissions is one of the most pressing problems that our planet faces and more than 80% of these emissions stem from the combustion of fossil fuels. Here we discuss approaches for CO2 capture from flue gas using metal-organic frameworks (MOFs). We illustrate how various compositions of flue gas require materials with different capture characteristics and mechanisms. Different analytical methods frequently used to characterize the bound CO2 species are outlined to give a deeper understanding of possible interaction between CO2 and MOFs. The CO2 adsorption in MOFs with structural features such as open metal sites, –OH-modified secondary building units (SBUs), and amines appended to the SBU or the linker of the MOF are outlined. Different ways for cycled CO2 adsorption (pressure swing, temperature swing, and vacuum swing adsorption) are discussed and a compilation of MOFs with good CO2 adsorption properties is given.

ConspectusElectrochemical technologies represent a transformative frontier for environmental remediation, offering unparalleled advantages such as precise redox control, seamless integration with renewable energy, and chemical-free operation. However, their practical implementation in water and wastewater treatment remains constrained by inefficient mass transport, poor utilization of catalytic sites under dilute conditions, and persistent challenges in energy consumption and overall system sustainability. These limitations are particularly pronounced when treating trace contaminants or pursuing selective transformation pathways. In this Account, we summarize our recent efforts to overcome these hurdles through the development of single atom-based electrified membrane (SAEM). By integrating atomically dispersed catalytic sites into flow-through and electrically conductive membrane architectures, we have successfully coupled atomic-level active-site engineering with device-level transport intensification.We first outline the construction principles of SAEM, highlighting how coordination environment, defect engineering, and membrane architecture collectively govern catalytic stability and site accessibility. We then examine how flow-through operation fundamentally alters transport regimes by suppressing diffusion limitations that dominate conventional flow-by and batch electrochemical systems. Building on these concepts, we discuss representative reaction systems in which SAEM exhibit clear advantages, including peroxymonosulfate activation for micropollutant degradation, in situ production of reactive oxygen species from oxygen reduction reaction for wastewater treatment, and electrocatalytic nitrate reduction for nitrogen transformation. Finally, we assess the stability, scalability, and sustainability of SAEM from a system-level perspective. Rather than focusing solely on catalytic metrics, we emphasize circularity and life-cycle considerations. This analysis underscores that the long-term viability of this platform depends on its performance as a durable, modular, and resource-efficient device within realistic treatment infrastructure.Overall, this Account positions SAEM as a platform for integrating catalysis, separation, and environmental sustainability withinelectrochemistry, offering guiding principles for the development of advanced electrochemical technologies that are both scientifically rigorous and practically relevant.

New molecular aluminophosphates of different nuclearity are synthesized by a stepwise process and structurally characterized. The alkane elimination reaction of bis(trimethylsiloxy)phosphoric acid, OP(OH)(OSiMe3)2, with trialkylalanes, AlR3 (R = Me, Et, (i)Bu), provides the cyclic dimeric aluminophosphates, [(AlR2{μ2-O2P(OSiMe3)2})2] (R = Me (1), Et (2), (i)Bu (3)). Unsymmetrically substituted cyclic aluminophosphonate [(AlMe2{μ2-O2P(OSiMe3)((c)Hex)})2] (cis/trans-4) is prepared by dealkylsilylation reaction of (c)HexP(O)(OSiMe3)2 with AlMe3. Molecules 1-4 containing the [Al2(μ2-O2P)2] inorganic core are structural and spectroscopic models for the single four-ring (S4R) secondary building units (SBU) of zeolite frameworks. Compound 1 serves as a starting point in construction of larger molecular units by reactions with OP(OH)(OSiMe3)2 as a cage-extending reagent and with diketones, such as Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-dione) and Hacac (pentan-2,4-dione), as capping reagents. Reaction of 1 with 4 equiv of Hhfacac leads to new cyclic aluminophosphate [(Al(hfacac)2{μ2-O2P(OSiMe3)2})2] (5), existing in two isomeric (D2 and C2h) forms. Reaction of 1 with 2 equiv of OP(OH)(OSiMe3)2 and 1 equiv of Hhfacac provides a molecular aluminophosphate [AlMe{Al(hfacac)}2{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}2{OP(OSiMe3)3}] (6), while by adding first the Hhfacac and using 3 equiv of OP(OH)(OSiMe3)2 we isolate [Al{Al(hfacac)}2{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}2H{OP(O)(OSiMe3)2}2] (7). These molecules contain units in their cores that imitate 4=1 SBU of zeolite frameworks. Reaction with the order of component mixing 1, Hhfacac, OP(OH)(OSiMe3)2 at a 1:2:2 molar ratio lead to formation of a larger cluster [(Al(AlMe){Al(hfacac)}{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}3)2] (8) containing both S4R and 4=1 structural units. Similarly, Hacac (pentan-2,4-dione) provides an isostructural [(Al(AlMe){Al(acac)}{μ3-O3P(OSiMe3)}2{μ2-O2P(OSiMe3)2}3)2] (9). Both molecules display Al centers in three different coordination environments.

Reaction of the metalloligand IrIII(ppy-COOH)3 and the anisotropic paramagnetic CoII ion under solvothermal conditions resulted in a metal-metalloligand coordination polymer, [CoII3(μ3-O)(μ-OH2){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)4]·2DMF·xH2O (I). It consists of trimeric Co3O secondary building units (SBUs) bridged by pairs of Ir to form chains of alternate orthogonal squares. The compound undergoes two single-crystal to single-crystal transformations while retaining its general structural features. A chemical transformation occurs to give [CoII3(μ3-O){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)4(DMF)]·DMF·H2O (II) by soaking in acetone, where a bridging water molecule departs and the solvent DMF bonds to the vacant site of the Co center. Both I and II undergo a temperature-induced transformation to [CoII3(μ3-O){IrIII(ppy-COO)2(ppy-COOH)}2(H2O)3(DMF)]·DMF (III), where one more coordinated water molecule is lost. The major difference in the three phases is in the Co coordination spheres, which have considerable consequences on the magnetism. Compound I displays paramagnetism down to 2 K, whereas II and III show weak ferromagnetism with TC values of 14 and 17 K, respectively.

The separation of a mixture of C2H2 and CO2 is a great challenge due to their similar molecular sizes and shapes. Al-based metal-organic frameworks (Al-MOFs) have great promise for gas separation applications due to their light weight, high stability, and low cost. However, the cultivation of suitable Al-MOF single crystals is extremely difficult and has limited their explorations up to now. Since In, Ga, and Al are all 3p-block metal elements, a systematic application of the periodic law to investigate 3p-MOFs will undoubtedly help in the understanding and development of worthy Al-MOF materials. Herein, we report the design of a robust 3p metal-organic framework platform (SNNU-150) and the systematic regulation of C2H2/CO2 separation by open 3p-block metal sites. X-ray single-crystal diffraction analysis reveals that SNNU-150 is a 3,6-connected 3D framework consisting of [M3O(COO)6] trinuclear secondary building units (SBUs) and tritopic nitrilotribenzoate (NTB) linkers. Small {[M3O(COO)6]4(NTB)6} tetrahedral cages and extra-large {[M3O(COO)6]10(NTB)14} polyhedral cages connect with each other to generate a hierarchically porous architecture. These 3p-MOFs present very high water, thermal, and chemical stability, especially for SNNU-150-Al, which can maintain its framework at 85 °C in water for 24 h and in a room-temperature environment for more than 30 days. IAST calculations, breakthrough experiments, and GCMC simulations all show that SNNU-150 MOFs have top-level C2H2/CO2 separation performance and follow the order Al-MOF > Ga-MOF > In-MOF.

Unsaturated Ni single-atom catalysts (SACs), Ni-Nx (x=1,2,3), have been investigated to break the conventional Ni-N4 structural limitation and provide more unoccupied 3d orbitals for CO2 reduction reaction (CO2RR) intermediates adsorption, but their intrinsically low structural stability has seriously hindered their applications. Here, we developed a strategy by integrating Ni nanoclusters to stabilize unsaturated Ni-N3 atomic sites for efficient CO2 electroreduction to CO at industrial-level current. Density Functional Theory (DFT) calculations revealed that the incorporation of Ni nanocluster effectively stabilizes the unsaturated Ni-N3 atomic sites and modulates their electronic structure to enhance the adsorption of the key intermediate *COOH during CO2RR. Guided by these insights, we prepared an optimal composite catalyst, Ni6@Ni-N3, which features a Ni6N6 nanocluster surrounded by six Ni-N3 single atoms sites, through low-temperature pyrolysis. The morphology and coordinative structure of Ni6@Ni-N3 were confirmed by an aberration-corrected transmission electron microscope (AC-TEM) and X-ray absorption spectroscopy (XAS). As a result, Ni6@Ni-N3 demonstrated a remarkably high CO Faradaic efficiency (FECO) of 99.7 % and a turnover frequency (TOF) of 83984.2 h-1 at 500 mA cm-2 under -1.15 VRHE, much better than those of Ni-N4 with a lower FECO of 86 % at 100 mA cm-2 and a TOF of 39309.9 h-1under identical potential. XAS analyses of Ni6@Ni-N3 before and after long-term CO2RR testing confirmed the excellent stability of its coordinative environment. This work highlights a generalizable approach for stabilizing unsaturated single-atom catalysts, paving the way for their application in high-performance CO2RR.

Vibrational analysis and crystal structure of two new 1D CuII and CoII coordination polymers, involving the ligands 2,5-dihydroxyterephthalate and glutarate

Solid polymer electrolytes (SPEs) are crucial in the development of lithium metal batteries. Recently, metal-organic frameworks (MOFs) with open metal sites (OMSs) have shown promise as solid fillers to improve the performance of SPEs. However, the number of OMS-containing MOFs is quite limited, comprising less than 5% of the total MOFs. When considering yield, cost, and processability, the commonly used OMS-containing MOFs are no more than 10 types, causing great limitations. Herein, we reported a simple and universal methodology that converted OMS-free MOFs to OMS-rich quasi-MOFs for developing high-performance SPEs, and explored the underlying mechanism. The "OMS-polymer" and "OMS-ion" interactions were investigated in detail to elucidate the role of quasi-MOFs on battery performance. It was found that quasi-MOFs, functioning as ion sieves, can effectively regulate ion migration, thus promoting uniform Li deposition and enabling an ultra-stable interface. As a result, the Li symmetric cell stably ran over 3000 h at 0.3 mA cm-2, while the full cell retained 85 % of its initial capacity after 1500 cycles at 1.0 C. Finally, universal testing was performed using other MOFs, confirming the generalizability and effectiveness of our design concept.

The Li dendrite issue is the major barrier that limits the implement of Li metal anode practically, especially at high current density. From the perspective of the nucleation and growth mechanism of the Li dendrite, we rationally develop a novel Prussian blue analogues (PBA)-derived separator, where tuning the metal ions bestows the PBAs with open metal site to confine anion movement and thereby afford a high Li+ transference number (0.78), and PBA with ordered micropores could act as an ionic sieve to selectively extract Li+ and thereby homogenize Li+ flux. This demonstrates a highly reversible Li plating/stripping cycling for 3000 h at a practically high current density (5.0 mA cm-2). Consequently, a high loading Li||LiFeO4 battery (∼10.0 mg cm-2) demonstrates ultralong cycling life at high current densities (∼5.1 mA cm-2). This work highlights the prospect of optimizing PBAs in regulating ion transport behavior to enable high-power Li metal batteries.

Sodium metal batteries (SMBs), leveraging the natural abundance of sodium and high theoretical capacity, emerge as promising candidates for next-generation energy storage. However, the generation of the unstable solid electrolyte interphase (SEI) layer and uncontrolled Na dendrite growth in SMBs with carbonate-based electrolytes leads to poor Coulombic efficiency and security risks. Herein, a multifunctional separator (N-U@PE) for SMBs is fabricated through an innovative strategy involving the in situ growth of zirconium-based metal-organic frameworks (Zr-MOFs) on NASICON-type fast-ion conductor to prepare a dual-phase composite (N-U) as PE separator modification. Benefiting from abundant open metal sites (OMSs) and 3D ion transport channels, the N-U@PE separator can effectively immobilize anions and induce the formation of NaF-rich SEI layer, resulting in Na+ flux homogenization and Na+ transport kinetics enhancement. Satisfactorily, the Na|N-U@PE|Na symmetric cell achieves stable cycling for 3000h at 0.5mA cm-2 and 0.5 mAh cm-2. Remarkably, the Na3V2(PO4)3|N-U@PE|Na pouch cell exhibits 95.2% capacity retention after 1000 cycles at 2 C. The design of N-U@PE integrates ion transport regulation and interfacial stability, giving a practical solution for high-performance SMBs.

Modification of conductive electrodes with chemically tunable molecular catalysts represents an interesting and relatively unexplored area of photoelectrocatalysis research. Here, we report an investigation of the electrochemical behavior of graphene nanoribbons (GNR) deposited onto a glassy carbon electrode using π−π stacking interactions. Using the bipyrimidine moiety on the nanoribbon edges as a reporter of the proton-coupled electron transfer chemistry, we illustrate that the simple electrochemical treatment of as-deposited nanoribbon generates a hybrid material that is in strong electronic communication with the conductive support.1 This work shows a strategy for modifying the basal plane of carbon materials and provides a potential platform for the incorporation of catalytic metal sites via coordination through the N-functionalities of GNR.We also investigate the coordination of Rh-based hydrogen evolution reaction catalyst onto the edges of GNRs to form metal-nanoribbon catalyst (Rh-GNR).2 The electrocatalytic hydrogen evolution reaction was observed when glassy carbon electrode is modified by Rh-GNR to form Rh-GNR@GC. The catalytic activity is maintained throughout the entire pH region, which contrasts the behavior of the homogeneous (molecular) analog catalyst, which becomes inactive in the basic pH. The Rh K-edge X-ray absorption spectroscopy reveals that the molecular analog and Rh-GNR exhibit identical coordination environment, indicating that the differences in electrochemical behavior do not arise due to functional group differences between the two catalysts. The effect of interfacial electric fields on the catalytic sites was evaluated by monitoring the proton-coupled electron transfer chemistry and in situ X-ray absorption. The results of this work indicate that the catalytic sites are located outside the electric double layer and that the observed catalytic enhancements are not associated with field-driven chemistry. The observed improvements for the immobilized catalyst are instead assigned to the prevention of undesired catalyst aggregation when it is attached to the electrode surface.(1) Zoric, M. R.; Askins, E. J.; Qiao, X.; Glusac, K. D. Strong Electronic Coupling of Graphene Nanoribbons onto Basal Plane of a Glassy Carbon Electrode, ACS Appl. Electron. Mater. 2021, 3 (2), 854-860.(2) Askins, E. J.; Navabi, P.; Kumar, K.; Finkelmeyer, S. J.; Presselt, M.; Cabana, J.; Glusac, K. D. Interfacial Electrochemistry of Catalyst-Coordinated Graphene Nanoribbons, J. Am. Chem Soc. 2024, 146, 32, 22360.

Due to scarcity of fossil fuels and their severe environmental consequences, the development of high efficiency energy conversion devices such as fuel cells (FCs) have gained considerable attention. The specific energy conversion efficiency of FC is highly influenced by the activity of the electrocatalysts. The Pt is widely used as an electrocatalyst due to its high activity and stability, but its high cost and depletion of resources hinder its commercialization. One of the workable strategies for the practical application of Pt is to reduce its content by alloying with some non-precious metals and simultaneously maintain its electrochemical performance. In this context, we developed a low Pt-loaded Pt-Ag/C alloy electrocatalyst via a gradual reduction process. The electrochemical performance of the as-synthesized catalyst was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) using the three-electrode electrochemical workstation at room temperature. The electrocatalytic investigations reveal that the resultant alloy has an activity of 32.7 mA cm-2, which is significantly higher than that of Pt/C (17.6 mA cm-2) in an alkaline electrolyte and makes it a very efficient electrocatalyst for the ethanol oxidation reaction (EOR). The partial electron transfer from Ag to Pt in Pt-Ag alloy, which weakens the CO binding and poisoning effect on the surface, may be partly responsible for the enhanced catalytic activity of Pt-Ag/C. The activated carbon support also favors charge transport by transferring charge from catalytic active sites to external circuits. The stability and durability studies reveal that Pt-Ag/C performs significantly better than Pt/C, making it a viable electrocatalyst for EOR. Keywords: Direct Ethanol Fuel Cell, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, Alloy.