Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries

In Situ Ligand-Transformation-Assisted Assembly of a Polyoxometalate and Silver-Phosphine Oxide Cluster for Colorimetric Detection of Phenol Contaminants

In situ ligand transformation strategies represent an efficient pathway for constructing function-oriented polyoxometalate (POM)-based crystalline materials. Herein, three POM-based hybrid networks were synthesized through in situ transformation of the phosphine ligand, formulated as [Ag(dppeo)6][H2PMo12O40]·5H2O (1), [Ag(dedpo)]4[SiW12O40]·6H2O (2), and [Ag(dppeo)]3[PW12O40]·3H2O (3) (dedpo = (2-(diphenylphosphaneyl)ethyl)diphenylphosphine oxide; dppeo = ethane-1,2-diylbis(diphenylphosphine oxide)). During the synthesis of these compounds, the 1,2-diphenylphosphine ethane molecule underwent in situ oxidation, transforming into dppeo and dedpo ligands, respectively. Compound 1 features a supramolecular architecture assembled from [Ag(dppeo)3]+/[Ag2(dppeo)6]2+ cationic clusters with disordered Ag centers and protonated [H2PMo12O40]- anions. Compound 2 presents a 3-D POM-supported metal-organic framework consisting of binuclear [Ag(dedpo)]22+ units, {-dedpo-Ag-dedpo-} chains, and [SiW12O40]4- polyoxoanions. Compound 3 displays a 2-D layered structure formed by {-dppeo-Ag3-dppeo-} chains and [PW12O40]3- clusters. Pronounced argentophilic interactions are observed in compounds 1 and 3. The three compounds demonstrate satisfactory heterogeneous catalytic activity in the colorimetric detection reactions toward phenol pollutants with detection limits of 1.73, 1.92, and 4.6 μM, respectively. Additionally, compounds 1-3 show high anti-interference capabilities and high sensitivity in differentiating phenol from its halogenated derivatives. This work presents some guidance for designing specific function-oriented POM-based materials via an in situ ligand transformation strategy.

Effective oxygen activation on polyoxometalate-based hybrids for epoxidation of alkenes

Two polyoxometalate-based hybrids, [M(btap)3(H2O)3(HPW12O40)]·xH2O (M-PW, M = Co/Mn, btap = 3,5-bis(1',2',4'-triazol-1'-yl)pyridine) were synthesized. Co-PW exhibited higher activity and selectivity towards olefin epoxidation than Mn-PW due to the synergistic effect between CoII and PW, in which the Co centers activate O2 to ˙O2- and further binding of free H+ from PW affords the active peroxyacid.

Two 3D Two-Fold Interpenetrated Dia-Like Polyoxometalate-Based Metal-Organic Frameworks: Synthesis and Sulfide Selective Oxidation Activity

Two new three-dimensional (3D) polyoxometalate-based metal-organic frameworks (POMOFs), [M2(btap)4(H2O)4(HPMo10VI Mo2VO40)] (M = Co (1) and Cd (2); btap = 3, 5-bis(1', 2', 4'-triazol-1'-yl)pyridine), have been synthesized under mild hydrothermal conditions and characterized in detail. Single-crystal X-ray diffraction (SXRD) analysis indicates that 1 and 2 are isostructural. In complexes 1 and 2, the metal ion is coordinated with the ligand to form two different left and right helical one-dimensional chains, which are alternately connected in a twisted form to build a two-fold interpenetrated three-dimensional structure, and the polyoxometalate is encapsulated into in the pores generated by the interpenetrating structure. It is noteworthy that 1 and 2, as recyclable catalysts, possess favorable heterogeneous catalytic activity and excellent sulfoxide selectivity in sulfide oxidation reactions, with H2O2 as an oxidant. By reason of the high dispersion of polyoxometalate with good intrinsic activity in the skeleton structure, the title complex has high activity. In addition, no obvious decrease of sulfoxide yield is observed after at least five cycles. These results indicate the excellent catalytic activity and sustainability of 1 and 2.

Self-Activation of Inorganic-Organic Hybrids Derived through Continuous Synthesis of Polyoxomolybdate and para-Phenylenediamine Enables Very High Lithium-Ion Storage Capacity

Inorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C₆ H₁₀ N₂ ]₂ [Mo₈ O₂₆ ] ⋅ 6 H₂ O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C₆ H₉ N₂ ]₄ [NH₄ ]₂ [Mo₇ O₂₄ ] ⋅ 3 H₂ O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g^-1 at 100 mA g^-1 after 150 cycles. The maximum capacity was reached after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li₂ MoO₄ and an additional in situ polymerization of PPD. The final hybrid material is a promising material for lithium-ion battery (LIB) applications.

Operando X-ray Studies of Ni-Containing Heteropolyvanadate Electrode for High-Energy Lithium-Ion Storage Applications

Ni-containing heteropolyvanadate, Na₆[NiV₁₄O₄₀], was synthesized for the first time to be applied in high-energy lithium storage applications as a negative electrode material. Na₆[NiV₁₄O₄₀] can be prepared via a facile solution process that is suitable for low-cost mass production. The as-prepared electrode provided a high capacity of approximately 700 mAh g^-1 without degradation for 400 cycles, indicating excellent cycling stability. The mechanism of charge storage was investigated using operando X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), transition X-ray microscopy (TXM), and density functional theory (DFT) calculations. The results showed that V⁵⁺ was reduced to V²⁺ during lithiation, indicating that Na₆[NiV₁₄O₄₀] is an insertion-type material. In addition, Na₆[NiV₁₄O₄₀] maintained its amorphous structure with negligible volume expansion/contraction during cycling. Employed as the negative electrode in a lithium-ion battery (LIB), the Na₆[NiV₁₄O₄₀]//LiFePO₄ full cell had a high energy density of 300 W h kg^-1. When applied in a lithium-ion capacitor, the Na₆[NiV₁₄O₄₀]//expanded mesocarbon microbead full cell displayed energy densities of 218.5 and 47.9 W h kg^-1 at power densities of 175.7 and 7774.2 W kg^-1, respectively. These findings reveal that the negative electrode material Na₆[NiV₁₄O₄₀] is a promising candidate for Li-ion storage applications.

MOF/POM hybrids as catalysts for organic transformations

Insertion of molecular metal oxides, e.g. polyoxometalates (POMs), into metal-organic frameworks (MOFs) opens up new research opportunities in various fields, particularly in catalysis. POM/MOF composites have strong acidity, oxygen-rich surface, and redox capacity due to typical characteristics of POMs and the large surface area, highly organized structures, tunable pore size, and shape are due to MOFs. Such hybrid materials have gained a lot of attention due to astonishing structural features, and hence have potential applications in organic catalysis, sorption and separation, proton conduction, magnetism, lithium-ion batteries, supercapacitors, electrochemistry, medicine, bio-fuel, and so on. The exceptional chemical and physical characteristics of POMOFs make them useful as catalysts in simple organic transformations with high capacity and selectivity. Here, the thorough catalytic study starts with a brief introduction related to POMs and MOFs, and is followed by the synthetic strategies and applications of these materials in several catalytic organic transformations. Furthermore, catalytic conversions like oxidation, condensation, esterification, and some other types of catalytic reactions including photocatalytic reactions are discussed in length with their plausible catalytic mechanisms. The disadvantages of the POMOFs and difficulties faced in the field have also been explored briefly from our perspectives.

Cu/Ag Complex Modified Keggin-Type Coordination Polymers for Improved Electrochemical Capacitance, Dual-Function Electrocatalysis, and Sensing Performance

Different metal-organic units were introduced into the {PMo₁₂} polyoxometalate (POM) system to yield three porous coordination polymers with distinct characteristics, {Cu(pra)₂}[{Cu(pra)₂}₃{PMo₁₁^VIMo^VO₄₀}] (1), [{Ag₅(pz)₆(H₂O)_0.5Cl}{PMo₁₁^VIMo^VO₄₀}] (2), and [{Cu₃(bpz)₅(H₂O)}{PMo₁₂O₄₀}] (3) (pra = pyrazole; pz = pyrazine; bpz = benzopyrazine), via an in situ hydrothermal method. In comparison with the maternal Keggin cluster and most reported POM electrode materials, compounds 1-3 exhibit larger specific capacitances (672.2, 782.1, and 765.2 F g^-1 at a current density of 2.4 A g^-1, respectively), superior cyclic stability (91.5%, 89.3%, and 87.8% of cycle efficiency after 5000 cycles, respectively), and boosted conductivity, which may be attributed to the introduction of metal-organic units. The result indicates that metal-organic units can effectively enhance the capacitance performance of POMs. This may be due to the fact that they provide additional redox centers, induce the formation of stable porous structures, and improve ion/electron transfer efficiency. Compounds 1-3 present excellent electrocatalytic activity in reducing peroxide (H₂O₂) and oxidizing ascorbic acid (AA). In addition, compound 2 shows an outstanding sensing performance detection of AA and H₂O₂.

Self-Assembly of Polyoxometalate-Resorcin[4]arene-Based Inorganic-Organic Complexes: Metal Ion Effects on the Electrochemical Performance of Lithium Ion Batteries

With their adjustable structures and diverse functions, polyoxometalate (POM)-resorcin[4]arene-based inorganic-organic complexes are a kind of potential multifunctional material. They have potential applications for lithium ion batteries (LIBs). However, the relationship between different coordinated metal ions and electrochemical performance has rarely been investigated. Here, three functionalized POM-resorcin[4]arene-based inorganic-organic materials, [Co₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅2 EtOH⋅4.5 H₂ O (1), [Ni₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅4 EtOH⋅13 H₂ O (2), and [Zn₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅2 EtOH⋅2 H₂ O (3), have been synthesized. Furthermore, to enhance the conductivities of these compounds, 1-3 were doped with reduced graphene oxide (RGO) to give composites 1@RGO-3@RGO, respectively. As anode materials for LIBs, 1@RGO-3@RGO can deliver very high discharge capacities (1445.9, 1285.0 and 1095.3 mAh g^-1 , respectively) in the initial run, and show discharge capacities of 898, 665 and 651 mAh g^-1 , respectively, at a current density of 0.1 A g^-1 over 100 runs. More importantly, the discharge capacities of 319, 283 and 329 mAh g^-1 were maintained for 1@RGO-3@RGO even after 400 cycles at large current density (1 A g^-1 ).

The Association Between Inflammatory and Oxidative Stress Biomarkers and Plasma Metabolites in a Longitudinal Study of Healthy Male Welders

INTRODUCTION

Human metabolism and inflammation are closely related modulators of homeostasis and immunity. Metabolic profiling is a useful tool to understand the association between metabolism and inflammation at a systemic level.

OBJECTIVE

To investigate the longitudinal associations between the concentration of plasma metabolites and biomarkers related to inflammation and oxidative stress.

METHODS

We conducted a repeated cross-sectional analysis consisting of 8 short-term panels that included 88 healthy adult male welders in Massachusetts, USA. In each panel, we collected 1-6 repeated measurements of blood and urine. We used a human vascular injury panel assay and custom cytokine/chemokine assay to quantify inflammatory biomarker plasma levels, liquid chromatography-mass spectrometry to quantify the concentrations of 665 plasma metabolites, and a competitive enzyme-linked immunoassay to quantify urinary 8-OHdG and 8-isoprostane levels. We used linear mixed effects models to estimate the longitudinal association between each inflammatory and oxidative stress biomarker and each metabolite.

RESULTS

At a 5% FDR threshold, we detected ≥1metabolite association for 8 unique inflammatory and oxidative stress biomarkers: urinary 8-isoprostane, plasma C-reactive protein (CRP), serum amyloid A (SAA), intercellular adhesion molecule 1, circulating vascular cell adhesion molecule-1, interleukin 8 (IL-8), interleukin 10 (IL-10) and vascular endothelial growth factor. Specifically, 3 metabolites in the androgenic steroids pathway were negatively associated with SAA; 3 dihydrosphingomyelins metabolites were positively associated with 1 or more of CRP, SAA, IL-8 and IL-10; 4 metabolites in acyl choline metabolism pathways were negatively associated with IL-8; 7 lysophospholipid metabolites were negatively associated with 1 or more of CRP, SAA and IL-8; 4 sphingomyelins were positively associated with CRP and/or SAA; and 10 metabolites in the xanthine pathway were positively associated with urinary 8-isoprostane.

CONCLUSION

We found that metabolites in phospholipid groups had strong associations with multiple inflammatory biomarkers, especially CRP, SAA and IL-8. The mechanism of these associations warrants further investigation.

Wells-Dawson Arsenotungstate Porous Derivatives for Electrochemical Supercapacitor Electrodes and Electrocatalytically Active Materials

Two Wells-Dawson arsenotungstate coordination polymers, [{Cu^II(bim)₂}₃(As₂W₁₈O₆₂)] (1) and [(Cu^I₁₀pz₁₀Cl₄)(As₂W₁₈O₆₂)] (bim = 2,2'-biimidazole; pz = pyrazine), have been assembled via a hydrothermal method and fully characterized. Compound 1 exhibits a 2,6-connected two-dimensional hybrid layer based on asymmetrically modified {As₂W₁₈} anions and {Cu(bim)₂} linkers, which is extended to a three-dimensional network with a special interlayer structure and a one-dimensional tunnel. Compound 2 is a host-guest framework that consists of a Cu-pz-Cl network with 20-member square rings, 16-member irregular rings, and embedded eight-node {As₂W₁₈} guest molecules. Compounds 1 and 2 show uncommon specific capacitance (834.8 and 960.1 F g^-1, respectively, at a current density of 2.4 A g^-1), enduring cycling stability (capacitance retention rates of 89.3% and 91.9%, respectively, after 5000 cycles), and good electrical conductivity, which are superior to those of the unmodified zero-dimensional Dawson arsenotungstate compound and most reported electrode materials in terms of their stable structure, special layer spacing, and orderly channels. Moreover, the title compounds exhibit excellent electrocatalytic activity for oxidizing ascorbic acid and reducing nitrite.

A Copper-Containing Polyoxometalate-Based Metal-Organic Framework as an Efficient Catalyst for Selective Catalytic Oxidation of Alkylbenzenes

A copper-containing polyoxometalate-based metal-organic framework (POMOF), Cu^I₁₂Cl₂(trz)₈[HPW₁₂O₄₀] (HENU-7, HENU = Henan University; trz = 1,2,4-triazole), has been successfully synthesized and well-characterized. In addition, the excellent catalytic ability of HENU-7 has been proved by the selective oxidation of diphenylmethane. Under the optimal conditions, the diphenylmethane conversion obtained over HENU-7 is 96%, while the selectivity to benzophenone is 99%, which outperforms most noble-metal-free POM-based catalysts. Moreover, HENU-7 is stable to reuse for five runs without an obvious loss in activity and also can catalyze the oxidation of different benzylic C-H with satisfactory conversions and selectivities, which implied the significant catalytic activity and recyclability.

Keggin-type polyoxometalate-containing metal–organic hybrids as friction materials for triboelectric nanogenerators

The POM-based inorganic–organic hybrids with different structures were assembled and used as the friction materials to construct TENGs and the results demonstrated that the output performance was closely related to the dielectric constant.

POM-Based MOF-Derived Co3O4/CoMoO4 Nanohybrids as Anodes for High-Performance Lithium-Ion Batteries

Polyoxometalate (POM)-based metal-organic framework (MOF)-derived Co₃O₄/CoMoO₄ nanohybrids were successfully fabricated by a facile solvothermal method combined with a calcination process, in which a Co-based MOF, that is, ZIF-67 acts as a template while a Keggin-type POM (H₃PMo₁₂O₄₀) serves as a compositional modulator. The materials were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) mapping, and electrochemical measurements. When the Co₃O₄/CoMoO₄ nanohybrids were applied as anode materials for lithium-ion batteries (LIBs), they display large lithium storage capacity (around 900 mAh g^-1 at 0.1 A g^-1) and high cycling stability, and they can also exhibit good rate performances. This work might shed some light on the POM-based MOF host-guest synthesis strategy for the preparation of polymetallic oxides for enhanced electrochemical energy storage and further applications.

In Operando X-ray Studies of High-Performance Lithium-Ion Storage in Keplerate-Type Polyoxometalate Anodes

Polyoxometalates (POMs) have emerged as potential anode materials for lithium-ion batteries (LIBs) owing to their ability to transfer multiple electrons. Although POM anode materials exhibit notable results in LIBs, their energy-storage mechanisms have not been well-investigated. Here, we utilize various in operando and ex situ techniques to verify the charge-storage mechanisms of a Keplerate-type POM Na₂K₂₃{[(Mo^VI)Mo^VI₅O₂₁(H₂O)₃(KSO₄)]₁₂ [(V^IVO)₃₀(H₂O)₂₀(SO₄)_0.5]}·ca200H₂O ({Mo₇₂V₃₀}) anode in LIBs. The {Mo₇₂V₃₀} anode provides a high reversible capacity of up to ∼1300 mA h g^-1 without capacity fading for up to 100 cycles. The lithium-ion storage mechanism was studied systematically through in operando synchrotron X-ray absorption near-edge structure, ex situ X-ray diffraction, ex situ extended X-ray absorption fine structure, ex situ transmission electron microscopy, in operando synchrotron transmission X-ray microscopy, and in operando Raman spectroscopy. Based on the abovementioned results, we propose that the open hollow-ball structure of the {Mo₇₂V₃₀} molecular cluster serves as an electron/ion sponge that can store a large number of lithium ions and electrons reversibly via multiple and reversible redox reactions (Mo⁶⁺ ↔ Mo¹⁺ and V⁵⁺/V⁴⁺↔ V¹⁺) with fast lithium diffusion kinetics (D_Li⁺: 10^-9-10^-10 cm² s^-1). No obvious volumetric expansion of the microsized {Mo₇₂V₃₀} particle is observed during the lithiation/delithiation process, which leads to high cycling stability. This study provides comprehensive analytical methods for understanding the lithium-ion storage mechanism of such complicated POMs, which is important for further studies of POM electrodes in energy-storage applications.

Graphite-like polyoxometalate-based metal–organic framework as an efficient anode for lithium ion batteries

A new porous POM supported graphite-like MOF (Cu-POM) as a LIB anode material was designed and synthesized, and its lithium storage mechanism was explored using impedance spectra.

Polyoxometalates-Based Metal-Organic Frameworks Made by Electrodeposition and Carbonization Methods as Cathodes and Anodes for Asymmetric Supercapacitors

Hybrid materials have obtained well-deserved attention for energy storage devices, because they show high capacitances and high energy densities induced by the synergistic effect between complementary components. Polyoxometalate-based metal-organic frameworks (POMOFs) possess the abundant redox-active sites and ordered structures of polyoxometalates (POMs) and metal-organic frameworks (MOFs), respectively. Here, an asymmetric supercapacitor (ASC) NENU-5/PPy/60//FeMo/C was fabricated in which both its electrodes are prepared from POMOF precursors. A typical POMOF material, NENU-5, was first connected with polypyrrole (PPy) through electrodeposition to form the cathode material NENU-5/PPy. Another representative POMOFs material, PMo₁₂ @MIL-100, was carbonized to obtain the anode material FeMo/C. Cathode NENU-5/PPy exhibited an extraordinary capacitance of 508.62 F g^-1 (areal capacitance: 2034.51 mF cm^-2 ). In addition, anode FeMo/C shows excellent cyclic stability attributed to its unique structure. Finally, benefiting from the outstanding capacitances and structural merits of the anode and cathode, assembled asymmetric supercapacitor NENU-5/PPy/60//FeMo/C achieves an energy density of 1.12 mWh cm^-3 at a power density output of 27.78 mW cm^-3 , as well as a notable life of 10 000 cycles with an capacity retention of 80.62 %. Thus, the unique ASC is strongly competitive in high capacitance, long cycle life, and high energy-required energy storage devices.

Polyoxometalate Metal-Organic Frameworks: Keggin Clusters Encapsulated into Silver-Triazole Nanocages and Open Frameworks with Supercapacitor Performance

To investigate the relationship between the structures of polyoxometalate host-guest materials and their energy-storage performance, three novel polyoxometalate-based metal-organic compounds, [Ag₁₀(C₂H₂N₃)₈][HVW₁₂O₄₀], [Ag₁₀(C₂H₂N₃)₆][SiW₁₂O₄₀], and [Ag(C₂H₂N₃)][Ag₁₂(C₂H₂N₃)₉][H₂BW₁₂O₄₀] are synthesized by a one-step hydrothermal method and further confirmed by single-crystal X-ray diffraction analyses and other numerous characterization techniques. In compound [Ag₁₀(C₂H₂N₃)₈][HVW₁₂O₄₀], the Keggin clusters are intersected into channels formed by a 3D open metal-organic framework. In contrast, in compounds [Ag₁₀(C₂H₂N₃)₆][SiW₁₂O₄₀] and [Ag(C₂H₂N₃)][Ag₁₂(C₂H₂N₃)₉][H₂BW₁₂O₄₀], the Keggin clusters are encapsulated into silver-triazole metal-organic nanocages to construct core-shell structures, which are further fused together by covalent bonds to form 3D polyoxometalate-based metal-organic frameworks. The electrochemical properties of three compound-based electrodes are estimated by cyclic voltammetry, galvanostatic charge-discharge, electrochemically active surface area, and electrochemical impedance spectroscopy. The results of the electrochemical performance tests indicate that these compounds possess high specific capacitance and cycling stability, especially [Ag₁₀(C₂H₂N₃)₈][HVW₁₂O₄₀], showing a specific capacitance of 93.5 F g^-1, which is higher than that of many other polyoxometalate-based electrode materials. A possible mechanism of the electrochemical performance is explored, which is mainly related to the redox capacity of polyoxometalate, the electrochemically active surface area, the electrochemical impedance spectroscopy, and the microstructures of polyoxometalate-based metal-organic frameworks.

Modified polyoxometalate: a novel monocapped bi-supporting and reduced α-Keggin structure {PMo12O40[Cu(2,2'-bpy)]}[Cu(2,2'-bpy)(en)(H2O)]2

A novel modified polyoxometalate, {PMo₁₂O₄₀[Cu(2,2'-bpy)]}[Cu(2,2'-bpy)(en)(H₂O)]₂ [2,2'-bpy is 2,2'-bipyridyl (C₁₀H₈N₂) and en is ethylenediamine (C₂H₈N₂)], has been synthesized hydrothermally and structurally characterized by elemental analysis, TG, IR, XPS and single-crystal X-ray diffraction. The structural analysis reveals that the compound contains the reduced Keggin polyanion [PMo₁₂O₄₀]^6- as the parent unit, which is monocapped by [Cu(2,2'-bpy)]²⁺ fragments via four bridging O atoms on an {Mo₄O₄} pit and bi-supported by two [Cu(2,2'-bpy)(en)(H₂O)]²⁺ coordination cations simultaneously. There exist strong intramolecular π-π stacking between the capping and supporting units, which play a stabilizing role during the crystallization of the compound. Adjacent POM clusters are further aggregated to form a three-dimensional supramolecular network through noncovalent forces, hydrogen bonding and π-π stacking interactions. In addition, the photocatalytic properties were investigated in detail, and the results indicated that the compound can be used as a photocatalyst towards the decomposition of the organic pollutant methylene blue (MB).

Polyoxometalate-Incorporated Metallacalixarene@Graphene Composite Electrodes for High-Performance Supercapacitors

Composites of polyoxometalate (POM)/metallacalixarene/graphene-based electrode materials not only integrate the superiority of the individual components perfectly but also ameliorate the demerits to some extent, providing a promising route to approach high-performance supercapacitors. Herein, first, we report the preparations, structures, and electrochemical performance of two fascinating POM-incorporated metallacalixarene compounds [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiMo₁₂O₄₀] (1) and [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiW₁₂O₄₀] (2); (C₂H₂N₃ = 1 H-1,2,4-triazole). Single-crystal X-ray diffraction analyses illustrated that both 1 and 2 possess intriguing POM-sandwiched metallacalix[6]arene frameworks. Nevertheless, our investigations, including the electrochemical cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy, reveal that the oxidation ability of the Keggin ions is a primary effect in electrochemical performance of these POM-incorporated metallacalixarene compounds. Namely, the electrodes containing Mo as metal atoms in the Keggin POM shows much higher capacitance than the corresponding W-containing ones. Moreover, compound 1@graphene oxide (GO) composite electrodes are fabricated and systematically explored for their supercapacitor performance. Thanks to the synergetic effects of GO and POM-incorporated metallacalixarenes, the compound 1@15%GO-based electrode exhibits the highest specific capacitance of up to 230.2 F g^-1 (current density equal to 0.5 A g^-1), which is superior to majority of the reported POM-based electrode materials.

Polyoxometalates as components of supramolecular assemblies

The non-covalent interaction of polyoxometalates (POMs) with inorganic- or organic-based moieties affords hybrid assemblies with specific physicochemical properties that are of high interest for both fundamental and applied studies, including the discovery of conceptually new compounds and unveiling the impact of their intra-supramolecular relationships on the fields of catalysis, molecular electronics, energy storage and medicine. This minireview summarises the recent advances in the synthetic strategies towards the formation of such non-covalent POM-loaded assemblies, shedding light on their key properties and the currently investigated applications. Four main emerging categories according to the nature of the conjugate are described: (i) POMs in metal-organic frameworks, (ii) POMs merged with cationic metal complexes, (iii) architectures generated with solely POM units and (iv) POMs assembled with organic molecular networks.

Surfactant-assisted synthesis and electrochemical properties of an unprecedented polyoxometalate-based metal–organic nanocaged framework

The first polyoxometalate-based nanocaged three-dimensional metal–organic framework was synthesized by a surfactant-assisted hydrothermal method.

Polyanthraquinone-Triazine-A Promising Anode Material for High-Energy Lithium-Ion Batteries

A novel covalent organic framework polymer material that bears conjugated anthraquinone and triazine units in its skeleton has been prepared via a facile one-pot condensation reaction and employed as an anode material for Li-ion batteries. The conjugated units consist of C═N groups, C═O groups, and benzene groups, which enable a 17-electron redox reaction with Li per repeating unit and bring a theoretical specific capacity of 1450 mA h g^-1. The polymer also shows a large specific surface area and a hierarchically porous structure to trigger interfacial Li storage and contribute to an additional capacity. The highly conductive conjugated polymer skeleton enables fast electron transport to facilitate the Li storage. In this way, the polymer electrode shows a large specific capacity and favorable cycling and rate performance, making it an appealing anode choice for the next-generation high-energy batteries.

Polyoxometalates/Active Carbon Thin Separator for Improving Cycle Performance of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have great potential for the next generation of energy-storage devices owing to their high theoretical energy density. However, the polysulfides' shuttling effect seriously degraded the cycle stability and capacity and hindered their commercial applications. Here, we design and fabricate a bifunctional composite separator including a polypropylene (PP) matrix layer and Keggin polyoxometalate [PW₁₂O₄₀]^3-/Super P composite retarding layer by utilizing the Coulombic repulsion between polyanion and polysulfides. Such a binary composite separator shows the effects in enhancing the Coulombic efficiency and cycling stability. Compared with the polypropylene (PP) matrix separator, the capacity is improved by 41% after 120 cycles when using the PW₁₂/Super P separator. It is the first time that the polyoxometalate (POM) matrix is used as a bifunctional separator for lithium-sulfur batteries, demonstrating the promise of POM-based separators in reducing the shuttling effect of Li-S battery.

A series of new polyoxometalate-based metal-organic complexes with different rigid pyridyl-bis(triazole) ligands: assembly, structures and electrochemical properties

Five new polyoxometalate (POM)-based metal-organic complexes (MOCs) with different rigid pyridyl-bis(triazole) ligands, namely, H{Co2(Hpyttz-I)2(H2O)6[CrMo6(OH)6O18]}·8H2O (1), {Co2(H2pyttz-I)2(H2O)4[TeMo6O24]}[Co(H2O)6]·3H2O (2), {Co3(Hpyttz-II)2(H2O)6[γ-Mo8O26]}·10H2O (3), {Ni3(Hpyttz-II)2(H2O)6[γ-Mo8O26]}·10H2O (4), {Ni3(Hpyttz-III)2(H2O)8[γ-Mo8O26]}·10H2O (5) (H2pyttz-I = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H2pyttz-II = 3-(pyrid-3-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H2pyttz -III = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 is a two-dimensional (2D) supramolecular network based on the binuclear complex unit: [Co2(Hpyttz-I)2(H2O)6 [CrMo6(OH)6O18]]. Complex 2 is a 1D supramolecular chain derived from the binuclear cobalt complex: {Co2(H2pyttz-I)2(H2O)4[TeMo6O24]}2-, the discrete [Co(H2O)6]2+ units act as counter cations. Complexes 3 and 4 are isostructural with different center metals (M = Co or Ni), the adjacent γ-Mo8O26 4- anions are linked by the MII ions to form a 1D M-γ-Mo8O26 inorganic chain. Then 1D M-γ-Mo8O26 inorganic chains are linked together by the 1D metal-organic M-(Hpyttz-II) chains to form a 3D framework. In complex 5, γ-Mo8O26 4- anions are bridged by the NiII ions to give a 1D Ni-γ-Mo8O26 inorganic chain, the adjacent 1D Ni-γ-Mo8O26 chains are connected through [Ni(Hpyttz-III)2] units to form a 2D layer. The effect of POM type and coordination site of the ligands on the structures of the title complexes were discussed. The title complexes 1, 2 and 5 exhibit excellent bifunctional electrocatalytic activities toward the reduction of bromate/hydrogen peroxide and the oxidation of ascorbic acid. In addition, the redox potentials of complexes 1, 2 and 5 are highly sensitive to pH and may be used as a kind of potential pH sensor.

One-step synthesis of ZnS-N/C nanocomposites derived from Zn-based chiral metal–organic frameworks with highly efficient photocatalytic activity for the selective oxidation of cis-cyclooctene

ZnS-N/C derived from Zn-based chiral MOFs exhibits excellent photocatalytic activity for the selective oxidation of cis-cyclooctene under mild conditions.

Boosting the ultrastable Li storage performance in electron-sponge-like polyoxovanadates by constructing inorganic 3D structures

Mg₂(NH₄)₂V₁₀O₂₈·nH₂O with a 3D extended structure tuned by counter cations has been prepared as an active electrode material for a Li ion battery.