Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting.

In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe3C) modified on biomass-derived nitrogen-doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe3C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe3C/NC-550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at -10 mA cm-2) and oxygen evolution reaction (281.4 mV at 10 mA cm-2), favorable overall water splitting activity (1.57 V at 10 mA cm-2). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

Heterostructured CoFeP/CoP as an Electrocatalyst for Hydrogen Evolution in Alkaline Media.

Developing highly efficient and persistent transition-metal-phosphide (TMP)-based electrocatalysts is critical for the hydrogen evolution reaction (HER) via water splitting in alkaline media. Herein, we constructed a unique heterostructured CoFeP/CoP grown on a nickle foam (NF) via hydrothermal and dipping methods followed by phosphorization at different temperatures for HER. The experimental results exhibit that the HER activity of CoFeP/CoP-400 is accelerated after the construction of heterostructures. The unique heterostructure provides plentiful active sites and a large surface area, which are beneficial for HER in 1.0 M KOH. CoFeP/CoP-400 displays a small overpotential of 78 mV at a current density of 10 mA cm-2 and a smaller Tafel slope of 55.5 mV dec-1. Moreover, CoFeP/CoP-400 shows excellent stability with a long-term operating time of 12 h. This work provides an effective method for the construction of TMPs with heterostructures for promoting energy conversion.

Preparation of MoFs-Derived Cobalt Oxide/Carbon Nanotubes Composites for High-Performance Asymmetric Supercapacitor.

Metal-organic frameworks (MOFs)-derived metallic oxide compounds exhibit a tunable structure and intriguing activity and have received intensive investigation in recent years. Herein, this work reports metal-organic frameworks (MOFs)-derived cobalt oxide/carbon nanotubes (MWCNTx@Co3O4) composites by calcining the MWCNTx@ZIF-67 precursor in one step. The morphology and structure of the composite were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization. The compositions and valence states of the compounds were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Benefiting from the structurally stable MOFs-derived porous cobalt oxide frameworks and the homogeneous conductive carbon nanotubes, the synthesized MWCNTx@Co3O4 composites display a maximum specific capacitance of 206.89 F·g-1 at 1.0 A·g-1. In addition, the specific capacitance of the MWCNT3@Co3O4//activated carbon (AC) asymmetric capacitor reaches 50 F·g-1, and has an excellent electrochemical performance. These results suggest that the MWCNTx@Co3O4 composites can be a potential candidate for electrochemical energy storage devices.

A structure-property study for konjac glucomannan and guar galactomannan: Selective carboxylation and scale inhibition.

The effect of structural difference for konjac glucomannan (KGM) and guar galactomannan (GGM) on their physicochemical properties including selective carboxylation, biodegradation and scale inhibition was firstly investigated. Compared with GGM, KGM can be specially modified by amino acid to prepare carboxyl-functionalized polysaccharides. The structure-activity relationship explaining the difference in carboxylation activity and the anti-scaling abilities of polysaccharides and carboxylated derivatives were explored by static anti-scaling, iron oxide dispersion and biodegradation tests coupled with structural and morphological characterizations. KGM with linear structure was preferred for carboxylated modification by glutamic acid (KGMG) and aspartic acid (KGMA) while GGM with branched structure failed to accomplish that due to steric hindrance. GGM and KGM showed limited scale inhibition performance, which was probably attributed to the moderate adsorption and isolation effect of macromolecular stereoscopic structure. While KGMA and KGMG performed as effective and degradable inhibitors for CaCO3 scale with inhibitory efficiencies > 90 %.

Design of an Internal/External Bicontinuous Conductive Network for High-Performance Asymmetrical Supercapacitors.

High-energy density supercapacitors have attracted extensive attention due to their electrode structure design. A synergistic effect related to core-shell structure can improve the energy storage capacity and power density of electrode materials. The Ni-foam (NF) substrate coupled with polypyrrole (PPy) conductive coating can serve as an internal/external bicontinuous conductive network. In this work, the distinctive PPy@FeNi2S4@NF and PPy@NiCo2S4@NF materials were prepared by a simple two-step hydrothermal synthesis with a subsequent in situ polymerization method. PPy@FeNi2S4@NF and PPy@NiCo2S4@NF could deliver ultrahigh specific capacitances of 3870.3 and 5771.4 F·g-1 at 1 A·g-1 and marvelous cycling capability performances of 81.39% and 93.02% after 5000 cycles. The asymmetric supercapacitors composed of the prepared materials provided a high-energy density of over 47.2 Wh·kg-1 at 699.9 W·kg-1 power density and 67.11 Wh·kg-1 at 800 W·kg-1 power density. Therefore, the self-assembled core-shell structure can effectively improve the electrochemical performance and will have an effective service in advanced energy-storage devices.

Two Polyoxometalate-Encapsulated Two-Fold Interpenetrating dia Metal-Organic Frameworks for the Detection, Discrimination, and Degradation of Phenolic Pollutants.

Phenols are widely used for commercial production, while they pose a hazard to the environment and human health. Thus, investigation of convenient and efficient methods for the detection, discrimination, and degradation of phenols becomes particularly important. Herein, two new polyoxometalate (POM)-based compounds, [Co2(btap)4(H2O)4][SiW12O40] (Co-POM) and [Ni2(btap)4(H2O)4][SiW12O40] (Ni-POM) (btap = 3,5-bis(triazol-1-yl)pyridine), are prepared via a hydrothermal synthesis method. The compounds show a fascinating structural feature of a POM-encapsulated twofold interpenetrating dia metal-organic framework. More importantly, besides the novel structures, the compound Co-POM realizes three functions, namely, the simultaneous detection, discrimination, and degradation of phenols. Specifically, Co-POM shows an excellent colorimetric detection performance toward phenol with a detection limit (LOD) ca. 1.32 µM, which is lower than most reported colorimetric detectors for phenol. Also, a new colorimetric sensor system based on Co-POM can discriminate phenol, 4-chlorophenol, and o-cresol with ease. Further, Co-POM exhibits a photocatalytic degradation property for 4-chlorophenol under irradiation of visible light with the highest degradation rate at 62% after irradiation for 5 h. Therefore, this work provides the first example of a POMs-based multifunctional material for achieving the detection, discrimination, and degradation of phenolic pollutants.

A MOF-Derivative Decorated Hierarchical Porous Host Enabling Ultrahigh Rates and Superior Long-Term Cycling of Dendrite-Free Zn Metal Anodes.

Aqueous Zn metal batteries have attracted much attention due to their high intrinsic capacity, high safety, and low cost. Nevertheless, uncontrollable dendrite growth and adverse side reactions of Zn anodes seriously hinder their further application. Herein, a three-dimensional (3D) porous graphene-carbon nanotubes scaffold decorated with metal-organic framework derived ZnO/C nanoparticles (3D-ZGC) is fabricated as the host for dendrite-free Zn-metal composite anodes. The zincophilic ZnO/C nanoparticles act as preferred deposition sites with low nucleation barriers to induce homogeneous Zn deposition. The mechanically robust 3D scaffold with high conductivity not only suppresses the formation of dendritic Zn by reducing the local current density and homogenizing Zn2+ ion flux, but also inhibits volume changes during the long-term plating/stripping process. As a result, the 3D-ZGC composite anodes afford unprecedented Zn plating-stripping stability at an ultrahigh current density of 20 mA cm-2 for 1500 cycles with low overpotential (<65 mV) when used in a symmetric cell. When coupled with MnO2 cathodes, the assembled Zn@3D-ZGC//MnO2 full batteries deliver an enhanced cycling stability for up to 6000 cycles at 2000 mA g-1 , demonstrating the potential of the 3D-ZGC composite anode for advanced Zn metal batteries.

Hierarchical CoS2/MoS2 flower-like heterostructured arrays derived from polyoxometalates for efficient electrocatalytic nitrogen reduction under ambient conditions.

Electrochemical nitrogen reduction reaction (NRR) has been identified as a prospective alternative for sustainable ammonia production. Developing cost-effective and highly efficient electrocatalysts is critical for NRR under ambient conditions. Herein, the hierarchical cobalt-molybdenum bimetallic sulfide (CoS2/MoS2) flower-like heterostructure assembled from well-aligned nanosheets has been easily fabricated through a one-step strategy. The efficient synergy between different components and the formation of heterostructure in CoS2/MoS2 nanosheets with abundant active sites makes the non-noble metal catalyst CoS2/MoS2 highly effective in NRR, with a high NH3 yield rate (38.61 µg h-1 mgcat.-1), Faradaic efficiency (34.66%), high selectivity (no formation of hydrazine) and excellent long-term stability in 1.0 mol L-1 K2SO4 electrolyte (pH = 3.5) at -0.25 V versus the reversible hydrogen electrode (vs. RHE) under ambient conditions, exceeding much recently reported cobalt- and molybdenum-based materials, even catch up with some noble-metal-based catalyst. Density functional theory (DFT) calculation indicates that the formation of N2H* species on CoS2(200)/MoS2(002) is the rate-determining step via both the alternating and distal pathways with the maximum ΔG values (1.35 eV). These results open up opportunities for the development of efficient non-precious bimetal-based catalysts for NRR.

Fe Foam-Supported FeS2-MoS2 Electrocatalyst for N2 Reduction under Ambient Conditions.

Highly efficient catalysts with enough selectivity and stability are essential for electrochemical nitrogen reduction reaction (e-NRR) that has been considered as a green and sustainable route for synthesis of NH3. In this work, a series of three-dimensional (3D) porous iron foam (abbreviated as IF) self-supported FeS2-MoS2 bimetallic hybrid materials, denoted as FeS2-MoS2@IFx, x = 100, 200, 300, and 400, were designed and synthesized and then directly used as the electrode for the NRR. Interestingly, the IF serving as a slow-releasing iron source together with polyoxomolybdates (NH4)6Mo7O24·4H2O as a Mo source were sulfurized in the presence of thiourea to form self-supported FeS2-MoS2 on IF (abbreviated as FeS2-MoS2@IF200) as an efficient electrocatalyst. Further material characterizations of FeS2-MoS2@IF200 show that flower cluster-like FeS2-MoS2 grows on the 3D skeleton of IF, consisting of interconnected and staggered nanosheets with mesoporous structures. The unique 3D porous structure of FeS2-MoS2@IF together with synergy and interface interactions of bimetallic sulfides would make FeS2-MoS2@IF possess favorable electron transfer tunnels and expose abundant intrinsic active sites in the e-NRR. It is confirmed that synthesized FeS2-MoS2@IF200 shows a remarkable NH3 production rate of 7.1 ×10-10 mol s-1 cm-2 at -0.5 V versus the reversible hydrogen electrode (vs RHE) and an optimal faradaic efficiency of 4.6% at -0.3 V (vs RHE) with outstanding electrochemical and structural stability.

Nickel/Cobalt Molybdate Hollow Rods Induced by Structure and Defect Engineering as Exceptional Electrode Materials for Hybrid Supercapacitor.

Oxygen defects and hollow structures positively impact pseudocapacitive properties of diffusion/surface-controlled processes, a component of critical importance when building high-performance supercapacitors. Hence, we fabricated hollow nickel/cobalt molybdate rods with O-defects (D-H-NiMoO4 @CoMoO4 ) through a soft-template and partial reduction method, enhancing D-H-NiMoO4 @CoMoO4 's electrochemical performance, yielding a specific capacitance of 1329 F g-1 , and demonstrating excellent durability with 95.8 % capacity retention after 3000 cycles. D-H-NiMoO4 @CoMoO4 was used as the positive electrode to construct an asymmetric supercapacitor, displaying an energy density of up to 34.13 Wh kg-1 and demonstrating good predisposition towards practical applications. This work presents an effective approach to fabricate and use hollow nickel/cobalt molybdate rods with O-defects as pseudocapacitor material for high-performance capacitive energy storage devices.

In situ hierarchical encapsulation of bimetallic selenides into honeycomb-like nitrogen doped porous carbon nanosheets for highly sensitive and selective guanosine detection.

An innovative electrochemical nanocomposite for the detection of guanosine (Gua) was proposed by in situ encapsulation of nickel-iron bimetallic selenides confined into honeycomb-like nitrogen doped porous carbon nanosheets, denoted as (Ni,Fe)Se2/N-PCNs. The porous carbon nanosheets were prepared by utilizing nickel-iron layered double hydroxide (Ni-Fe LDH) as the substrate and zeolitic imidazolate frameworks (ZIF-67) nanocrystals as the sacrificial templates via hydrothermal synthesis, followed by a process of acid etching and pyrolysis selenylation. Interestingly, the nickel-ferric bimetallic selenides material (Ni,Fe)Se2, is rarely fabricated successfully using selenylation treatment, which is a highly conductive and robust support to promote the electron transport. Meanwhile, the obtained (Ni,Fe)Se2/N-PCNs have the favorable architectural features of both unique three-dimensional (3D) porous structural and hierarchical connectivity, which are expected to provide more active sites for electrochemical reactions and ease of electron, ion, and biomolecule penetration. Benefiting from the inherent virtues of its composition, together with unique structural advantages, the (Ni,Fe)Se2/N-PCNs possess ideal sensing properties for guanosine detection with a low detection limit of 1.20 × 10-8 M, a wide linear range of 5.30 × 10-8 ~ 2.27 × 10-4 M and a good stability. Superb selectivity for potential interfering species and superb recoveries in serum suggests its feasibility for practical applications.

Construction of an ultra-sensitive electrochemical sensor based on polyoxometalates decorated with CNTs and AuCo nanoparticles for the voltammetric simultaneous determination of dopamine and uric acid.

A composite modified electrode was prepared based on α-K7P2VW17O62·18H2O (P2W17V), CNTs and AuCo nanoparticles (AuCo NPs), and used as a structurally stable and highly sensitive electrochemical sensor for simultaneous determination of dopamine (DA) and uric acid (UA). The combination of three active components endows the electrode with large specific surface area, high electrical conductivity, and excellent electrochemical activity. The as-prepared modified electrode exhibited impressive electrocatalytic oxidation performance of DA and UA at an optimum working potential (0.172 V vs. Ag/AgCl for DA and 0.288 V vs. Ag/AgCl for UA) with linear detection range from 1.25 × 10-6 to 2.81 × 10-4 M and 0.75 × 10-6 to 1.66 × 10-4 M and the detection limit of 0.15 and 0.25 µM (S/N = 3) for DA and UA, respectively. Additionally, the peak-to-peak separation signals in DPV are 116 mV. The influence of several possible co-existing substances was investigated. The applicability of the method for real samples analysis was tested by determination of DA and UA in human serums. This new sensor holds great promise for sensitive determination of DA and UA in real application. Graphical abstract.

A High-Capacity Negative Electrode for Asymmetric Supercapacitors Based on a PMo12 Coordination Polymer with Novel Water-Assisted Proton Channels.

The development of a negative electrode for supercapacitors is a critical challenge for the next-generation of energy-storage devices. Herein, two new electrodes formed by the coordination polymers [Ni(itmb)4 (HPMo12 O40 )]·2H2 O (1) and [Zn(itmb)3 (H2 O)(HPMo12 O40 )]·4H2 O (2) (itmb = 1-(imidazo-1-ly)-4-(1,2,4-triazol-1-ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g-1 , respectively. An asymmetric supercapacitor device assembled using 2 which has novel water-assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of 23.4 W h kg-1 and 3864.4 W kg-1 , respectively. Moreover, the ability to feed a red light emitting diode (LED) also demonstrates the feasibility for practical use. The results allow a better elucidation of the storage mechanism in polyoxometalate-based coordination polymers and provide a promising direction for exploring novel negative materials for new-generation high-performance supercapacitors.

3D Hollow Flower-like CoWO4 Derived from ZIF-67 Grown on Ni-foam for High-Performance Asymmetrical Supercapacitors.

A three-dimensional (3D) hollow CoWO4 composite grown on Ni-foam (3D-H CoWO4 /NF) based on a flower-like metal-organic framework (MOF) is designed by utilizing a facile dipping and hydrothermal approach. The 3D-H CoWO4 /NF not only possesses large specific areas and rich active sites, but also accommodates volume expansion/contraction during charge/discharge processes. In addition, the unique structure facilitates fast electron/ion transport of 3D-H CoWO4 /NF. Meanwhile, a series of characterization measurements demonstrate the appropriate morphology and excellent electrochemical performance of the material. The 3D-H CoWO4 /NF possesses a high specific capacitance of 1395 F g-1 , an excellent cycle stability with 89% retention after 3000 cycles and superior rate property. Furthermore, the 3D-H CoWO4 /NF can be used as a cathode to configurate an asymmetric supercapacitor (ASC), and 3D-H CoWO4 /NF//AC shows a good energy density (29.0 W h kg-1 ). This work provides a facile method for the preparation of 3D-hollow electrode materials with high electrochemical capability for advanced energy storage devices.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor.

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe2O4) - based composite (NiFe2O4-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe2O4 from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe2O4 possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe2O4-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe2O4-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg-1). Moreover, NiFe2O4-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm-2, the wide linear range of 3.500 × 10-5 - 4.525 × 10-3 M, and the detection limit of 12.94 × 10-6 M with a signal to noise ratio of 3. Consequently, the NiFe2O4-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

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.

Facile Dual-Ligand Modulation Tactic toward Nickel-Cobalt Sulfides/Phosphides/Selenides as Supercapacitor Electrodes with Long-Term Durability and Electrochemical Activity.

The use of high electrochemical active binary nickel-cobalt sulfides/phosphides/selenides (Ni-Co-X, X = S, P, Se) as electrochemical energy storage materials still has a space for improvement because they become electrochemically unstable during long-term use. Herein, a facile and cost-effective dual-ligand synergistic modulation tactic is described to substantially improve the durability of Ni-Co-X (X = S, P, Se) at the atomic level by partially substituting S, P, and Se ligands into the nickel-cobalt hydroxide precursor, respectively. Remarkably, the dual-ligand electrodes on Ni-foam achieve superior durability and high electrochemical activity when used as positive electrodes in supercapacitors. Impressively, the density functional theory calculations demonstrate that the OH ligand in NiCo2(MOH)x (M = S, P, Se) could attract electrons from metal-S/metal-P/metal-Se bonds to the metal-O bond, enhancing the binding energy of metal-S/metal-P/metal-Se bonds and improving the long-term durability of Ni-Co-X (X = S, P, Se) in alkaline electrolytes. Moreover, OH and S/P/Se ligands could effectively alter the electron structure and result in favorable electrochemical activity. Overall, this tactic could offer an exciting avenue to achieve long-term durability and electrochemical activity of supercapacitor electrodes simultaneously.

Mo-Based crystal POMOFs with a high electrochemical capacitor performance.

Mo-Based crystalline polyoxometalate-based metal-organic frameworks (POMOFs), namely, [CuIH2(C12H12N6)(PMo12O40)]·[(C6H15N)(H2O)2] (1) and [Cu(C12H12N6)4(PMoMoO39)] (2) (C12H12N6, 1,4-bis(triazol-1-ylmethyl) benzene, abbreviation btx) as promising capacitor electrode materials were synthesized by a hydrothermal reaction. Compound 1 consisted of two-dimensional (2D) lattice structures with free triethylamine (abbreviation, TEA) molecules and H2O molecules, and compound 2 showed a 3D host-guest structure, in which 1D polyoxometalate (POM) chains were encapsulated into a 3D Cu(ii)-btx metal-organic framework (MOF). The compound 1-based electrode showed much higher specific capacitance (249.0 F g-1 at 3 A g-1) than the 2-based one (154.5 F g-1 at 3 A g-1). Moreover, the specific capacitance of the 1-based electrode was not only higher than those of the majority of the reported POMOF materials as supercapacitors, but also higher than those of most state-of-the-art MOF-based and POM-based supercapacitor electrode materials. This superior capacitance performance of the 1-based electrode could be attributed to the high redox capacity and excellent electronic conductivity. More importantly, this work may open a new avenue for optimizing the performance of POMOF-based capacitor electrode materials.

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.

Freestanding hierarchical nickel molybdate@reduced graphene oxide@nickel aluminum layered double hydroxides nanoarrays assembled from well-aligned uniform nanosheets as binder-free electrode materials for high performance supercapacitors.

Herein, the hierarchical nickel molybdate@reduced graphene oxide@nickel aluminum layered double hydroxides (NiMoO4@rGO@NiAl-LDHs) architecture assembled from well-aligned nanosheets is successfully constructed on Ni-foam through a three-step strategy. For the first time, ultrathin graphene nanosheets are introduced by a novel spraying process to avoid the stack. NiAl-LDHs is prepared via situ growth procedure in which NiAl-LDH self-assembles on the surface of graphene to prevent graphene from aggregating, resulting in an enlarged specific surface area. Electrochemical analysis manifests that NiMoO4@rGO@NiAl-LDHs yields exceptional specific capacitance (3396 Fg-1 at 1 Ag-1), favorable charge/discharge rate and approving long-term stability. Furthermore, the NiMoO4@rGO@NiAl-LDHs//AC device delivers superior specific capacitance (137.2 Fg-1 at 1 Ag-1), high energy density (48.7 Whkg-1) associated with pleasurable power output (7987 Wkg-1). Importantly, the well-aligned NiMoO4@rGO@NiAl-LDHs provides a prospective conception constructing hierarchical structural materials in the area of supercapacitor.