Metal-organic framework derived bimetallic selenide embedded in nitrogen-doped carbon hierarchical nanosphere for highly reversible sodium-ion storage.

Bimetallic selenides with various valence transitions and high theoretical capacities are extensively studied as anodes for sodium-ion-batteries (SIBs), but their huge volume changes and poor capacity retention limit their practicality. Herein, a facile and controllable strategy using a binary Ni-Co metal-organic framework (MOF) precursors followed by the selenization process, which produced a cobalt nickel selenide/N-doped carbon composite ((CoNi)Se2/NC) that maintained the hierarchical nanospheres structure. Such a distinctive structure affords both Na+ and electron diffusion pathways in the electrochemical reactions as well as high electrical conductivity, thus leading to superior electrochemical performance when the designed composite is utilized as an anode in SIBs. The resulting nanospheres-like (CoNi)Se2/NC hierarchical structure exhibits a high specific capacity of 526.8 mA h g-1 at 0.2 A/g over 100 cycles, a stable cycle life with no obvious capacities loss at 1.0 and 3.0 A/g after 500 cycles, and exceptional rate capability of 322.9 mA h g-1 at 10.0 A/g.

Hierarchical MnV2O4 double-layer hollow sandwich nanosheets confined by N-doped carbon layer as anode for high performance lithium-ion batteries.

Binary transition metal oxides, especially vanadate metal oxides, are highly desirable for lithium-ion batteries (LIBs) anode materials due to their low-budget and high theoretical lithium storage capacity. However, low conductivity and poor cycle stability caused by volume changes during charge and discharge limit their grid-scale applications. Herein, a novel spinel MnV2O4 double-layer hollow sandwich nanosheets enclosed in N-doped porous carbon layer (MnV2O4/NC) was efficiently synthesized in 5 min by microwave-assisted and in-situ pyrolysis the coated polydopamine. MnV2O4/NC shows the superior performance as anode for LIBs with a specific capacities of 760 mA h g-1 at 1000 mA g-1 and outstanding of cycling stability with a specific capacities of 525.5 mA h g-1 after 1000 cycles even at 5000 mA g-1, respectively, which due to its unique double-layer hollow sandwich microstructure, mixed lithium storage mechanism and in-situ coating of nitrogen-doped carbon layer.

Crystalline carbon modified hierarchical porous iron and nitrogen co-doped carbon for efficient electrocatalytic oxygen reduction.

Hierarchical porous iron and nitrogen co-doped carbon (Fe-N/C) materials have been considered as an appealing non-noble metal-based catalyst in oxygen reduction reactions (ORR). However, the conductivity loss caused by the scattering of electrons on pores and defects markedly limits their catalytic activity, which attracted seldom attention in this area. Herein, a novel crystalline carbon modified hierarchical porous Fe-N/C electrocatalyst with enhanced electronic conductivity is designed and prepared via a two-step calcination-catalysis process. The resistivity of hierarchical porous Fe-N/C is decreased from 2.123 Ω cm to 0.479 Ω cm after crystalline carbon introduction. The electrocatalyst annealed at 800 °C (Fe-N/C-800) exhibits a superior activity with the half-wave potential (E1/2) of 0.89 V, which outperforms the commercial carbon-supported platinum (Pt/C) catalyst (0.85 V). The strategy of crystalline carbon modification provides a fresh approach to improve the electronic conductivity of porous carbon-based materials.

Metal-organic framework derived amorphous VOx coated Fe3O4/C hierarchical nanospindle as anode material for superior lithium-ion batteries.

Lithium-ion batteries (LIBs) are widely regarded as a promising electrochemical energy storage device, due to their high energy density and good cycling stability. To date, the development of anode materials for LIBs is still confronted with many serious problems, and much effort is required for constructing more ideal anode materials. Herein, starting with metal-organic frameworks (MOFs), an amorphous VOx coated Fe3O4/C hierarchical nanospindle has been successfully synthesized. The obtained Fe3O4/C@VOx nanospindle has a uniform particle size of ∼100 nm in diameter and ∼400 nm in length and consists of ultrafine Fe3O4 nanoparticles (∼5 nm) embedded in a porous carbon matrix as the core and an amorphous VOx layer as the shell. Notably, as the anode material for LIBs, Fe3O4/C@VOx delivers a high coulombic efficiency (74.2%) and a large capacity of 845 mA h g-1 after 500 cycles at 1000 mA g-1. A prominent discharge reversible capacity of 340 mA h g-1 is also still retained at 5000 mA g-1. More importantly, the presented facile MOF-derived route could be easily extended to other functional materials for widespread applications.

Two unusual 3D honeycomb networks based on Wells-Dawson arsenomolybdates with d10 transition-metal-pyrazole connectors.

Herein, two Wells -Dawson-type arsenomolybdates, formulated as [Cu(pyr)2]6[As2Mo18O62] (1) and [Ag(pyr)2]6[As2Mo18O62] (2) (pyr = pyrazole), were hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction, elemental analysis, IR and UV-vis-NIR spectroscopies, XPS, XRD, and TG analysis. The structural analysis indicated that compounds 1 and 2 were isomorphic. They are the first reported 3D honeycomb structures of Wells-Dawson-type arsenomolybdates. The [M(pyr)2] (M = Cu and Ag) connected with [As2Mo18O62]6- polyoxoanions to form the {812·123}{8}3 topological structure. The contributions of organic ligands, pH value, reaction temperature, and transition-metal (TM) to the construction of 3D networks were elucidated. Furthermore, compounds 1 and 2 exhibited fluorescence properties in the solid state at room temperature, highly efficient catalytic ability for the degradation of five organic dyes (MB, RhB, MO, AP, and CR) under UV irradiation, and obvious electrocatalytic activities for the reduction of H2O2. The mechanisms of photocatalysis and electrocatalysis have also been discussed in detail.