Design and Fabrication of Hierarchical NiCoP-MOF Heterostructure with Enhanced Pseudocapacitive Properties.

Metal-organic framework (MOF)-derived heterostructures possessing the merits of each component are thought to display the enhanced energy storage performance due to their synergistic effect. Herein, a functional heterostructure (NiCoP-MOF) composed of nickel/cobalt-MOF (NiCo-MOF) and phosphide (NiCoP) is designed and fabricated via the localized phosphorization of unusual lamellar brick-stacked NiCo-MOF assemblies obtained by a hydrothermal method. The experimental and computational analyses reveal that such-fabricated heterostructures possess the modulated electronic structure, abundant active sites, and hybrid crystalline feature, which is kinetically beneficial for fast electron/ion transport to enhance the charge storage capability. Examined as the supercapacitor electrode, the obtained NiCoP-MOF compared to the NiCo-MOF delivers a high capacity of 728 C g-1 (1.82 C cm-2 ) at 1 A g-1 with a high capacity retention of 430 C g-1 (1.08 C cm-2 ) when increasing the current density to 20 A g-1 . Importantly, the assembled solid-state NiCoP-MOF-based hybrid supercapacitor displays superior properties regarding the capacity (226.3 C g-1 ), energy density (50.3 Wh kg-1 ), and durability (≈100% capacity retention over 10 000 cycles). This in situ heterogenization approach sheds light on the electronic structure modulation while maintaining the well-defined porosity and morphology, holding promise for designing MOF-based derivatives for high performance energy storage devices.

Selenide-doped bismuth sulfides (Bi2S3-xSex) and their hierarchical heterostructure with ReS2for sodium/potassium-ion batteries.

In this work, selenide-doped bismuth sulfides (Bi2S3-xSex) was successfully prepared through Se doping Bi2S3 Se to improve the electronic conductivity and increase the interlayer spacing. Then the anisotropic ReS2 nanosheet arrays were grown on the surface of Bi2S3-xSex to form a hierarchical heterostructure (Bi2S3-xSex@ReS2). The doping and construction of heterostructure processes can greatly improve the electrochemical conductivity of electrode materials and relieve the volume expansion during the continuous charge/discharge processes. While applied as SIBs anode, the specific capacity of 330 mAh g-1 was maintained after 450 cycles at the current density of 1.0 A g-1. It can also keep 200 mAh g-1 specific capacity after 900 cycles at 1.0 A g-1 for the anode of PIBs. This heterogeneous engineering and doping dual strategies could provide a good idea for the synthesis of new bimetallic sulfides with outstanding battery performance for SIBs and PIBs.

Metal-Organic-Framework-Derived Ball-Flower-like Porous Co3O4/Fe2O3 Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Activity.

A porous ball-flower-like Co3O4/Fe2O3 heterostructural photocatalyst was synthesized via a facile metal-organic-framework-templated method, and showed an excellent degradation performance in the model molecule rhodamine B under visible light irradiation. This enhanced photocatalytic activity can be attributed to abundant photo-generated holes and hydroxyl radicals, and the combined effects involving a porous structure, strong visible-light absorption, and improved interfacial charge separation. It is notable that the ecotoxicity of the treated reaction solution was also evaluated, confirming that an as-synthesized Co3O4/Fe2O3 catalyst could afford the sunlight-driven long-term recyclable degradation of dye-contaminated wastewater into non-toxic and colorless wastewater.

Cobalt/Nickel Ions-Assisted Synthesis of Laminated CuO Nanospheres Based on Cu(OH)2 Nanorod Arrays for High-Performance Supercapacitors.

The development for environmentally friendly energy conversion and storage equipment has given rise to tremendous research efforts as a result of the growing requirements for environmental friendly resources and the rapid consumption of traditional fossil fuel. Herein, a novel hierarchical CoO/NiO-Cu@CuO heterostructure is successfully devised and synthesized. Cobalt/nickel ions are used to generate novel CoO/NiO-doped laminated CuO nanospheres through the facile in situ wet oxidation combined with cation exchange and calcination strategies. As a result, the electrochemical supercapacitance of the as-prepared CoO/NiO-Cu@CuO electrode can reach 875 C cm-2 (2035 mF cm-2), which exhibits much better electrochemical performance compared to other precursor electrodes at a same current density of 2 mA cm-2. Moreover, an excellent rate capacity of 1395 mF cm-2 (50 mA cm-2) can be achieved when measured at a relative high current density; 90.3% of the initial supercapacitance remains even after 5000 cycles. Furthermore, the as-prepared hierarchical hybrid of laminated CoO/NiO-CuO nanospheres in situ generated on three-dimensional (3D) porous Cu foam is applied to prepare a solid-state asymmetric supercapacitor equipment unit. The fabricated equipment unit shows an energy density of 69.3 W h kg-1 at a power density of 1080 W kg-1. Additionally, the commercially applied 2.5 V light-emitting-diode indicator with blue light can be energized for 4 min when two as-fabricated supercapacitor devices are in series connection. The unique hierarchical heterostructure of the novel laminated nanospheres combined with the 3D grid structure brings about the outstanding electrochemical capacitor performances. This strategy for the fabrication of hierarchical heterostructure electrodes could have an enormous potential for high-performance electrochemical equipment.

Hierarchical 0D-2D Co/Mo Selenides as Superior Bifunctional Electrocatalysts for Overall Water Splitting.

Development of efficient electrocatalysts combining the features of low cost and high performance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still remains a critical challenge. Here, we proposed a facile strategy to construct in situ a novel hierarchical heterostructure composed of 0D-2D CoSe2/MoSe2 by the selenization of CoMoO4 nanosheets grafted on a carbon cloth (CC). In such integrated structure, CoSe2 nanoparticles dispersed well and tightly bonded with MoSe2 nanosheets, which can not only enhance kinetics due to the synergetic effects, thus promoting the electrocatalytic activity, but also effectively improve the structural stability. Benefiting from its unique architecture, the designed CoSe2/MoSe2 catalyst exhibits superior OER and HER performance. Specifically, a small overpotential of 280 mV is acquired at a current density of 10 mA·cm-2 for OER with a small Tafel slope of 86.8 mV·dec-1, and the overpotential is 90 mV at a current density of 10 mA·cm-2 for HER with a Tafel slope of 84.8 mV·dec-1 in 1 M KOH. Furthermore, the symmetrical electrolyzer assembled with the CoSe2/MoSe2 catalysts depicts a small cell voltage of 1.63 V at 10 mA·cm-2 toward overall water splitting.

A Universal Process: Self-Templated and Orientated Fabrication of XMoO4 (X: Ni, Co, or Fe) Nanosheets on MoO2 Nanoplates as Electrocatalysts for Efficient Water Splitting.

Fabrication of superior nonprecious electrocatalysts is essential for water electrolysis. Herein, the epitaxial growth of the XMoO4 (X = Ni, Co, Fe) nanosheets on the hexagonal MoO2 nanoplates are carried out. The preoxidation of MoO2 nanoplate is fatal to the epitaxial growth of a nanosheets array on MoO2 nanoplates. The hierarchical heterostructure of the vertically aligned NiMo nanosheets on MoO2 nanoplate (NiMo/MoO2) is well-maintained in the process of in situ topotactic reduction transformation from NiMoO4·xH2O/MoO2. Attributing it to the rich electroactive sites from nanosheets array, together with the intrinsic electrocatalytic performance of NiMo alloy, the as-engineered NiMo/MoO2 as electrocatalyst exhibits admirable hydrogen evolution reaction (HER) activity with a small onset potential of -12 mV vs RHE (1 mA cm-2) and a tafel value of 43.6 mV dec-1 at alkaline media. Furthermore, the obtained CoMoO4/MoO2 possesses excellent oxygen evolution performance, which is verified by an ultralow overpotential of 230 mV@10 mA cm-2, small Tafel slope (51 mV dec-1), and robust durability. The developed NiMo/MoO2 and CoMoO4/MoO2 electrocatalysts are assembled into an alkaline electrolyzer, which affords a cell potential of 1.51 V at 10 mA cm-2, as well as outstanding operational durability, which is superior to the typically constructed 20 wt % Pt/C-RuO2 system (1.59 V at 10 mA cm-2). Hence, the universal strategy using MoO2 nanoplates as Mo source and epitaxial substrate may be extended to explore and construct economical and superior Mo-based electrocatalysts for water electrolysis.

Hierarchical assembly of urchin-like alpha-iron oxide hollow microspheres and molybdenum disulphide nanosheets for ethanol gas sensing.

In this paper, we fabricated a high-performance ethanol sensor using layer-by-layer self-assembled urchin-like alpha-iron oxide (α-Fe2O3) hollow microspheres/molybdenum disulphide (MoS2) nanosheets heterostructure as sensitive materials. The nanostructural, morphological, and compositional properties of the as-prepared α-Fe2O3/MoS2 heterostructure were characterized by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS), which confirmed its successful preparation and rationality. The α-Fe2O3/MoS2 nanocomposite sensor shows good selectivity, excellent reproducibility, fast response/recovery time and low detection limit towards ethanol gas at room temperature, which is superior to the single component of α-Fe2O3 hollow microspheres and MoS2 nanosheets. Furthermore, the response of the α-Fe2O3/MoS2 nanocomposite sensor as a function of ethanol gas concentration was also demonstrated. The enhanced ethanol sensing properties of the α-Fe2O3/MoS2 nanocomposite sensor were ascribed to the synergistic effect and heterojunction between the urchin-Like α-Fe2O3 hollow microspheres and MoS2 nanosheets. This work verifies that the hierarchical α-Fe2O3/MoS2 nanoheterostructure is a potential candidate for fabricating room-temperature ethanol gas sensor.

Three-Dimensional Lupinus-like TiO2 Nanorod@Sn3O4 Nanosheet Hierarchical Heterostructured Arrays as Photoanode for Enhanced Photoelectrochemical Performance.

A novel photoelectrode of three-dimensional (3D) lupinus-like TiO2 nanorod@Sn3O4 nanosheet hierarchical heterostructured arrays (TiO2@Sn3O4 HHAs) on a transparent F-doped SnO2 glass substrate was designed and fabricated by a two-step solvothermal growth process. Photoelectrochemical (PEC) measurements showed that the 3D lupinus-like TiO2@Sn3O4 HHAs photoelectrode displayed enhanced photocurrent density (3-fold increase with respect to that of pure TiO2), improved conversion efficiency, more negative onset potential (from -0.13 to -0.33 V vs normal hydrogen electrode), and higher light on/off cycle stability. The improved PEC properties may be ascribable to the enhancement of light harvesting and large contact area with the electrolyte by increased surface area as well as improvement of charge transfer and collection through the synergistic effects between band structures and morphology.

The interlace of Bi2S3 nanowires with TiO2 nanorods: An effective strategy for high photoelectrochemical performance.

A netlike heterostructure is constructed by interlacing the Bi2S3 nanowires with well-aligned TiO2 nanorod arrays via a facile and effective solvothermal method. The winding Bi2S3 nanowires with several hundred nanometers long and 20-30nm wide are distributed in the interspace of TiO2 nanorods and cross-linked with these nanorods reducing the isolation of nanorods. The photoelectrochemical characterizations show that in addition to the high stability in air without any encapsulation, the netlike heterostructure exhibits an enhanced photoelectrochemical performance compared with TiO2 nanorods and controlled Bi2S3/TiO2 nanoparticle structure. The dual roles of Bi2S3 nanowires (1) as sensitizer for the enlargement of photoresponse range and (2) as multiple electron transport channels facilitating the fast separation of photogenerated electron-hole pairs are considered as key factors for the high energy conversion efficiency of 2.96%. This facile synthesis method offers an attractive strategy to further improve the photoelectrochemical performance of semiconductors and undoubtedly shows promising applications in solar conversion and storage devices.