Meihong Fan

Metallic Co9S8 nanosheets grown on carbon cloth as efficient binder-free electrocatalysts for the hydrogen evolution reaction in neutral media

The development of efficient non-noble metal hydrogen-evolving electrocatalysts is of paramount importance for sustainable hydrogen production from water. Herein, we report the direct growth of metallic Co9S8 nanosheets on carbon cloth (CC) through a facile one-pot solvothermal method. We also show that the introduction of a tiny amount of Zn2+ ions (Zn : Co mol ratio of 0.5–1 : 100) in the synthesis system can reduce the thickness, improve the crystallinity, and optimize the surface structure of Co9S8 nanosheets, without Zn-doping. Furthermore, we show that the resulting Co9S8/CC materials can serve as efficient, binder-free, non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) under neutral conditions (pH 7). In particular, the Co9S8/CC material (synthesized in the presence of Zn2+ ions) affords a current density of 10 mA cm−2 at a low overpotential of 175 mV, has great catalytic stability as long as 100 h, and gives about 100% faradaic yield towards the HER in neutral media. The materials excellent catalytic performance toward the HER is attributed primarily to the synergistic effects of Co9S8s intrinsic catalytic ability, the ultrathin nanosheet array architecture and the self-supporting feature.

Growth of molybdenum carbide micro-islands on carbon cloth toward binder-free cathodes for efficient hydrogen evolution reaction

Design and synthesis of efficient noble metal-free hydrogen evolution catalysts is of paramount importance for the practical application of water-splitting devices. Herein, we report a novel synthetic method to grow dispersed molybdenum carbide (Mo2C) micro-islands on flexible carbon cloth (CC). This method involves the controlled synthesis of a supramolecular hybrid between cetyltrimethyl ammonium cations and molybdate anions on CC, followed by simple thermal treatment of this supramolecular hybrid in Ar to form Mo2C on CC in situ. In this synthesis, the presence of cetyltrimethyl ammonium bromide is proven to be important because it effectively immobilizes molybdate ions on CC on the one hand and functions as a carbon source for the formation of Mo2C on the other. Moreover, the as-prepared Mo2C/CC composite material can serve as efficient binder-free cathodes toward the hydrogen evolution reaction (HER). The Mo2C/CC affords a current density of 10 mA cm−2 at a low overpotential of 140 mV and works stably in acidic media with a Faraday yield of ∼100%. The isolated island architecture of Mo2C ensures rich active sites to be exposed and allows the easy interaction of reactants (e.g., protons) with the active sites. Also, the strong adhesion between Mo2C and carbon cloth facilitates electron transport/transfer in the composite material and is helpful for the achievement of excellent catalytic stability.

Electrospinning Synthesis of Bimetallic Nickel–Iron Oxide/Carbon Composite Nanofibers for Efficient Water Oxidation Electrocatalysis

The development of earth‐abundant water oxidation electrocatalysts with high activity and durability is very important for many renewable energy conversion/storage processes. Herein, we report a facile synthetic method for the preparation of amorphous nickel–iron oxide/carbon composite nanofibers with high electrocatalytic activity and stability for the oxygen evolution reaction (OER). This method involves two main steps: (i) the electrospinning synthesis of Ni‐ and Fe‐embedded polyvinylpyrrolidone (PVP) polymer nanofibers as the precursor and (ii) the thermal conversion of this precursor in air at 250 °C into nickel–iron oxide/carbon composite nanofibers. Moreover, we show that the as‐obtained composite material exhibits a comparable catalytic activity and a superior catalytic stability to IrOx/C and RuOx, which are state‐of‐the‐art noble‐metal‐based water oxidation electrocatalysts. In particular, the obtained amorphous nickel–iron oxide/carbon composite nanofibers with an optimal Ni/Fe molar ratio of 1:2 afford a small overpotential of 310 mV at a current density of 10 mA cm−2, show high catalytic stability for >15 h, and give >90 % Faradaic yield toward the OER. The efficient catalytic activity of the material can be attributed to its overall conducive structural features for the OER, mainly including the amorphous phase structure of nickel–iron oxide, tunable Ni/Fe atomic ratio, and strongly coupled interaction between nickel–iron oxide and nanocarbon.

From solid-state metal alkoxides to nanostructured oxides: a precursor-directed synthetic route to functional inorganic nanomaterials

Functional nanostructured oxides are important inorganic materials for various energy- and environment-related applications, such as photocatalysis and lithium ion batteries. To optimize their properties/functions, synthetic methods that can lead to nanomaterials with unique composition, morphology and size are highly desirable. In this review, we summarize recent research efforts towards the construction of nanostructured solid-state metal alkoxides-a family of inorganic–organic hybrid compounds and their conversion into functional inorganic nanomaterials. The chemical transformation from metal alkoxides to nanostructured oxides represents a novel precursor-directed synthetic route to functional inorganic nanomaterials. The uniqueness of this method mainly lies in: (i) the crystal/molecular structure of metal alkoxides which plays a crucial role in their nanosized structures; (ii) the use of metal alkoxides as precursor materials which determines the composition and (micro)structure of the finally-obtained oxide nanomaterials; and (iii) that this method can be employed to synthesize nanomaterials that cannot be readily achieved using other approaches.

Facile precursor-mediated synthesis of porous core–shell-type Co3O4 octahedra with large surface area for photochemical water oxidation

A porous Co3O4 material with unique octahedron-in-octahedron core–shell-type morphology is prepared via a facile precursor-mediated synthetic route. This material possesses large surface area and good catalytic activity for water oxidation reaction.

Enhanced electrochemical performance of Li3V2(PO4)3 microspheres assembled with nanoparticles embedded in a carbon matrix

We report on uniform Li3V2(PO4)3 microspheres with a size distribution of 1–3 μm assembled with nanoparticles embedded in a carbon matrix. LVP particles have a size of about 50–100 nm and carbon accounts for about 6% in total mass for the one with the best electrochemical performance. An initial capacity of 121 mA h g−1 or 101 mA h g−1 was achieved when cycled at 1 C or 10 C at room temperature with an admissible capacity fading of 8% after 100 cycles. The high rate capability and cycling stability may attribute to the unique microsize, electron conductive continuous carbon matrix and stable 3D skeleton of Li3V2(PO4)3.

Precursor-mediated synthesis of double-shelled V2O5 hollow nanospheres as cathode material for lithium-ion batteries

Hollow micro-/nanostructures have a wide range of applications in catalysis, rechargeable batteries, drug delivery, and gas sensors, as well as energy storage and conversion. Herein, we report a facile, template-free, precursor-mediated method to synthesize V2O5 nanomaterials with three different architectures: double-shelled hollow nanospheres, single-shelled hollow nanospheres and nanoparticles. These V2O5 nanostructures are obtained via a simple thermal treatment in air of a “pre-synthesized” vanadyl glycerolate precursor, and their morphologies can be easily tuned by varying the thermal treatment temperatures. Electrochemical studies show that the double-shelled V2O5 hollow nanospheres as a cathode material for lithium-ion batteries deliver an initial capacity of 256.7 mA h g−1 with a Coulombic efficiency of nearly 100%, and their capacity is superior to the two other V2O5 nanostructures (i.e., single-shelled hollow nanospheres and nanoparticles), mainly due to their unique double-shelled hollow structure.