Guilue Guo

One‐Pot Synthesis of Tunable Crystalline Ni3S4@Amorphous MoS2 Core/Shell Nanospheres for High‐Performance Supercapacitors

Transition metal sulfides gain much attention as electrode materials for supercapacitors due to their rich redox chemistry and high electrical conductivity. Designing hierarchical nanostructures is an efficient approach to fully utilize merits of each component. In this work, amorphous MoS(2) is firstly demonstrated to show specific capacitance 1.6 times as that of the crystalline counterpart. Then, crystalline core@amorphous shell (Ni(3)S(4)@MoS(2)) is prepared by a facile one-pot process. The diameter of the core and the thickness of the shell can be independently tuned. Taking advantages of flexible protection of amorphous shell and high capacitance of the conductive core, Ni(3)S(4) @amorphous MoS(2) nanospheres are tested as supercapacitor electrodes, which exhibit high specific capacitance of 1440.9 F g(-1) at 2 A g(-1) and a good capacitance retention of 90.7% after 3000 cycles at 10 A g(-1). This design of crystalline core@amorphous shell architecture may open up new strategies for synthesizing promising electrode materials for supercapacitors.

Hydrophilic Nitrogen and Sulfur Co‐doped Molybdenum Carbide Nanosheets for Electrochemical Hydrogen Evolution

Nitrogen and sulfur dual-doped Mo2 C nanosheets provide low operating potential (-86 mV for driving 10 mA cm(-2) of current density). Co-doping of N and S heteroatoms can improve the wetting property of the Mo2C electrocatalyst in aqueous solution and induce synergistic effects via σ-donation and π-back donation with hydronium cation.

Controlled synthesis of zinc cobalt sulfide nanostructures in oil phase and their potential applications in electrochemical energy storage

A unique controlled synthesis of zinc cobalt sulfide nanostructures is obtained by a facile oil phase approach. Nanoartichokes composed of self-assembled nanosheets and nanoparticles have been fabricated by using different sulfur sources. The application of such nanomaterials is demonstrated as electrodes for supercapacitors and lithium-ion batteries. Serving as lithium-ion battery electrodes, the ZnxCo1−xS nanoartichokes deliver a higher specific capacity of 750 mA h g−1 during the 100th cycle as compared to only 220 mA h g−1 for nanoparticles. In supercapacitor tests, the ZnxCo1−xS nanoartichokes possess an improved specific capacitance (486.2 F g−1 at a current density of 2.0 A g−1) and excellent cycling stability (retaining 86.4% after 2000 cycles), both of which are much higher than those of nanoparticles (e.g. 406.7 F g−1 and 73.3%). This effective nanostructure design of ternary transition metal sulfides could provide a promising method to construct high-performance materials for energy and environment applications.

Synergistic Effect of Mesoporous Co3O4 Nanowires Confined by N‐Doped Graphene Aerogel for Enhanced Lithium Storage

A one-step multipurpose strategy is developed to realize a sophisticated design that simultaneously integrates three desirable components of nitrogen dopant, 3D graphene, and 1D mesoporous metal oxide nanowires into one hybrid material. This facile synthetic strategy includes a one-step hydrothermal reaction followed by topotactic calcination. The utilization of urea as the starting reagent enables the precipitation of precursor nanowires and concurrent doping of nitrogen heteroatoms on graphene during hydrothermal reaction, while at the same time the graphene nanosheets are self-assembled to afford a 3D scaffold. Detailed characterizations on the final calcined product are conducted to confirm the phase purity, porosity, nitrogen composition, and morphology. The integration of two building blocks, i.e., flexible graphene nanosheets and Co3 O4 nanowires, enables various intertwining behaviors such as seaming, bridging, hooping, bundling, and sandwiching, of which synergistic effect substantially enhances electrical and electrochemical properties of the resultant hybrid. For lithium ion battery application of the hybrid, a remarkably high capacity more than 1200 mA h g(-1) (at 100 mA g(-1) ) is stabilized over 100 cycles with coulombic efficiency higher than 97%. Even during rapid discharge/charge processes (1000 mA g(-1) ), a reversible charge capacity of 812 mA h g(-1) is still retained after 230 cycles.

In Situ Integration of Anisotropic SnO2 Heterostructures inside Three-Dimensional Graphene Aerogel for Enhanced Lithium Storage

Three-dimensional (3D) graphene aerogel (GA) has emerged as an outstanding support for metal oxides to enhance the overall energy-storage performance of the resulting hybrid materials. In the current stage of the studies, metals/metal oxides inside GA are in uncrafted geometries. Introducing structure-controlled metal oxides into GA may further push electrochemical properties of metal oxide-GA hybrids. Using rutile SnO2 as an example, we demonstrated here a facile hydrothermal strategy combined with a preconditioning technique named vacuum-assisted impregnation for in situ construction of controlled anisotropic SnO2 heterostructures inside GA. The obtained hybrid material was fully characterized in detail, and its formation mechanism was investigated by monitoring the phase-transformation process. Rational integration of the two advanced structures, anisotropic SnO2 and 3D GA, synergistically led to enhanced lithium-storage properties (1176 mAh/g for the first cycle and 872 mAh/g for the 50th cycle at 100 mA/g) as compared with its two counterparts, namely, rough nanoparticles@3D GA and anisotropic SnO2@2D graphene sheets (618 and 751 mAh/g for the 50th cycle at 100 mA/g, respectively). It was also well-demonstrated that this hybrid material was capable of delivering high specific capacity at rapid charge/discharge cycles (1044 mAh/g at 100 mA/g, 847 mAh/g at 200 mA/g, 698 mAh/g at 500 mA/g, and 584 mAh/g at 1000 mA/g). The in situ integration strategy along with vacuum-assisted impregnation technique presented here shows great potential as a versatile tool for accessing a variety of sophisticated smart structures in the form of anisotropic metals/metal oxides within 3D GA toward useful applications.

Integrating three-dimensional graphene/Fe3O4@C composite and mesoporous Co(OH)2 nanosheets arrays/graphene foam into a superior asymmetric electrochemical capacitor

Aqueous electrolyte-based asymmetric electrochemical capacitors (AECs) are promising in the field of energy storage because of their wider potential windows compared to the symmetric capacitors and higher ionic conductivity compared to the organic electrolytes. Most of the research works on AECs are directed towards cathode materials, while anode materials have rarely been investigated. Herein, a novel AEC is constructed, in which two highly conductive and lightweight graphitic substrates, graphene framework and graphene foam, are hybridized with Fe3O4@C core–shell nanoparticles (anodes) and mesoporous Co(OH)2 nanosheets arrays (NAs) (cathodes), respectively. The as-assembled AEC device shows extended cell voltage (0.0–1.6 V) and excellent cycle stability (72% retention after 8000 cycles). More importantly, a high specific energy of 75 W h kg−1 is achieved at a specific power of 400 W kg−1. Even at a 10.3 s charge/discharge rate, specific energy as high as 33 W h kg−1 can be retained.

From fibrous elastin proteins to one-dimensional transition metal phosphides and their applications

One-dimensional (1D) carbon-supported nanostructured CoP and FeP4 were prepared using fibrous elastin proteins that served as starting materials through an oil-phase method and the as-synthesized products were investigated for their lithium and sodium storage properties. The 1D CoP and FeP4 are composed of nanosized particles decorated on carbon supports. The 1D CoP and FeP4 nanostructures are ∼2 μm in length and 20–50 nm in diameter. The particles on the exterior of the 1D structure are 5–10 nm in diameter. To investigate the as-synthesized 1D TMPs in energy storage applications, the as-synthesized 1D CoP nanostructures are applied as an anode material in half-cells for LIBs and SIBs. For lithium storage performances, the anode delivers a specific capacity as high as ∼740 mAh g−1 at 0.2C and shows good rate performance and capacity retention as well as high rate capability (e.g. a stable specific capacity of ∼365 mAh g−1 for 120 cycles at 3.0C). In SIBs, at 0.2 and 5.0C, the specific capacities of 491.60 and 314.84 mAh g−1 are delivered, respectively. When tested at 1.0, 2.0, and 5.0C, the specific capacities are stable at ∼400, 360, and 300 mAh g−1 over 250, 250, and 1000 cycles, respectively.

Platinum and Palladium Nanotubes Based on Genetically Engineered Elastin–Mimetic Fusion Protein-Fiber Templates: Synthesis and Application in Lithium-O2 Batteries

The coupling of proteins with self-assembly properties and proteins that are capable of recognizing and mineralizing specific inorganic species is a promising strategy for the synthesis of nanoscale materials with controllable morphology and functionality. Herein, GPG-AG3 protein fibers with both of these properties were constructed and served as templates for the synthesis of Pt and Pd nanotubes. The protein fibers of assembled GPG-AG3 were more than 10 μm long and had diameters of 20-50 nm. The as-synthesized Pt and Pd nanotubes were composed of dense layers of ~3-5 nm Pt and Pd nanoparticles. When tested as cathodes in lithium-O2 batteries, the porous Pt nanotubes showed low charge potentials of 3.8 V, with round-trip efficiencies of about 65% at a current density of 100 mA g(-1).

Scalable Synthesis of Honeycomblike V2O5/Carbon Nanotube Networks as Enhanced Cathodes for Lithium-Ion Batteries

A green and scalable route to form a honeycomblike macroporous network by homogeneously weaving V2O5 nanowires and carbon nanotubes (CNTs) was developed. The intertwinement between V2O5 nanowires and CNTs not only integrates nanopores into the macroporous system but also elevates the collection and transfer of charges through the conductive network. The unique combination of V2O5 nanowires and CNTs renders the composite monolith with synergic properties for substantially enhancing electrochemical kinetics of lithiation/delithiation when used as a lithium-ion battery (LIB) cathode. This work presents a useful approach for a large-scale production of cellular monoliths as high-performance LIB cathodes.

Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12,441 mAh g(-1) at a current density of 100 mA g(-1). When they were cycled at a limited capacity of 800 mAh g(-1) at current densities of 200 or 400 mA g(-1), these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.