Xuefeng Song

Facile synthesis of nitrogen-doped graphene-ultrathin MnO2 sheet composites and their electrochemical performances.

Nitrogen-doped graphene-ultrathin MnO2 sheet composites (NGMCs) were prepared through a one-step hydrothermal method at low temperature (120 °C). Ultrathin MnO2 sheets were well-dispersed and tightly anchored on graphene sheets, which were doped with nitrogen simultaneously. NGMCs electrode exhibited enhanced capacitive performances relative to those of undoped graphene-ultrathin MnO2 sheets composites (GMCs). As the current density increased from 0.2 to 2 A/g, the capacitance of NGMCs still retained ~74.9%, which was considerablely higher than that of GMCs (27%). Moreover, over 94.2% of the original capacitance was maintained after 2000 cycles, indicating a good cycle stability of NGMCs electrode materials.

Self-Assembled α-Fe2O3 Mesocrystals/Graphene Nanohybrid for Enhanced Electrochemical Capacitors

Self-assembled α-Fe2O3 mesocrystals/graphene nanohybrids have been successfully synthesized and have a unique mesocrystal porous structure, a large specific surface area, and high conductivity. Mesocrystal structures have recently attracted unparalleled attention owing to their promising application in energy storage as electrochemical capacitors. However, mesocrystal/graphene nanohybrids and their growth mechanism have not been clearly investigated. Here we show a facile fabrication of short rod-like α-Fe2O3 mesocrystals/graphene nanohybrids by self-assembly of FeOOH nanorods as the primary building blocks on graphene under hydrothermal conditions, accompanied and promoted by concomitant phase transition from FeOOH to α-Fe2O3. A systematic study of the formation mechanism is also presented. The galvanostatic charge/discharge curve shows a superior specific capacitance of the as-prepared α-Fe2O3 mesocrystals/graphene nanohybrid (based on total mass of active materials), which is 306.9 F g(-1) at 3 A g(-1) in the aqueous electrolyte under voltage ranges of up to 1 V. The nanohybrid with unique sufficient porous structure and high electrical conductivity allows for effective ion and charge transport in the whole electrode. Even at a high discharge current density of 10 A g(-1), the enhanced ion and charge transport still yields a higher capacitance (98.2 F g(-1)), exhibiting enhanced rate capability. The α-Fe2O3 mesocrystal/graphene nanohybrid electrode also demonstrates excellent cyclic performance, which is superior to previously reported graphene-based hematite electrode, suggesting it is highly stable as an electrochemical capacitor.

Covalently Coupled Ultrafine H-TiO2 Nanocrystals/Nitrogen-Doped Graphene Hybrid Materials for High-Performance Supercapacitor

Hydrogenated TiO2 (H-TiO2) are considered one of the most promising materials for supercapacitors given its low-cost, high conductivity, and enhanced electrochemical activity. However, the electrochemical performances of H-TiO2 due to lacking suitable structures is unsatisfactory, and thus how to design energetic H-TiO2-based electrode architectures still remains a great challenge. Herein, covalently coupled ultrafine H-TiO2 nanocrystals/nitrogen-doped graphene (H-TiO2/NG) hybrid materials were developed through a simple hydrothermal route followed by hydrogenation. Within this architecture, the strong interaction between H-TiO2 nanocrystals and NG sheets via covalent chemical bonding affords high structural stability inhibiting the aggregation of H-TiO2 nanocrystals. Meanwhile, the NG matrices function as an electrical highway and a mechanical backbone so that most of well-dispersed ultrafine H-TiO2 nanocrystals are electrochemically active but stable. As a result, the optimized H-TiO2/NG (H-TiO2/NG-B) exhibited high reversible specific capacity of 385.2 F g(-1) at 1 A g(-1), enhanced rate performance of 320.1 F g(-1) at a high current density of 10 A g(-1), and excellent cycling stability with 98.8% capacity retention.

Heating-Rate-Induced Porous α-Fe2O3 with Controllable Pore Size and Crystallinity Grown on Graphene for Supercapacitors

Porous α-Fe2O3/graphene composites (S-PIGCs) have been synthesized by a simple hydrothermal method combined with a slow annealing route. The S-PIGCs as a supercapacitors electrode material exhibit an ultrahigh specific capacitance of 343.7 F g(-1) at a current density of 3 A g(-1), good rate capability, and excellent cycling stability. The enhanced electrochemical performances are attributed to the combined contribution from the optimally architecture of the porous α-Fe2O3, as a result of a slow annealing, and the extraordinary electrical conductivity of the graphene sheets.

Crumpled nitrogen-doped graphene–ultrafine Mn3O4 nanohybrids and their application in supercapacitors

Crumpled nitrogen-doped graphene–ultrafine Mn3O4 nanohybrids (CNGMNs) were synthesized through a one-step strategy under hydrothermal conditions for promising application as supercapacitor materials. Doping of N atoms in the lattice of graphene and anchoring of Mn3O4 nanoparticles on graphene sheets were achieved concomitantly during the process under the assistance of aniline. The specific capacitance of this nanostructured hybrid was nearly six times that of the Mn3O4 counterpart. Additionally, enhanced rate capability and cycling stability (∼98.7% retention after 2000 cycles) were also obtained. The facile approach to prepare CNGMNs and exceptional electrochemical properties indicate that the CNGMNs could be a promising candidate material for supercapacitors.

Micro- and Nanostructures of Photoelectrodes for Solar-Driven Water Splitting

Artificial photosynthesis of clean fuels has aroused great interest to meet the great demand for clean and renewable energy. Great advances have recently been made in various photoelectrodes with their efficiencies and stabilities significantly improved by the design and implementation of novel structures, which are determinative for the optical absorption, charge-transport path, surface area, and electronic conductivity. This Research News article discusses perspectives of the synthetic methods and micro- and nanostructures (planar structures, 1D structures, and mesoporous structures) of photoelectrodes, and their relationships with the photo-electrochemical performance. Structural features, such as particle size, crystallinity, morphology, and film thickness, as well as the trade-offs among them are also evaluated and discussed for each category of structure.

Surfactant-free hydrothermal synthesis of Cu2ZnSnS4 (CZTS) nanocrystals with photocatalytic properties

As a low cost and environment-friendly solar absorber material, Cu2ZnSnS4 (CZTS) has aroused great interest for both photovoltaic and photocatalytic applications. The development of low temperature and green chemical route for the preparation of this quaternary sulfide compound still remains a challenge. In the present study, we present a surfactant-free hydrothermal method for the preparation of CZTS nanocrystals with an average size of 12 nm and photoactivity in hydrogen production. Ammonia was proposed to play a key role in confining the particle sizes. The properties of the CZTS nanoparticles were characterized using XRD, Raman, XPS, TEM, and UV-vis absorption. The photocatalytic properties of the as-synthesized CZTS nanoparticles were tested both in thin films and in slurry systems.

Cu–Ni@SiO2 alloy nanocomposites for methane dry reforming catalysis

Cu–Ni alloy nanoparticles (12 ± 3 nm) encapsulated in a silica shell have been successfully synthesized through a microemulsion method followed by polymerization of TEOS. The morphologies of the Cu–Ni@SiO2 nanocomposites can be controlled by tuning the metal ion concentrations. The alloy nanostructure shows a superior performance in catalytic methane dry reforming to the pure Ni nanocomposite catalyst.

Active Fe2O3 nanoparticles encapsulated in porous g-C3N4/graphene sandwich-type nanosheets as a superior anode for high-performance lithium-ion batteries

Designing sandwich-like hybrid nanosheets with a porous structure effectively improves the electrochemical performance of graphene-based materials in lithium-ion batteries (LIBs) owing to the mitigated restack of graphene and decreased diffusion distance of Li+ ions for electron storage. Herein, a novel composite of active Fe2O3 nanoparticles encapsulated in g-C3N4/graphene hybrid nanosheets (Fe2O3/CN–G) has been developed, in which the 2D sandwich-type hybrid nanosheets constructed using porous g-C3N4 and highly conductive graphene offer readily accessible channels and sufficient conductive pathways for ionic diffusion and charge transport. This unique architecture greatly inhibits the restacking or aggregation of graphene and ensures the stability of electro-active Fe2O3 nanoparticles. Benefiting from these intriguing features, the as-prepared Fe2O3/CN–G as an anode for LIBs shows excellent electrochemical behaviors, including considerably large reversible capacity (1023 mA h g−1), great coulombic efficiency (97.6%), strong durability and comparable rate performance. Therefore, the work described here can provide a new insight for designing high-performance electrode materials with a porous and sandwich-type hybrid structure for application in LIBs.

Photoelectrochemical Hydrogen Production of TiO2 Passivated Pt/Si-Nanowire Composite Photocathode

Si nanowire (SiNW) arrays decorated with Pt nanoparticles are passivated with TiO2 surface layer using atomic layer deposition (ALD). The sandwich structure TiO2/Pt/SiNW shows superior photoelectrochemical performance to the control planar silicon electrodes, especially under the concentrated solar radiation. Pt nanoparticles separated from aqueous electrolyte by TiO2 layer of more than 15 nm still well catalyze surface photoelectrochemical hydrogen production without direct contact to the electrolyte. This structural configuration shows remarkable chemical stability and anodically shifted onset potential, suggesting great promise for applications in solar hydrogen production. The maximum photon-to-energy conversion efficiency of the TiO2/Pt/SiNW reaches 15.6%.