Lian Gao

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.

Solvothermal‐Induced Self‐Assembly of Fe2O3/GS Aerogels for High Li‐Storage and Excellent Stability

A novel solvothermal-induced self-assembly approach, using colloid sol as precursor, is developed to construct monolithic 3D metal oxide/GS (graphene sheets) aerogels. During the solvothermal process, graphene oxide (GO) is highly reduced to GS and self-assembles into 3D macroscopic hydrogels, accompanying with in situ transformation of colloid sol to metal oxides. As a proof of concept, Fe2 O3 /GS aerogels are synthesized based on Fe(OH)3 sol, in which GS self-assemble into an interconnected macroporous framework and Fe2 O3 nanocrystals (20-50 nm) uniformly deposit on GS. Benefitting from the integration of macroporous structures, large surface area, high electrical conductivity, and good electrode homogeneity, the hybrid electrode manifests a superior rate capability (930, 660 and 520 mAh g(-1) at 500, 2000 and 4000 mA g(-1), respectively) and excellent prolonged cycling stability at high rates (733 mAh g(-1) during 1000 charge/discharge cycles at 2000 mA g(-1)), demonstrating its great potential for application in high performance lithium ion batteries. The work described here provides a versatile pathway to construct various graphene-based hybrid aerogels.

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.

High rate lithium-ion batteries from hybrid hollow spheres with a few-layered MoS2-entrapped carbon sheath synthesized by a space-confined reaction

Hybrid hollow spheres with a few-layered MoS2 entrapped carbon sheath (HFMECs) have been successfully synthesized by a 0D spatial confinement approach. In this facile process, a glucose-derived polysaccharide interacted with thiomolybdate on the surface of silica spheres followed by high temperature annealing to form an MoS2–C hybrid sheath. The glucose-derived polysaccharide layers not only serve as a carbon source, but also provide a 0D space-confined nanoreactor to restrict the kinetic growth of MoS2 sheets. When the HFMECs are used as a lithium-ion battery anode, the ultrathin shell (∼12 nm) and few-layered MoS2 nanosheets (≤5 layers) in the hybrid enhance the kinetics of Li+ and electron transport, resulting in excellent rate capability (739, 676, 613 and 563 mA h g−1 at 3, 5, 8 and 10 A g−1, respectively). The hollow structure and high mass content (91 wt%) of MoS2 in the composite guarantee cycle stability and allow for efficient storage (823 mA h g−1 at 1 A g−1 after 200 cycles). The exceptional performance of HFMECs combined with the straightforward approach makes these materials very promising for lithium ion batteries.

Facile synthesis of hollow hierarchical Ni/γ-Al2O3 nanocomposites for methane dry reforming catalysis

Hydrogen reduction of hierarchical spinel intermediates that were synthesized by a facile hydrothermal method results in Ni/γ-Al2O3 nanocomposites with Ni nanoparticles (∼5.5 nm) well dispersed and embedded in nanoflakes of the hollow Al2O3 microspheres. The good dispersion of small metal nanoparticles and strong metal–support interactions that resulted from decomposition of spinel intermediates during reduction are essential for the efficient and sustainable high temperature dry reforming of methane (DRM) catalysis. The high surface area (170 m2 g−1) composite catalysts show coke and sintering resistance in long term DRM catalysis at 750 °C, the highest temperature ever tested for hierarchical nanostructures. Ni loadings and the calcination temperatures of the spinel intermediate are investigated for their effect on the morphology and the catalytic performance of the final catalysts. It is interesting that some initially non-active control catalysts can be activated during long term testing.

Cu2ZnSnS4 thin films: spin coating synthesis and photoelectrochemistry

Cu2ZnSnS4 (CZTS) has attracted great interest in both photovoltaic and photoelectrochemical applications as a low cost and environmentally-friendly solar absorber material. The development of a facile and green chemical route for the preparation of a well crystallized and stable CZTS photoelectrode still remains a challenge. We present here the preparation of well crystallized CZTS thin films using a facile spin-coating method based on methanol solution and their applications as photoelectrocathodes for hydrogen production. The bare CZTS thin films demonstrate outstanding photoelectrochemical (PEC) efficiency and chemical stability, which are further improved by surface modification of CdS and TiO2 layers using chemical bath and atomic layer deposition, respectively. The incident-photon-to-current efficiency (IPCE) and long term photoelectrochemistry of the CZTS thin films are measured. The characterization of XRD, Raman, SEM, and UV-vis absorption is also performed.