Bu Yuan Guan

Formation of Onion-Like NiCo2S4 Particles via Sequential Ion-Exchange for Hybrid Supercapacitors

Onion-like NiCo2 S4 particles with unique hollow structured shells are synthesized by a sequential ion-exchange strategy. With the structural and compositional advantages, these unique onion-like NiCo2 S4 particles exhibit enhanced electrochemical performance as an electrode material for hybrid supercapacitors.

A dual-metal–organic-framework derived electrocatalyst for oxygen reduction

High-performance electrocatalysts for the oxygen reduction reaction are indispensable in many electrochemical energy storage and conversion technologies. However, the lack of efficient and inexpensive catalysts or catalyst systems that can compete with noble metal catalysts hinders their large-scale industrial applications. As an important class of porous materials, metal–organic frameworks (MOFs) with systematically tailored structures and compositions have recently been suggested as promising precursors for the preparation of diverse functional materials. Here we report a dual-MOF confined-pyrolysis approach for the preparation of iron carbide nanoparticle-embedded carbon nanotube assemblies. Starting from a novel MOF-in-MOF precursor consisting of a Zn-based MOF polyhedron host and many engulfed Fe-based MOF nanorods, a complex structured composite material constructed from iron carbide nanocrystallite-embedded carbon nanotubes encapsulated in a porous carbon matrix is successfully prepared. We further demonstrate that the as-derived composite material manifests remarkable electrocatalytic performance for the oxygen reduction reaction in an alkaline electrolyte. The present strategy significantly expands the toolbox for the design and synthesis of MOF-derived functional materials for a wide range of applications.

Complex Nanostructures from Materials based on Metal–Organic Frameworks for Electrochemical Energy Storage and Conversion

Metal-organic frameworks (MOFs) have drawn tremendous attention because of their abundant diversity in structure and composition. Recently, there has been growing research interest in deriving advanced nanomaterials with complex architectures and tailored chemical compositions from MOF-based precursors for electrochemical energy storage and conversion. Here, a comprehensive overview of the synthesis and energy-related applications of complex nanostructures derived from MOF-based precursors is provided. After a brief summary of synthetic methods of MOF-based templates and their conversion to desirable nanostructures, delicate designs and preparation of complex architectures from MOFs or their composites are described in detail, including porous structures, single-shelled hollow structures, and multishelled hollow structures, as well as other unusual complex structures. Afterward, their applications are discussed as electrode materials or catalysts for lithium-ion batteries, hybrid supercapacitors, water-splitting devices, and fuel cells. Lastly, the research challenges and possible development directions of complex nanostructures derived from MOF-based-templates for electrochemical energy storage and conversion applications are outlined.

Coordination Polymers Derived General Synthesis of Multishelled Mixed Metal-Oxide Particles for Hybrid Supercapacitors

Metal-organic frameworks (MOFs) or coordination polymers (CPs) have been used as precursors for synthesis of materials. Unlike crystalline MOF, amorphous CP is nonspecific to metal cation species, therefore its composition can be tuned easily. Here, it is shown that amorphous CP can be used as general synthesis precursors of highly complex mixed metal oxide shells. As a proof of concept, NiCo coordination polymer spheres are first synthesized and subsequently transformed into seven-layered NiCo oxide onions by rapid thermal oxidation. This approach is very versatile and can be applied to produce ternary and quaternary metal oxide onions with tunable size and composition. The NiCo oxide onions exhibit exceptional charge storage capability in aqueous electrolyte with high specific capacitance (≈1900 F g-1 at 2 A g-1 ), good rate capability, and ultrahigh cycling stability (93.6% retention over 20 000 cycles). A hybrid supercapacitor against graphene/multishelled mesoporous carbon sphere shows a high energy density of 52.6 Wh kg-1 at a power density of 1604 W kg-1 (based on active materials weight), as well as remarkable cycling stability.

A universal cooperative assembly-directed method for coating of mesoporous TiO2 nanoshells with enhanced lithium storage properties

A universal cooperative assembly method is developed for growing mesostructured TiO2 shells on diverse functional particles. TiO2 is exceptionally useful, but it remains a great challenge to develop a universal method to coat TiO2 nanoshells on different functional materials. We report a one-pot, low-temperature, and facile method that can rapidly form mesoporous TiO2 shells on various inorganic, organic, and inorganic-organic composite materials, including silica-based, metal, metal oxide, organic polymer, carbon-based, and metal-organic framework nanomaterials via a cooperative assembly-directed strategy. In constructing hollow, core-shell, and yolk-shell geometries, both amorphous and crystalline TiO2 nanoshells are demonstrated with excellent control. When used as electrode materials for lithium ion batteries, these crystalline TiO2 nanoshells composed of very small nanocrystals exhibit remarkably long-term cycling stability over 1000 cycles. The electrochemical properties demonstrate that these TiO2 nanoshells are promising anode materials.

Rational Design of Three‐Layered TiO2@Carbon@MoS2 Hierarchical Nanotubes for Enhanced Lithium Storage

Here we demonstrate the rational design and synthesis of three-layered TiO2 @carbon@MoS2 hierarchical nanotubes for anode applications in lithium-ion batteries (LIBs). Through an efficient step-by-step strategy, ultrathin MoS2 nanosheets are grown on nitrogen-doped carbon (NC) coated TiO2 nanotubes to achieve the TiO2 @NC@MoS2 tubular nanostructures. This smart design can effectively shorten the diffusion length of Li+ ions, increase electric conductivity of the electrode, relax volume variation of electrode materials upon cycling, and provide more active sites for electrochemical reactions. Owing to these structural and compositional features, the hierarchical TiO2 @NC@MoS2 nanotubes manifest remarkable lithium storage performance with good rate capability and long cycle life.

Formation of Asymmetric Bowl-Like Mesoporous Particles via Emulsion-Induced Interface Anisotropic Assembly

Mesoporous colloidal particles with tailored asymmetric morphologies and radially oriented large channels are of great importance for development of new carriers for nanoencapsulation, high-performance mass transport nanosystems, and complex assembly structures. However, controllable anisotropic growth to asymmetric mesoporous particles is very challenging via the universal surfactant-directed soft-templating method. Herein we report a simple emulsion-induced interface anisotropic assembly approach to synthesize bowl-like mesoporous polydopamine particles with diameter of ∼210 nm, well-controlled radially oriented mesochannels, and large pore size of ∼11 nm. This interface-driven approach also creates opportunities for tailoring the assembly and formation of various asymmetric and symmetric polydopamine particles. Bowl-like mesoporous carbon particles with radially oriented channels, high accessible surface area of 619 m(2) g(-1), and large pore size of ∼8 nm can be fabricated by subsequent hydrothermal treatment and calcination under nitrogen atmosphere. Lastly, we demonstrate that the as-derived bowl-like mesoporous carbon particles manifest enhanced electrocatalytic performance for oxygen reduction reaction in alkaline electrolyte.

Formation of Hierarchical In2S3–CdIn2S4 Heterostructured Nanotubes for Efficient and Stable Visible Light CO2 Reduction

We demonstrate rational design and fabrication of hierarchical In2S3-CdIn2S4 heterostructured nanotubes as efficient and stable photocatalysts for visible light CO2 reduction. The novel self-templated strategy, including sequential anion- and cation-exchange reactions, integrates two distinct sulfide semiconductors into hierarchical tubular hybrids with homogeneous interfacial contacts and ultrathin two-dimensional (2D) nanosheet subunits. Accordingly, the hierarchical heterostructured nanotubes facilitate separation and migration of photoinduced charge carriers, enhance the adsorption and concentration of CO2 molecules, and offer rich active sites for surface redox reactions. Benefiting from these structural and compositional features, the optimized hierarchical In2S3-CdIn2S4 nanotubes without employing noble metal cocatalysts in the catalytic system manifest remarkable performance for deoxygenative reduction of CO2 with high CO generation rate (825 μmol h-1 g-1) and outstanding stability under visible light irradiation.

Formation of Single-Holed Cobalt/N-Doped Carbon Hollow Particles with Enhanced Electrocatalytic Activity toward Oxygen Reduction Reaction in Alkaline Media

Abstract Design and construction of metal‐organic framework (MOF) composite precursors have recently been considered as a promising strategy for the preparation of different structured metal/carbon‐based functional materials. Here, an MOF composite‐assisted strategy to synthesize single‐holed cobalt/N‐doped carbon hollow particles is reported. The yolk–shell polystyrene@zeolitic imidazolate framework‐67 (PS@ZIF‐67) composite precursors are first synthesized, followed by a controlled pyrolysis to obtain cobalt/N‐doped carbon hollow particles with a large single hole on each shell. Moreover, the MOF‐coating approach reported in this work can be extended to prepare various core‐shell ZIF‐67 composites with different structures and compositions. Benefiting from the structural and compositional advantages, the as‐derived single‐holed cobalt/N‐doped carbon hollow particles manifest superior electrocatalytic oxygen reduction performance with high activity and excellent durability.

Chemically Assisted Formation of Monolayer Colloidosomes on Functional Particles

A chemically assisted method is developed to form a monolayer polymer colloidosome shell on various functional materials. Functional carbon nanobubble colloidosomes or their derived hybrid structures can be fabricated by a subsequent thermal treatment.