Yuying Meng

N-, O-, and S-Tridoped Nanoporous Carbons as Selective Catalysts for Oxygen Reduction and Alcohol Oxidation Reactions

Replacing rare and expensive metal catalysts with inexpensive and earth-abundant ones is currently among the major goals of sustainable chemistry. Herein we report the synthesis of N-, O-, and S-tridoped, polypyrrole-derived nanoporous carbons (NOSCs) that can serve as metal-free, selective electrocatalysts and catalysts for oxygen reduction reaction (ORR) and alcohol oxidation reaction (AOR), respectively. The NOSCs are synthesized via polymerization of pyrrole using (NH4)2S2O8 as oxidant and colloidal silica nanoparticles as templates, followed by carbonization of the resulting S-containing polypyrrole/silica composite materials and then removal of the silica templates. The NOSCs exhibit good catalytic activity toward ORR with low onset potential and low Tafel slope, along with different electron-transfer numbers, or in other words, different ratios H2O/H2O2 as products, depending on the relative amount of colloidal silica used as templates. The NOSCs also effectively catalyze AOR at relatively low temperature, giving good conversions and high selectivity.

Chestnut-Like TiO2@α-Fe2O3 Core–Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO2@α-Fe2O3 core-shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO2 and α-Fe2O3 are observed and supposed to provide synergistic effect. The TiO2 microsphere framework significantly improves the mechanical stability, while the α-Fe2O3 provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g-1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g-1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe0 phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe2O3-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs.

Yeast Cells-Derived Hollow Core/Shell Heteroatom-Doped Carbon Microparticles for Sustainable Electrocatalysis

The use of renewable resources to make various synthetic materials is increasing in order to meet some of our sustainability challenges. Yeast is one of the most common household ingredients, which is cheap and easy to reproduce. Herein we report that yeast cells can be thermally transformed into hollow, core-shell heteroatom-doped carbon microparticles that can effectively electrocatalyze the oxygen reduction and hydrazine oxidation reactions, reactions that are highly pertinent to fuel cells or renewable energy applications. We also show that yeast cell walls, which can easily be separated from the cells, can produce carbon materials with electrocatalytic activity for both reactions, albeit with lower activity compared with the ones obtained from intact yeast cells. The results reveal that the intracellular components of the yeast cells such as proteins, phospholipids, DNAs and RNAs are indirectly responsible for the latters higher electrocatalytic activity, by providing it with more heteroatom dopants. The synthetic method we report here can serve as a general route for the synthesis of (electro)catalysts using microorganisms as raw materials.

N- and O-doped mesoporous carbons derived from rice grains: efficient metal-free electrocatalysts for hydrazine oxidation

Nitrogen and oxygen co-doped mesoporous carbons that can serve as metal-free electrocatalysts are synthesized via a novel synthetic route using milled rice as a precursor and colloidal silica as a template. The materials efficiently electrocatalyze the hydrazine oxidation reaction with only a small onset potential, while giving a high peak current density and showing good long-term stability.

Anatase TiO2 single crystal hollow nanoparticles: their facile synthesis and high-performance in dye-sensitized solar cells

In this paper, we successfully synthesized anatase TiO2 hierarchical microspheres (S0), anatase TiO2 sub-micro hollow mesospheres (S50), anatase TiO2 single crystal hollow nanoparticles (S100), nanoparticles (S250) and (S500) by using different amounts of hydrofluoric acid (HF) versus titanium n-tetrabutoxide (TBT) and acetic acid (AcOH). The structure and morphology of the as-prepared materials were confirmed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DSSCs (dye-sensitized solar cells) based on anatase single crystal hollow TiO2 nanoparticles (S100) as a photoanode showed an efficient power conversion efficiency of 8.94% along with a current density of 17.39 mA cm−2 and an open circuit voltage of 778 mV, which is higher than the DSSCs based on S0 (8.10%), S50 (8.57%), S250 (7.25%) and S500 (6.12%). The high performance of S100 as a DSSC is attributed to their hollow structure which might help to harvest more light, higher light scattering and trapping abilities and comparatively higher surface area. Therefore, we can expect that our materials are promising for assembling superior photoelectrodes for future preparation of highly-efficient DSSCs and may lead to applications for energy storage, water splitting, catalysis, and gas sensing.

White Light Emission and Enhanced Color Stability in a Single-Component Host

Eu3+ ion can be effectively sensitized by Ce3+ ion through an energy-transfer chain of Ce3+-(Tb3+) n-Eu3+, which has contributed to the development of white light-emitting diodes (WLEDs) as it can favor more efficient red phosphors. However, simply serving for WLEDs as one of the multicomponents, the design of the Ce3+-(Tb3+) n-Eu3+ energy transfer is undoubtedly underused. Theoretically, white light can be achieved with extra blue and green emissions released from Ce3+ and Tb3+. Herein, the design of the white light based on these three multicolor luminescence centers has been realized in GdBO3. It is the first time that white light is generated via accurate controls on the Ce3+-(Tb3+) n-Eu3+ energy transfer in such a widely studied host material. Because the thermal quenching rates of blue, green, and red emissions from Ce3+, Tb3+, and Eu3+, respectively, are well-matched in the host, this novel white light exhibits superior color stability and potential application prospect.

Hollow nanocubes constructed from oriented anatase TiO2 nanoarrays: topotactic conversion and fast lithium-ion storage

Mechanically stable titanium dioxide (TiO2) with the abilities of rapidly storing and releasing Li+ can be potentially applied in electric and hybrid electric vehicles, due to its ability to enhance the stability and safety, as well as the high current performance, of lithium ion batteries (LIBs). Herein, we rationally and facilely synthesized oriented anatase TiO2 nanoarrays (OATNs) from the NH4TiOF3 mesocrystal precursor through topotactic conversion and in situ epitaxial growth under moderate conditions. This study proves that the crystallization, porous structure, and orientation of OATNs are controllable, which affect the electronic and electrochemical properties and the Li+ diffusion coefficient. The optimal OATNs formed by hydrothermally treating NH4TiOF3 mesocrystals with an H3BO3 aqueous solution for 10 h (OATNs-10) delivered a high capacity of ca. 115 mA h g−1 at a current density of 50 C (170 mA g−1 of 1 C) even after continuous 2000 cycles with a Coulombic efficiency of ca. 100%. This indicates a high current rate performance and excellent stability. The unique properties of OATNs-10 make them a promising candidate for practical applications in LIBs.

Ultrathin nanobelts-assembled Chinese knot-like 3D TiO 2 for fast and stable lithium storage

Nanostructured TiO2 has applications in solar cells, photocatalysts, and fast-charging, safe lithium ion batteries (LIBs). To meet the demand of high-capacity and high-rate LIBs with TiO2-based anodes, it is important to fine-tune the nanoarchitecture using a well-controlled synthesis approach. Herein, we report a new approach that involves epitaxial growth combined with topotactic conversion to synthesize a unique type of 3D TiO2 nanoarchitecture that is assembled by well-oriented ultrathin nanobelts. The whole nanoarchitecture displays a 3D Chinese knot-like morphology; the core consists of robust perpendicular interwoven nanobelts and the shell is made of extended nanobelts. The nanobelts oriented in three perpendicular [001]A directions facilitate Li+ penetration and diffusion. Abundant anatase/TiO2-B interfaces provide a large amount of interfacial pseudocapacitance. A high and stable capacity of 130 mA·h·g−1 was obtained after 3,000 cycles at 10 A·g−1 (50 C), and the high-rate property of our material was greater than that of many recently reported high-rate TiO2 anodes. Our result provides, not only a novel synthesis strategy, but also a new type of 3D anatase TiO2 anode that may be useful in developing long-lasting and fast-charging batteries.