Shuai Chen

Self-Assembly of Perylene Imide Molecules into 1D Nanostructures: Methods, Morphologies, and Applications

Methods, Morphologies, and Applications Shuai Chen,†,‡ Paul Slattum, Chuanyi Wang,*,† and Ling Zang* †Laboratory of Environmental Sciences and Technology, Xinjiang Technical Institute of Physics & Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi 830011, China ‡The Graduate School of Chinese Academy of Science, Beijing 100049, China Nano Institute of Utah and Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112, United States Vaporsens Inc., Salt Lake City, Utah 84112, United States

Porous TiO2 Nanotubes with Spatially Separated Platinum and CoOx Cocatalysts Produced by Atomic Layer Deposition for Photocatalytic Hydrogen Production

Efficient separation of photogenerated electrons and holes, and associated surface reactions, is a crucial aspect of efficient semiconductor photocatalytic systems employed for photocatalytic hydrogen production. A new CoOx /TiO2 /Pt photocatalyst produced by template-assisted atomic layer deposition is reported for photocatalytic hydrogen production on Pt and CoOx dual cocatalysts. Pt nanoclusters acting as electron collectors and active sites for the reduction reaction are deposited on the inner surface of porous TiO2 nanotubes, while CoOx nanoclusters acting as hole collectors and active sites for oxidation reaction are deposited on the outer surface of porous TiO2 nanotubes. A CoOx /TiO2 /Pt photocatalyst, comprising ultra-low concentrations of noble Pt (0.046u2005wtu2009%) and CoOx (0.019u2005wtu2009%) deposited simultaneously with one atomic layer deposition cycle, achieves remarkably high photocatalytic efficiency (275.9u2005μmolu2009h-1 ), which is nearly five times as high as that of pristine TiO2 nanotubes (56.5u2005μmolu2009h-1 ). The highly dispersed Pt and CoOx nanoclusters, porous structure of TiO2 nanotubes with large specific surface area, and the synergetic effect of the spatially separated Pt and CoOx dual cocatalysts contribute to the excellent photocatalytic activity.

Tuning the Shell Number of Multishelled Metal Oxide Hollow Fibers for Optimized Lithium-Ion Storage

Searching the long-life transition-metal oxide (TMO)-based materials for future lithium-ion batteries (LIBs) is still a great challenge because of the mechanical strain resulting from volume change of TMO anodes during the lithiation/delithiation process. To well address this challenging issue, we demonstrate a controlled method for making the multishelled TMO hollow microfibers with tunable shell numbers to achieve the optimal void for efficient lithium-ion storage. Such a particularly designed void can lead to a short diffusion distance for fast diffusion of Li+ ions and also withstand a large volume variation upon cycling, both of which are the key for high-performance LIBs. Triple-shelled TMO hollow microfibers are a quite stable anode material for LIBs with high reversible capacities (NiO: 698.1 mA h g-1 at 1 A g-1; Co3O4: 940.2 mA h g-1 at 1 A g-1; Fe2O3: 997.8 mA h g-1 at 1 A g-1), excellent rate capability, and stability. The present work opens a way for rational design of the void of multiple shells in achieving the stable lithium-ion storage through the biomass conversion strategy.

Nanoscale engineering of nitrogen-doped carbon nanofiber aerogels for enhanced lithium ion storage

We developed a unique industrial-scale sustainable biomass conversion strategy for the synthesis of multifunctional, three-dimensional (3D) carbon nanofiber (CNF) aerogels with hierarchical porosity. The above aerogels were also highly nitrogen-doped through pyrolysis of bamboo cellulose. The important and critical part of our synthesis strategy was to assemble the nanofibers of cellulose (NFC) from bamboo to make aerogels of controlled porosity with a hierarchical porous structure. The as-prepared CNF aerogels with abundant chemical reaction sites and three-dimensional electron and ion transport pathways were found to be new high-performance anode materials for lithium-ion batteries (LIBs). In particular, the N-doped CNF aerogel prepared with 1 D fibers of 50 nm in diameter as building-blocks exhibited a high reversible capacity of 630.7 mA h g−1 at 1 A g−1, excellent rate capability (289 mA h g−1 at 20 A g−1) and excellent cycling performance (651 mA h g−1 at 1 A g−1 after 1000 cycles) in LIBs.

Electronic Structure Tuning in Ni3FeN/r-GO Aerogel toward Bifunctional Electrocatalyst for Overall Water Splitting

Searching for the highly active, stable, and high-efficiency bifunctional electrocatalysts for overall water splitting, e.g., for both oxygen evolution (OER) and hydrogen evolution (HER), is paramount in terms of bringing future renewable energy systems and energy conversion processes to reality. Herein, three-dimensional (3D) Ni3FeN nanoparticles/reduced graphene oxide (r-GO) aerogel electrocatalysts were fabricated using precursors of (Ni,Fe)/r-GO alginate hydrogels through an ion-exchange process, followed by a convenient one-step nitrogenization treatment in NH3 at 700 °C. The resultant materials exhibited excellent electrocatalytic performance for OER and HER in alkaline media, with only small overpotentials of 270 and 94 mV at a current density of 10 mA cm-2, respectively. The good performance was attributed to abundant active sites and high electrical conductivity of the bimetallic nitrides and efficient mass transport of the 3D r-GO aerogel framework. Furthermore, an alkaline electrolyzer was set up using Ni3FeN/r-GO as both the cathode and the anode, which achieved a 10 mA cm-2 current density at 1.60 V with durability of 100 h for overall water splitting. Density functional theory calculations support that Ni3FeN (111)/r-GO is more favorable for overall water splitting since the surface electronic structure of Ni3FeN is tuned by transferring electrons from Ni3FeN cluster to the r-GO through interaction of two metal species. Thus, the currently developed Ni3FeN/r-GO with superior water-splitting performance may potentially serve as a material for use in industrial alkaline water electrolyzers.

Highly stable supercapacitors with MOF-derived Co9S8/carbon electrodes for high rate electrochemical energy storage

Co9S8 has received intensive attention as an electrode material for electrical energy storage (EES) systems due to its unique structural features and rich electrochemical properties. However, the instability and inferior rate capability of the Co9S8 electrode material during the charge/discharge process has restricted its applications in supercapacitors (SCs). Here, MOF-derived Co9S8 nanoparticles (NPs) embedded in carbon co-doped with N and S (Co9S8/NS–C) were synthesized as a high rate capability and super stable electrode material for SCs. The Co9S8/NS–C material was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the Co9S8/NS–C material possessed a unique nanostructure in which Co9S8 NPs were encapsulated in porous graphitic carbon co-doped with N and S. The N/S co-doped porous graphitic carbon of composite led to improved rate performance by enhancing the stability of the electrode material and shortening the ion diffusion paths due to a synergistic effect. The as-prepared Co9S8/NS–C-1.5 h material exhibited a high specific capacitance of 734 F g−1 at a current density of 1 A g−1, excellent rate capability (653 F g−1 at 10 A g−1) and superior cycling stability, i.e., capacitance retention of about 99.8% after 140u2006000 cycles at a current density of 10 A g−1. Thus, a new approach to fabricate promising electrode materials for high-performance SCs is presented here.

1D nanofiber composites of perylene diimides for visible-light-driven hydrogen evolution from water

A series of novel nanocomposite structures have been fabricated by in situ deposition of TiO2 layers and/or a co-catalyst (Pt) on one-dimensional (1D) self-assembled nanofibers of perylene diimide derivatives (PDIs). The PDI molecules were functionalized with dodecyl and/or phenylamino groups to compare the effect of nanofiber morphology and intramolecular charge transfer on the photocatalytic performance. Under visible-light irradiation (λ > 420 nm), hydrogen production for all composite systems has been detected through photocatalytic water splitting in aqueous solutions with sacrificial reagent methanol or triethanolamine, proving the applicability of organic nanofibers in the photocatalytic system. Compared to the well-defined nanofibril morphology obtained from dodecyl-substituted PDI molecules, donor–accepter type PDIs with electron-rich phenylamino moieties attached show much improved photocatalytic activity due to efficient inter- and intra-molecular charge transfer. This work provides insight into the role of molecular design and nanomorphology of organic semiconductor materials in the field of photocatalysis.

Heterojunctions between amorphous and crystalline niobium oxide with enhanced photoactivity for selective aerobic oxidation of benzylamine to imine under visible light

The formation of heterojunctions between two crystals with different band gap structures, acting as a tunnel for the unidirectional transfer of photogenerated charges, is an efficient strategy to enhance the photocatalytic performance of semiconductor photocatalysts. Considering that surface complex photocatalysts also exhibit charge separation and recombination processes, the heterojunctions may also promote the visible-light-response photoactivity of any surface complex catalysts by influencing the transfer of photogenerated electrons. Herein, Nb2O5 microfibers, with a high surface area of interfaces between an amorphous phase and a crystalline phase, were designed and synthesised by the calcination of hydrogen-form niobate while controlling the crystallisation. The photoactivity of these microfibres towards selective aerobic oxidation reactions was investigated. As predicted, the Nb2O5 microfibres containing heterojunctions exhibited the highest photoactivity. This could be due to the band gap difference between the amorphous phase and the crystalline phase that allows electron transfer unidirectionally, which decreased the recombination rate and improved the efficiency.

Highly dispersed Pt nanoparticles supported on carbon nanotubes produced by atomic layer deposition for hydrogen generation from hydrolysis of ammonia borane

Uniformly dispersed Pt nanoparticles with controlled size and loading supported on multi-walled carbon nanotubes (CNTs) are synthesized by atomic layer deposition (ALD) with (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) as the Pt precursor and ozone as the reactant gas. All the ALD-prepared Pt/CNT catalysts with various cycle numbers show excellent catalytic activities towards hydrolysis reaction of ammonia borane (AB), and especially the Pt/CNT catalyst produced with 20 ALD cycles exhibits the highest hydrogen generation rate among the ALD-prepared catalysts, with a total turnover frequency value as high as 416.5 molH2 molPt−1 min−1. The porous TiO2 overcoat further improves the durability of the Pt/CNT catalysts while preserving their catalytic activities.

Highly Efficient Gas Sensor Using a Hollow SnO2 Microfiber for Triethylamine Detection

Triethylamine (TEA) gas sensors having excellent response and selectivity are in great demand to monitor the real environment. In this work, we have successfully prepared a hollow SnO2 microfiber by a unique sustainable biomass conversion strategy and shown that the microfiber can be used in a high-performance gas sensor. The sensor based on the hollow SnO2 microfiber shows a quick response/recovery toward triethylamine. The response of the hollow SnO2 microfiber is up to 49.5 when the concentration of TEA gas is 100 ppm. The limit of detection is as low as 2 ppm. Furthermore, the sensor has a relatively low optimal operation temperature of 270 °C, which is lower than those of many other reported sensors. The excellent sensing properties are largely attributed to the high sensitivity provided by SnO2 and the good permeability and conductivity of the one-dimensional hollow structure. Thus, the hollow SnO2 microfiber using sustainable biomass as a template is a significant strategy for a unique TEA gas sensor.