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Killing Two Birds with One Stone: A Highly Active Tubular Carbon Catalyst with Effective N Doping for Oxygen Reduction and Hydrogen Evolution Reactions
No full textThe oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two of the core reactions that occur in fuel cells and water electrolysis devices. Heteroatom-doped carbon materials are promising metal-free electrocatalysts to improve the conversion efficiency of these devices. To optimize the nanostructures of such carbon-based catalysts, herein, we reported an effective template method to synthesize N doped carbon nanotubes by using polydopamine as a precursor. The use of the ZnO nanowire not only serves as a self-sacrificial template to direct the formation of the nanotube, but also greatly extends the porosity of the carbon nanotube. Moreover, the polydopamine precursor also leads to effective N doping. An optimized sample, NCNT-900, shows high ORR performance comparable with that of Pt/C as well as good HER performance in both alkaline and acid media, making it one of the most effective carbon-based HER catalysts. This strategy offers an opportunity to synthesize catalysts with higher activity by rational design of a carbon precursor with higher N content or multi-heteroatom co-doping.
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Application of In Situ Techniques for the Characterization of NiFe-Based Oxygen Evolution Reaction (OER) Electrocatalysts
No full textDeveloping high-efficiency and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a crucial bottleneck on the way to the practical applications of rechargeable energy storage technologies and water splitting for producing clean fuel (H-2). In recent years, NiFe-based materials have proven to be excellent electrocatalysts for OER. Understanding the characteristics that affect OER activity and determining the OER mechanism are of vital importance for the development of OER electrocatalysts. Therefore, in situ characterization techniques performed under OER conditions are urgently needed to monitor the key intermediates together with identifying the OER active centers and phases. In this Minireview, recent advances regarding in situ techniques for the characterization of NiFe-based electrocatalysts are thoroughly summarized, including Raman spectroscopy, X-ray absorption spectroscopy, ambient pressure X-ray photoelectron spectroscopy, Mcssbauer spectroscopy, Ultraviolet-visible spectroscopy, differential electrochemical mass spectrometry, and surface interrogation scanning electrochemical microscopy. The results from these in situ measurements not only reveal the structural transformation and the progressive oxidation of the catalytic species under OER conditions, but also disclose the crucial role of Ni and Fe during the OER. Finally, the need for developing new in situ techniques and theoretical investigations is discussed to better understand the OER mechanism and design promising OER electrocatalysts
Boosting Potassium-Ion Battery Performance by Encapsulating Red Phosphorus in Free-Standing Nitrogen-Doped Porous Hollow Carbon Nanofibers
No full textPotassium-ion batteries (KIBs) are a promising alternative to lithium-ion batteries (LIBs) for large-scale renewable energy storage owning to the natural abundance and low cost of potassium. However, the biggest challenge for KIBs application lies in the lack of suitable electrode materials that can deliver long cycle life and high reversible capacity. In this work, we realized unprecedented long cycle life with high reversible capacity (465 mAh g(-1) at 2 A g(-1) after 800 cycles) as well as outstanding rate capability (342 mAh g(-1) at 5 A g(-1)) for KIBs by embedding red P into free-standing nitrogen-doped porous hollow carbon nanofibers (red P@N-PHCNFs). This design circumvents the problems of pulverization and aggregation of P particles. The in situ transmission electron microscopy (TEM) investigation reveals the structural robustness of the composite fibers during potassiation. The formation of P-C chemical bonds as well as nitrogen doping in the carbon matrix can facilitate the sturdy contact and enhance the adsorption energy of P atoms evidenced by DFT results. In situ Raman and ex situ XRD demonstrate that the final discharge product of the red P@N-PHCNFs is K4P3
Dual-phase membrane reactor for hydrogen separation with high tolerance to CO2 and H2S impurities
No full textCatalytic membrane reactors based on oxygen-permeable membranes are recently studied for hydrogen separation because their hydrogen separation rates and separation factors are comparable to those of Pd-based membranes. New membrane materials with high performance and good tolerance to CO2 and H2S impurities are highly desired. In this work, a new membrane material Ce0.85Sm0.15O1.925-Sr2Fe1.5Mo0.5O6-delta (SDC-SFM) was prepared for hydrogen separation. It exhibits high conductivities at low oxygen partial pressures, which is benefit to electron transfer and ion diffusion. A high hydrogen separation rate of 6.6 mL cm(-2) min(-1) was obtained on a 0.5-mm-thick membrane coated with Ni/SDC catalyst at 900 degrees C. The membrane reactor was operated steadily for 532 h under atmospheres containing CO2 and H2S impurities. Various characterizations reveal that SDC-SFM has good stability in the membrane reactor for hydrogen separation. All facts confirm that SDC-SFM is promising for hydrogen separation in practical applications. (c) 2018 American Institute of Chemical Engineer
Self-assembling nanoprobes that display two-dimensional fluorescent signals for identification of surfactants and bacteria
No full textThe imidazolium-pyrene self-assembling nanoprobes can rapidly discriminate four types of surfactants. The surfactants disassembled the probes to turn on significant fluorescence and transform between a pyrene monomer and an excimer, generating a two-dimensional analysis map. The probes were further used to identify different bacterial species
Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium-Based Long Dication
No full textAs the spacer length in 1,2-dimethylimidazolium-based dications increases beyond a specific point (six methylene units), they fail in structure-directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight-methylene-unit structure-directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining "structural" silanolates, regular "connectivity defects" and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen-bonding system that holds the layers together in the as-made material. The F-19 magic-angle spinning (MAS) NMR presented two distinct resonances at -71 and -83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [4(6)6(2)] and [4(1)5(2)6(2)] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl C-13 nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance
Synthesis of spiropyrrolidine oxindoles through Rh(II)-catalyzed olefination/cyclization of diazooxindoles and vinyl azides
No full textA simple and efficient process involving the Rh(II)-catalyzed [1+1+3] annulation of diazooxindoles and vinyl azides has been developed for the synthesis of spiropyrrolidine oxindoles with potential biological activity and significant synthetic applications. This process involves a novel rhodium-catalyzed olefination of diazo compounds, followed by annulation with vinyl azides. This method is compatible with a broad range of substrates and affords moderate to good yields under mild reaction conditions. (C) 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved
Artificial light-driven ion pump for photoelectric energy conversion
No full textBiological light-driven ion pumps move ions against a concentration gradient to create a membrane potential, thus converting sunlight energy directly into an osmotic potential. Here, we describe an artificial light-driven ion pump system in which a carbon nitride nanotube membrane can drive ions thermodynamically uphill against an up to 5000-fold concentration gradient by illumination. The separation of electrons and holes in the membrane under illumination results in a transmembrane potential which is thought to be the foundation for the pumping phenomenon. When used for harvesting solar energy, a sustained open circuit voltage of 550 mV and a current density of 2.4 mu A/cm(2) can reliably be generated, which can be further scaled up through series and parallel circuits of multiple membranes. The ion transport based photovoltaic system proposed here offers a roadmap for the development of devices by using simple, cheap, and stable polymeric carbon nitride
Rapid Quantitative Fluorescence Detection of Copper Ions with Disposable Microcapsule Arrays Utilizing Functional Nucleic Acid Strategy
No full textIn this work, an economical and easy-to-use microcapsule array fabricated by ice printing technique has been realized for ultrasensitive fluorescence quantification of copper ions employing functional nucleic acid strategy. With ice printing, the detection reagents are sealed by polystyrene (PS) film isolation and photopolymer, which guarantees a stable and contamination-free environment for functional nucleic acid reaction. Our microcapsule arrays have shown long-term stability (20 days) under -20 degrees C storage in frozen form before use. During the Cu2+ on-site detection, 1 mu L sample is simply injected into the thawy microcapsule by a microliter syringe under room temperature, and after 20 minutes the fluorescence result can be obtained by an LED transilluminator. This method can realize the detection limit to 100 nM (100 fmol/mu L) with high specificity
Effect of Na Promoter on Fe-Based Catalyst for CO2 Hydrogenation to Alkenes
No full textA series of Fe-based catalysts with accurately controlled amounts of Na are synthesized to investigate the relationship between the promoter and the catalytic performance for CO2 hydrogenation to alkenes. With the increasing amount of Na, both CO2 conversion and alkenes selectivity increase at low and moderate amounts and then plateau (with the highest to be 36.8% and 64.3%, respectively), while the corresponding methane production decreases to 7.2%. It is found that the addition of Na enhances the adsorption of CO2, facilitates the formation and stability of active species Fe5C2, and inhibits the secondary hydrogenation of alkenes. All these effects lead to the desirable catalytic performance. Besides, it is observed that the content of Fe5C2 is related to the amount of Na. This study can provide scientific guidance to the design and the synthesis of high-efficiency catalysts for CO2 hydrogenation to high-value chemicals