Fe/Co-based Bimetallic MOF-derived Co3 Fe7 @NCNTFs Bifunctional Electrocatalyst for High-Efficiency Overall Water Splitting.

Electrocatalytic water splitting to produce hydrogen and oxygen is regarded as one of the most promising methods to generate clean and sustainable energy for replacing fossil fuels. However, the design and development of an efficient bifunctional catalyst for simultaneous generation of hydrogen and oxygen remains extremely challenging yet is critical for the practical implementation of water electrolysis. Here, we report a facile method to fabricate novel N-doped carbon nanotube frameworks (NCNTFs) by the pyrolysis of a bimetallic metal organic framework (MIL-88-Fe/Co). The resultant electrocatalyst, Co3 Fe7 @NCNTFs, exhibits excellent oxygen evolution reaction (OER) activity, achieving 10 mA/cm2 at a low overpotential of just 264 mV in 1 M KOH solution, and 197 mV for the hydrogen evolution reaction. The high electrocatalytic activity arises from the synergistic effect between the chemistry of the Co3 Fe7 and the NCNTs coupled to the novel framework structure. The remarkable electrocatalytic performance of our bifunctional electrocatalyst provides a promising pathway to high-performance overall water splitting and electrochemical energy devices.

Three-Dimensional N-Doped Carbon Nanotube Frameworks on Ni Foam Derived from a Metal-Organic Framework as a Bifunctional Electrocatalyst for Overall Water Splitting.

Rational design of bifunctional, high-performance, and stable non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great importance and challenging for the realization of overall water splitting. Metal-organic frameworks (MOFs) have been intensively studied as pyrolyzing precursors to prepare electrocatalysts. However, the aggregation of powder and the low conductivity of polymer binders have limited the applications of powder electrocatalysts. Therefore, the direct growth of MOFs on conductive and porous substrates will be a favorable way to prepare efficient electrocatalysts for electrocatalytic water splitting. Herein, we report a facile strategy for constructing three-dimensional N-doped carbon nanotube frameworks derived from metal-organic framework on Ni foam as a bifunctional electrocatalyst for overall water splitting. The resulting electrocatalyst exhibits excellent stability and high OER and HER activity with rather low overpotentials of 230 and 141 mV at 10 mA/cm2 in 1.0 M KOH, respectively. Specifically, the as-synthesized electrodes were used as both the cathode and anode for overall water splitting with 10 mA/cm2 at a cell voltage of only 1.62 V. The outstanding electrocatalytic performance is mainly attributed to a large number of accessible active sites of Co nanoparticles dispersed by the N-doped carbon nanotubes (CNTs) and the ultra-high surface area of CNT frameworks. The presented strategy offers a novel approach for developing MOF-derived nanocarbon materials on Ni foam for electrocatalysis and electrochemical energy devices.

Impacts of Alternative Fuels on Morphological and Nanostructural Characteristics of Soot Emissions from an Aviation Piston Engine.

Soot emissions from aviation piston engines (APEs) are a major source of environment pollution in airport vicinity, stratosphere, and troposphere, and their nanostructure and surface chemistry play a critical role in determining the impact on human health and environment. In this work, the morphology and nanostructure of soot emitted from an aviation piston engine burning five different fuels including blends of promising alternative jet and biofuels were investigated via high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The graphitic structures were observed by analyzing primary particles in the HRTEM images. Morphological analysis demonstrated that the separation distance of the graphene layers of soot particles from the kerosene-pentanol blend combustion was larger than that from kerosene-Fischer-Tropsch blend combustion, indicating that adding pentanol tended to generate particles with more loosely stacked layers and higher oxidation tendency. Raman results were in agreement with primary particle nanostructure analysis based on the HRTEM images. Furthermore, soot particles from different fuels exhibited different concentrations of amorphous carbon and structural defects.

Structurally Well-Defined Au@Cu2- x S Core-Shell Nanocrystals for Improved Cancer Treatment Based on Enhanced Photothermal Efficiency.

Au@Cu2- x S core-shell nanocrystals (NCs) have been synthesized under large lattice mismatch with high crystallinity, controllable shape, and nonstoichiometric composition. Both experimental observations and simulations are used to verify the flexible dual-mode plasmon coupling. The enhanced photothermal effect is harnessed for diverse HeLa cancer cell ablation applications in the NIR-I window (750-900 nm) and the NIR-II window (1000-1400 nm).

Modulation of Photocatalytic Properties by Strain in 2D BiOBr Nanosheets.

BiOBr nanosheets with highly reactive {001} facets exposed were selectively synthesized by a facile hydrothermal method. The inner strain in the BiOBr nanosheets has been tuned continuously by the pH value. The photocatalytic performance of BiOBr in dye degradation can be manipulated by the strain effect. The low-strain BiOBr nanosheets show improved photocatalytic activity. Density functional calculations suggest that strain can modify the band structure and symmetry in BiOBr. The enhanced photocatalytic activity in low-strain BiOBr nanosheets is due to improved charge separation attributable to a highly dispersive band structure with an indirect band gap.

Manipulation of domain wall mobility by oxygen vacancy ordering in multiferroic YMnO3.

The mobility of the ferroelectric domain phases and the local conductivity of ferroelectric domain walls in multiferroic YMnO3 crystals grown in air and reduced atmosphere were studied by piezoresponse force microscopy (PFM), tip-enhanced Raman spectroscopy (TERS) and conductive atomic force microscopy (CAFM). Oxygen vacancies were found to reduce the strength of 4d-2p (Y(3+)-O(2-)) hybridization and structural trimerization distortion, leading to the disappearance of the six wedge-shaped ferroelectric domain phases in oxygen deficient YMnO3-δ crystals. We observed anisotropic domain wall motion such that the wedge-shaped domain configuration joined at one point could be changed to the stripe domain configuration by applying high electric fields in oxygen deficient YMnO3-δ single crystals. The local conductivity of the domain walls increased significantly in poled YMnO3-δ single crystals. The straight conductive domain walls in YMnO3-δ, instead of the twisted insulating ones in the stoichiometric crystal, are induced by the ordered oxygen vacancies which are verified by TERS measurements.

Improving the solubility of Mn and suppressing the oxygen vacancy density in Zn(0.98)Mn(0.02)O nanocrystals via octylamine treatment.

Zn(0.98)Mn(0.02)O nanocrystals were synthesized by the wet chemical route and were treated with different content of octylamine. The environment around Mn and the defect type and concentration were characterized by photoluminescence, Raman, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. It is found that N codoping effectively enhances the solubility of Mn substituting Zn via reducing donor binding energy of impurity by the orbital hybridization between the N-acceptor and Mn-donor. On the other hand, the O atoms released from MnO(6) and the N ions from octylamine occupy the site of oxygen vacancies and result in reduction of the concentration of oxygen vacancies in Zn(0.98)Mn(0.02)O nanocrystals.

Growth mechanism for ZnO nanorod array in a metastable supersaturation solution.

ZnO nanorod array with vertical orientation was fabricated by a simple aqueous solution way in the mild condition. ZnO granular film coated on glass substrate was used as a seeds film for the growth of ZnO ordered array. A metastable supersaturation area where there was no homogeneous nucleation of ZnO in the bulk solution but heterogeneous nucleation on the ZnO granular film was found. It was proved that high-quality and dense ZnO nanorod array could be obtained under this condition. The microstructures of ZnO nanorod array were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometer (EDS). The results indicated that ZnO nanorod array nucleated and grew vertically on the ZnO granular film along the [002] direction. The diameter and length of ZnO rod was greatly affected by growth solution concentration, reaction temperature, and metastable supersaturation status. The growth mechanism was discussed in detail.