•The specific exposed surfaces of monoclinic LaPO4 was revealed with HRTEM.•DFT calculations were used to calculate the surface structure and energies.•The equilibrium shapes of monoclinic LaPO4 were predicted.•The mechanism for the morphology evolution of LaPO4 was identified.•Provide a theoretical method to calculate the morphologies of phosphates.The morphology of the nanocrystals has a considerable effect on their performances in particular applications, and the study of morphology has become a challenging topic in nanometer materials. In our experimental work, LaPO4 with diverse morphologies were synthesized by hydrothermal method to investigate the morphology evolution. The results revealed the corresponding relationship between the pH value of growth solution and the specific exposed surfaces and morphologies of monoclinic LaPO4. Combining the experimental findings, density functional theory calculations were used to calculate the surface energies and to simulate the morphologies. With the increase of pH value, the surface energies increased with different rates, which can be responsible for the evolution of the morphologies. The equilibrium shapes of monoclinic LaPO4 nanorods for each type of surface chemistry were predicted according to the calculated surface energies, whose tendency was consistent with our experimental findings. This work identified the mechanism for the morphology evolution of LaPO4 and provided a theoretical method to calculate the morphologies of lanthanide orthophosphates, which was crucial to gain better control of materials growth.

•Passivation of 2507 stainless steel in desulfurized flue gas condensates is studied.•Oxygen participates in cathodic reaction when the temperature is raised to 60 °C.•Higher temperature results in thickening and Cr enrichment of the passive film.•Property of passive film is mainly controlled by film structure and carrier density.Influence of temperature on the electrochemical and passivation behavior of 2507 super duplex stainless steel in the simulated desulfurized flue gas condensates in thermal power plant chimney are investigated. Cathodic reactions are enhanced with temperature, accompanying with the involvement of oxygen reduction when the temperature is raised to 60 °C or higher. The unchanged semiconductor type, enrichment of Cr and thickening of the passive film are observed as the temperature increases. The temperature-induced variations of film structure and doping concentrations are responsible for the degradation of protective ability of the passive film.

Thanks to the intrinsic p-type conductivity, NiO films show great potential for applications in various domains. In this work, NiOx films were deposited in three dimensional physical vapor deposition (3D-PVD) system from metallic nickel target in pure oxygen conditions. Optical emission spectroscopy (OES) was employed to analyze the plasma state during the deposition. The variation of the film's structural and optoelectronic properties as a function of the oxygen pressure was investigated. It is found that the oxygen content in NiOx films is more evident for the films deposited with lower oxygen pressure. More Ni3+ ions and interstitial oxygen associated with more Ni2+ vacancies and holes are believed to exist in these films. Therefore, their conductivity is higher than the films deposited at higher oxygen pressure. Additionally, with an increase of oxygen pressure, the film's crystallinity is enhanced, and the film's transmittance as well as the film's band gap improves.

Polymer matrix high-k composites are of considerable interest in various electronic devices, such as capacitors, antennas, actuators, etc. However, how to enhance the permittivity without elevating the loss remains a challenge for us. Here we present a novel design of bilayer high-k metacomposites consisting of two stacked single layers with positive permittivity and negative permittivity. Interestingly, the bilayer system shows an obvious permittivity boost effect with a permittivity improved by a 40-fold increase compared with the polymer matrix, while maintaining a loss tangent as low as 0.06. Further calculation results indicate that the permittivity of the bilayer composites could be enhanced by 4000-fold or even a greater increase as compared with the polymer matrix via balancing the dielectric properties of single layers. Insights into how the thickness ratios and dielectric properties of single layers interfere with the dielectric performances of bilayer composites were discussed. This study provides a new route for the design of high-k materials, and it will have great significance on the development of dielectric materials. Hopefully, multilayer high-k metacomposites with fascinating dielectric performances could be achieved via balancing the dielectric properties of single layers.Keywords: dielectric property; high-k material; metamaterial; multilayer composite; negative permittivity;

Molecular dynamics (MD) simulations are performed to study the freezing process of Al–Si melts on heterogeneous Si substrates in detail. We highlight the inherent nanostructure of both the Si primary phase and the Al–Si binary phase. It is found for the first time that the primary Si phase displays a “pyramidal configuration” when the Al–Si melt congeals. Experimental measurements could also verify our simulation results. It can be found that the binary Al–Si phase turns into a “Si–Al–Si sandwich construction” during solidification, regardless of freezing on a single substrate or in the restricted space between substrates. This peculiar phenomenon results from the combined effects of the van der Waals potential well and the interatomic interaction between Al and Si. Furthermore, it is also able to control the thickness of the Si atomic shell of the “sandwich construction”, resulting in the silicene-like unilaminar Si nanostructure. Our findings provide novel strategies to fabricate desired shaped nanostructures by means of nanocasting in Al–Si melts at the nanoscale.

•The interfacial reactions of various specimens at 800 °C were investigated.•The inter-diffusion was effectively restrained by the Ni–Re layer.•The specimens with Ni–Re layer exhibited excellent oxidation resistance at 800 °C.Electroplated Ni–Re film was fabricated as diffusion barrier between NiCoCrAlY coating and orthhombic-Ti2AlNb alloy. The plated Ni–Re film was intact, continuously grown and well-bonded with orthhombic-Ti2AlNb alloy. The oxidation and inter-diffusion behavior of coatings with and without diffusion barrier were both investigated in isothermal and cyclic oxidation tests at 800 °C. The results indicated that substantial inter-diffusion and rapid oxidation occurred in the coating without diffusion barrier; while deferred inter-diffusion and improved oxidation resistance were observed, and were attributed to the Ni–Re diffusion barrier.

The design of a non-noble-metal electrocatalyst for the oxygen reduction reaction (ORR) is crucial for the renewable energy technologies related to electrochemical energy conversion and storage. Herein, we demonstrate a facile one-pot protocol for the highly selective growth of nanosized cobalt oxide on hollow carbon spheres. The unique structural features enable them to be an efficient non-precious catalyst for the ORR and offer potential applications in the fields of alkaline fuel cells.

Chirality sensing is a very challenging task. Here, we report a method for ultrasensitive detection of chiral molecule l/d-carnitine based on changes in the recognition tunneling current across self-assembled core–satellite gold nanoparticle (GNP) networks. The recognition tunneling technique has been demonstrated to work at the single molecule level where the binding between the reader molecules and the analytes in a nanojunction. This process was observed to generate a unique and sensitive change in tunneling current, which can be used to identify the analytes of interest. The molecular recognition mechanism between amino acid l-cysteine and l/d-carnitine has been studied with the aid of SERS. The different binding strength between homo- or heterochiral pairs can be effectively probed by the copper ion replacement fracture. The device resistance was measured before and after the sequential exposures to l/d-carnitine and copper ions. The normalized resistance change was found to be extremely sensitive to the chirality of carnitine molecule. The results suggested that a GNP networks device optimized for recognition tunneling was successfully built and that such a device can be used for ultrasensitive detection of chiral molecules.Keywords: biosensors; chiral molecule differentiation; chiral sensing; core satellite GNPs; molecular electronics; tunneling current recognition

To improve the electrochemical performance of cobalt oxide owing to its inherent poor electrical conductivity and large volume expansion/contraction, Co3O4-carbon nanosheet hybrid nanoarchitectures were synthesized by a facile and scalable chemical process. However, it is still a challenge to control the size of Co3O4 particles down to ∼5 nm. Herein, we created nanosized cobalt oxide anchored 3D arrays of carbon nanosheets by the control of calcination condition. The uniformly dispersed Co3O4 nanocrystals on carbon nanosheets held a diameter down to ∼5 nm. When tested as anode materials for lithium-ion batteries, high lithium storage over 1200 mAh g–1 is achieved, whereas high rate capability with capacity of about 390 mAh g–1 at 10 A g–1 is maintained through nanoscale diffusion distances and interconnected porous structure. After 500 cycles, the cobalt oxide-carbon nansheets hybrid display a reversible capacity of about 970 mAh g–1 at 1 A g–1. The synergistic effect between nanosized cobalt oxide and sheetlike interconnected carbon nanosheets lead to the greatly improved specific capacity and the initial Coulombic efficiency of the hybrids.Keywords: anode; cobalt oxide; electrochemistry; energy storage; hybrid; Li-ion battery

The percolation phenomenon has great significance for multi-component materials, especially for the preparation of high-k composites. At present, most research focuses on composites below the percolation threshold because the high filling fraction usually results in enhanced losses, which are undesirable for high-k applications. However, it should be noted that lossy materials also may have huge potential applications in microwave absorbing, electromagnetic attenuation and shielding fields, etc. Therefore, it is of interest to clarify the dielectric behaviors of composites beyond percolation. Herein, the dielectric properties of silver/alumina composites beyond percolation are investigated. Interestingly, metal–insulator transition, capacitive–inductive transition, and radio frequency dielectric resonances appear along with the percolation phenomenon. The interrelationships between these phenomena are discussed. The mechanism of the radio frequency dielectric resonance-induced negative permittivity is discussed in detail. Clarification of the dielectric properties of conductor/insulator composites beyond percolation has great significance for the development of novel dielectric materials with fascinating properties and applications.

Iron–alumina composites consisting of different loadings of iron particles dispersed in an alumina matrix were prepared via a facile impregnation–calcination process. The frequency dispersions of conductivity and permittivity were investigated in detail. An ultra low percolation threshold of 2.3 vol%, which is much lower than that of dense metal–ceramic composites, was obtained. Meanwhile, a significant enhancement of permittivity ε′ (from ∼7.5 to ∼800) was achieved when the iron content increases from 0 to 4.2 vol% at 10 MHz. The ultra low percolation threshold can be explained by the fact that the porous microstructure of the composites will facilitate the formation of a layer of two dimensional conductive networks on the pore wall of porous alumina. And the significant enhancement of permittivity should be attributed to the interfacial polarization phenomenon that takes place at the iron–alumina interfaces. This paper demonstrates that the loading of a conductive component into a porous matrix is an effective way to fabricate composites with simultaneously high permittivity and ultra-low percolation threshold. Hopefully, various porous metal–ceramic composites with tailored dielectric properties could be fabricated using the impregnation–calcination process.

•The absorption performances of hydrogel is employed to synthesize proton exchange membranes.•Incorporated H3PO4 is sealed in the 3D framework of polyacrylamide-g-starch hydrogel.•A proton conductivity of 0.046 S cm−1 at 180 °C under anhydrous atmosphere is obtained.•A fuel cell shows a peak power density of 517 mW cm−2.To enhance the anhydrous proton conductivities of proton exchange membranes, we report here the incorporation of H3PO4 into three-dimensional (3D) framework of polyacrylamide-graft-starch (PAAm-g-starch) hydrogel materials using extraordinary absorption of hydrogels to H3PO4 aqueous solution. Intrinsic microporous structure can close to seal H3PO4 molecules in the interconnected 3D frameworks of PAAm-g-starch after suffering from dehydration. The hydrogel membranes are thoroughly characterized by morphology observation, thermal stability, swelling kinetics, proton-conducting performances as well as electrochemical behaviors. The results show that the H3PO4 loadings and therefore the proton conductivities of the hydrogel membranes are dramatically enhanced by employing PAAm-g-starch matrix. H3PO4 loading of 88.68 wt% and an anhydrous proton conductivity as high as 0.046 S cm−1 at 180 °C are recorded. A fuel cell using a thick membrane shows a peak power density of 517 mW cm−2 at 180 °C by feeding with H2/O2 streams. The high H3PO4 loading, reasonable proton conductivity in combination with simple preparation, low cost and scalable matrix demonstrates the potential use of PAAm-g-starch hydrogel membranes in high-temperature proton exchange membrane fuel cells.

Iron–alumina composites consisting of different loadings of iron particles dispersed in an alumina matrix were prepared via a facile impregnation–calcination process. The frequency dispersions of conductivity and permittivity were investigated in detail. An ultra low percolation threshold of 2.3 vol%, which is much lower than that of dense metal–ceramic composites, was obtained. Meanwhile, a significant enhancement of permittivity ε′ (from ∼7.5 to ∼800) was achieved when the iron content increases from 0 to 4.2 vol% at 10 MHz. The ultra low percolation threshold can be explained by the fact that the porous microstructure of the composites will facilitate the formation of a layer of two dimensional conductive networks on the pore wall of porous alumina. And the significant enhancement of permittivity should be attributed to the interfacial polarization phenomenon that takes place at the iron–alumina interfaces. This paper demonstrates that the loading of a conductive component into a porous matrix is an effective way to fabricate composites with simultaneously high permittivity and ultra-low percolation threshold. Hopefully, various porous metal–ceramic composites with tailored dielectric properties could be fabricated using the impregnation–calcination process.