Ruimin Ding

A broadband antireflective coating based on a double-layer system containing mesoporous silica and nanoporous silica

A double-layer broadband antireflective (AR) coating with excellent transmittance was successfully fabricated using two kinds of silica coatings. The excellent optical performance in a wide wavelength range came from a reasonable refractive index gradient from air to the substrate produced by the mesopores in the bottom-layer silica coating and the particle-packed pores in the top-layer silica coating. The maximum transmittance of the broadband AR coating was approximated to 100.0% at the peak value and above 99.6% in the visible region from 400 to 800 nm. Meanwhile, the average transmittance of the coating was more than 99.0% over the range of 360 to 920 nm. In addition, the double-layer broadband silica AR coating showed strong mechanical performance and good environmental stability. This work provides an alternative way to prepare a broadband AR coating for some applications in energy harvesting and optical devices.

Facile synthesis of porous nitrogen-doped holey graphene as an efficient metal-free catalyst for the oxygen reduction reaction

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions (ORRs). The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene (PHNG) via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale (5–15 nm) holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.

Facile synthesis of self-assembled ultrathin α-FeOOH nanorod/ graphene oxide composites for supercapacitors

A one-pot facile, impurity-free hydrothermal method to synthesize ultrathin α-FeOOH nanorods/graphene oxide (GO) composites is reported. It is directly synthesized from GO and iron acetate in water solution without inorganic or organic additives. XRD, Raman, FT-IR, XPS and TEM are used to characterize the samples. The nanorods in composites are single crystallite with an average diameter of 6nm and an average length of 75nm, which are significantly smaller than GO-free α-FeOOH nanorods. This can be attributed to the confinement effect and special electronic influence of GO. The influences of experimental conditions including reaction time and reactant concentration on the sizes of nanorods have been investigated. It reveals that the initial Fe2+ concentration and reaction time play an important role in the synthetic process. Furthermore, a possible nucleation-growth mechanism is proposed. As electrode materials for supercapacitors, the α-FeOOH nanorods/GO composite with 20% iron loading has the largest specific capacitance (127Fg-1 at 10Ag-1), excellent rate capability (100Fg-1 at 20Ag-1) and good cyclic performance (85% capacitance retention after 2000 cycles), which is much better than GO-free α-FeOOH nanorods. This unique structure results in rapid electrolyte ions diffusion, fast electron transport and high charging-discharging rate. In virtue of the superior electrochemical performance, the α-FeOOH nanorods/GO composite material has a promising application in high-performance supercapacitors.

Tri-wavelength broadband antireflective coating built from refractive index controlled MgF2 films

Regulation of the refractive index over a wide range is very important in the realization of tri-wavelength antireflective (AR) coating in high power laser systems, but many regulation approaches are too complex or violent to satisfy the practical requirements. Here, a simple, template-free sol–gel route was proposed to regulate the refractive index of MgF2 film by heat treating MgF2 sol and hence to control the self-assembly process of colloidal MgF2 nanocrystals. In this self-assembly process, the originally packed nanocrystals gradually evolved into bigger hollow vesicles, which reduced the refractive index of the MgF2 film from 1.38 to 1.2. When the refractive indices of the bottom and top layers were set as 1.34 and 1.2, the tri-wavelength broadband AR coating was finally realized on a quartz substrate, with the transmittance of 99.54%, 98.65% and 98.58% at 351 nm, 527 nm and 1053 nm, respectively.

Broadband antireflective double-layer mesoporous silica coating with strong abrasion-resistance for solar cell glass

To enhance the efficiency of solar cells, a broadband double-layer antireflective (AR) coating with excellent transmittance and abrasion-resistance, was successfully fabricated using two layer mesoporous silica coatings. Both layers were prepared via a solvent evaporation self-assembly method in which the top- and bottom-layer mesoporous silica coatings used Pluronic F127 and cetyltrimethylammonium bromide (CTAB) as templates, respectively. The grazing incidence small angle X-ray scattering (GISAXS) and the transmission electron microscope (TEM) results indicated that the mesopores in the double-layer AR coating belonged to a Fmmm orthorhombic symmetry structure of the SBA-16 in the top layer and a P6/mmc 3D-hexagonal structure of the MCM-41 in the bottom layer. The solar-weighted average transmittance (TPV) of the broadband AR coating is approximately 99.10% on quartz, 98.62% on borosilicate glass, and 98.55% on K9 glass in the solar spectrum range of 300–2400 nm. By introducing broadband AR coating, the overall power conversion efficiency (η) of the solar cell showed an increase of 1.23% for quartz, 1.31% for borosilicate glass, and 1.37% for K9 glass. Meanwhile, the double-layer AR coating had excellent mechanical stability; the TPV value of coating after abrasion by CS-10F wearaser only decreased 0.16% on quartz, 0.29% on borosilicate glass and K9 glass. The pencil hardness of the double-layer AR coating was found to be 6H.

Fast production of β-Ni(OH)2 nanostructures with (001) and (100) plane exposure and their electrochemical properties

Based on theoretical analysis of the crystal structure of β-Ni(OH)2, the (001) and (100) planes have the highest and the second highest Ni2+ cation concentration, respectively. Therefore, F− anions were selected to control the growth behavior of β-Ni(OH)2 through the selective adsorption of F− anions because of their small size, simple effect and ability to coordinate with Ni2+ cations. As a result, a series of β-Ni(OH)2 nanostructures with (001) and (100) planes exposed were successfully synthesized within several tens of minutes under the stimulation of microwave irradiation. The surface area ratio of (100) to (001) planes can be changed by altering the reaction time. The exposure of (100) planes was found to be favorable to the electrochemical activity rather than (001) planes.

A hydrophobic and abrasion-resistant MgF2 coating with an ultralow refractive index for double-layer broadband antireflective coatings

An ultralow-index top layer is a prerequisite to preparing high-performance broadband AR coatings. When coupled with hydrophobicity and the abrasion-resistance required in practical applications, the challenge becomes even greater. In this work, a MgF2 AR coating was studied because of the low refractive index of MgF2 and its easily realized strong adhesion through low-temperature heat treatment. In order to obtain an ultralow refractive index and endow the coating with hydrophobicity, we designed several experimental routes and finally adopted MTES/TEOS co-precursors to direct MgF2 particles to form a honeycomb-like network structure without a template. A final refractive index of 1.15 and good hydrophobicity, with a water contact angle of 122°, were obtained using the MgF2–SiO2(CH3) coating. These superior properties were attributed to the incorporation of methyl groups, which not only endowed the coating with hydrophobicity, but also changed the original linear assembly of MgF2 particles to a circular assembly. Using this hydrophobic ultralow-index coating as a top layer, a high-performance double-layer AR coating was fabricated with a high average transmittance of 99.43% in the wavelength range of 400–1000 nm, good abrasion-resistance, and damp heat resistance after a low-temperature heat treatment of 250 °C. This MgF2 double-layer AR coating may be used in display devices or lenses.

Iron cation-induced biphase symbiosis of h-WO3/o-WO3·0.33H2O and their crystal phase transition

Herein, tungsten oxide hexagonal prisms with a biphase of h-WO3 and o-WO3·0.33H2O were prepared by a facile hydrothermal method using Fe3+ cations. The combination of instrumental characterization and software simulation proved that two phases coexisted in one nanoparticle with same morphology. The ratio of two phases could be changed by adjusting the concentration of Fe3+ cations. On the basis of controlled experiments, a mechanism was proposed to illustrate the formation of this biphase WO3 structure, and it was also proved that the self-growth of Fe species was unfavorable for the coexistence of two phases.