Efficiency Enhancement by Insertion of ZnO Recombination Barrier Layer in CdS Quantum Dot-Sensitized Solar Cells.

In this investigation we report the formation of thin ZnO recombination barrier layer at TiO2/CdS interface aimed for the improvement in performance of CdS sensitized solar cell. The film was deposited upon nanocrystalline mesoporous TiO2 surface by following a simple chemical process and characterized, using UV-Visible spectroscopy, X-ray diffraction and electron dispersive X-ray measurements. The insertion of ZnO thin layer enhances the QDSC (Quantum dot sensitized solar cell) performance, contributed mainly by an increase in open circuit voltage (Voc) due to reduced electron back transfer from TiO2 conduction band. Moreover, the analysis of photovoltaic characteristics upon increasing the thickness of the ZnO film reveals that the ZnO recombination barrier layer with optimum thickness at porous TiO2/CdS interface proved to be an effective potential barrier for minimizing electron back recombination.

Structural modulation of lithium metal-electrolyte interface with three-dimensional metallic interlayer for high-performance lithium metal batteries.

The use of lithium (Li) metal anodes has been reconsidered because of the necessity for a higher energy density in secondary batteries. However, Li metal anodes suffer from 'dead' Li formation and surface deactivation which consequently form a porous layer of redundant Li aggregates. In this work, a fibrous metal felt (FMF) as a three-dimensional conductive interlayer was introduced between the separator and the Li metal anode to improve the reversibility of the Li metal anode. The FMF can facilitate charge transfer in the porous layer, rendering it electrochemically more active. In addition, the FMF acted as a robust scaffold to accommodate Li deposits compactly in its interstitial sites. The FMF-integrated Li metal (FMF/Li) electrode operated with a small polarisation even at a current density of 10 mA cm(-2), and it exhibited a seven times longer cycle-life than that of an FMF-free Li electrode in a symmetric cell configuration. A Li metal battery (LMB) using the FMF/Li electrode and a LiFePO4 electrode exhibited a two-fold increase in cycling stability compared with that of a bare Li metal electrode, demonstrating the practical effectiveness of this approach for high performance LMBs.

Lanthanum-catalysed synthesis of microporous 3D graphene-like carbons in a zeolite template.

Three-dimensional graphene architectures with periodic nanopores­reminiscent of zeolite frameworks­are of topical interest because of the possibility of combining the characteristics of graphene with a three-dimensional porous structure. Lately, the synthesis of such carbons has been approached by using zeolites as templates and small hydrocarbon molecules that can enter the narrow pore apertures. However, pyrolytic carbonization of the hydrocarbons (a necessary step in generating pure carbon) requires high temperatures and results in non-selective carbon deposition outside the pores. Here, we demonstrate that lanthanum ions embedded in zeolite pores can lower the temperature required for the carbonization of ethylene or acetylene. In this way, a graphene-like carbon structure can be selectively formed inside the zeolite template, without carbon being deposited at the external surfaces. X-ray diffraction data from zeolite single crystals after carbonization indicate that electron densities corresponding to carbon atoms are generated along the walls of the zeolite pores. After the zeolite template is removed, the carbon framework exhibits an electrical conductivity that is two orders of magnitude higher than that of amorphous mesoporous carbon. Lanthanum catalysis allows a carbon framework to form in zeolite pores with diameters of less than 1 nanometre; as such, microporous carbon nanostructures can be reproduced with various topologies corresponding to different zeolite pore sizes and shapes. We demonstrate carbon synthesis for large-pore zeolites (FAU, EMT and beta), a one-dimensional medium-pore zeolite (LTL), and even small-pore zeolites (MFI and LTA). The catalytic effect is a common feature of lanthanum, yttrium and calcium, which are all carbide-forming metal elements. We also show that the synthesis can be readily scaled up, which will be important for practical applications such as the production of lithium-ion batteries and zeolite-like catalyst supports.

Sustainable Redox Mediation for Lithium-Oxygen Batteries by a Composite Protective Layer on the Lithium-Metal Anode.

A synergic combination of a soluble -redox mediator and a protected Li metal -electrode to prevent the self-discharge of the redox mediator is realized by -exploiting a 2,2,6,6-tetramethylpiperidinyl 1-oxyl (TEMPO) redox mediator and an Al2 O3 /PVdF-HFP composite -protective layer (CPL). Stabilization of Li metal by simple CPL coating is effective at -suppressing the chemical reduction of the oxidized TEMPO and opens up the possibility of sustainable redox mediation for robust cycling of Li-O2 batteries.

Patient's Satisfaction in Skeletal Class III Cases Treated With Two-Jaw Surgery Using Orthognathic Quality of Life Questionnaire: Conventional Three-Stage Method Versus Surgery-First Approach.

OBJECTIVE: To compare the quality of life (QoL) of Class III patients between conventional three-stage method (CTM) and surgery-first approach (SFA) using Orthognathic QoL Questionnaire (OQLQ). MATERIALS AND METHODS: The subjects consisted of 26 Class III patients treated with nonextraction and two-jaw surgery. They were divided into CTM group (N = 15) and SFA group (N = 11). They retrospectively rated the OQLQ scores of 4 domains (social relationship, facial esthetics, function, and awareness of dentofacial deformity) using 0 to 4 scale at initial (T0), just before surgery (T1), 3 month after surgery (T2), and at debonding (T3). Mann-Whitney test and Wilcoxon signed-rank test were performed for statistical analysis. RESULTS: After total OQLQ score of CTM group was deteriorated at T1 stage compared with T0 stage, it was improved at T2 and T3 stages (T0 = 53.9, T1 = 58.1, T2 = 23.5, and T3 = 11.6). Total OQLQ score of SFA group, however, was improved at T2 and T3 stages compared with T0 stage (T0 = 51.6, T2 =  3.1, and T3 = 11.4; T1 was omitted.). Orthognathic QoL Questionnaire scores and their amounts of change did not show any significant difference in each domain and at each stage between 2 groups (T0, T2, T3, ΔT2 - T0, ΔT3 - T2, ΔT3 - T0; all P > 0.05). Both groups showed large change in effect size (ES) of all domains with descending order during T3 - T0: facial esthetics, oral function, social relationship, and awareness of dentofacial deformity (CTM group: -3.97, -3.40, -2.23, -1.25; SFA group: -2.83, -2.33, -1.76, -1.73) CONCLUSIONS: SFA might have an advantage over CTM group in terms of no deterioration stage of OQLQ score.

Ionomer-Liquid Electrolyte Hybrid Ionic Conductor for High Cycling Stability of Lithium Metal Electrodes.

The inhomogeneous Li electrodeposition of lithium metal electrode has been a major impediment to the realization of rechargeable lithium metal batteries. Although single ion conducting ionomers can induce more homogeneous Li electrodeposition by preventing Li(+) depletion at Li surface, currently available materials do not allow room-temperature operation due to their low room temperature conductivities. In the paper, we report that a highly conductive ionomer/liquid electrolyte hybrid layer tightly laminated on Li metal electrode can realize stable Li electrodeposition at high current densities up to 10 mA cm(-2) and permit room-temperature operation of corresponding Li metal batteries with low polarizations. The hybrid layer is fabricated by laminating few micron-thick Nafion layer on Li metal electrode followed by soaking 1 M LiPF6 EC/DEC (1/1) electrolyte. The Li/Li symmetric cell with the hybrid layer stably operates at a high current density of 10 mA cm(-2) for more than 2000 h, which corresponds to more than five-fold enhancement compared with bare Li metal electrode. Also, the prototype Li/LiCoO2 battery with the hybrid layer offers cycling stability more than 350 cycles. These results demonstrate that the hybrid strategy successfully combines the advantages of bi-ionic liquid electrolyte (fast Li(+) transport) and single ionic ionomer (prevention of Li(+) depletion).

Light-Induced Surface Patterning of Silica.

Manipulating the size and shape of silica precursor patterns using simple far-field light irradiation and transforming such reconfigured structures into inorganic silica patterns by pyrolytic conversion are demonstrated. The key concept of our work is the use of an azobenzene incorporated silica precursor (herein, we refer to this material as azo-silane composite) as ink in a micromolding process. The moving direction of azo-silane composite is parallel to light polarization direction; in addition, the amount of azo-silane composite movement can be precisely determined by controlling light irradiation time. By exploiting this peculiar phenomenon, azo-silane composite patterns produced using the micromolding technique are arbitrarily manipulated to obtain various structural features including high-resolution size or sophisticated shape. The photoreconfigured patterns formed with azo-silane composites are then converted into pure silica patterns through pyrolytic conversion. The pyrolytic converted silica patterns are uniformly formed over a large area, ensuring crack-free formation and providing high structural fidelity. Therefore, this optical manipulation technique, in conjunction with the pyrolytic conversion process, opens a promising route to the design of silica patterns with finely tuned structural features in terms of size and shape. This platform for designing silica structures has significant value in various nanotechnology fields including micro/nanofluidic channel for lab-on-a-chip devices, transparent superhydrophobic surfaces, and optoelectronic devices.

Effects of Electron Beam Irradiation on the Electrospinning of Polyacrylonitrile.

Electron beam (e-beam) irradiation of polyacrylonitrile (PAN) was performed to investigate the effects of radiation on the electrospinning process. For this study, polyacrylonitrile powder was subjected to e-beam irradiation with different doses of up to 100 kGy under an N2 atmosphere. Polymer solutions were prepared by dissolving PAN in N,N-dimethyl-formamide (DMF) at a 1:9 ratio by weight. The prepared PAN/DMF solutions showed different colors with different e-beam doses. The resulting structures in solutions contained conjugated C=N bonds, which caused the observed color formation. In addition, the conductivity of the PAN/DMF solution increased with an increase in e-beam irradiation dose. In the DSC spectra of electrospun PAN fibers, the peak temperature of the exothermic reactions was observed to decrease with an increase in the e-beam irradiation strength.

Reduction of charge and discharge polarization by cobalt nanoparticles-embedded carbon nanofibers for Li-O2 batteries.

The problem of high charge polarization is one of the most significant challenges in current nonaqueous Li-O2 batteries. The development of an electrode for the oxygen evolution reaction (OER) at reduced overpotential is thus essential. Here, we suggest a binder-free electrode based on Co nanoparticles embedded in carbon nanofibers (Co-CNFs), which simultaneously reduces the charge and discharge polarization and extends cycling stability. Co-CNF gives rise to a lower discharge polarization because of an enhanced oxygen reduction reaction activity compared to Co-free CNF. Although the embedment of Co does not enhance the OER activity, it significantly reduces charge overvoltage by forming easily decomposable amorphous Li2 O2 . A mechanism for the formation of amorphous Li2 O2 is suggested in terms of charge localization induced by the Co NPs. The findings suggest a new electrode design strategy of combining inexpensive metals and carbon materials for modulating the phase of the discharge product.

Interlocking membrane/catalyst layer interface for high mechanical robustness of hydrocarbon-membrane-based polymer electrolyte membrane fuel cells.

A physical interlocking interface that can tightly bind a sulfonated poly(arylene ether sulfone) (SPAES) membrane and a Nafion catalyst layer in polymer electrolyte fuel cells is demonstrated. Owing to higher expansion with hydration for SPAES than for Nafion, a strong normal force is generated at the interface of a SPAES pillar and a Nafion hole, resulting in an 8-fold increase of the interfacial bonding strength at RH 50% and a 4.7-times increase of the wet/dry cycling durability.

Directional Superficial Photofluidization for Deterministic Shaping of Complex 3D Architectures.

The fabrication of micro- and nanostructures is one of the cornerstones of current materials science and technology. There is a strong interest in processing methods capable of manufacturing engineered complex structures on a large area. A method that is gaining a growing attention in this context is based on surface reshaping of photosensitive materials, such as certain azobenzene derivatives by way of a process of light-induced mass migration, also described as "athermal photofluidization". Here, we apply this method to prestructured substrate, converting simple periodic structures initially patterned only in two dimensions into complex-shaped three-dimensional (3D) structures by a single processing step over a large area. The optical variables of the irradiating beam are used to gain unprecedented deterministic control on the resulting 3D architectures. We also provide some initial demonstrations of the potential application of this novel shaping method, including unidirectional wetting surfaces and micro- and nanoscaled fluidic channel manufactured with it.

Complete magnesiothermic reduction reaction of vertically aligned mesoporous silica channels to form pure silicon nanoparticles.

Owing to its simplicity and low temperature conditions, magnesiothermic reduction of silica is one of the most powerful methods for producing silicon nanostructures. However, incomplete reduction takes place in this process leaving unconverted silica under the silicon layer. This phenomenon limits the use of this method for the rational design of silicon structures. In this effort, a technique that enables complete magnesiothermic reduction of silica to form silicon has been developed. The procedure involves magnesium promoted reduction of vertically oriented mesoporous silica channels on reduced graphene oxides (rGO) sheets. The mesopores play a significant role in effectively enabling magnesium gas to interact with silica through a large number of reaction sites. Utilizing this approach, highly uniform, ca. 10 nm sized silicon nanoparticles are generated without contamination by unreacted silica. The new method for complete magnesiothermic reduction of mesoporous silica approach provides a foundation for the rational design of silicon structures.

Perfluorinated ionomer-enveloped sulfur cathodes for lithium-sulfur batteries.

Nafion is known to suppress the polysulfide (PS) shuttle effect, a major obstacle to achieving high capacity and long cycle life for lithium-sulfur batteries. However, elaborate control of the layer's configuration is required for high performance. In this regard, we designed a Nafion-enveloped sulfur cathode, where the Nafion layer is formed on the skin of the cathode, covering its surface and edge while not restricting the porosity. Discharge capacity and efficiency were enhanced with the enveloping configuration, demonstrating suppression of shuttle. The edge protection exhibited better cycling stability than an edge-open configuration. In the absence of the Nafion envelope, charged sulfur concentrated on the top region of the cathode because of the relatively lower PS concentration at the cathode surface. Surprisingly, for the Nafion-enveloped cathode, sulfur was evenly distributed along the cathode, indicating that the configuration imparts a uniform PS concentration within the cathode.

Vertically oriented, three-dimensionally tapered deep-subwavelength metallic nanohole arrays developed by photofluidization lithography.

The field-gradient, superficial photo fluidization of azomaterials allows a specific 3D nano-silhouette to be shaped over a large area, so as to get easy access to a 3D-tapered, deep sub-wavelength Au nanohole (20 nm spatial size) array. The squeezing of visible light into the deep sub-wavelength point and the relevant extraordinary optical transmission (EOT) are achieved using this 3D-tapered, 20 nm Au nanohole.

Flexible binder-free metal fibril mat-supported silicon anode for high-performance lithium-ion batteries.

We report the fabrication of a flexible and binder-free metal fibril mat-supported Si anode (Si@SFM) by a simple process. The fabricated Si@SFM anode showed a high discharge capacity, ∼3000 mAh g(-1) at a current rate of 300 mA g(-1), and exhibited stable capacity retention, 90% at a 1 C rate (2000 mA g(-1)) after 200 cycles. The rate capability of the electrode was still high even when both the charge and the discharge current rates were markedly increased at the same time (1234 mAh g(-1) for charge-discharge time of ∼12 min). Moreover, owing to its mechanical flexibility, the Si@SFM can be adopted as a key component of flexible lithium-ion batteries (LIBs). After cell packaging, the rechargeable flexible battery under bending stress showed only a little capacity fading (86% of initial capacity) at 1000 mA g(-1) over 150 cycles. These results suggest that the Si@SFM electrode is readily suitable for use in rechargeable flexible LIBs.

Defect-free, size-tunable graphene for high-performance lithium ion battery.

The scalable preparation of graphene in control of its structure would significantly improve its commercial viability. Despite intense research in this area, the size control of defect-free graphene (df-G) without any trace of oxidation or structural damage remains a key challenge. Here, we propose a new scalable route for generating df-G with a controllable size of submicron to micron through sequential insertion of potassium and pyridine at low temperature. Structural and chemical analyses confirm that the df-G perfectly preserves the intrinsic properties of graphene. The Co3O4 (<50 nm) wrapped by ∼ 10.5 µm(2) df-G has unprecedented capacity, rate capability, and cycling stability with capacities as high as 1050 mAh g(-1) at 500 mA g(-1) and 900 mAh g(-1) at 1000 mA g(-1) even after 200 cycles, which suggests enticing potential for the use in high performance lithium ion batteries.

Enhanced durability of polymer electrolyte membrane fuel cells by functionalized 2D boron nitride nanoflakes.

We report boron nitride nanoflakes (BNNFs), for the first time, as a nanofiller for polymer electrolyte membranes in fuel cells. Utilizing the intrinsic mechanical strength of two-dimensional (2D) BN, addition of BNNFs even at a marginal content (0.3 wt %) significantly improves mechanical stability of the most representative hydrocarbon-type (HC-type) polymer electrolyte membrane, namely sulfonated poly(ether ether ketone) (sPEEK), during substantial water uptake through repeated wet/dry cycles. For facile processing with BNNFs that frequently suffer from poor dispersion in most organic solvents, we non-covalently functionalized BNNFs with 1-pyrenesulfonic acid (PSA). Besides good dispersion, PSA supports efficient proton transport through its sulfonic functional groups. Compared to bare sPEEK, the composite membrane containing BNNF nanofiller exhibited far improved long-term durability originating from enhanced dimensional stability and diminished chronic edge failure. This study suggests that introduction of properly functionalized 2D BNNFs is an effective strategy in making various HC-type membranes sustainable without sacrificing their original adventurous properties in polymer electrolyte membrane fuel cells.

Modulated ionomer distribution in the catalyst layer of polymer electrolyte membrane fuel cells for high temperature operation.

Ionomer distribution is an important design parameter for high performance polymer electrolyte membrane fuel cells (PEMFCs); however, the nano-scale modulation of the ionomer morphology has not been intensively explored. Here, we propose a new route to modulate the ionomer distribution that features the introduction of poly(ethylene glycol) (PEG) to the cathode catalyst layer and the leaching the PEG phase from the catalyst layer using a water effluent during operation. The key concept in the approach is the expansion of the ionomer thin film through the PEG addition. We demonstrate that the modulated ionomer distribution increases the electrochemical active area and proton transport property, without loss in oxygen transport, at a fixed ionomer content. At a high temperature of 120 °C, the power performance at 0.6 V is increased by 1.73-fold with the modulated ionomer distribution as a result of 1.25-fold increase in the electrochemical active area and two-fold increase in the proton transport rate in the catalyst layer.

Electrospun three-dimensional mesoporous silicon nanofibers as an anode material for high-performance lithium secondary batteries.

Mesoporous silicon nanofibers (m-SiNFs) have been fabricated using a simple and scalable method via electrospinning and reduction with magnesium. The prepared m-SiNFs have a unique structure in which clusters of the primary Si nanoparticles interconnect to form a secondary three-dimensional mesoporous structure. Although only a few nanosized primary Si particles lead to faster electronic and Li(+) ion diffusion compared to tens of nanosized Si, the secondary nanofiber structure (a few micrometers in length) results in the uniform distribution of the nanoparticles, allowing for the easy fabrication of electrodes. Moreover, these m-SiNFs exhibit impressive electrochemical characteristics when used as the anode materials in lithium ion batteries (LIBs). These include a high reversible capacity of 2846.7 mAh g(-1) at a current density of 0.1 A g(-1), a stable capacity retention of 89.4% at a 1 C rate (2 A g(-1)) for 100 cycles, and a rate capability of 1214.0 mAh g(-1) (at 18 C rate for a discharge time of ∼3 min).

Multi-level micro/nanotexturing by three-dimensionally controlled photofluidization and its use in plasmonic applications.

The Field-Gradient Effect extends the photofluidization of azobenzene materials to 3D, multi-level micro/nanotexturing with a newly conceptualized design strategy based on "field-gradient photofluidization". In particular, we successfully characterized the vertical gradient optical absorption within the azobenzene material and the resulting field-gradient photofluidization both theoretically and experimentally. Furthermore, we could create the heterogeneously integrated micro/nanotextures at any desired surface heights, capability that is potentially beneficial for plasmonic applications.