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Electrochemical CO2 reduction offers a promising approach to alleviate environmental and climate impacts attributed to increasing atmospheric CO2. Intensive research work has been performed over th...

Zeolites are 3D aluminosilicate materials having subnanometer pore channels. The Lewis basic pores have charge-balancing cations, easily tuned to metallic ions as more chemically active sites. Among the ion-exchanged zeolites, Cu2+ ion-exchanged ZSM-5 (Cu-ZSM-5) is one of the most active zeolites with chemical interactions of Lewis basic compounds. Even though the chemical interactions of hydrocarbons with Cu2+ sites in Cu-ZSM-5 have been tremendously studied in the category of zeolite catalysts, it is not yet thoroughly investigated how such interactions affect the structural lattice of the zeolite. Hydrocarbons with different chemical properties and their relative size can induce lattice strain by different chemical adsorption effects on the Cu2+ sites. In this work, we investigate the internal deformation of the Cu-ZSM-5 crystal using Bragg coherent X-ray diffraction imaging during the adsorption of four hydrocarbons depending on the alkyl chain length, the existence of a double bond in the molecule, linear structure versus benzene ring structure, and so forth. In the three-carbon system (propane and propene), relatively weak chemical adsorption occurred at room temperature and 100 °C, whereas strong adsorption was observed over 150 °C. For the six-carbon system (n-hexane and benzene), strong strains evolved in the crystal by active chemical adsorption from 150 °C. The observations suggest that propene and propane adsorb at the Cu2+ sites from the outer shell to the center with increasing temperature. In comparison, n-hexane and benzene adsorb at both parts at the same temperature. The results provide the internal structural information for the lattice with the chemical interactions of hydrocarbons in the Cu-ZSM-5 zeolite and help to understand zeolite-based chemisorption or catalysis research.

This paper describes a new type of electrowetting (EW)-driven digital microfluidic (DMF) platform incorporated with an acoustic bubble for improving the viscous droplet mixing performance on an open surface. First, it is experimentally verified that the working principle of the two different actuation methods: EW-driven droplet actuation on an open surface and acoustically driven bubble excitation in an aqueous medium, respectively. Then, it is investigated that the acoustic excitation of the bubble injected into the droplet. When an acoustically excited bubble inside the droplet generates microstreaming at the natural frequency of the bubble, the microstreaming inside the droplet is visualized using fluorescent particles and a high-speed camera. To examine the effect of the microstreaming inside the droplet on mixing performance, the mixture droplet consisting of safranin and glycerol (60 wt%) is used in this experiment. The mixing efficiency is measured through the mixing index calculated by image analysis. The mixture droplet with an acoustically excited bubble is completely mixed within 40 seconds owing to the microstreaming generated by the acoustically oscillating bubble at its natural frequency. On the other hand, the same mixture droplet with only a diffusion process remains unmixed for more than 5 mins. The transportation of a droplet ( $10~\mu \text{l}$ ) containing a bubble ( $800~\mu \text{m}$ in diameter) and the removal of the bubble from the droplet are demonstrated using an EW chip. Finally, as a proof of concept, the manipulation of droplets with the enhanced mixing performance on the proposed digital microfluidic platform is demonstrated by the combination of EW droplet actuation and acoustic bubble excitation. [2021-0057]

Precise control of the local electronic structure and properties of electrocatalysts is important for enhancing the multifunctionality and durability of electrocatalysts and for correlating the structure/chemistry with the catalytic properties. Herein, we report electronically coupled metallic hybrids of NiFe layered double hydroxide nanosheet/Ti3C2 MXene quantum dots deposited on a nitrogen‐doped graphene surface (LDH/MQD/NG) for high‐performance flexible Zn–air batteries (ZABs). As verified from the Mott–Schottky and Nyquist plots, as well as spectroscopic, electrochemical, and computational analyses, the electronic and chemical coupling of LDH/MQD/NG modulates the local electronic and surface structure of the active LDH to provide metallic conductivity and abundant active sites, leading to significantly improved bifunctional activity and electrocatalytic kinetics. The rechargeable ZABs with LDH/MQD/NG hybrids are superior to the previous LDH‐based ZABs, demonstrating a high power density (113.8 mW cm−2) and excellent cycle stability (150 h at 5 mA cm−2). Moreover, the corresponding quasi solid‐state ZABs are completely flexible and practical, affording a high power density of 57.6 mW cm−2 even in the bent state, and in real‐life operation of tandem cells for powering various electronic devices.

Crystallographically engineered Relaxor-PT single crystals, specifically PMN-PT (Generation I) and PIN-PMN-PT/PMN-PZT (Generation II), offer much higher piezoelectric and electromechanical coupling coefficients (d33>1,500 pC/N, k33>0.9), when compared to polycrystalline PZT-5H ceramics (d33>600 pC/N, k33>0.75). Recently Ceracomp Co., Ltd. (www.ceracomp.com) has developed the solid-state single crystal growth (SSCG) technique and successfully fabricated Gen III PMN-PZT single crystals modified with acceptors or donors. The piezoelectric constants (d33) of (001) Gen III PMN-PZT single crystals were measured to be higher than 4,000 pC/N and thus about two times higher than those of PMN-PT/PZN-PT (Gen I) and PIN-PMN-PT/PMN-PZT (Gen II) single crystals. The Gen III PMN-PZT single crystals have been firstly applied to single crystal-epoxy composites, ultrasonic transducers, piezoelectric sensors, and piezoelectric actuators. In this paper we introduce the development of Gen III PMN-PZT single crystals, piezoelectric composites and multilayer single crystal actuators.

A recent study found that magnetization curves for Y3Fe5O12 (YIG) slab and thick films (>20 μm thick) differed from bulk system curves by their longitudinal spin Seebeck effect in a Pt/YIG bilayer system. The deviation was due to intrinsic YIG surface magnetic anisotropy, which is difficult to adopt extrinsic surface magnetic anisotropy even when in contact with other materials on the YIG surface. This study experimentally demonstrates evidence for extrinsic YIG surface magnetic anisotropy when in contact with a diamagnetic graphene interlayer by observing the spin Seebeck effect, directly proving intrinsic YIG surface magnetic anisotropy interruption. We show the Pt/YIG bilayer system graphene interlayer role using large area single and multilayered graphenes using the longitudinal spin Seebeck effect at room temperature, and address the presence of surface magnetic anisotropy due to magnetic proximity between graphene and YIG layer. These findings suggest a promising route to understand new physics of spin Seebeck effect in spin transport.

Solid refuse fuels (SRF) and biomass contain significant amounts of KCl and NaCl which result in operation problems such as hard deposit formation in combustion. The effect of kaolinite in the decomposition of mineral chlorides in a commercial SRF-burning CFBC boiler is investigated. The injection of kaolinite with SRF in a commercial CFBC shows its effect on mineral chloride decomposition thus softens the hardness of the deposit on the heat exchanger tubes in the convection pass. By the reaction of molten salt with kaolinite, particles under 5 μm in the flue gas is significantly reduced. After 37 days operation with kaolinite use the PM 10 particle in flue gas is reduced originally 86 mg/Nm3 to 16 mg/Nm3, which is 81% reduction. The reaction of physical and chemical adsorption of metallic oxide component to kaolinite particle is also monitored by SEM images. This result is reflected to the particle side distribution of the fly ash in that the shift of the abundant particle size peak to a larger size cut after the use of the kaolinite.

The spatial distribution and the energy spectrum of the neutron yield were investigated with the neutron activation analysis and MCNP simulation was carried out to verify the analysis results and to extend the results to a 3D mapping of the neutron yield distribution in the KSTAR. High purity Ni specimen was selected in the neutron activation analysis. Total neutron yields turned out to be 3.76 × 1012 n/s – 7.56 × 1012 n/s at the outer vessel of the KSTAR, two orders of magnitude lower than those at the inner vessel of the KSTAR, which demonstrates the attenuation of neutron yield while passing through the different structural materials of the reactor. Based on the fully expanded 3D simulation results, 2D cross-sectional distributions of the neutron yield on XY and ZX planes of KSTAR were examined. The results reveal that the neutron yield has its maximum concentration near the center of blanket and decreases with increasing proximity to the vacuum vessel wall.

We report the characteristics of AlN epilayers grown directly on cylindrical-patterned sapphire substrates (CPSS) by hydride vapor-phase epitaxy (HVPE). To evaluate the effect of CPSS, we analyzed the threading dislocation densities (TDDs) of AlN films grown simultaneously on CPSS and flat sapphire substrate (FSS) by transmission electron microscopy (TEM). The corresponding TDD is measured to be 5.69 x 108 cm−2 for the AlN sample grown on the CPSS that is almost an order of magnitude lower than the value of 3.43 × 109 cm−2 on the FSS. The CPSS contributes to reduce the TDs originated from the AlN/sapphire interface via bending the TDs by lateral growth during the coalescence process. In addition, the reduction of direct interface area between AlN and sapphire by CPSS reduce the generation of TDs.

High efficiency thermoelectric (TE) materials still require high thermopower for energy harvesting applications. A simple elemental metallic semiconductor, tellurium (Te), has been considered critical to realize highly efficient TE conversion due to having a large effective band valley degeneracy. This paper demonstrates a novel approach to directly probe the out-of-plane Seebeck coefficient for one-dimensional Te quantum wires (QWs) formed locally in the aluminum oxide layer by well-controlled electrical breakdown at 300 K. Surprisingly, the out-of-plane Seebeck coefficient for these Te QWs ≈ 0.8 mV/K at 300 K. This thermopower enhancement for Te QWs is due to Te intrinsic nested band structure and enhanced energy filtering at Te/AO interfaces. Theoretical calculations support the enhanced high Seebeck coefficient for elemental Te QWs in the oxide layer. The local-probed observation and detecting methodology used here offers a novel route to designing enhanced thermoelectric materials and devices in the future.

To accelerate the discovery of materials through computations and experiments, a well-established protocol closely bridging these methods is required. We introduce a high-throughput screening protocol for the discovery of bimetallic catalysts that replace palladium (Pd), where the similarities in the electronic density of states patterns were employed as a screening descriptor. Using first-principles calculations, we screened 4350 bimetallic alloy structures and proposed eight candidates expected to have catalytic performance comparable to that of Pd. Our experiments demonstrate that four bimetallic catalysts indeed exhibit catalytic properties comparable to those of Pd. Moreover, we discover a bimetallic (Ni-Pt) catalyst that has not yet been reported for H2O2 direct synthesis. In particular, Ni61Pt39 outperforms the prototypical Pd catalyst for the chemical reaction and exhibits a 9.5-fold enhancement in cost-normalized productivity. This protocol provides an opportunity for the catalyst discovery for the replacement or reduction in the use of the platinum-group metals.

Highly efficient vacuum-deposited CsPbBr3 perovskite light-emitting diodes (PeLEDs) are demonstrated by introducing a separate polyethylene oxide (PEO) passivation layer. A CsPbBr3 film deposited on the PEO layer via thermal co-evaporation of CsBr and PbBr2 exhibits an almost 50-fold increase in photoluminescence quantum yield intensity compared to a reference sample without PEO. This enhancement is attributed to the passivation of interfacial defects of the perovskite, as evidenced by temperature-dependent photoluminescence measurements. However, direct application of PEO to an LED device is challenging because of the electrically insulating nature of PEO. This issue is solved by doping PEO layers with MgCl2. This strategy results in an enhanced luminance and external quantum efficiency (EQE) of up to 6887 cd m-2 and 7.6%, respectively. To the best of our knowledge, this is the highest EQE reported to date among vacuum-deposited PeLEDs.

We demonstrate a flexible and stretchable supercapacitor assembled via straightforward interfacial gelation of reduced graphene oxide (rGO) with carbon nanotube (CNT) on a stretchable fabric surface. The difference between the redox potential of aqueous graphene oxide (GO) dispersion, prepared using a modified Hummers' method, and of a solid Zn plate, which was used as an external stimulus, induces a spontaneous reduction of GO flakes forming porous CNT–rGO hydrogel at the liquid–solid interface. With the aid of Zn, a macroporous and flexible CNT–rGO hydrogel was fabricated on a stretchable fabric platform using a facile fabrication method, and the CNT–rGO fabric composite was assembled into a supercapacitor to demonstrate its feasibility as a wearable electrode. The porous structure of the as-formed CNT–rGO fabric composite allows excellent electrolyte accessibility and ion transport that result in a fast charge/discharge rate up to 100 mV/s and a large areal capacity of 10.13 mF/cm2 at a discharge rate of 0.5 mA (0.1 mA/cm2). The inclusion of one-dimensional CNT as conductive bridges allows an excellent capacity retention of 95.2% after complete folding of the electrode and a capacity retention of 93.3% after 1000 bending cycles. Additional stretching test displayed a high capacity retention of 90.0% even at an applied strain as high as 50%, overcoming previous limitations of brittle graphene-based electrodes. This low-cost, lightweight, easy to synthesize, stretchable supercapacitor holds promise for next-generation wearable electronics and energy storage applications.

Diglycolamides (DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores. The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal. To understand the origin of this phenomenon, three binuclear crystals [Ln(TEDGA)3][Ln(NO3)6] of N,N,N′,N′-tetraethyldiglycolamide (TEDGA) with rare earth ions La(III), Pr(III) and Eu(III) were prepared and characterized crystallographically. The three complexes belong to the triclinic crystal system, P-1 space group. The bond lengths of Ln–Oamide are significantly shorter than those of Ln–Oether in the same crystal. The Ln–Oamide and Ln–Oether bond lengths gradually decrease with increasing atomic number of the rare earth ion. The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number, tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions. The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations. We find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy, WBIs, Mulliken charge, natural electron configurations, and molecular orbital interaction. The covalent component of the Ln–O bonds of the complexes increases with increasing metal atomic number. The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two five-member rings by one tridentate ligand. The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.

The strain behavior of 0.71 Pb(Mg1/3Nb2/3)O3-0.29 PbTiO3 (PMN-PT) single crystal prepared by a solid-state single crystal growth method was investigated on two most widely used orientations, i.e., (001)- and (011)-oriented. A special emphasis was put on the correlation among longitudinal and transverse strains and the consequent volume change. We show that seemingly different strain behavior of (001)- and (011)-oriented crystals has the same origin, and the underlying mechanism excludes possible contribution from the frequently cited polarization rotation. In situ monitoring of electric field induced Poisson’s ratio further suggested that the polarization vectors contributing to the strain properties in PMN-PT are not confined to a unique direction forced by the crystallographic symmetry but possess a span of angular range.

Herein, we identify the unique trifunctional active sites of ReS2 and NiFe layered double hydroxide (NiFe-LDH) heteronanosheets (ReS2/NiFe-LDH) for integrated cascade Zn–air battery/electrolyzer systems. Along with the edge and surface sites of NiFe-LDH for both oxygen evolution reaction and oxygen reduction reaction activities, the unprecedented activity of the ReS2/NiFe-LDH heteronanosheets for the hydrogen evolution reaction emerges from the S–O bonds at the heterointerfaces, together with the strong coupling effect and vertical alignment of NiFe-LDH and ReS2. The outstanding trifunctional activities and a well understood mechanism ensure the use of ReS2/NiFe-LDH heteronanosheets for the development of integrated cascade battery/electrolyzer systems, in which electricity storage in the battery mode and H2 production in the electrolyzer mode are efficiently switched with high round-trip efficiency (61%) and Faraday efficiency (96%). The systems show great promise for cost-effective energy storage and H2 production applications ranging from the distribution in households to the assembly for electrical vehicles.

Thin filament pyrometry is used to measure the time-varying temperature field in a 1-m methanol pool fire. A digital camera with optical filters and zoom lens recorded the emission intensity of an array of 12-µm silicon–carbide filaments oriented horizontally at various heights across the steadily burning pool fire. A 50-µm-diameter thermocouple measured the temperature at locations corresponding to the filament positions. A correlation was developed between the local probability density functions of the thermocouple time-series measurements corrected for radiation and thermal inertia effects and the camera grayscale pixel intensity of the filaments. A regression analysis yields the local mean temperature and its variance. The time series of the temperature field is transformed into average values during consecutive phases of the fire’s puffing cycle, providing quantitative insight into the complex and dynamic structure of a turbulent fire.

Achieving high ionic conductivity, wide voltage window, and good mechanical strength in a single material remains a key challenge for polymer-based electrolytes for use in solid-state supercapacitors (SCs). Herein, we report cross-linked composite gel polymer electrolytes (CGPEs) based on multi-cross-linkable H-shaped poly(ethylene oxide)–poly(propylene oxide) (PEO-PPO) tetrablock copolymer precursors, SiO2 nanoparticles, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, an ionic liquid (IL). Self-standing CGPE membranes with a high IL content were prepared using in situ cross-linking reactions between the silane groups present in the precursor and the SiO2 surface. The incorporation of an optimal amount of SiO2 increased the cross-linking density of the resulting CGPE while reducing polymer-chain ordering and, consequently, increasing both ionic conductivity and mechanical strength. As a result, the CGPE with 0.1 wt % SiO2 exhibited a high ionic conductivity (2.22 × 10–3 S cm–1 at 25 °C), good tensile strength (453 kPa), and high thermal stability up to 330 °C. Finally, an all-solid-state SC assembled with the prepared CGPE showed a high operating voltage (3 V), a large specific capacitance (103.9 F g–1 at 1 A g–1), and excellent durability (94% capacitance retention over 10,000 charge/discharge cycles), which highlights its strong potential as a solid-state electrolyte for SCs.

Gelatin/polyvinyl alcohol (PVA) (g/P) porous scaffolds with a glutaraldehyde/g ratio of 3 were synthesized by freeze/thaw and lyophilization to evaluate the effect of the g/P ratio (10/0 to 7/3) on the mechanical properties and cell growth behavior of the scaffolds. Fourier transform infrared spectroscopy results showed that the g/P scaffolds exhibited good crosslinking between gelatin and gelatin (imine), PVA and PVA (acetal group), and gelatin and PVA (imine). The pore size decreased gradually from 170±63 μm, to 140±60 μm, 129±64 μm, and 74 ±23 μm by varying the g/P ratio from 10/0, to 9/1, 8/2, and 7/3, respectively. As the g/P ratio was changed from 10/0 to 7/3, the compressive strength and swelling rate increased gradually from 150± 17 kPa to 290 ±28 kPa and 1268± 11% to 1640 ±35%, respectively. Among the scaffolds, 7/3 g/P scaffolds with tailored properties are suitable for wound healing.

In this research, various types of nitride additives were incorporated into titanium diboride attaining dense TiB2-based ceramics by field-assisted sintering technique. The addition of different types of nitride additives, namely Si3N4, BN, AlN, and TiN, significantly improved the sinterability of TiB2, achieving near fully dense ceramics. The X-ray diffraction analysis and microstructural evaluation confirmed the presence of the h-BN compound in all specimens. In the TiB2-Si3N4 ceramic, Si3N4 additive reacted with B2O3 oxide, in-situ generating h-BN, and SiO2 phases. Although the h-BN phase was produced in the TiB2-AlN specimen, the main proportion of AlN remained in the sample as an unreacted ex-situ phase. In terms of the TiB2-TiN ceramic, some of the nitrogen and boron atoms could leave the TiN and TiB2 crystalline structures, contributing to the in-situ formation of h-BN.

Poly(vinylidene fluoride) (PVDF) fiber biosensors are prepared by a near-field electrospinning (NFES) to evaluate the effect of PVDF concentration (16–20 wt%) and number of fiber lines (10-90) on the sensitivity of PVDF sensors. Among various PVDF fiber arrays consisting of 50 lines, the highest peak voltage of 132.0±8.3 mV is observed for the 18 wt% PVDF sensor due to the formation of straight-line-shape fibers. A beads-on-string fibers are observed for the PVDF fibers containing more than 18 wt%. The voltage increases linearly with increasing the number of PVDF fiber lines from 10 to 90. The spectral results of the sensors exhibit the same signal generated by natural frequency of Al cantilever. An equivalent RC circuit model, consisting of two resistors and one capacitance, is incorporated to describe the piezoelectric behavior of PVDF sensors. Simulation results are consistent with the cantilever test results and no cytotoxicity is observed, implying that the sensitivity of PVDF biosensor is mainly governed by PVDF concentration and number of PVDF fiber lines.

The spin Seebeck effect (SSE) has attracted renewed interest as a promising phenomenon for energy harvesting systems. A noteworthy effort has been devoted to improving the SSE voltage by inserting ...

During the braking process, frictional heat generated between a disc and a pad can lead to high temperatures. The location of friction blocks on the brake pad can lead directly to differences in friction contact time and friction speed at each point on the brake disc surface, this can lead to non-uniform temperature distribution on the brake disc surface. In this paper, the optimum design for friction blocks on a brake pad is investigated using the design of experiments (DOE) of Taguchi approach and response surface method (RSM) with an aim to minimize the deviation in the rate of friction heating in each area along the radial direction of brake disc. 18 design variables on 2 levels are adjusted. A table of orthogonal arrays, L32 (218), is used. Finite element analysis (FEA) is performed to analyze the mean squared error (MSE) values in the temperature deviations from frictional heat, the disc’s thermo-mechanical characteristics are taken into account. Analysis of variance (ANOVA) is carried out using the data gathered from the DOE stage, we find 7 significant factors among the design variables. A meta-model using RSM is proposed for reduction of temperature deviations over the brake disc. An optimized brake pad is analyzed in terms of the temperature and thermal stress imparted on the brake disc, this optimized pad is then compared with the original pad. The maximum temperatures of the optimized pad and original pad were 399.8 °C and 480.6 °C, respectively. The thermal stress of the optimized pad and original pad were 640.4 MPa and 721.4 MPa, respectively. In the optimized model, the size of the hot band on the disc is larger than that from the original model, so the thermal stress distribution on the disc is smaller. Finally, the optimized pad was found to give significant performance benefits with a 16.8 % decrease in maximum temperature and 11.2 % decrease in thermal stress.

The development of efficient electrocatalysts for the CO2 reduction reaction (CO2 RR) remains a challenge. Demonstrated here is a NiSn atomic-pair electrocatalyst (NiSn-APC) on a hierarchical integrated electrode, which exhibits a synergistic effect in simultaneously promoting the activity and selectivity of the CO2 RR to formate. The NiSn atomic pair consists of adjacent Ni and Sn, each coordinated with four nitrogen atoms (N4 -Ni-Sn-N4 ). The as-prepared NiSn-APC displays exceptional activity for the CO2 RR to formate with a turnover frequency of 4752 h-1 , a formate productivity of 36.7 mol h-1 gSn -1 and an utilization degree of active sites (57.9 %), which are superior to previously reported single-atomic catalysts. Both experimental data and density-functional theory calculations verify the electron redistribution of Sn imposed by adjacent Ni, which reduces the energy barrier of the *OCHO intermediate and makes this potential-determining step thermodynamically spontaneous. This synergistic catalysis provides a successful paradigm for rational design and preparation of atomic-pair electrocatalysts with enhanced performance.

In this study, the influence of the microstructural evolution of galvannealed (GA) coating and the thermomechanical characteristics of liquid metal embrittlement (LME) cracking during resistance sp...

To investigate the effects of their surface recovery and optical properties, extremely small sized (12 µm × 12 µm mesa area) red AlGaInP micro light emitting diodes ($$\upmu$$ μ LED) were fabricated using a diluted hydrofluoric acid (HF) surface etch treatment. After the chemical treatment, the external quantum efficiencies (EQEs) of $$\upmu$$ μ -LED at low and high injection current regions have been improved by 35.48% and 12.86%, respectively. The different phenomena of EQEs have a complex relationship between the suppression of non-radiative recombination originating from the etching damage of the surface and the improvement of light extraction of the sidewalls. The constant enhancement of EQE at a high injection current it is attributed to the expansion of the active region’s sidewall surface area by the selective etching of AlInP layers. The improved EQE at a low injection current is related to the minimization of the surface recombination caused by plasma damage from the surface. High-resolution transmission electron microscopy (HR-TEM) revealed physical defects on the sidewall surface, such as plasma-induced lattice disorder and impurity contamination damage, were eliminated using chemical treatment. This study suggests that chemical surface treatment using diluted HF acid can be an effective method for enhancing the $$\upmu$$ μ -LED performance.

Current steerable catheters or guidewires often cannot advance into small diameter vessels due to their large diameters or lack of sharp steering capacity. This paper proposes a hydraulically steerable guidewire with 400 μm diameter, which can access 1 mm diameter vessels whose branching angle is larger than 90 degrees. The designed steering mechanism consists of a flexible eccentric tube with inner micro patterns, which can bend in two different curvatures when pressurized. Its distal sharp curve of the 2 mm segment allows access to small diameter vessels because it provides a large steering angle even in confinement inside the narrow vessels. Its proximal gradual curve of the 9 mm segment allows access to relatively large diameter vessels because of its large steering distance. Fabrication of the steering mechanism uses a template and does not use adhesion or division. A 3D printed cylindrical template is patterned by stamping and chemically removed after silicone coating. The performance of selective insertion of the proposed guidewire is evaluated in a blood circulatory system specially developed to mimic human arterial environment. It emulates viscosity, pressure, and flow velocity inside the blood vessels as well as bifurcation geometry. Experiment result shows that the proposed guidewire can access 1 mm diameter vessels with 128 degrees of bifurcation angle. The developed guidewire uses only biocompatible materials including driving fluid.

Thermochemical heat storage is a promising energy storage method and has received much attention in recent years. To improve the design and application of such systems, a better understanding of the characteristics of thermochemical heat storage is required. In this study, we analyze the heat release characteristics of thermochemical heat storage considering various operating parameters, such as charging temperature, humidity, and material. Three different thermochemical materials are considered herein, namely, zeolite 13X, zeolite 5A, and silica gel. The temperature profile at the inlet and outlet of the storage chamber, and that inside the chamber packed with thermochemical material, were measured. The pressure drop across the chamber was measured as well. The results indicate that the heat release characteristics change with position and time. Furthermore, the temporal curves of released heat are significantly affected by charging temperature and humidity. Zeolite 13X rapidly released a large amount of heat within a short period of time, whereas silica gel gradually released a small amount of heat, over a longer duration of time. The pressure drop across the chamber was found to vary with the bead size of the thermochemical material. Thus, the operating parameters including charging temperature, humidity, and material, have a significant effect on the characteristics of heat release. The data obtained herein can serve as a reference for the design of thermochemical storage systems.

The durability of the membrane electrode assembly (MEA) is one of the important requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). While chemical stabilities of the components (the catalyst, membrane, and ionomer) have been assessed by ex situ tests, the degradation mode of the components in a single-cell is still not fully understood. Herein, the degradation of a MEA based on an ionomer having a polycarbazole main chain and a trimethyl ammonium side group was systematically investigated for a single-cell level under constant current conditions. The degradations of the catalyst, membrane, and ionomer were compared by in situ electrochemical and ex situ post-mortem analyses. The catalyst and ionomer in the cathode showed significant degradation, whereas the membrane was relatively durable, suggesting that the formation of a strong alkaline environment in the cathode catalyst layer is a major cause of the performance fade. The use of an alkaline-stable ionomer with an N,N-dimethylhexylamine group, which is designed based on density functional theory (DFT) calculations, in the cathode catalyst layer leads to 87% durability improvement. This work enhances the understanding of the key factors affecting the durability of AEMFCs under real operation and suggests practical strategies toward higher durability.

Nitrogen/fluorine doping of TiO2 nanoparticles (NPs) serves to play an important role with regard to visible light absorption and charge carrier dynamics. However, it is largely unknown how nitrogen/fluorine doping retards electron–hole recombination. We carried out density functional theory and nonadiabatic molecular dynamics to demonstrate that the dopant levels, formation energies, and charge carrier dynamics depend strongly on the doping site. N-doping introduces both a hole and an electron trap without the presence of oxygen vacancies, while F-doping introduces only an electron trap. Quantum dynamics simulations show that holes are trapped within several picoseconds; N-doped NPs requires longer hole-trapping time than F-doped NPs due to the presence of an extra hole trap originating from the N 2p state. Electrons are trapped at a longer time scale than holes. F-doped NPs required longer electron-trapping time due to more strongly localized electron densities than N-doped TiO2 NPs. In general, Nitrogen and fluorine doping suppressed electron–hole recombination compared to pristine NP. NPs doped at the tip domain showed different charge recombination pathways by passing several hole traps (N-doping) or by dual channel routes (F-doping). NPs doped at edge domains showed relatively shorter excited state lifetime due to greater electronic coupling between trapped holes and electrons. NPs with doping at the inside domain effectively suppressed charge recombination due to a moderate energy gap and a reduced propensity to electron/hole localization. The diverse charge recombination scenarios revealed by nonadiabatic molecular dynamics simulations provided guidelines for the rational design of nanoscale metal oxides for solar energy harvesting and utilization.

To achieve highly efficient organic photovoltaics (OPVs), control of the molecular orientation is one of the prime important factors, for the interfacial dipole orientation and energy offset at the donor/acceptor (D/A) interface influence the device performance. We examine the effect of the planar-shape molecular orientation on the D/A interface, by comparing two different metal phthalocyanine molecules under identical process conditions. From the noticeable changes in the near edge X-ray absorption fine structure and ionization potential, copper phthalocyanine (CuPc) on a thin CuI layer reveals a strong change in molecular orientation compared to zinc phthalocyanine (ZnPc). To account for the different templating effect between CuPc and ZnPc, Cu d–d orbital coupling is evidenced as for the interaction between CuI and CuPc. The apparent change of the CuPc orientation reveals a relatively large energy offset at the CuPc/C60 D/A interface and increased open-circuit voltage in the corresponding OPV device. The lying-down orientation of CuPc on CuI or face-on geometry at the C60/CuPc interface induces strong electron–electron coupling and long-lived charge transfer exciton states, which is directly related to better charge separation and correspondingly good OPV performance.

We report on a direct comparison of the out-of-plane thermoelectric properties, such as Seebeck coefficient and electrical conductivity, of atomically thin MoS2 films. The films were prepared by a chemical vapor deposition method and were simultaneously investigated using a Cu-sandwiched structure. Specifically, this is the first study that measures the out-of-plane Seebeck coefficients of atomically thin mono- and bilayer MoS2 at 300 K. At room temperature, out-of-plane Seebeck coefficients for MoS2 films with one, two, and seven layers were measured to be approximately 129.4, 143.3, and 152.2 μV/K, respectively. Such behavior is seen because the increasing number of MoS2 layers increases the density of states of a system. In contrast to conventional thermoelectric materials, the electrical conductivities of these MoS2 films have the same tendency as the Seebeck coefficients. Our results show that thermoelectric devices can utilize the out-of-plane properties of MoS2 thin films with high power factors.

Despite the excellent electrical conductivity of metal thin film electrodes, their poor mechanical stretchability makes it extremely difficult to apply them as stretchable interconnect electrodes. Thus, we propose a novel stretchable hybrid electrode (SHE) by adopting two strategies to overcome the metal thin film electrode limitations: grain size engineering and hybridization with conductive interlayers. The grain size engineering technique improves the inherent metal thin film stretchability according to the Hall-Petch theory, and the hybridization of the conductive interlayer materials, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and carbon nanotube (CNT), suppresses crack propagation. Especially, the CNT-inserted SHE exhibits a decreased resistance change of approximately 32% in tensile test and 75% in a 10 000 cycle fatigue test because of the rough surface of the designed electrode, which relieves maximum stress by redistributing it more evenly to prevent penetrating crack propagation.

Air bubble entrainment is a phenomenon that can significantly reduce the efficiency of liquid motion in piping systems. In the present study, the bubble formation mechanism in a globe valve with 90% water fraction flow is explained by visualization study and pressure oscillation analysis. The shadowgraph imaging technique is applied to illustrate the unsteady flow inside the transparent valve. This helps to study the effect of bubbles induced by the globe valve on pressure distribution and valve flow coefficient. International Society of Automation (ISA) recommends locations for measuring pressure drop of the valve to determine its flow coefficient. This paper presents the comparison of the pressures at different locations along with the upstream and the downstream of the valve with the values at recommended positions by the ISA standard. The results show that in partially filled pipe flow, the discrepancies in pressure between different measurement locations in the valve downstream are significant at valve openings less than 30%. The aerated flow induces the oscillation in pressure and flow rate, which leads to the fluctuation in the flow coefficient of the valve. The flow coefficients have a linear relationship with the Reynolds number. For the same increase of Reynolds number, the flow coefficients grow faster with larger valve openings and level off at the opening of 50%.

Nitrogen doped carbon functionalized CoSe2 nanowires (CoSe2@N-C NWs), which act as potential oxygen evolution reaction (OER) catalysts with a large current density and high stability have been reported. Owing to the collaborative optimization of electrical conductivity, free adsorption energy and binding strength of OER intermediates, the prepared CoSe2@N-C NWs exhibit an enhanced 6.61-fold catalytic activity compared to the pristine CoSe2 NW electrode in 1.0 M KOH solution at the overpotential of 340 mV.

The photoluminescence (PL) and Raman spectra of molybdenum disulfide (MoS2) can be tuned with liquid crystals. A nematic liquid crystal, 5CB, was aligned in a zigzag direction on an MoS2 monolayer flake. The PL and A1g Raman mode peaks of the MoS2 monolayer were shifted by 46 meV and 2 cm-1, respectively, owing to the interaction between MoS2 and the liquid crystal. Based on Lorentzian fitting analysis, it was confirmed that the peak positions and intensity ratios of the trion PL and exciton PL varied with the phase transition of the liquid crystal. This phenomenon was possibly caused by the transfer of electrons from MoS2 to the liquid crystal. This electron transfer varies with the temperature-dependent change in the liquid crystal phase. Therefore, the PL spectra of MoS2 can be tuned simply by controlling the phase, without changing the type of added material.

Various structural patterns are used to control light properties during propagation. In particular, when light is trapped and concentrated onto solar cells, they generate more electricity than without concentration. Since the sun moves continuously, a compound parabolic concentrator (CPC) can enhance the efficiency of solar cells by light-trapping and concentration because a CPC minimizes optical loss by reducing the reflection and the scattering on the surface of solar cells. However, CPC devices are generally expensive to manufacture and are too large in size to be used for applications requiring portability. Here, we developed a novel manufacturing process for a small CPC device and verified the enhanced efficiency of solar cells. Based on ultra-fine planing and injection molding, this process is an efficient method for mass production because it relies on replication. Two metal molds were precisely machined using an ultra-fine planing method with a diamond tool, and a CPC device was accurately manufactured by injection molding at low cost and within one minute. The variation of the specific cutting resistance during machining of the metal molds increased by four times, and the minimum uncut chip thickness decreased from 1.3 to 0.5 μm, which is called a size effect. The finished CPC device exhibited a surface roughness less than 40 nm and showed high optical efficiency in virtue of light-trapping. Finally, the efficiency of a solar cell with the CPC device was enhanced about 10%.

We first observed the spin-to-charge conversion due to both the inverse Rashba-Edelstein effect (IREE) and inverse spin-Hall effect in a holey multilayer molybdenum disulfide (MoS2) intermediate layer in a Pt/YIG structure via LSSE measurements under nonequilibrium magnetization. We found an enhancement of approximately 238%, 307%, and 290% in the longitudinal spin Seebeck effect (LSSE) voltage, spin-to-charge current, and thermoelectric (TE) power factor, respectively, compared with the monolayer MoS2 interlayer in a Pt/YIG structure. Such an enhancement in the LSSE performance of Pt/holey MoS2/YIG can be explained by the improvement of spin accumulation in the Pt layer by induced spin fluctuation as well as increased additional spin-to-charge conversion due to in-plane IREE. Our findings represent a significant achievement in the understanding of spin transport in atomically thin MoS2 interlayers and pave the way toward large-area TE energy-harvesting devices in two-dimensional transition metal dichalcogenide materials.

This study proposes a reliable and self-powered hydrogen (H2) gas sensor composed of a chemo-mechanically operating nanostructured film and photovoltaic cell. Specifically, the nanostructured film ...

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.