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The electrolysis of water using renewable energy inputs is a promising sustainable approach to produce clean hydrogen fuel. The conventional water electrolysis, where the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are tightly coupled to satisfy the thermodynamic potential of at least 1.23 V, occasionally encounters gas crossover through the membrane, resulting in the formation of explosive gas mixtures and reactive oxygen species. In this study, an asymmetric cell design of 3 M H2SO4|V(II)/V(III)|1 M KOH equipped with nickel foam electrodes is used for achieving decoupled HER and OER under kinetically favorable conditions by dividing the process into two steps using vanadium ions as redox mediators. The actual overall water splitting at an average cell voltage of 1.3 V and a current density of 10 mA cm−2 is accomplished even in the presence of membranes with outstanding cycling stability. The well-designed system for decoupled water electrolysis can allow the production of clean energy fuel using a low-power input in renewables–to–hydrogen conversion.

Electrochemical devices are constructed for continuous syngas (CO + H2) production with controlled selectivity between CO2 and proton reduction reactions. The ratio of CO to H2, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO3 catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO2 reduction device using Au NPs presented a stable operation for more than 23 h at different H2:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.

A two-dimensional resistance temperature detector (RTD) array sensor for the measurement of temperature distribution inside a tissue-mimicking material was proposed to validate focused ultrasound (FUS) devices. The fully two-dimensional $10\times10$ RTD array sensor with 1 mm inter-RTD distance was fabricated on the $2.5~ \boldsymbol {\mu } \text{m}$ thick film and placed inside the tissue-mimicking material. The measurement uncertainty for the RTD array was 0.18 K. The temperature distribution inside the phantom caused by a FUS transducer was measured and compared depending on the input power and focal plane. A tissue-mimicking phantom with an implanted RTD array can be applied to validate the performance and safety of both high- and low-intensity focused ultrasound (HIFU and LIFU) devices.

As the oxygen evolution reaction (OER) imposes a high energy barrier during electrochemical water splitting, designing highly efficient, stable, and cost-effective electrocatalysts for OERs is an ongoing challenge. In this study, we present a facile approach to prepare villi-shaped Ni-Fe hydroxides incorporated with oxalate derived from Ni-Fe oxalate through the in situ precipitation growth and subsequent immersion in an alkaline solution. The electrode with an optimized Ni-Fe ratio improves the OER kinetics, on which the electronic structure of the active site is adjusted based on a mutual effect between the adjacent nickel and iron atoms. The OER performance was significantly better than that of monometallic Ni(OH)2 and pristine Ni foam, with a low overpotential of 277 mV at 100 mA cm-2 and excellent stability. The enhanced OER performance is ascribed to the advanced intrinsic electrocatalytic activity of the electrode as a result of the synergetic effect of optimized Ni-Fe ratio mixing at the atomic level which leads to an increased surface area, a high number of active sites, and a reduced charge transfer resistivity.

Silicon monoxide (SiO) is regarded as a strong candidate for next-generation lithium ion battery anode materials because of its high energy density, low cost, and relatively low volume expansion compared to silicon (Si). However, the intrinsic low electrical conductivity and non-negligible volume expansion limit the practical application of SiO. Herein, dual-carbon-confined hydrangea-like SiO clusters are developed via chemical vapor deposition (CVD) growth, followed by a spray drying approach as a novel anode material for high-performance and stable lithium ion batteries. The evolution of the buffer layer along with sufficient void spaces to alleviate the volume expansion, besides the increased electrical conductivity, contributes to the improved discharge capacity of 1071 mAh g−1 after 200 cycles at a high current density of 0.75 A g−1 with a low expansion ratio of 9%. The distinct dual-carbon-confined hydrangea-like structure leads to synergistic improvements in battery performance, which will pave the way for promoting the commercial application of silicon-based anode materials.

In this study, 10 μm-thick TiO2 nanotube arrays (TNAs) coated with a MoO3 layer were prepared by electrochemical oxidation on titanium foil followed by successive cyclic voltammetric deposition, aiming at the fabrication of a thick binder-free anode with high capacity and good cycling stability for lithium ion batteries (LIBs). Through the evaluation of the electrochemical performance of electrodes prepared under various conditions, the electrode obtained at a precursor concentration of 5 mM showed the best electrochemical performance, exhibiting high reversible capacity and enhanced cycling stability. With the structural advantage and intrinsic characteristics of TNAs, the large volume expansion of MoO3 is successfully accommodated, resulting in 97% retention at a rate of 5 C over 500 cycles and 91% retention even at a high rate of 25 C.

Developing catalytically active, acid-stable, and electronically conductive catalysts is essential for efficient water electrolysis systems, but it is challenging to balance the three criteria prop...

Herein, we present a simple and innovative method for preparing Ni–Fe oxide doped with trace amounts of Ru on a stainless steel 304 substrate by single-step anodization. The procedure yields a highly efficient, durable, and flexible bifunctional catalyst for water splitting. The material exhibits outstanding electrocatalytic performance with high stability in both the hydrogen and oxygen evolution reactions, owing to the enhanced activity resulting from the incorporation of a small amount of Ru into anodic Ni–Fe oxide and a change in morphology that facilitates mass transfer. A stable cell voltage of 1.83 V is achieved at a current density of 100 mA cm−2 in a symmetric electrolyzer composed of flexible Ru-doped Ni–Fe oxide electrodes that can be formed into various shapes. The applicability of bifunctional electrodes of various shapes is demonstrated by their excellent stability for 100 h.

Producing practical chemical feedstocks via electrochemical CO2 reduction is a promising technology for carbon recycling and renewable energy storage. To improve CO2 reduction performance, electroc...

Mold oscillations, widely used in continuous casting for infiltrating the mold flux between the mold and the solidified shell, change periodically the heat flux from the meniscus to mold. These variations of the heat flux affect the solidification behavior near an initial solidification position. Because the surface shape of the solidified shell is influenced by the initial solidification behavior, it is important to understand the relation between the mold oscillation, the heat flux and initial solidification behavior. In the present study, we developed a numerical model that simulates the flow and thermal behavior of the mold flux near the meniscus. Using this model, we analyze the effects of the variations of the heat flux from the meniscus on the initial solidification position and suggest the formation mechanism of the oscillation marks (OMs) and the hooks. Also, we will present quantitative results about the depth of the OMs and the length of the hooks at the conditions used in the present study. The factors that influence the hooks’ types and the causes of the irregularity of the shell surface are also discussed.

A kinetic model was developed for the methane dehydroaromatization over a Mo2C/H-ZSM5 catalyst. Because the experimental observations show that the reaction and deactivation simultaneously take place in the catalyst activation (carburization) stage, the initial simulation time was specified as the time at which the activation was completed and the initial activities under each operating condition were estimated. The estimated values show that the initial activity of the Mo2C site is low in the early stage of the catalyst bed, which is probably due to the carbonization, while that of the H-ZSM5 site is very low in the later stage of the bed due to the encapsulation of coupled aromatics caused by the low confinement of Mo2C in the zeolite. Kinetic models were developed for the reaction and deactivation and the kinetic parameters were estimated by fitting the experimental data that were obtained after the activation was completed. The simulated results are in good agreement with the experimental data. The deactivation model indicates a higher temperature dependency of the Mo2C site compared with the H-ZSM5 site. In addition, the benzene and toluene yields abruptly decrease at very high temperature, indicating that a too high temperature should be avoided, although high temperatures are favored because of the endothermic characteristics of the production rate.

Repetitive start-up and shut-down events in polymer electrolyte membrane fuel cells for automotive applications lead to serious corrosion of the cathode due to an instantaneous potential jump that results from unintended air leakage into the anodic flow field followed by a parasitic oxygen reduction reaction (ORR) on the anode. Here we report a solution to the cathode corrosion issue during the start-up/shut-down events whereby intelligent catalyst design is used to selectively promote the hydrogen oxidation reaction (HOR) while concomitantly suppressing the ORR on the anode. Platinum thin layers supported on hydrogen tungsten bronze (Pt/HxWO3) suppressed the ORR by converting themselves into an insulator following exposure to oxygen, while selectively promoting the HOR by regaining metallic conductivity following subsequent exposure to hydrogen. The HOR-selective electrocatalysis imparted by a metal–insulator transition in Pt/HxWO3 demonstrated a remarkably enhanced durability of membrane electrode assemblies compared to those with commercial Pt/C catalysts. The stability of polymer electrolyte membrane fuel cells is limited by the degradation of the cathode catalyst during repetitive start-up/shut-down events — a parasitic oxygen reduction reaction on the anode causes an instantaneous potential jump at the cathode. The issue is now addressed by selectively suppressing the oxygen reduction reaction on the anode by exploiting the metal–insulator transition behaviour of Pt/HxWO3 catalysts.

A hurdle to the commercialization of thermoelectrochemical cells (TECs) based on the redox reaction of hexacyanoferrate (HCF) to convert low-grade waste heat into electricity is the high manufactur...

Atomically dispersed precious metal catalysts have emerged as a frontier in catalysis. However, a robust, generic synthetic strategy toward atomically dispersed catalysts is still lacking, which has limited systematic studies revealing their general catalytic trends distinct from those of conventional nanoparticle (NP)-based catalysts. Herein, we report a general synthetic strategy toward atomically dispersed precious metal catalysts, which consists of "trapping" precious metal precursors on a heteroatom-doped carbonaceous layer coated on a carbon support and "immobilizing" them with a SiO2 layer during thermal activation. Through the "trapping-and-immobilizing" method, five atomically dispersed precious metal catalysts (Os, Ru, Rh, Ir, and Pt) could be obtained and served as model catalysts for unravelling catalytic trends for the oxygen reduction reaction (ORR). Owing to their isolated geometry, the atomically dispersed precious metal catalysts generally showed higher selectivity for H2O2 production than their NP counterparts for the ORR. Among the atomically dispersed catalysts, the H2O2 selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e- ORR activity, the atomically dispersed Rh catalyst showed the best activity. Our general approach to atomically dispersed precious metal catalysts may help in understanding their unique catalytic behaviors for the ORR.

Rapid and efficient nucleic acid (NA) extraction and concentration are required for point-of-care analysis in order to prevent an epidemic/pandemic disease outbreak. Typical silica-based NA extraction methods have limitations such as being time-consuming, requiring human intervention, and resulting in a low recovery yield. In this study, we have developed a pathogenic DNA extraction device based on electrokinetic separation incorporated with a silicon nitride (SiNx) nanofilter, which expedites the DNA extraction procedure with advantages of being convenient, efficient, and inexpensive. This DNA extraction device consists of a computer numerical control (CNC) milled-Teflon gadget with a cis-chamber as a cell lysate reservoir and a trans-chamber as a elution solution reservoir, with the SiNx nanofilter being inserted between the two chambers. The SiNx nanofilter was fabricated using a photolithographic method in conjunction with nanoimprinting. Approximately 7.2 million nanopores of 220 nm diameter were located at the center of the nanofilter. When a DC electric field is applied through the nanopores, DNA is transferred from the cis-chamber to the trans-chamber to isolate the DNA from the cell debris. To demonstrate the DNA extraction performance, we measured the absorbances at 260 and 280 nm and performed a real-time polymerase chain reaction (real-time PCR) using the recovered DNA to verify its feasibility for downstream genetic analysis. Moreover, the DNA extraction device was successfully operated using a 1.5 V alkaline battery, which verifies the portability of the device for point-of-care testing. Such an advanced DNA extraction system can be utilized in various fields including clinical analysis, pathogen detection, forensic analysis, and on-site detection.

We report two-terminal threshold devices that use niobium oxide (NbOx) thin films that were synthesized using atomic layer deposition (ALD) then pulsed-laser annealing. The ALD growth conditions for NbOx thin films were optimized using niobium(V) ethoxide and deionized water at 170 °C. As-deposited NbOx films were amorphous with Nb5+ valence state, but laser annealing led to partial conversion to NbO2 crystallites with Nb4+ valence states. This two-terminal device with ALD-NbOx exhibits excellent threshold switching with low off current ∼847 nA at 1 V, high on/off current ratio (∼103), high reliability, fast switching time ( 1 MHz).

Although branched WO3 nanostructures have been investigated for electrochromic devices and catalytic electrodes, a detailed study on their structural evolution mechanism has rarely been carried out. In this work, we have demonstrated the microwave-assisted synthesis of branched WO3 nanotrees consisting of [001]-oriented WO3 needle-like structures growing radially from the surface of WO3 nanohelixes. The mechanism for the evolution of WO3 nanotrees with the preferred orientation was systematically investigated in terms of the reaction temperature and the distribution of the electric field applied by microwave irradiation. In addition, it was shown that the WO3 nanotrees can be easily converted into WS2/WO3 hierarchical nanotrees by a simple sulfurization process, and used as an efficient catalytic electrode for the hydrogen evolution reaction.

The unitized regenerative fuel cell (URFC) is a useful electrochemical energy conversion/storage device, in which catalysts for the dual-function (oxygen reduction reaction, ORR, and oxygen evoluti...

To realize the potential of bioinspired fibrillar adhesive applications ranging from biomedical devices to robotic grippers, there has been a significant effort to improve their adhesive strength and understanding of the underlying adhesion and detachment mechanisms. These efforts include changes to the backing layer, which connects the roots of all of the pillars in the fibrillar adhesive. However, previous approaches such as thickness or elastic modulus changes are selectively advantageous to the adhesive strength depending on the substrate condition because of the trade-off between conformity to misaligned/rough surfaces and increased interfacial stress concentrations. In this work, we explore mechanical divisions (cuts) in the backing layer as a new approach to improve the adhesive strength without this trade-off. We combine experiments and finite element analysis (FEA) to study the effect of the divisions, which decouples the mechanical interaction between the pillars on the divided layers, and show that the adhesive strength can be improved regardless of the substrate condition. Tensile adhesion experiments show increased adhesive strength with cuts to a micropost array (150 μm diameter posts) by approximately 25% for 4 divisions. In situ imaging of pillar detachment shows a transition of the detachment process from a peel-like detachment to a random detachment sequence. FEA simulations of the detachment process suggest that the increased strength may originate from a simultaneous enhancement of the load distribution between the pillars and the compliance of the backing layer.

Nucleic acid (NA) extraction and purification are one of the crucial steps for NA-based molecular diagnosis. However, the currently developed methods are still suffering from many issues including long process time, complicated steps, requirement of trained personnel and potential inhibition caused by chaotropic agents and/ or residual reagents. Herein, a surface-modified NA extraction microchip (SNC) is newly fabricated by introducing poly(2-dimethylaminomethyl styrene) (pDMAMS) film engaged directly on the microchip surface via initiated chemical vapor deposition (iCVD) process. The positively charged SNC inner surface could directly capture the negatively charged NA efficiently and its performance is confirmed by fluorescence microscopy and X-ray photoelectron spectroscopy. The developed SNC exhibits the deoxyribonucleic acid (DNA) capture efficiency higher than 92% regardless of initial DNA concentration in range of 20 ng/µL to 0.01 ng/µL. With this versatile DNA-capturing surface, the genomic DNAs of Escherichia Coli O157:H7 (E. coli O157:H7) is successfully extracted directly from cell lysate in the SNC with higher than 90% of efficiency within 30 min. The extraction time can be reduced to at least of 10 min maintaining extraction efficiency higher than 50%. Furthermore, the genomic DNAs are directly extracted using the SNC without loss from various real samples including juice, milk and blood serum. The proposed SNC enables us to perform an one-step NA extraction for molecular diagnosis and has the potential to be integrated into a micro-total analysis in the fields of point-of-care diagnosis.

To overcome the reliability issue of phase-change memory, the development of stable phase-change materials is extremely important. In this study, we analyze 13 dopants for Ge2Sb2Te5 (GST) based on two criteria: i) the change in thermal stability by doping and ii) a lattice distortion. After doping the elements, 11 elements showed a negative doping formation energy compared with pure GST. The angular distortion of the Zn dopant is the largest. The hole carrier decreases, and the electrical resistance increases through Zn-doping in GST. The increased resistance of the material can lead to low power consumption with a high energy effectiveness.

Double raster scanning approach to 3D laser forming was investigated to obtain a large deformation with one-step laser irradiation, avoiding repetitive scanning. The magnitude of the deformation during raster scanning was found to be strongly dependent on the overlapping between adjacent passes, which can be controlled by changing their spacing and the beam diameter. Therefore, 3D deformation during raster scanning has been analyzed at various overlap ratios, whose effect on the temperature and strain distribution were discussed. As the heat transfer mode significantly influences the uniformity of the bending process, the variations in bending angles with negative and positive overlapping ratios have also been investigated. The ratio of the longitudinal and lateral curvatures decreased with the increasing overlap ratio. Therefore, the effect of the lateral side is more important for specifying the final symmetry of the part, playing a critical role in bending with higher overlap ratios. In a rectangular part, deformation of the lateral side was found to be more difficult, showing strong dependence on the length of the scanning track, compared with the space of the adjacent passes. Through process characterization, the double raster scanning process has been well understood and proved to be a feasible approach to 3D laser forming of rectangular parts. Keywords: Raster scanning, Laser forming, Curvature, Laser bending, Overlap, Heat transfer

Control of polymer architecture can be a powerful strategy to refine the structure and properties without changing the chemical structure of the monomers. Here, we exploit a highly branched bottlebrush architecture to access tailored self-assembled morphologies and nanoporous structures. To this end, a series of well-defined bottlebrush random copolymers are synthesized by macromonomer approach, where polystyrene (PS) and poly(D,L-lactide) (PLA) side chains of non-equal molecular weights are grafted to the polynorbornene backbone. These bottlebrush copolymers exhibit microphase-separated structures including lamellar, hexagonal cylinders and disordered structures with the domain sizes of 13–20 nm depending on the relative volume fraction (f) of PS and PLA side chain. Due to highly asymmetric nature, these bottlebrush copolymers exhibit cylinders at fPS = 41–50% and lamellar at fPS = 67–70%, unlike the case of linear diblock copolymers. The selective degradation of PLA from these bottlebrushes allows for nanoporous structures to be created of which size, distribution and connectivity of pores are dictated by the composition of bottlebrush precursors. The ability to exploit the bottlebrush architecture to manipulate self-assembled morphologies and nanoporous structures may be a useful way to design materials for adsorptions, separations, catalysis and gas storages.

In order to be able to control the phase transition of engineered phase-change materials, the specific understanding of phase transition processes is essential. To understand the effect of dopant o...

The bit-patterned media (BPM) technology is a promising approach for developing high-density memory devices. Porous templates such as anodized aluminum oxide and self-assembled block copolymer films have been explored for use in BPM. In this work, in order to further increase the pore density, we used a mesoporous silica thin film (MSTF) with 8 nm sized regularly ordered pores and 4 nm thick walls as a template to grow CoPt3 nanoparticles (NPs) into two-dimensional hexagonal arrays. The use of a Au(111)/SiO2 substrate induced epitaxial growth of single-crystalline CoPt3 NPs in the face-centered cubic structure, as evidenced by high-resolution transmission electron microscopy and grazing-incidence X-ray scattering data. Direction-dependent magnetic measurements showed that the CoPt3 NPs had out-of-plane magnetic polarization. Magnetic force microscopy (MFM) data indicated that individual CoPt3 NPs could be addressed independently. First-principles electronic structure calculations indicated that the observ...

Computational fluid dynamics (CFD) studies have been carried out for CO2 reforming of methane in both a packed-bed reactor (PBR) and a membrane reactor (MR) with a heating tube as a heat source at the center of a reactor. The effect of a reactor geometry on the temperature and H2 and CH4 concentration profiles within a PBR and a MR have been investigated numerically by changing the distance of membranes from the center of a heating tube (Dcenter = radial distance between the center of the reactor and the center of the membrane) for a given heating tube temperature. The distances of the center of the membranes in a MR from the reactor center were 0.028 m, 0.03 m, 0.033 m, 0.035 m, 0.038 m, 0.04 m, 0.042 m, 0.044 m and 0.045 m. With the help of COMSOL Multiphysics® modeling software, it was possible to visualize temperature and concentration profiles both axially and radially. Interestingly, it was found that H2 enhancement is proportional to both Dcenter and the magnitude of the H2 flux. Further studies for the effect of a heating tube radius proposed an optimum radius for a maximum H2 yield enhancement in a MR. Consequently, it turned out that CFD studies can be used as a critical guideline for an efficient reactor design focusing on a reactor geometry in a MR for given conditions.

Process simulation and design as well as economic analysis were carried out to evaluate technical and economic feasibility of steam reforming of methanol in a membrane reactor (MR) for ultra-pure H2 production. Using a commercial process simulator, Aspen HYSYS®, comparative studies were conducted to investigate the effect of operating conditions including the H2 permeance (1 × 10−5 - 6 × 10−5 mol m−2 s−1 Pa−1), a H2O sweep gas flow rate (1–20 kmol h−1), and a reaction temperature (448–493 K) in a conventional packed-bed reactor (PBR) and the MR using a previously reported reaction kinetics. Improved performances such as methanol conversions and H2 yields were observed in the MR compared to the PBR and several design guidelines for the MR were obtained to develop H2 separation membranes with optimal H2 permeance and to select a suitable H2O sweep gas flow rate. In addition, economic analysis based on itemized cost estimations was conducted for a small-sized H2 fueling station by calculating a unit H2 production cost for both the PBR and the MR reflecting a current economic status in Korea. As a result, a cost saving of about 23% was obtained in the MR (7.24 $ kgH2−1) compared to the PBR (9.37 $ kgH2−1) confirming the benefit of employing the MR for ultra-pure H2 production.

This paper addresses the low-frequency noise characterization of Z2-FET structures. These double-gated p-i-n diode devices have been fabricated at STMicroelectronics in an ultrathin body and box (UTBB) 28-nm FDSOI technology and designed to operate as 1T-DRAM memory cells, although other applications, as for example electro static discharge (ESD) protection, have been reported. The experimentally extracted power spectral density of current reveals that the high-diode series resistance, carrier number fluctuations due to oxide traps, and gate leakage current are the main noise contributors at high-current regimes. These mechanisms are expected to contribute to the degradation of cell variability and retention time. Higher flicker noise levels have been reported when increasing the vertical electric field. A simple model considering the contribution of the main noise sources is proposed., This work was supported in part by the European REMINDER 687931 Grant, in part by the Consejeria de Economia, Conocimiento, Empresas y Universidad de la Junta de Andalucia and European Regional Development Fund (ERDF), under Grant SOMM17/6109/ UGR, and in part by the TEC2017-89800-R Projects

Hydrogels allow for controlling the diffusion rate and amount of solute according to the hydrogel network and thus have found many applications in drug delivery, biomaterials, toxicology, and tissue engineering. This paper describes a 3D-printed microfluidic chip for the straightforward partitioning of hydrogel barriers between microchannels. We use a previously-reported 3-channel architecture whereby the middle channel is filled with a hydrogel - acting like a porous barrier for diffusive transport - and the two side channels act as sink and source; the middle channel communicates with the side channels via orthogonal, small capillary channels that are also responsible for partitioning the hydrogel during filling. Our 3D-printed microfluidic chip is simple to fabricate by stereolithography (SL), inexpensive, reproducible, and convenient, so it is more adequate for transport studies than a microchip fabricated by photolithographic procedures. The chip was fabricated in a resin made of poly(ethylene glycol) diacrylate (PEG-DA) (MW = 258) (PEG-DA-258). The SL process allowed us to print high aspect ratio (37 : 1) capillary channels (27 μm-width and 1 mm-height) and enable the trapping of liquid-phase hydrogels in the hydrogel barrier middle channel. We studied the permeability of hydrogel barriers made of PEG-DA (MW = 700) (PEG-DA-700, 10% polymer content by wt. in water) - as a model of photopolymerizable barriers - and agarose (MW = 120 000, 2% polymer content by wt. in water) - as a model of thermally-gelled barriers. We measured the diffusion of fluorescein, 10k-dextran-Alexa 680 and BSA-Texas Red through these barriers. Fluorescein diffusion was observed through both 10% PEG-DA-700 and 2% agarose barriers while 10k-dextran-Alexa 680 and BSA-Texas Red diffused appreciably only through the 2% agarose hydrogel barrier. Our microfluidic chip facilitates the tuning of such barriers simply by altering the hydrogel materials. The straightforward trapping of selective barriers in 3D-printed microchannels should find wide applicability in drug delivery, tissue engineering, cell separation, and organ-on-a-chip platforms.

Fischer–Tropsch synthesis (FTS), which converts CO and H2 into useful hydrocarbon products, has attracted considerable attention as an efficient method to replace crude oil resources. Fe-based catalysts are mainly used in industrial FTS, and Fe7C3 is a common carbide phase in the FTS reaction. However, the intrinsic catalytic properties of Fe7C3 are theoretically unknown. Therefore, as a first attempt to understand the FTS reaction on Fe7C3, direct CO* dissociation on orthorhombic Fe7C3(001) (o-Fe7C3(001)) surfaces was studied using density functional theory (DFT) calculations. The surface energies of 14 terminations of o-Fe7C3(001) were first compared, and the results showed that (001)0.20 was the most thermodynamically stable termination. Furthermore, to understand the effect of the surface C atom coverage on CO* activation, C–O bond dissociation was performed on the o-Fe7C3(001)0.85, (001)0.13, (001)0.20, (001)0.09, and (001)0.99 surfaces, where the surface C atom coverages were 0.00, 0.17, 0.33, 0.33, and 0.60, respectively. The results showed that the CO* activation linearly decreased as the surface C atom coverage increased. Therefore, it can be concluded that the thermodynamic and kinetic selectivity toward direct CO* dissociation increased when the o-Fe7C3(001) surface had more C* vacancies.

Herein, we investigated the influence of oxygen partial pressure (pO2) on average long- and short-range transformations in the crystal structures of ultra-smooth Fe2O3-doped NiO thin films that were epitaxially grown at room temperature. The films were deposited via pulsed laser deposition, and the oxygen content in the films was controlled by adjusting the pO2 to 1, 10 - 3 , and 10 - 5 Pa. Result showed that d-spacing and lattice strain decreased with increasing pO2. The thin film grown at 10 - 5 Pa had a rock salt structure, whereas films grown at pO2s of 10 - 3 and 1 Pa had spinel structures. The local structures and valence states indicate that local Fe coordination transitioned from a distorted octahedral geometry to a tetrahedral/distorted octahedral geometry at higher pO2s. Additionally, the valence of Fe increased from Fe2+ to Fe3+, indicating structural phase transformation, which is supported by the X-ray diffraction analysis results. In contrast, the valence and local environment of Ni varied little. The structural transformation of the films was accompanied by the narrowing of the optical bandgap for direct transition and an increase in electrical resistivity.

Mesoporous metal oxides consisting of fully interconnected network structures with small pores (20–50 nm) have high surface areas and decreased ion intercalation distances, making them ideal for use in high-performance electrochromic supercapacitors (ECSs). Evaporation-induced self-assembly (EISA), which combines sol–gel chemistry and molecular self-assembly, is a powerful method for the fabrication of mesoporous metal oxides through a solution phase synthesis. Herein, we introduce ultrafast sub-1 s ECSs based on an amorphous mesoporous tungsten trioxide (WO3) that is prepared by EISA. Compared to that of a compact-WO3 film-based device, the performances of an ECS with mesoporous WO3 exhibits a large optical modulation (76% at 700 nm), ultrafast switching speeds (0.8 s for coloration and 0.4 s for bleaching), and a high areal capacitance (2.57 mF/cm2), even at a high current density (1.0 mA/cm2). In addition, the excellent device stability during the coloration/bleaching and charging/discharging cycles is observed under fast response conditions. Moreover, we fabricated a patterned mesoporous WO3 for ECS displays (ECSDs) via printing-assisted EISA (PEISA). The resulting ECSDs can be used as portable energy-storage devices, and their electrochromic reflective displays change color according to their stored energy level. The ECSDs in this work have enormous potential for use in next-generation smart windows for buildings and as portable energy storage displays. Networks of tiny holes improve the energy storage properties of materials that can also be used for smart windows. In electrochromic materials, the fraction of light passing through the material can be controlled using an electrical voltage. This is useful for smart windows which electrically switch from being transparent to opaque. This change is associated with the storage or release of energy, so the same materials are being investigated for energy storage. Keon-Woo Kim from Pohang University of Science and Technology, South Korea, and co-workers have developed an improved electrochromic supercapacitor made from tungsten trioxide. They used an evaporation-induced self-assembly process to deposit a film of tungsten trioxide containing pores approximately 30 nanometers across. This porous structure increased the material’s switching speed and capacitance compared to a conventional tungsten trioxide thin film. Ultra-fast electrochromic supercapacitors (ECSs) are demonstrated based on mesoporous WO3 prepared by evaporation-induced self-assembly (EISA). Mesoporous WO3 based ECSs show excellent electrochromic and supercapacitor performances under fast operating condition. Furthermore, printing assisted EISA is introduced to produce patterned mesoporous WO3 for ECS displays (ECSDs). The resulting ECSDs have great potential as next-generation smart electrochemical components.

Physiologically relevant phantoms with high reliability are essential for extending the therapeutic applications of high-intensity therapeutic ultrasound. Here we describe a tissue-mimicking phantom capable of quantifying temperature changes and observing non-thermal phenomena by high-intensity therapeutic ultrasound. Using polydiacetylene liposomes, we fabricated agar-based polydiacetylene hydrogel phantoms (PHPs) that not only respond to temperature, but also have acoustic properties similar to those of human liver tissue. The color of PHPs changed from blue to red depending on the temperature in the range 40°C-70°C, where the red/blue ratio of PHP had a good linearity of 99.06% for the temperature changes. Furthermore, repeated high-intensity focused ultrasound led to histotripsy on the PHP with liquefied and damaged areas measuring 0.7 and 4.0 cm2, respectively, at the signal generator amplitude setting voltage of 80 mV. Our results indicate not only the usability of the thermochromic phantom, but also its potential for evaluating non-thermal phenomena in various high-intensity focused ultrasound therapies.

Ruhrstahl–Heraeus (RH) processor is widely applied to the refining process to produce steel with very low carbon contents. In this study, to investigate the effect of ultrasound treatment on RH decarburization process, we have developed two kinds of the water models simulated the RH process and study the removal rate of dissolved oxygen. The one is the RH water model of 1/8 size of actual RH degasser simulated the late-stage of the RH process when surface reaction and plume reaction mainly occur. Through this model, it is found that the ultrasound treatment accelerates dissolved oxygen removal reaction and this tendency is maintained even at low concentrations. Also, the results show that there is a difference in the degassing efficiency depending on the frequencies and the positions of the ultrasonic transducer. Also, to simulate the Early-stage Reaction of the process including the inner-site reaction which is difficult to investigate through the RH water model, the other water model has been developed (the RH-ER water model). This model shows that the ultrasound treatment facilitates the early-stage reaction including inner-site reaction, like the RH water model. These results show that the addition of the ultrasound treatment can accelerate decarburization reaction during RH process compared to conventional process.

Antireflection (AR) layers for Si were investigated for applications in optical communication in the wavelength range of 1270–1330 nm. The Essential Macleod software was used to find the optimal thicknesses of the AR coatings with two different structures of AlOx/TiOx bilayer and SiNx single-layer. The simulations revealed reflectances lower than 0.5% for both AlOx/TiOx and SiNx AR structures. Furthermore, atomic layer deposition and plasma-enhanced chemical vapor deposition were used to grow the AlOx/TiOx and SiNx layers, respectively. For the fabricated structures, average reflectances of 0.2% (AlOx/TiOx) and 0.3% (SiNx) were achieved in the wavelength range of 1270–1330 nm. For the AlOx/TiOx bilayer, a lower transmittance of ~88% was obtained, compared with that of the SiNx single-layer of ~99%. An additional air annealing at 300 °C for 2 h led to a crystallization of the amorphous TiOx into anatase phase, which yielded an improved transmittance of ~99%, comparable with that of the SiNx single-layer structure. X-ray photoelectron spectroscopy revealed that the oxidation state of Ti in TiOx influenced the absorption in the near-infrared region.

Biomaterials derived via programmable supramolecular protein assembly provide a viable means of constructing precisely defined structures. Here, we present programmed superstructures of AuPt nanoparticles (NPs) on carbon nanotubes (CNTs) that exhibit distinct electrocatalytic activities with respect to the nanoparticle positions via rationally modulated peptide-mediated assembly. De novo designed peptides assemble into six-helix bundles along the CNT axis to form a suprahelical structure. Surface cysteine residues of the peptides create AuPt-specific nucleation site, which allow for precise positioning of NPs onto helical geometries, as confirmed by 3-D reconstruction using electron tomography. The electrocatalytic model system, i.e., AuPt for oxygen reduction, yields electrochemical response signals that reflect the controlled arrangement of NPs in the intended assemblies. Our design approach can be expanded to versatile fields to build sophisticated functional assemblies.

This study is aimed at alleviating the inherent disadvantages of sulfur cathodes in lithium-sulfur (Li-S) batteries by encapsulating the sulfur particles with a dual (ionic and electronic)-conducting polymer via a simple, single-step procedure. Successful encapsulation by the polymer was confirmed by microscopic analyses. The encapsulated sulfur electrodes exhibit stable cycling performance and high sulfur utilization; in particular, the cell with 1 wt% dual conducting polymer-coated sulfur particles exhibit the best cycle performance with a discharge capacity of 1002 mAh g−1 after 100 cycles at 0.2 C-rate. As opposed to various sulfur-carbon composites reported previously, our 1 wt% dual conducting polymer-coated sulfur composite achieves a very high loading level of 99%. This simple strategy of encapsulating sulfur particles with functional polymers could be a potential pathway toward the commercialization of Li-S batteries.

The sluggish disproportionation of short-chain lithium polysulfides, Li2Sx, is known to be one of the major causes to limit the rate capability of lithium–sulfur batteries. Herein, we report that tungsten carbide not only affords strong sulfiphilic surface moieties but also provides an efficient catalysis to enhance the polysulfide fragmentation, leading to a drastic improvement in the electrode kinetics. We show that tungsten carbide acts as a superb anchoring material for the long-chain polysulfide and also promotes the dissociation of short-chain polysulfide during the electroreduction process. This leads to a high-rate performance of the composite cathode loaded with tungsten carbide, delivering a markedly enhanced discharge capacity of 780 mA h g–1 at a high current rate of 5 C, when it is applied with a combination of a carbon-coated separator for the polysulfide confinement. Hence, this work presents a new strategic approach for a high-power lithium–sulfur battery.

We synthesized ordered mesoporous Fe/N/C with highly active Fe-N x /C sites denoted as m-FePhen-C as a non-precious metal catalyst (NPMC) for the oxygen reduction reaction in fuel cells. This was the first study that incorporated a catalyst precursor with Fe-N coordination directly in a simple block co-polymer-assisted soft-template method for the synthesis of mesoporous Fe/N/C. The synthesized catalyst (m-FePhen-C) showed a high catalytic performance comparable to that of Pt/C in half-cell tests, and a membrane electrode assembly (MEA) with an m-FePhen-C cathode exhibited 40% higher power density than did an MEA with a commercial Pt/C cathode in single-cell tests, with comparable electrode thicknesses. This result is highly meaningful in that generation of the Fe-N x /C active sites and formation of ordered mesoporous structure were achieved simultaneously in the simple soft-template-assisted process, and in that the advantages of mesoporous structure with appropriate pore size in metal-containing NPMC were elucidated for high-performance MEAs.

In a complex reaction system, in which gas, liquid, and solid catalysts work together, understanding the impact of mass transfer that varies with the catalyst pore structure is very challenging but also essential to designing selective catalysts. We investigated the effect of mesopores introduced into bi-functional Co/ZSM-5 catalysts on the direct production of liquid fuel by low-temperature Fischer–Tropsch synthesis (FTS). The influence of mesopores on the textural properties, Co dispersion, zeolite crystallinity, the density of acid sites, and the resulting FTS performance was studied in detail. The presence of mesopores facilitated the dispersion of Co nanoparticles and the regulation of acidity, affording high CO conversion and a moderate degree of isomerization. In addition, close proximity between FTS active sites and acid functionalized sites could be achieved by the introduction of mesopores. However, the relationship between the structural parameter and liquid fuel productivity suggested that the mesopores did not reduce the mass transfer resistance of the reactants and intermediates during the FTS reaction.

Improving the activity of Ag-based catalysts for oxygen reduction reaction (ORR) is a challenge for achieving economic alkaline-based fuel cells. Here, vertically-aligned nanoporous Ag nanowires (NWs) are developed as electrocatalysts for the ORR. Electrochemical reduction of vertically-aligned AgCl NWs eliminate Cl− ions from the NWs, and thereby reduces Ag+ cations to metallic Ag atoms, to yield nanoporous Ag NWs with a large amount of catalytic active Ag (110) surfaces. The gap between Ag NWs can be a pathway for the electrolyte and increase mass transport of dissolved oxygen to the electrode surface. Consequently, the Ag NWs have 36.4 times higher electrochemical surface area but less than 0.08 times as much charge-transfer resistance as Ag film. As a result, the Ag NWs achieve an ORR-onset potential of 0.97 VRHE and a good long-term stability with only 50 mV decrease in ORR-onset potential even after 30,000 cycles (480,000 s).

A thin-film resistance temperature detector (RTD) array is proposed to measure the temperature distribution inside a phantom. HIFU (high-intensity focused ultrasound) is a non-invasive treatment method using focused ultrasound to heat up a localized region, so it is important to measure the temperature distribution without affecting the ultrasonic field and heat conduction. The present 25 µm thick PI (polyimide) film is transparent not only to an ultrasonic field, because its thickness is much smaller than the wavelength of ultrasound, but also to heat conduction, owing to its negligible thermal mass compared to the phantom. A total of 33 RTDs consisting of Pt resistors and interconnection lines were patterned on a PI substrate using MEMS (microelectromechanical systems) technology, and a polymer phantom was fabricated with the film at the center. The expanded uncertainty of the RTDs was 0.8 K. In the experimental study using a 1 MHz HIFU transducer, the maximum temperature inside the phantom was measured as 70.1 °C just after a HIFU excitation of 6.4 W for 180 s. The time responses of the RTDs at different positions also showed the residual heat transfer inside the phantom after HIFU excitation. HIFU results with the phantom showed that a thin-film RTD array can measure the temperature distribution inside a phantom.

Indium vacancies in Bi-doped In3SbTe2 (BIST) cause local distortion or and faster phase transition of BIST with good stability. The formation energy of the In vacancy in the BIST is relatively lower compared to that in IST due to triple negative charge state of the In vacancy (V 3− In) and higher concentration of the V 3− In in BIST. The band gap of BIST is substantially reduced with increasing concentrations of the V 3− In and the hole carriers, which results in a higher electrical conductivity. The phase-change memory (PRAM) device fabricated with the BIST shows very fast, stable switching characteristics at lower voltages.