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There is an increasing interest in developing next-generation wearable ultrasound patch systems because of their wide range of applications, such as home healthcare systems and continuous monitoring systems for physiological conditions. A wearable ultrasound patch system requires a stable interface to the skin, an ultrasound coupling medium, a flexible transducer array, and miniaturized operating circuitries. In this study, we proposed a patch composed of calcium (Ca)-modified silk, which serves as both a stable interface and a coupling medium for ultrasound transducer arrays. The Ca-modified silk patch provided not only a stable and conformal interface between the epidermal ultrasound transducer and human skin with high adhesion but also offered acoustic impedance close to that of human skin. The Ca-modified silk patch was flexible and stretchable (∼400% strain) and could be attached to various materials. In addition, because the acoustic impedance of the Ca-modified silk patch was 2.15 MRayl, which was similar to that of human skin (1.99 MRayl), the ultrasound transmission loss of the proposed patch was relatively low (∼0.002 dB). We also verified the use of the Ca-modified silk patch in various ultrasound applications, including ultrasound imaging, ultrasound heating, and transcranial ultrasound stimulation for neuromodulation. The comparable performance of the Ca-modified patch to that of a commercial ultrasound gel and its durability against various environmental conditions confirmed that the Ca-modified silk patch could be a promising candidate as a coupling medium for next-generation ultrasound patch systems.

Single-phase formation of active metal oxides on supports has been vigorously pursued in many catalytic applications to suppress undesired reactions and to determine direct structure-property relationships. However, this is difficult to achieve in nanoscale range because the effect of non-uniform metal-support interfaces becomes dominant in the overall catalyst growth, leading to the nucleation of various metastable oxides. Herein, we develop a supported single-phase corundum-Rh2 O3 (I) nanocatalyst by utilizing controlled interaction between metal oxide and h-BN support. Atomic-resolution electron microscopy and first-principle calculation reveal that single-phase formation occurs via uniform and preferential attachment of Rh2 O3 (I) (110) seed planes on well-defined h-BN surface after decomposition of rhodium precursor. By utilizing the Rh/h-BN catalyst in methane partial oxidation, syngas is successfully produced solely following the direct route with keeping a H2 /CO ratio of 2, which makes it ideal for most downstream chemical processes.

The ex-solution phenomenon has received attention as a promising technique to prepare highly durable heterogeneous catalysts. Perovskite materials have been mainly used as host oxides for ex-solution, but their small surface areas have limited their practical use. Here, Rh was ex-solved by reducing Rh-doped ceria solid solution, and nanosized Rh catalysts with a high surface area of 70.7 m2/g were prepared. The Rh nanoparticles ex-solved from the ceria nanodomains were directly monitored by in situ transmission electron microscopy. The Rh nanoparticles whose sizes are 2-3 nm were not coarsened during the propane steam reforming process carried out at 700 °C for 65 h, leading to high resistance against sintering and coke formation. On the contrary, the Rh catalyst simply deposited on CeO2 was significantly sintered after the reaction, and the size of Rh nanoparticles increased to 25 nm, resulting in severe coke formation. Our work shows that ex-solution from a ceria-based nanodomain can be a good way to prepare metal nanoparticle catalysts with a large surface area and excellent durability for gas-phase reactions at high temperatures.

Much effort has been devoted to developing electrocatalysts applicable to anion exchange membrane water electrolyzers (AEMWEs). Among many candidates for oxygen evolution reaction, NiFe-layered double hydroxide (LDH)-based electrocatalysts show the highest activity in an alkaline medium. Unfortunately, the poor electrical conductivity of NiFe-LDH limits its potential as an electrocatalyst, which was often solved by hybridization with conductive carbonaceous materials. However, we find that using carbonaceous materials for anodes has detrimental effects on the stability of AEMWEs at industrially relevant current densities. In this work, a facile monolayer structuring is suggested to overcome low electrical conductivity and improve mass transport without using carbonaceous materials. The monolayer NiFe-LDH deposited on Ni foam showed much better AEMWE performance than conventional bulk NiFe-LDH due to better electrical conductivity and higher hydrophilicity. A high energy conversion efficiency of 72.6% and outstanding stability at a current density of 1 A cm-2 over 50 h could be achieved without carbonaceous material. This work highlights electrical conductivity and hydrophilicity of catalysts in membrane-electrode-assembly as key factors for high-performance AEMWEs.

Achieving high electrochemical conversion of carbon dioxide (CO2) into valuable fuels and chemicals is one of the most promising directions to address environmental and energy challenges. Although ...

Background Low-intensity transcranial focused ultrasound stimulation is a promising candidate for noninvasive brain stimulation and accurate targeting of brain circuits because of its focusing capability and long penetration depth. However, achieving a sufficiently high spatial resolution to target small animal sub-regions is still challenging, especially in the axial direction. Objective To achieve high axial resolution, we designed a dual-crossed transducer system that achieved high spatial resolution in the axial direction without complex microfabrication, beamforming circuitry, and signal processing. Methods High axial resolution was achieved by crossing two ultrasound beams of commercially available piezoelectric curved transducers at the focal length of each transducer. After implementation of the fixture for the dual-crossed transducer system, three sets of in vivo animal experiments were conducted to demonstrate high target specificity of ultrasound neuromodulation using the dual-crossed transducer system (n = 38). Results The full-width at half maximum (FWHM) focal volume of our dual-crossed transducer system was under 0.52 μm3. We report a focal diameter in both lateral and axial directions of 1 mm. To demonstrate successful in vivo brain stimulation of wild-type mice, we observed the movement of the forepaws. In addition, we targeted the habenula and verified the high spatial specificity of our dual-crossed transducer system. Conclusions Our results demonstrate the ability of the dual-crossed transducer system to target highly specific regions of mice brains using ultrasound stimulation. The proposed system is a valuable tool to study the complex neurological circuitry of the brain noninvasively.

Catalyst design with good stability beyond simply having high activity is crucial for a variety of reactions. Here, we evaluate the ceria catalyst for CO oxidation as a model reaction to rationally...

Recent advances in heterogeneous single-atom catalysts (SACs), which have isolated metal atoms dispersed on a support, have enabled a more precise control of their surface metal atomic structure. SACs could reduce the amount of metals used for the surface reaction and have often shown distinct selectivity, which the corresponding nanoparticles would not have. However, SACs typically have the limitations of low-metal content, poor stability, oxidic electronic states, and an absence of ensemble sites. In this review, various efforts to overcome these limitations have been discussed: The metal content in the SACs could increase up to over 10 wt %; highly durable SACs could be prepared by anchoring the metal atoms strongly on the defective support; metallic SACs are reported; and the ensemble catalysts, in which all the metal atoms are exposed at the surface like the SACs but the surface metal atoms are located nearby, are also reported. Metal atomic multimers with distinct catalytic properties have been also reported. Surface metal single-atoms could be decorated with organic ligands with interesting catalytic behavior. Heterogeneous atomic catalysts, whose structure is elaborately controlled and the surface reaction is better understood, can be a paradigm with higher catalytic activity, selectivity, and durability and used in industrial applications.

Acoustic matching layer films (MLFs) were fabricated using B-stage thermosetting polymer resins with various volume fractions of alumina and tungsten powders. After making certain thickness MLFs, ultrasonic matching layers were fabricated using a simple molding process. The thickness of the matching layers can be precisely adjusted from several micrometer to hundreds of micrometer, without any grinding process. Experimental values of acoustic impedances of the matching layers were in good agreement with theoretical values calculated by the Devaney model. Using the optimized acoustic matching layer by the MLFs, the maximum intensity and the fractional bandwidth of the ultrasonic transducer were increased by 10% and 37% respectively. The effectiveness of the matching layer using MLFs was successfully verified.

The load–displacement curves of flow drill screw (FDS) and high-speed bolt joining process (hereafter referred to as RIVTAC) joints between dissimilar materials are predicted via development of an artificial neural network (ANN) model. The predicted load–displacement curves accurately describe the joint strength and failure mode of joints. From a lap shear test with 14 material combinations of aluminum alloys and steels for FDS joints, it was found that the load–displacement curves of FDS joints could be classified as a pull-out of fastener, plate failure, and fastener failure. From a lap shear test with 10 material combinations of aluminum alloys and steels for RIVTAC joints, it was found that the failure modes of RIVTAC can be classified as a plate failure and fastener failure. With the obtained experimental results, the ANNs were trained to predict the load–displacement curves that include the failure modes and lap shear strengths of FDS and RIVTAC joints with the material properties and plate thicknesses. The coefficients of determination between the measured and predicted loads were 0.84 and 0.96 for the FDS and RIVTAC joints, respectively. This indicates that the trained ANNs exhibit a strong correlation between the measured and predicted loads. The errors of the predicted lap shear strength were within 15.2 % and 11.1 % for the FDS and RIVTAC joints, respectively. This study provides a systematic analysis of the characteristics of FDS and RIVTAC joints between dissimilar materials and an efficient and accurate tool for predicting the load–displacement curves of FDS and RIVTAC joints between dissimilar materials.

Precipitation hardening of Al alloys is an essential aging process for industrial applications demanding lightweight and high-mechanical strength materials. However, this process drastically reduces the thermal conductivity of the Al alloy owing to the formation of intermetallic precipitates. Because the growth of the intermetallic precipitates is a complicated process involving the diffusion of alloying elements as well as phase transformation, the prediction of the thermal conductivity during the precipitation process has not been accomplished. Herein, an accurate prediction method for the effective thermal conductivity of Al alloys during the precipitation process is presented. Interestingly, the study finds that the inhomogeneous distribution of the composition in the Al solid solution generates a considerably inhomogeneous distribution of the thermal conductivity around the precipitates; consequently, the accuracy of our prediction is 30% higher than that in previous studies.

Reducing the size of metal nanoparticles down to the single-atom level has been actively pursued to maximize the use of precious metals. Recently, single-atom catalysts, in which all the metal atoms are isolated on a support with 100% dispersion, have received much attention. However, the lack of ensemble sites prevents valuable surface reactions that require metal proximity to occur. Here, we present metal (Pt, Pd and Rh) ensemble catalysts with 100% dispersion and a reduced metallic surface state. More specifically, nanoceria particles were anchored on Al3+penta sites of activated γ-alumina, and then metal was deposited and reduced. The ensemble catalysts are highly durable: their structure was maintained even after hydrothermal ageing at 900 °C for 24 h or after long-term reaction. These catalysts have superior activity and durability for three-way catalytic reactions and can provide insights beyond single-atom catalysts for heterogeneous catalysis. Supported single atoms can minimize metal utilization in catalysis, although reactivity restrictions exist. Here, fully exposed Pt, Pd and Rh ensembles localized on CeO2 islands anchored onto partially reduced γ-Al2O3 are introduced as a superior and durable alternative for three-way catalysis.

The electrochemical CO2 reduction reaction (CO2RR) has undergone great advances recently. The gas diffusion electrode (GDE) has been introduced to enhance productivity. However, the studies on catalysts on the GDE are scarce, especially for the production of liquid products. Here, we deposited Sn electrocatalysts electrochemically with dense tips (SnDT) on a gas permeable carbon cloth electrode. The prepared cathode had a uniform surface covered with SnDT catalysts. We achieved a high specific production rate of the CO2RR towards formate, 1 mmol m−2 s−1, at only −0.76 VRHE where partial current density and faradaic efficiency toward formate were −18.7 mA cm−2 and 62.5%, respectively, in neutral electrolyte. Formate productivity of 65 mg h−1 was achieved using a customized cell with 4 cm2 of the SnDT GDE. Formate was stably produced for 72 h without changes in faradaic efficiency and current density. The product distribution was affected by local pH. The effect of catalyst shape was also investigated by comparing with commercial Sn nanoparticles deposited on a carbon cloth electrode.

Electrochromic devices (ECDs) have been widely investigated for application in next-generation displays and smart windows thanks to their highly efficient optical transmittance modulation properties. However, several challenges such as chemical and environmental instabilities and leakage of electrolytes limit their practical applications. In this paper, we report a simple and efficient approach for synthesising ultraviolet (UV)-cured poly(methyl methacrylate) (PMMA) gels that can be used as safe electrolytes. The ECDs fabricated with the 10 min UV-cured PMMA gel electrolyte deliver remarkable device performances with a wide optical transmittance transition (ΔT) of 51.3% at a wavelength of 550 nm under −1.2–0 V bias range and fast switching times (Δt) of 1.5 s and 2.0 s for bleaching and colouration, respectively. In addition, excellent operational stability of 98.9% after 11 500 cycles and environmental stability at a wide temperature range of −20 to +70 °C are exhibited. Moreover, a smart electrochromic window system, including an ECD connected with an Arduino circuit, is developed. These smart windows can change colour by simultaneously monitoring the illumination and UV intensities of sunlight.

Minimizing the use of Pt catalysts in proton exchange membrane fuel cells (PEMFCs) is important, considering its high price and scarcity. Herein, we demonstrate novel catalysts for PEMFCs with exceptionally high mass activity and durability, in which block copolymer-based carbon supports are loaded with an ultra-small amount of Pt. The mass activity measured after 30 000 cycles of single cell tests was 0.81 A mgPt−1 at 0.9 V, which is the highest performance reported to date. The newly developed catalyst yielded nearly the same power density as that of the commercial Pt/C, even with 1/20 of the Pt usage. The carbon supports were prepared by carbonizing crosslinked domains of block copolymer particles selectively, resulting in mesoporous carbon particles with ∼25 nm pores. When Pt was deposited, thin carbon shells were formed encapsulating PtFe nanoparticles, catalyzing the oxygen reduction reaction efficiently with high durability.

Fuel cells recombine water from H-2 and O-2 thereby can power, for example, cars or houses with no direct carbon emission. In anion-exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen-reduction reaction occurs. However, the sluggish kinetics of the hydrogen-oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet-chemistry, gaining control over this B-doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H- and OH-adsorption on B-doped Pd. Using this "impurity engineering" approach, they thus design Pt-free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long-term stability, to enable the "hydrogen economy."

Single-atom catalysts (SACs) have attracted growing attention because they maximize the number of active sites, with unpredictable catalytic activity. Despite numerous studies on SACs, there is little research on the support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SAC by comparing with single-atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO3-x (Pt NP/WO3-x ). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO3-x (Pt SA/WO3-x ). The Pt SA/WO3-x exhibited a higher degree of hydrogen spillover from Pt atoms to WO3-x at the interface, compared with Pt NP/WO3-x , which drastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides a new framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.

The development of new amine solvents without the major drawbacks of conventional amines is crucial to industrial applications of CO2 capture. This paper presents a water-lean CO2 capture solvent having a low regeneration energy and low degradation. The water-lean solvent, K2Sol, is a sterically hindered diamine; because of the hindered amine site, K2Sol easily forms bicarbonate, resulting in a high absorption capacity. The minimum solvent regeneration energy is obtained using Gaussian process Bayesian optimization (GPBO) and bench-scale pilot plant experiments. GPBO finds the optimal solution using the input and output relationship of experiments; thus, expensive first-principle model construction can be avoided. According to the pilot plant experiment, the optimal regeneration energies of monoethanolamine (MEA) and K2Sol are 4.3 and 2.8 GJ/t CO2, respectively, indicating that K2Sol requires only 65% of the regeneration energy of MEA. Fewer than 30 experiments are required to find the optimal pilot plant operation for both the MEA and K2Sol experiments. We also describe the superior properties of K2Sol in terms of the CO2 loading, cyclic capacity, regeneration temperature, and degradation.

Proton exchange membrane fuel cells (PEMFCs) are promising mobile power supply systems, and operate without noise or polluting emissions. Because the oxygen reduction reaction (ORR) at the cathode suffers from high overpotential and sluggish kinetics, many catalysts have been developed in efforts to enhance activity and durability for the ORR. However, most of them have complicated synthetic procedures which cannot be scaled-up easily, and have only been tested in a half-cell. High activity in a half-cell does not necessarily guarantee better performance in a single-cell. In this work, we synthesized an Au-doped PtCo/C catalyst using a simple method of gas-phase reduction and subsequent galvanic replacement, and its activity and durability were tested in a single-cell. When current densities were compared at 0.6 V after a durability test of 30,000 cycles in 0.6–1.0 V, the values were 1.40, 0.81, and 0.63 A cm−2 for the Au-doped PtCo/C, acid-treated PtCo/C, and commercial Pt/C catalysts, respectively. Co leaching was much less in the Au-doped PtCo/C. Density functional theory (DFT) calculations confirmed that surface oxygen species bound more weakly at the catalyst surface and migration of a Co atom (Co segregation) to the surface was suppressed in the presence of Au. This facile method can provide a more realistic strategy to design better ORR catalysts for PEMFC application.

Electrochemical CO2 reduction reaction (CO2RR) has received much attention as a promising technology to reduce CO2 using renewable electricity, but it typically suffers from low CO2 solubility in aqueous phase and a high cell resistance of a conventional liquid phase reactor. Here, we report the CO2RR using a membrane electrode assembly that consists of gas diffusion electrode (GDE) and anion exchange membrane (AEM). The GDE enabled facile mass transfer of gaseous CO2 directly to the catalyst and the AEM could suppress hydrogen evolution reaction (HER) by increasing local pH at the catalyst. Various metal powders of Pd, Ag, Zn, Cu, Sn, Ru, Pt, Ni were tested as cathode catalysts. Pd and Ag showed high current density of >200 mA cm−2 at -3.0 V and faradaic efficiency >95% for CO production with a low cell resistance of

A ternary oxide catalyst composed of CuO Co3O4 CeO2 (CCC) has great potential for automotive exhaust treatment due to its excellent CO oxidation activity and high resistance against hydrocarbon inhibition. However, current CCC catalyst exhibits significantly lower hydrocarbon oxidation activity comparing to CO oxidation, and deactivation occurs severely after hydrothermal aging. Here, we show that a Mn-doped CCC (CCCM) catalyst exhibits enhanced activity and durability for C3H6 oxidation, while maintaining the high activity for CO oxidation. The Mn-doping prevented sintering and phase separation of the Co3O4 phase even after hydrothermal aging at 750 °C for 25 h. The Mn was selectively doped into Co3O4 by substituting Co3+ octahedral sites in the Co3O4 spinel structure. The presence of Mn with a larger cation radius induced lattice expansion of the Co3O4 phase with more surface active oxygen. This strategy can provide a facile way to develop better non-PGM catalysts for emission control.

As climate change becomes increasingly evident, reducing greenhouse gases including CO2 has received growing attention. Because CO2 is thermodynamically very stable, its conversion into value-added chemicals such as CO, CH4, or C2H4 is difficult, and developing efficient catalysts for CO2 conversion is important work. CO2 can be converted using the gas-phase reaction, liquid-phase reaction, photocatalytic reaction, or electrochemical reaction. The gas-phase reaction includes the dry reforming of methane using CO2 and CH4, or CO2 hydrogenation using CO2 and H2. The liquid-phase reaction includes formic acid formation from pressurized CO2 and H2 in aqueous solution. The photocatalytic reaction is commonly known as artificial photo-synthesis, and produces chemicals from CO2 and H2O under light irradiation. The electrochemical reaction can produce chemicals from CO2 and H2O using electricity. In this review, the heterogeneous catalysts used for the gas-phase reaction or electrochemical reactions are discussed, because the liquid-phase reaction and photocatalytic reaction typically suffer from low productivity and poor durability. Because the gas-phase reaction requires a high reaction temperature of > 600 °C, obtaining good durability is important. The strategies for designing catalysts with good activity and durability will be introduced. Various materials have been tested for electrochemical conversion, and it has been shown that specific metals can produce specific products, such as Au or Ag for CO, Sn or Bi for formate, Cu for C2H4. Other unconventional catalysts for electrochemical CO2 reduction are also introduced.

The long-term reliability of MEMS devices related to the dielectric charging phenomenon is one of the main hurdles in the commercialization of these devices. This paper presents a comprehensive review of the dielectric charging and its associated reliability issues in capacitive micromachined ultrasonic transducers (CMUTs). Due to the ease of versatile fabrication and large bandwidth in immersion, CMUTs are one of the promising technologies for ultrasonic applications that require miniaturized transducers, but due to electrostatic actuation, CMUTs suffer from inherent dielectric charging issues. In this review, the effects of dielectric charging and discharging on the CMUT performance, modeling of dielectric charging, and the methods to mitigate the reliability issue due to dielectric charging are extensively discussed. The mechanisms of dielectric charging are presented in detail to demonstrate the effects of dielectric charging on the drift. Structural, operational, and material modifications suggested in the literature to improve the long-term reliability of CMUTs are also reviewed. It is concluded that these methods have improved the reliability issues to great extent but there is still a room for improvements such as through exploration of different dielectric materials.

Enhancing the luminescence efficiency and stability of solid-state phosphors with facile processability is important for various applications. Carbon-based materials might have proper optical features and durability under ambient conditions. However, carbon-based phosphors usually showed severe quenching of the photoluminescence in the absence of solvent. Alkylamine-functionalization of carbon-based phosphors can alleviate the quenching, but it also resulted in low luminous efficiency. In this study, tailoring the functional groups of carbon nanodots (CNDs) was carefully studied through alkylamine-functionalization and reduction. The reduction with NaBH4 changed the electron-withdrawing functional groups on the alkylamine-functionalized CNDs to electron-donating groups, enhancing the luminescence efficiency. The delicate modulation of alkylamine-functionalization and reduction enabled efficient and robust photoluminescence in the film without any host materials.

For steady electroconversion to value-added chemical products with high efficiency, electrocatalyst reconstruction during electrochemical reactions is a critical issue in catalyst design strategies. Here, we report a reconstruction-immunized catalyst system in which Cu nanoparticles are protected by a quasi-graphitic C shell. This C shell epitaxially grew on Cu with quasi-graphitic bonding via a gas–solid reaction governed by the CO (g) - CO2 (g) - C (s) equilibrium. The quasi-graphitic C shell-coated Cu was stable during the CO2 reduction reaction and provided a platform for rational material design. C2+ product selectivity could be additionally improved by doping p-block elements. These elements modulated the electronic structure of the Cu surface and its binding properties, which can affect the intermediate binding and CO dimerization barrier. B-modified Cu attained a 68.1% Faradaic efficiency for C2H4 at −0.55 V (vs RHE) and a C2H4 cathodic power conversion efficiency of 44.0%. In the case of N-modified Cu, an improved C2+ selectivity of 82.3% at a partial current density of 329.2 mA/cm2 was acquired. Quasi-graphitic C shells, which enable surface stabilization and inner element doping, can realize stable CO2-to-C2H4 conversion over 180 h and allow practical application of electrocatalysts for renewable energy conversion., Surface reconstruction of electrocatalysts is an important issue for electroconversion of carbon dioxide to value-added chemical products. Here the authors address this issue by using copper nanoparticles protected by self-formed quasi graphitic carbon shell for stable CO2 to C2H4 conversion.

The purpose of this study is to optimize the composition of CSA (calcium sulfoaluminate) cement with sodium silicate (Na2SiO3) and gypsum for binder jetting 3D printing. The preliminary test was carried out with an applicator to decide the proper thickness of one layer before using the 3D printer. A liquid binder was then selected to maintain the shape of the particles. Based on the results, the optimal mixture of dry materials and a liquid activator was derived through various parametric studies. For dry materials, the optimum composition of CSA cement, gypsum, and sand was suggested, and the liquid activator made with sodium silicate solution and VMA (viscosity modified agent) were selected. The setting time with gypsum and sodium silicate was controlled within 30 s. In case of the delayed setting time and the rapid setting mixture, the jetting line was printed thicker or thinner and the accuracy of the printout was degraded. In order to adjust the viscosity of the liquid activator, 10% of the VMA was used in 35% of sodium silicate solution and the viscosity of 200–400 cP was suitable to be sprayed from the nozzle. With this optimal mixture, a prototype of atypical decorative wall was printed, and the compressive strength was measured at about 7 MPa.

The current chemical industry is encountering an urgent need for CO2 reduction. Producing CO and H2 from CO2 and H2O by using renewable electricity might be a feasible solution to produce “carbon-neutral” chemicals and fuels. Developing easily scalable catalysts is key to this. In this issue of Chem Catalysis, Hahn and co-workers show that Zn–Cu catalysts enable efficient CO2 electro-reduction.

The synthesis of carbon nanotubes (CNTs) from CO2 is an attractive strategy to reduce CO2 emission, but involves extreme reaction conditions and has low scalability. This work introduces continuous chemical vapor deposition for the conversion of CO2 to CNTs using the NaBH4 reductant and NiCl2 catalyst. Multi-walled CNT fibers were synthesized from gaseous CO2 under mild conditions (500–700 °C and 1 atm). Based on in situ analyses, the proposed mechanism behind the formation of CO2-derived CNTs (CCNTs) is CO2 activation and subsequent hydroboration for the generation of methane, which can induce the growth of CCNTs on the catalyst. Their intrinsic properties give rise to an enhanced capacitive performance. The boron and oxygen of CCNTs provide a pseudo-capacitance of 302 F g−1 at a low charging rate of 0.1 A g−1 in 1 M TEABF4/acetonitrile. The mesoporous networks between CCNT fibers enhance ion transport at a high current density of 205 A g−1, leading to an outstanding energy density of 13 W h kg−1 at a high power density of 115 kW kg−1. A well-developed graphitized structure of CCNTs contributes to the reduction of the electrochemical resistance and leads to their superior stability at 65 °C during 10 000 cycles.

Operating proton exchange membrane fuel cell (PEMFC) under low humidity is important for applications of small electrical devices such as drone. Hydrophilic catalyst is prepared by depositing Pt nanoparticles on oxygen-functionalized carbon supports while commercial Pt/C is used as hydrophobic catalyst. Dual catalyst layer (dual-CL) electrodes are prepared with an inner hydrophilic layer and an outer hydrophobic layer for a membrane electrode assembly (MEA), and it is applied for PEMFC under low humidity. The dual-CL MEA shows enhanced cell performance and durability than MEAs with a single hydrophobic or hydrophilic catalyst layer. Hydrophilicity in anode is the most important to enhance performance. Keywords: PEMFC, Low humidity, Dual catalyst layer, Functionalized carbon, Drone

Silk fibroin is an excellent candidate for biomedical implantable devices because of its biocompatibility, controllable biodegradability, solution processability, flexibility, and transparency. Thus, fibroin has been widely explored in biomedical applications as biodegradable films as well as functional microstructures. Although there exists a large number of patterning methods for fibroin thin films, multilayer micropatterning of fibroin films interleaved with metal layers still remains a challenge. Herein, we report a new wafer-scale multilayer microfabrication process named aluminum hard mask on silk fibroin (AMoS), which is capable of micropatterning multiple layers composed of both fibroin and inorganic materials (e.g., metal and dielectrics) with high-precision microscale alignment. To the best of our knowledge, our AMoS process is the first demonstration of wafer-scale multilayer processing of both silk fibroin and metal micropatterns. In the AMoS process, aluminum deposited on fibroin is first micropatterned using conventional ultraviolet (UV) photolithography, and the patterned aluminum layer is then used as a mask to pattern fibroin underneath. We demonstrate the versatility of our fabrication process by fabricating fibroin microstructures with different dimensions, passive electronic components composed of both fibroin and metal layers, and functional fibroin microstructures for drug delivery. Furthermore, because one of the crucial advantages of fibroin is biocompatibility, we assess the biocompatibility of our fabrication process through the culture of highly susceptible primary neurons. Because the AMoS process utilizes conventional UV photolithography, the principal advantages of our process are multilayer fabrication with high-precision alignment, high resolution, wafer-scale large area processing, no requirement for chemical modification of the protein, and high throughput and thus low cost, all of which have not been feasible with silk fibroin. Therefore, the proposed fabrication method is a promising candidate for batch fabrication of functional fibroin microelectronics (e.g., memristors and organic thin film transistors) for next-generation implantable biomedical applications.

We use a combination of density functional theory (DFT) calculations and experimental approaches to explore the stability and electrocatalytic activity of a wide range of transition-metal single at...

With the anticipation for a more connected world through the Internet of Things, there is still a strong demand for miniaturized chemical sensors. Here, we report on a miniaturized resonant chemical sensor based on a Capacitive Micromachined Ultrasonic Transducer (CMUT) with a low operating voltage suitable for portable gas sensor applications. Previously reported CMUT chemical sensors required a DC operating voltage (16∼50 V) higher than the supply voltages of common circuits (e.g., 1.8–5 V). Thus, additional circuitry such as a charge pump circuit often was required as a part of the sensor interface circuits to supply the DC voltage to CMUT. This resulted in additional power consumption and a larger footprint. In this work, the vacuum gap of the CMUT which determines the operating voltage was reduced to 50 nm through the development of a double oxidation process with a high wafer-level yield. We achieved a significantly smaller pull-in voltage (

Proton exchange membrane fuel cells (PEMFC) are regarded as a promising renewable energy source for a future hydrogen energy society. However, highly active and durable catalysts are required for the PEMFCs because of their intrinsic high overpotential at the cathode and operation under the acidic condition for oxygen reduction reaction (ORR). Since the discovery of the exceptionally high surface activity of Pt3Ni(111), the octahedral PtNi nanoparticles have been synthesized and tested. Nonetheless, their milligram-scale synthesis method and poor durability make them unsuitable for the commercialization of PEMFCs. In this study, we focus on gram-scale synthesis of octahedral PtNi nanoparticles with Pt overlayers (PtNi@Pt) supported on the carbon, resulting in enhanced catalytic activity and durability. Such PtNi@Pt catalysts show high mass activity (1.24 A mgPt−1) at 0.9 V (vs RHE) for the ORR, compared to commercial Pt/C (0.22 A mgPt−1). Single-cell performance and electrochemical impedance spectroscopy (EIS) were also tested. The PtNi@Pt catalysts showed enhanced current density of 3.1 A cm−2 at 0.6 V in O2 flow while the commercial Pt/C had the value of 2.5 A cm−2. After 30,000 cycles of the accelerated degradation test (ADT), the PtNi@Pt still showed better performance than the commercial Pt/C in a single-cell system. The Pt layers deposition could enhance the catalytic performance and durability of octahedral PtNi nanoparticles.

The valorization of waste is of prime importance for sustainable chemistry and replacement of fossil fuel-derived counterparts. However, existing synthetic methods are critically hampered by complicated and uncontrollable chemistry arising from heterogeneous sources. Herein, we demonstrate a separation-free, straightforward, and controllable chemical approach for the valorization of lignocellulosic biomass by conversion to heteroatom-doped and undoped carbon dots (CDs) and nanoporous carbons (CNs) via a novel mechanism. The incorporation of heteroatoms such as phosphorus (P), sulfur (S), and nitrogen (N) into the CDs and steam-activated CNs (aCNs) leads to changes in the electronic and surface properties, and affords morphological control based on the doping agents, for application to CO2 capture and supercapacitors. Controlling the chemical composition and structure of the CDs results in shifts and variations in the splittings of the PL peaks and fluorescence wavelength owing to the distinct optoelectronic features. The P, N, and S-doped aCNs (P-aCN, S-aCN, and N-aCN) have robust honeycomb, entirely exfoliated reed-like, and hollow isolated reed-like structures, respectively, with unique hierarchical porosity. N-aCN exhibits the highest CO2 capacity and regeneration capability owing to the existence of basic N-containing groups and the associated structural integrity. In terms of the supercapacitive performance, P-aCN achieves the highest capacitance owing to the pseudocapacitance of the P˭O bonds, whereas S-aCN leads to the best rate and cyclic capabilities owing to the unique porous structure and S-containing group. These distinctive energy and chemical storage behaviors of the CNs highlight the importance of controlling hierarchical structure and heteroatoms for improved ultracapacitive performance.

Despite the significant impact of sodium (Na) storage systems in terms of natural abundance and environmental friendliness, high-performance pseudocapacitive mterials in organic electrolytes remain challenging. Here, we demonstrate the pseudocapacitive Na-ion storage of hierarchically structured, phosphorus-incorporating steam-activated nanoporous carbons (P-aCNs) with improved rate and cyclic capabilities in organic electrolytes. The P-aCNs with a hierarchical honeycomb structure are derived from lignocellulosic biomass via a proposed synthetic process. The prominent pseudocapacitive behaviors of the P-containing groups in organic Na-ion electrolytes are confirmed by the surface area-independent and surface-confined capacitances, distinctive redox waves, and strong binding with Na-ions. In particular, the P-aCN demonstrates the cyclic stability of 96.0% over 100 000 cycles in the full cell, achieving a high capacitance of 265.43 F g–1 and rate capability of 75%. These Na-ion pseudocapacitive features of ...

In the attempt to reduce the high-cost and improve the overall durability of Pt-based electrocatalysts for the oxygen reduction reaction (ORR), density-functional theory (DFT) calculations have been performed to study the energetics of the elementary steps that occur during ORR on TiN(100)- and TiC(100)-supported single Pt atoms. The O2 and OOH* dissociation processes on Pt/TiN(100) are determined to be non-activated (i.e. “barrier-less” dissociation) while an activation energy barrier of 0.19 and 0.51 eV is found for these dissociation processes on Pt/TiC(100), respectively. Moreover, the series pathway (which is characterized by the stable OOH* molecular intermediate) on Pt/TiC(100) is predicted to be more favorable than the direct pathway. Our electronic structure analysis supports a strong synergistic co-operative effect by these non-oxide supports (TiN and TiC) on the reduced state of the single-atom Pt catalyst, and directly influences the rudimentary ORR steps on these single-atom platinized supports.

Surface catalytic reactions typically occur on metal nanoparticles deposited on inert supports with high surface area. Recently, many studies have reported that the catalytic activity of metal nanoparticles can be enhanced significantly under light irradiation. This ‘light-assisted surface reaction’ can lower reaction temperature, potentially reducing the energy use. Light can be absorbed via intra- or inter-band transition within metal nanoparticles or direct photoexcitation of adsorbates on the surface. The absorbed energy can be relaxed through a radiative or non-radiative process; the non-radiative relaxation can produce heat or energetic electrons, enhancing the surface catalytic reaction with lower activation energy. The enhancement depends on the light intensity or wavelength. Plasmonic metals Au, Ag, and Cu have been widely studied for the ‘light-assisted surface reaction’, but composites of plasmonic metals with semiconductors or other metals such as Pt, Pd, or Ni have also been used for the surface reaction. Most recently, non-plasmonic metal Pt has shown an enhancement upon light irradiation due to the photoexcitation of electrons in the orbitals of adsorbates. The light-assisted surface reaction is still in the infancy stage, but it would surely provide more facile ways to control surface reactions and minimize the overall energy use.

Doping metal atoms into a host metal oxide lattice can enhance its catalytic activity by modulating the properties of surface oxygen. Here, Pt-doped antimony–tin oxide (Pt/Sb–SnO2) was compared with Pt-deposited tin oxide (Pt/SnO2) and Pt-deposited silica (Pt/SiO2) for the oxidation of CO and propylene. 0.1 wt% Pt was deposited in all three cases. High angle annular dark field scanning transmission electron microscopy images, diffuse reflectance infrared Fourier transform spectra, pulsed H2 chemisorption results, and X-ray photoelectron spectra indicated that Pt/Sb–SnO2 has atomically doped Pt inside the SnO2 lattice while Pt/SnO2 has Pt nanoparticles covered with SnO2 layers and Pt/SiO2 has Pt nanoparticles exposed at the SiO2 surface. Pt/Sb–SnO2 showed the best activity for CO oxidation but the poorest activity for propylene oxidation. Propylene oxidation occurred the least on Pt/Sb–SnO2 due to the lack of surface Pt sites. CO temperature-programmed reduction and O2 temperature-programmed desorption results revealed that surface oxygen is the most active on Pt/Sb–SnO2. The formation of carbonates during CO oxidation was monitored, and Pt/Sb–SnO2 showed the least amount of surface carbonates with enhanced activity and durability. Doping a minimal amount of precious metal can be an efficient strategy to control the properties of metal oxide catalysts.

Titania nanoparticles (TNPs) and titania nanotubes (TNTs) are prepared using facile sol–gel and hydrothermal methods, respectively. The individual and combined effects of TNPs and TNTs-based photoanode materials are tested for dye-sensitized solar cells applications. The higher power conversion efficiency of 5.43% is obtained for the combined photoanode (TNTs coated on to TNPs layer) than that of the individual ones.

The oxidative coupling of methane (OCM) using hybrid catalysts containing BaTiO3 perovskite and Mn-Na2WO4 exhibited high activity and high selectivity at low temperature: 66.3 % C2+ (olefins and paraffins) selectivity and 25.9 % C2+ yield at 700 °C which is 100 °C lower than that used for Mn-Na2WO4 catalysts (800 °C). Upon the preparation of complex catalysts, the insertion of Mn into BaTiO3 (BaTi(Mn)O3) and the formation of NaxMn(Ti)O2 improved the oxygen-supplying ability of the catalysts. Additionally, strong interactions between the WO42− anions and BaTi(Mn)O3 or NaxMn(Ti)O2 stabilized the WO42− anions on the surface and improved the methane activation ability of the catalysts for the favorable production of hydrocarbons. The nanoscopic modification of catalysts was confirmed using H2–temperature-programmed reduction, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy results.

As part of an effort to prepare a refrigerant with zero ozone depletion potential (ODP) and with a low global warming potential (GWP), the catalytic dehydrofluorination of 1,1,1,2,3-tetrafluoropropane (HFC-245eb) is performed to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf). Cr2O3 prepared by the sol-gel method (Cr2O3(SG)) exhibits good catalytic activity attributable to the formation of surface chromium oxyfluoride, which exhibits better catalytic activity with high-valent chromium and a larger fluorine content. The formation of chromium oxyfluoride from chromium oxide is achieved by in-situ fluorination in the early stage of dehydrofluorination, avoiding the conventional fluorination method using toxic HF.

The dry reforming of methane (DRM; CH 4 + CO 2 ↔ 2H 2 + 2CO) can be a good way to utilize greenhouse gases for the production of valuable syn-gas. Ni-based catalysts have been used for this reaction; however, the Ni size effect and support effect were highly coupled and therefore could not be observed separately. Here, a unique catalyst in which the Ni nanoparticle size and support can be varied independently was devised. Highly uniform Ni nanoparticles with sizes of 2.6, 5.2, 9.0, and 17.3 nm were tested for DRM at 800 °C without a significant change in the Ni size, and overlayers of various metal oxides, including SiO 2 , Al 2 O 3 , MgO, ZrO 2 , TiO 2 , were tested with the 5.2 nm of Ni nanoparticles. The dependence of the CH 4 or CO 2 turnover frequency on the Ni size and support was evaluated separately. The 2.6 nm Ni nanoparticles showed 4.1 times higher methane turnover frequency than those with a size of 17.3 nm. When various metal oxide overlayers were tested with the same 5.2 nm Ni, Al 2 O 3 exhibited 4.3 times higher methane turnover frequency than SiO 2 . The independent observation of the effects of the Ni nanoparticle size and support will provide valuable guidelines for designing effective methane dry reforming catalysts.

Plasmonic metal nanoparticles absorb light energy and release the energy through radiative or nonradiative channels. Surface catalytic reactions take advantage of the nonradiative energy relaxation of plasmons with enhanced activity. Particularly, binary nanoparticles are interesting because diverse integration is possible, consisting of a plasmonic part and a catalytic part. Herein, we demonstrated ethanol dehydrogenation under light irradiation using Ag–Ni binary nanoparticles with different shapes, snowman and core–shell, as plasmonic catalysts. The surface plasmon formed in the Ag part enhanced the surface catalytic reaction that occurred at the Ni part, and the shape of the nanoparticles affected the extent of the enhancement. The surface plasmon compensated the thermal energy required to trigger the catalytic reaction. The absorbed light energy was transferred to the catalytic part by the surface plasmon through the nonradiative hot electrons. The effective energy barrier was greatly reduced from 41...