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Herein, we report the significance of posttreatment in the design of high-performance Fe-N-C-type catalysts for oxygen reduction reaction (ORR). Enhancing the catalytic performance of Fe-N-C requires a postprocess for removing the aggregated iron species formed during high-temperature pyrolysis since they have a negative effect on ORR. We were able to obtain a catalyst precursor for the Fe-N-C reaction via pyrolysis with iron-adsorbed 1,8-diaminonaphthalene (FeDN), which was then treated with a concentrated HCl solution for the removal of the aggregated iron species produced. The HCl-treated FeDN was subsequently annealed at various temperatures to investigate the effect of the annealing process on the physical properties and ORR performance. The annealing temperature was a critical factor affecting the residual contents of impurities, as well as the active component and the electronic state of nitrogen. We also examined the influence of different types of acid (HCl, H2SO4, and HNO3) on the catalytic performance. The type of acid used for removing aggregated iron species had an impact on both the Fe contents and the relative nitrogen species content. Among the catalysts tested, the catalyst prepared by annealing the HCl-treated FeDN at 700°C had the best ORR performance. Although its initial ORR performance in acidic conditions was lower than that of a commercial Pt/C, it was more durable. In alkaline conditions, it delivered a comparable initial ORR performance to Pt/C and also exhibited higher durability.

Hollow Pt-based nanoparticles are known to possess the properties of high electrocatalytic activity and durability. Nonetheless, their practical applications as catalytic materials are limited because of the requirement for exhaustive preparation. In this study, we prepared carbon-supported hollow PtNix (x = the moles of the Ni precursor to the Pt precursor in the catalyst preparation step) catalysts using a one-step preparation method, which substantially reduced the complexity of the conventional method for preparing hollow Pt-based catalysts. In particular, this hollow structure formation mechanism was proposed based on extensive characterizations. The prepared catalysts were examined to determine if they could be used as electrocatalysts for the oxygen reduction reaction (ORR). Among the investigated catalysts, the acid-treated hollow PtNi3/C catalyst demonstrated the best ORR activity, which was 3 times higher and 2.3 times higher than those of the commercial Pt/C and acid-treated particulate PtNi3/C catalysts, respectively.

In this paper, we report the preparation of highly active and durable ordered intermetallic PdFe catalyst supported on carbon black for formic acid oxidation reaction (FAOR) by high-temperature hea...

Platinum alloys with other transition metals are widely used as catalysts as a promising strategy to improve the activity. However, the vulnerability of transition metals to the liquid electrolyte and fuel gases present during the device operation results in degradation of the catalytic activity. Highly stable catalyst is achieved by encapsulating the carbon-supported PtCo intermetallic core nanoparticles in a robust Pt shell. The hydride from Hantzsch ester reduces the residual Cl on the surface of the Pt skeleton and slowly forms negatively charged defect sites without damaging the core structure. Then, a secondary Pt reduction reaction via the hydride is employed to cover the activated surfaces of the Pt skeleton to optimize the shell thickness without the formation of isolated Pt nanoparticles. The PtCo@Pt with the unique Pt shell shows higher catalytic activity and durability than commercial Pt/C for oxygen reduction reaction electrocatalysts in proton exchange membrane fuel cells.

Despite recent efforts on replacing a noble Pt to less expensive catalysts (such as Pt-Ni and Pt-Co alloys) for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst still remains superior. In the present study, we have proposed the systematic procedure for designing the Ir3M (M = 3d, 4 d, 5 d transition metal) nanoalloy as Pt alternatives with enhanced ORR activity and stability using density functional theory (DFT) and experimental methods. First, we computationally optimized the surface occupied/unoccupied d states and lattice distance of the thermodynamically-stable Ir3M nanoalloy in order to achieve the wanted oxygen affinity for promoting ORR. In the next screening process, the nanoalloy prone to the segregation of inside M atom toward the surface layer was excluded, leading ultimately to the potential candidates such as the pure Ir monolayer on the top of Ir3Cr, Ir3V, Ir3Re, and Ir3Tc alloy cores. Finally, a pure Ir monolayer on the top of Ir3Cr core (which was expected to show the most enhanced ORR activity among the computationally-screened candidates) was experimentally prepared via physical vapor deposition method (PVD) and electrochemically evaluated for confirming our DFT prediction. Our synthesis successfully produced a 3 nm Ir-covered (so-called Ir skinlayer) Ir3Cr nanoparticle (Ir/Ir3Cr), which displayed the surface lattice contraction by 1.03% compared to the pure Ir case. The specific activity (at 0.7 V vs RHE) of a Ir/Ir3Cr catalyst with the very high durability (showing only 0.05% decrease from the initial activity after 3000 potential cycles) was 12.3 times higher than a Ir catalyst. The detail mechanism on the enhanced activity in Ir-M alloy was also examined. The design principle of alloy catalysts used in this study can be further extended to the screening of catalytic materials for the application to the next-level electrochemical reaction.

The strategy of employing Pt alloys with other transition metals (TMs) is advantageous owing to the enhancement of the oxygen reduction reaction (ORR) activity and the reduction of Pt usage. The ternary alloy system with early TMs can overcome stability issues and even enhance the intrinsic activity of the catalysts owing to rearrangement of electronic structures between three metal elements. Herein, efficient catalysts with V—an early TM—were successfully obtained via a plasma-induced alloying strategy. The effect of V in the PtCoV/C catalyst, which exhibits the highest ORR activity among the synthesized Pt–TM–V (TM = Co, Ni, Cu) catalysts, was determined. The addition of V induces electron rearrangement in PtCoV, inhibiting the oxidation of Co and V and optimizing the oxygen-binding energy of Pt. Thus, incorporation of V into PtCoV nanoparticles enhances the electrochemical ORR activity and stability. The catalytic performance of PtCoV achieved 966 mV of half-wave potential, 3.05 A/ mg PGM of mass activity, and 8.58 mA/ cm Pt 2 of specific activity. This systemic strategy not only proposes a novel and facile approach for the synthesis of ternary alloy catalysts but also reveals the intricacies of the catalytic activity, allowing the application of ternary alloy electrocatalysts.

Electrochemical water splitting is one of the most promising systems by which to store energy produced from sustainable sources, such as solar and wind energy. Designing robust and stable electrocatalysts is urgently needed because of the relatively sluggish kinetics of the anodic reaction, i.e. the oxygen evolution reaction (OER). In this study, we investigate the anomalous in situ activation behaviour of carbon-supported Ni2P nanoparticles (Ni2P/C) during OER catalysis in alkaline media. The activated Ni2P/C shows an exceptionally high activity and stability under OER conditions in which the overpotential needed to achieve 10 mA cm−2 was reduced from approximately 350 mV to approximately 300 mV after 8,000 cyclic voltammetric scans. In situ and ex situ characterizations indicate that the activity enhancement of Ni2P catalysts is due to a favourable phase transformation of the Ni centre to β-NiOOH, including increases in the active area induced by structural deformation under the OER conditions. These findings provide new insights towards designing transition metal/phosphide-based materials for an efficient water splitting catalyst.

Recently, nonnoble-metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co

Although thermoelectric energy conversion technology has received much attention because of its noiseless and economical operations, a low figure of merit (ZT) values of thermoelectric materials has prevented a wider variety of practical applications. Recently thermoelectric composite structures with metal or oxide nanoparticles have been widely investigated to enhance the ZT values by increasing the power factor and decreasing the thermal conductivity simultaneously. However, the difficulties in distributing the nanoparticles in the thermoelectric material matrix homogeneously have been the main problem. Herein we fabricated a thermoelectric nanocomposite structure by decorating the Mo nanoparticles on the surface of Bi2Te2.7Se0.3 powders. The Mo nanoparticles were uniformly coated on the Bi2Te2.7Se0.3 powder surface based on the sacrificial organic supporter composite consisting of Mo-coated glucose. The Mo nanoparticle/Bi2Te2.7Se0.3 composites exhibited a simultaneous decrease of thermal conductivity and electrical resistivity due to an Anderson localization effect. Therefore, the Mo nanoparticle composite structure showed enhanced ZT values by 1.31 times compared to that of bare Bi2Te2.7Se0.3 powders exhibiting a ZT value of 0.67 at 373 K.

Although the electrochemical hydrogen evolution reaction (HER) has been intensively investigated for decades as a promising hydrogen production source, its economic feasibility is still questionable because of the high cost of Pt-based electrocatalysts. Transition metal phosphides are potential replacements for Pt; however, a fundamental understanding of the active catalyst site chemistry is still lacking. Such an understanding is crucial to design robust catalytic materials. The aim of this study is to rationalize the HER on the active sites of nickel phosphide (Ni2P) nanowires. Using experimental and theoretical analyses, it can be concluded that the active site of Ni2P nanowires is an exposed Ni3P2 surface generated by the oxygenated Ni3P_P surface created during the HER. This work is a breakthrough in the efficient design of phosphide-based non-Pt catalysts for electrochemical hydrogen production.

To further improve the hydrogen-based energy system, there is an urgent need to replace precious metal-based hydrogen evolution reaction catalysts, including Pt-based materials, with nonprecious metal catalysts for electrochemical production of hydrogen from water. In this work, we propose a novel titanium-doped molybdenum phosphide (Ti–MoP) catalyst. Ti–MoP exhibits a low overpotential of 81.5 mV at 10 mA·cm−2. In particular, the remarkable improvement in material stability and electrochemical durability allows the catalyst to maintain its initial activity after prolonged exposure to air and shows accelerated electrochemical durability testing under acidic conditions. The experimental results and theoretical calculations revealed that the high durability is the result of electronically reduced Mo and P caused by Ti, and the high activity is a result of the optimization of the free energy of hydrogen adsorption (ΔGH) of the abnormally high-valence Ti.

Carbon-supported Pd3Au nanoparticle catalysts were synthesized via chemical reduction. Surface segregation of Pd in Pd3Au catalyst was achieved via heat treatment under air, Ar, CO–Ar, and CO atmospheres, in order to obtain a surface with changed structures and composition. The surface composition was analyzed by electrochemical methods, and the Pd surface composition was observed to increase from 67.2% (air (asp) sample) to 80.6% (CO sample) after heat treatment under a CO atmosphere. The CO-induced surface segregation of the Pd3Au electrocatalyst resulted in a significantly improved formic acid oxidation (from 6.93 to 18.11 mA cm–2) and stability (from 0.66 to 2.01 mA cm–2) compared to the sample prepared in air, as well as increased mass activity (from 199.20 to 520.55 A g–1), electrochemical surface area (ESAPd) (from 61.08 to 95.68 m2 gPd–1), and specific activity (from 0.33 to 0.55 mA cmPd–1), respectively. The electrochemical activities were significantly increased because of changes in the structu...

To predict ultrasonic guided waves generated by a piezoelectric transducer (PZT) in a structure accurately, the dynamic coupling between the base structure and the surface-bonded PZT must be modeled accurately and analyzed in an efficient way. For so-called smart beams, which consist of a metallic base beam and a surface-bonded PZT layer, we propose a spectral element model that has the capability to accurately predict high frequency dynamic responses and guided waves. For the spectral element model, Timoshenko beam theory is applied to both the base beam and PZT layer, and Mindlin-Herrmann rod theory is adopted to account for the effects of lateral contraction in the thickness direction of the base beam. The high accuracy of the spectral element model is validated by comparing the results of the spectral element model with conventional finite element method (FEM) results and results from the commercial finite element analysis package ANSYS. The effects of PZT-induced axial-bending coupling and structural damping on the dynamics and guided waves are then investigated using numeral simulation.

Simulation of ultrasonic guided waves in a beam-type structure with a bonded composite patch repair requires a proven modeling and analysis technique that can provide accurate dynamic solutions at a high frequency range. We developed a spectral element model for a metallic beam with a bonded composite patch by using the variational method. To that end, the governing equations of motion are derived by adopting Timoshenko beam theory for the transverse bending motion, and Mindlin–Herrmann rod theory for the longitudinal motion of the composite patched beam to take into account the effects of lateral contraction in the thickness direction. The high accuracy of the spectral element model is then evaluated by comparison with the solutions obtained by the conventional finite element method (FEM) and by the commercial finite element (FE) analysis package ANSYS. By using the spectral element model, the effects of the composite patch on the characteristics of guided waves are numerically investigated. In addition, the effects of debonding are also numerically investigated with respect to monitoring the integrity of the bonded composite patch repair.

The biggest issue in the fuel cell, which is believed to be the promising candidate as the next generation power source, is the oxygen reduction reaction (ORR). Due to the relatively high ORR activity, Pt-based catalysts are used predominantly, however, the scarcity, high cost and unsatisfactory durability of Pt make it difficult for commercialization of fuel cell. In this work, we developed a heteroatom doped carbon supported Co2P catalyst through the eco-friendly and simple method using bean sprouts. Final product exhibits excellent ORR activity and superior durability in alkaline media. The value of the half wave potential of NBSCo is 10 mV higher than that of commercial Pt/C. The excellent oxygen reduction activity is attributed to the synergistic effect of Co2P and N-doped carbon. NBSCo was applied in anion exchange membrane fuel cell (AEMFCs). At the optimized cathode composition, the NBSCo produce the max power density of 172 mW cm-2. It is considered to be competitive performance and it has demonstrated the potential for application to energy storage systems.

Polymer exchange membrane fuel cell (PEMFCs) is expected to be the promising candidate as the future clean energy sources. Especially, it is considered that the PEMFCs are suitable for applying to the transportation because of its various advantages such as high-power density, easy scale up and immediate response to change in the demand for power. However, due to the high cost of fuel cell system, it is difficult to commercialize of fuel cell automobiles. The system cost is usually depending on the usage of PGM catalyst in MEA. Herein, PtCu/C catalyst were synthesized by using sputtering method to reduce the amount of Pt which is occupying a large portion of the system cost. First, various ratio of PtCu nanoparticles were carried out onto the powder substrate by adjusting the sputter gun power. After then nanoparticles were transferred to carbon. Through the heat treatment and acid treatment, we can get mesoporous structured PtCu/C catalysts. This PtCu alloy catalyst shows similar or higher oxygen reduction reaction activity then that of commercial Pt/C even though the amount of Pt is much lower.

Recently, nonnoble-metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co2 P nanoparticles supported on heteroatom-doped carbon catalysts (NBSCP) are developed with an eco-friendly synthesis method using bean sprouts. NBSCP can be easily synthesized through metal precursor absorption and carbonization at a high temperature. It shows a very large specific surface area with various dopants such as nitrogen, phosphorus, and sulfur derived from small organic molecules. The catalyst can exhibit activity in various electrochemical reactions. In particular, excellent performance is noted for the ORR. Compared to the commercial Pt/C, NBSCP exhibits a lower onset potential, higher current density, and superior durability. This excellent ORR activity and durability is attributable to the synergistic effect between Co2 P nanoparticles and nitrogen-doped carbon. In addition, superior performance is noted on applying NBSCP to a practical anion exchange membrane fuel cell system. Through this work, the possibility of applying an easily obtained bio-derived material to energy conversion and storage systems is demonstrated.

Vine-like polyaniline (PANI) nanostructures were prepared using electrochemical polymerization on activated carbon nanofibers (ACNF) in order to use as a supercapacitor. Electrospun polyacrylonitrile (PAN)-based nanofibers were firstly carbonized and physically activated to increase the specific surface area. The PANI formed a vine-like shape and well-contacted with the surface of ACNF. The remarkably improved electrochemical performances of PANI-deposited ACNF electrode were investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge test, and electrochemical impedance analysis. The current area of the PANI-ACNF electrode is higher than that of ACNF electrode in CV curves and the specific capacitance of the PANI-ACNF was 832 F g −1 which is much higher than 353 F g −1 of ACNF at a current density of 1 A g −1 in galvanostatic charge/discharge analysis. During galvanostatic charge/discharge test of 1000 cycles at 1 A g −1 , the PANI-ACNF sample keeps its specific capacitance up to the value of 765 F g −1 (92% retention). Also, the PANI nanostructure on the ACNF substrate achieved a rapid doping/dedoping process between the surface of electrode and electrolyte ions in comparison with ACNF electrode.

IrO2, a water electrolysis catalyst, has been known to be effective in preventing corrosion of the carbon support in proton exchange membrane fuel cells (PEMFCs). Particulate IrO2 can agglomerate easily, which can decrease substantially the catalytic surface area required for oxygen evolution reaction, causing the loss of catalytic efficiency. Furthermore, agglomerated IrO2 nanoparticles can have an adverse effect on the oxygen reduction reaction by covering the active surface area of the Pt/C cathode catalyst, which is a damaging factor for the intrinsic performance of PEMFC. Carbon-supported iridium oxide, IrO2/C, which can prevent the agglomeration of Ir nanoparticles more effectively, was synthesized to overcome these problems. Compared to the cell with the Pt/C cathode only, the cell with 10 wt.% IrO2 particles and Pt/C cathode showed stronger durability during fuel starvation but the cell performance at normal operation decreased severely by 35%. The cell with the same amount of IrO2 dispersed on a carbon support, 10 wt.% IrO2/C, showed similar durability during fuel starvation maintaining the cell performance comparable to the cell using a Pt/C cathode only. Carbon-supported IrO2, IrO2/C, was more effective than IrO2 particles in both maintaining the intrinsic performance and improving the cell durability during fuel starvation.

Scientific Reports 5: Article number: 14245; published online: 18 September 2015; updated: 08 February 2016. The original version of this Article contained typographical errors in the spelling of the authors Jaeyune Ryu, Hyoung-Juhn Kim and Jong Hyun Jang, which were incorrectly given as Jae Yoon Ryu, Hyung Juhn Kim and Jong Hyung Jang.

In Pt-transition metal (TM) alloy catalysts, the electron transfer from the TM to Pt is retarded owing to the inevitable oxidation of the TM surface by oxygen. In addition, acidic electrolytes such as those employed in fuel cells accelerate the dissolution of the surface TM oxide, which leads to catalyst degradation. Herein, we propose a novel synthesis strategy that selectively modifies the electronic structure of surface Co atoms with N-containing polymers, resulting in highly active and durable PtCo nanoparticle catalysts useful for the oxygen reduction reaction (ORR). The polymer, which is functionalized on carbon black, selectively interacts with the Co precursor, resulting in Co-N bond formation on the PtCo nanoparticle surface. Electron transfer from Co to Pt in the PtCo nanoparticles modified by the polymer is enhanced by the increase in the difference in electronegativity between Pt and Co compared with that in bare PtCo nanoparticles with the TM surface oxides. In addition, the dissolution of Co and Pt is prevented by the selective passivation of surface Co atoms and the decrease in the O-binding energy of surface Pt atoms. As a result, the catalytic activity and durability of PtCo nanoparticles for the ORR are significantly improved by the electronic ensemble effects. The proposed organic/inorganic hybrid concept will provide new insights into the tuning of nanomaterials consisting of heterogeneous metallic elements for various electrochemical and chemical applications.

As the cardiovascular diseases are closely related to the blood flow characteristics such as blood flow rates and pressures in vessels, accurate prediction of the blood flow characteristics in an efficient way has been an important research issue. In this paper, one-dimensional (1D) nonlinear spectral element model is developed by using the variational approach for the blood flows in the vessels with slowly varying cross-sections. The mechanical behavior of the vessel walls is represented by the Kelvin viscoelastic model. The nonlinear spectral element model is formulated by using the frequency-dependent dynamic shape functions which are derived from the free wave solutions to the frequency-domain governing differential equations. The direct iterative method based on an alternating frequency–time method is used to obtain frequency-domain or time-domain solutions from the nonlinear spectral element model. The nonlinear spectral element model is applied to an example artery and its high accuracy is validated by comparing with the solutions obtained by the conventional finite element method. In addition, the effects of the viscoelasticity of artery wall and the nonlinear fluid terms on the blood flow characteristics in the example artery are investigated.

The use of frequency-dependent spectral element matrix (or exact dynamic stiffness matrix) in structural dynamics is known to provide extremely accurate solutions, while reducing the total number of degrees-of-freedom to resolve the computational and cost problems. Thus, in this paper, the spectral element model is developed for an axially loaded bending–shear–torsion coupled composite laminated beam which is represented by the Timoshenko beam model based on the first-order shear deformation theory. The high accuracy of the spectral element model is then numerically verified by comparing with exact theoretical solutions or the solutions obtained by conventional finite element method. For the numerical verification, the finite element model is also provided for the composite laminated beam.

Despite recent efforts on replacing a noble Pt to less expensive catalysts for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst remains superior. In this presentation, we have systematically designed the novel Ir-based ORR catalyst for the PEMFC application via the combined density functional theory (DFT) and experimental approach. First, we computationally screened the potential M element and near-surface composition in Ir3M nanoalloy (M = 3d, 4d, 5d metals) for the purpose of enhancing the activity and durability of catalyst in ORR by considering Gibbs free energy change for alloy formation process, oxygen binding energy and segregation energy of inside M element toward surface layer under vacuum and oxygen environment. Our DFT-based screening identified the pure Ir monolayer on the top of Ir3­Cr, Ir3­V, Ir3­Re, and Ir3­Tc alloy cores as the promising candidates for improving ORR activity and durability. Next, a pure Ir monolayer on the top of Ir3­Cr core (which was expected to show the most enhanced ORR activity among the computationally-screened candidates) was experimentally prepared via physical vapor deposition method (PVD) and electrochemically evaluated for confirming our DFT prediction. We successfully synthesized a 3nm Ir-covered (Ir skinlayer) Ir3­Cr nanoparticle whose surface lattice distance was contracted by 1.03% compared to the pure Ir case. The specific activity (at 0.7 V vs RHE) of a Ir skinlayer/Ir3Cr catalyst with the very high durability (showing only 0.05 % decrease from the initial activity after 3000 potential cycles) was 12.3 times higher than a Ir catalyst. The detail mechanism on the enhanced activity in Ir-M alloy was also examined. Our theoretical and experimental study highlight the general methodology for designing metal-based alloy catalysts for the application to ORR in PEMFC and such method can be further extended to the development of the next-level electrocatalyst for energy conversion.

It has been well recognized that cardiovascular diseases are closely related to blood flow characteristics. Thus, how to predict them accurately enough in an efficient way has been an important research issue. This paper introduces a 1D spectral element model for the blood flow in the human arteries with varying cross-sections. The variational approach is used to formulate the 1D spectral element model. The exact wave solutions to the frequency-domain governing differential equations are used to determine the frequency-dependent shape functions. The spectral finite element model is then applied to some example arteries to investigate flow characteristics such as blood flow rate and blood pressure through the arteries.

In this paper, the wave characteristics, divergence stability and dynamics of the oil pipelines conveying internal flow are investigated by using the spectral element method which has been known as the exact solution method. The spectral element model is formulated from the governing differential equation of motion transformed into the frequency-domain by using the discrete Fourier transform theory. The internal flow velocity at which the divergence instability occurs is derived in an analytical form. Numerical studies are conducted to investigate the wave characteristics, divergence stability and dynamics of an oil pipeline depending on its viscoelasticity and internal flow velocity.

As the blood flow characteristics are closely related to various cardiovascular diseases, it is very important to predict them accurate enough in an efficient way. Thus, this paper proposes a one-dimensional spectral element model for human blood vessels with varying cross-sections. The spectral element model is formulated by using the variational approach of finite element formulation. The wave solutions analytically solved in the frequency-domain to satisfy governing equations are used to determine the frequency-dependent interpolation functions. The spectral finite element model is then applied to an example blood vessel to investigate the blood flow rate and blood pressure through the blood vessel.

Axially moving beam-typed structures are of technical importance and present in a wide class of engineering problem. As the axial speed of a beam may significantly affect the dynamic characteristics of the structure even at a low velocity, it is important to accurately predict the dynamic characteristics and stability of such structures. In most previous studies, the net energy flux through the left-end and right-end boundaries of the finite beam over two simple supports has been implicitly assumed to be zero by completely ignoring the effects of its left (incoming) and right (outgoing) semi-infinite beam parts or by applying fixed boundary conditions for its longitudinal vibration, which seems to be very non-realistic from the physical point of view. Thus, this paper investigates the effects of the continuously incoming and outgoing semi-infinite beam parts on the dynamic characteristics and stability of an axially moving beam by using the spectral element method. The spectral element model is formulated from the equations of motion derived by using the Hamilton's principle extended for the systems of changing mass. It is numerically shown that the effects of the continuously incoming and outgoing semi-infinite beam parts should be taken into account for further accurate prediction of the dynamic characteristics and stability for such axially moving beams.

Metal and metal oxide nanoparticles (NPs) supported on high surface area carbon (NP/Cs) were prepared by the physical vapor deposition of bulk materials on an α-D-glucose (Glu) substrate, followed by the deposition of the NPs on carbon supports. Using Glu as a carrier for the transport of NPs from the bulk materials to the carbon support surfaces, ultrafine NPs were obtained, exhibiting a stabilizing effect through OH moieties on the Glu surfaces. This stabilizing effect was strong enough to stabilize the NPs, but weak enough to not significantly block the metal surfaces. As only the target materials and Glu are required in our procedure, it can be considered environmentally friendly, with the NPs being devoid of hazardous chemicals. Furthermore, the resulting NP/Cs exhibited an improvement in activity for various electrochemical reactions, mainly attributed to their high surface area.

Hydrogen (H2) production have received considerable attention resulting from the urgent need of clean and renewable energy. Water splitting is a typical and eco-friendly strategy for H2 production method through efficient acidic electrolyzers with expensive platinum group metal catalysts (Pt). Therefore, researchers have developed alternative, cheap and robust catalysts made from earth-abundant elements. Very recently, nickel phosphides (NixPy) have been proven to be promising catalysts with high activity and durability in strong acidic media (0.5M or 1M H2SO4) for hydrogen evolution reaction (HER). The crystalline phase of NixPy is an important factor for determining the activity for HER (better HER activity as higher P contents in NixPy). Herein, highly active and durable NixPy catalysts for HER are prepared using modified thermal decomposition method. In this process, nickel oxide (NiO) powder reduced to NixPy by phosphine gas (PH3) produced from sodium hypophosphite (NaH2PO2). Unlike conventional method, NiO is phosphidized from bi-located P source (NaH2PO2). One is placed upstream of furnace (traditional method) and the other is mechanically mixed with NiO powder. Based on X-ray diffraction analysis, synthesized NixPy catalysts had multi-phase crystalline structure (Ni2P, Ni5P4 and NiP2) and the NixPy with higher P content exhibited the smaller crystallite size. (Ni2P < 50 nm, Ni5P4 ~ 10 nm, NiP2 ~ 2nm). Consequently, Ni5P4 and NiP2 nanoparticles with higher HER activity are supported on micro-scaled Ni2P with better conductivity (self-supported NixPy nanoparticles), which result in improvement of electrochemical properties for HER. The NixPy catalysts showed exceptionally higher HER activity and durability in acidic media than single-phased Ni2P or Ni5P4 and this performance of the NixPy is comparable with that of Pt. Therefore, modified phosphidation method and self-supported NixPy catalyst provide new instruction for designing excellent HER catalysts.

Recently, Nanoparticles supported on high surface area carbon (NP/C) have attracted increasing interest for application in electrical energy generation and storage systems. NPs/C can be prepared by the chemical and/or physical reduction of metal ions. Typically, impregnation is widely used for preparing supported NPs. Meanwhile, fine metal NPs have been prepared by the physical vapor deposition (PVD) of corresponding metals, in the absence of metal complexes. PVD on liquid substrates, such as ionic liquids (ILs), vegetable oils, and liquid N2-cooled acetone has been reported for the preparation of NPs with a tunable composition and size distribution. However, these approaches require expensive reagents, such as metal ion complexes, solvents, and stabilizing or reducing agents, which often exhibit potential environmental and biological hazards. In this study, we present a novel, facile and totally green approach toward the synthesis of NPs/C catalyst by using the α-D-glucose (Glu). This strategy consists of: 1) The deposition of NPs on α-D-glucose powder (NP/Glu) by PVD; and 2) Transfer of the NPs from Glu to carbon supports using a mixture of NP/Glu, high surface area carbon support, and solvent. PVD is employed for the facile preparation of various types of NPs, including noble metals, alloys, and transition-metal oxides. The prepared NPs are expected to exhibit a finite size and narrow size distribution. Moreover, our NPs will not contain surfactants, which often impede catalytic reactions. This strategy can be extended to prepare NPs on a range of supports, such as carbon nanotubes (CNTs), graphene oxide (GO), and TiO2, thereby demonstrating its generality. As only the target materials and Glu are required in our procedure, it can be considered environmentally friendly, with the NPs being devoid of hazardous chemicals. In this strategy, Glu act as not only carrier for the transport of NPs from the bulk materials to the support materials but also stabilizer through their OH moieties of the Glu surfaces, which prevent the agglomeration of NPs during the synthesis process. Furthermore, the prepared NPs/C exhibited an improvement in activity for various electrochemical reactions, mainly attributed to their high surface area.

It has been well‐known that the cardiovascular diseases are closely related to the blood flow characteristics such as blood pressure and blood flow rate in a blood vessel. Thus it is very important to predict such blood flow characteristics in an accurate and efficient way. To that end, this paper develops a nonlinear one‐dimensional (1D) viscoelastic spectral element model for the blood flow in an artery with slowly varying cross‐section by using the variational approach. In this study, the mechanical behavior of the artery wall is represented by the standard solid viscoelastic model and the nonlinear spectral element model is formulated by using the frequency‐dependent dynamic shape functions which are derived from the free wave solutions to the governing differential equations in frequency‐domain. A direct iterative method is used in conjunction with the alternating frequency‐time method to obtain either frequency‐domain or time‐domain solutions from the nonlinear spectral element model.

The frequency-dependent spectral element matrix (or exact dynamic stiffness matrix) has been known to provide very accurate solutions in structural dynamics by using only a minimum number of degrees of freedom which may resolve the computation and cost problems. Thus, this paper presents a spectral element model for thin plates by using the concept of plane-waves superposition.Copyright © 2010 by ASME