Search

The discovery presented here revealed that oxidative potentials could facilitate redox reactions and/or oxygen evolution depending on the catalytic activity at the bismuth and ruthenium sites of Bi2Ru2O7 during electrocatalysis.

Metal oxides are some of the most promising candidates as electrocatalysts for electrical-energy-storage (EES) systems. Particularly, perovskite and pyrochlore oxides have been intensively investigated as bifunctional electrocatalysts because of their superior catalytic activities during the oxygen-reduction and -evolution reactions. However, the origin of the outstanding catalytic activities and structural changes of the materials are not clear, in part due to the difficulty in identification during electrocatalysis. In this Minireview, we present a critical overview of recent progress in understanding catalytic mechanisms of perovskite and pyrochlore oxides, highlighting the innovative in-situ X-ray absorption spectroscopy (XAS) analysis for electrochemical tests.

Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O2− ions charge compensated by extraction of Li+ ions. Recent results have shown that for 3d transition metal oxides the oxidized O2− forms molecular O2 trapped in the bulk particles. Other forms of oxidised O2− such as O22− or (O–O)n− with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O2 is formed in the bulk particles on O2‒ oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li2RuO3, Li2Ru0.5Sn0.5O3 and Li2Ir0.5Sn0.5O3. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O2, i.e. the greater covalency of the 4d and 5d compounds still favours O2. RIXS and XAS data for Li2IrO3 are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization., In this work, authors show that O-redox in 4d and 5d transition metal oxides involves the formation of molecular oxygen trapped in the particles. These results are in accord with observations in 3d oxides and show that the greater covalency of the 4d and 5d oxides does not stabilise peroxo-like species.

In recent years, the number of extreme disasters such as floods, droughts, and heat waves worldwide has been increasing. In the case of droughts, it is most important to manage water that is most closely related to human life in the event of a disaster and to anticipate and respond to damage in advance.In this study, the methods for calculating domestic and foreign life and industrial water damage were reviewed, and the methods for estimating the amount of drought damages were developed so that local disaster managers could make decisions in the event of a drought, based on the living and industrial water data, which contained quantitative data. This research was supported by a grant(2019-MOIS31-010) from Fundamental Technology Development Program for Extreme Disaster Response funded by Korean Ministry of Interior and Safety(MOIS).

To realize the full performance of Zn-air batteries, the co-presence of a highly efficient oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) in the system is critical. Although copper and nickel are known to be bifunctional catalysts for ORR and OER, sluggish reactions as a result of the exceptionally strong O=O bond on the metal surface make it difficult to achieve high system efficiency. In this study, a metal carbide layer (CuCx and NiCx ) on dendritic copper and nickel is fabricated by a facile electrodeposition process to provide efficient catalytic active sites with moderate binding energy for easy electron transfer in both the OER and the ORR. The dendritic structure provides an enriched catalytic surface and the protective metal carbide layer offers an appropriate O binding energy and durability of Zn-air batteries. Owing to the presence of the stable metal carbide surface on the dendritic metal, the CuCx /Cu and NiCx /Ni catalysts exhibited well-defined limiting current densities of -5.19 and -5.11 mA cm-2 , respectively, and improved ORR and OER activities with lower polarization than the corresponding metal catalysts. Density functional theory revealed a 0.74 eV decrease in the overpotential of NiCx /Ni-catalyzed OER reactions compared with Ni-catalyzed OER reactions. The experimental and theoretical results prove that carbide layers on dendritic metal surfaces can greatly improve the activity of ORR and OER bifunctional electrocatalysts for Zn-air batteries.

Polyhedral structure has attracted attention as a promising morphology of bifunctional electrocatalysts, which is suitable for providing catalytic active facets. However, polyhedral metal oxides have been suffering from control of their morphology. Herein, we develop micrometer-sized polyhedral bismuth ruthenate pyrochlore (P-BRO) for Zn–air batteries, which achieve highly improved catalytic activity by development of (100), (110), and (111) planes regardless of particle size. To clarify the formation mechanism of polyhedral structure, in situ transmission electron microscopy analysis is performed at 1050 °C, resulting in observation of Ostwald ripening and facets formation. Furthermore, we reveal that A- and B-site cations on low-index facets of the P-BRO could mainly contribute to catalytic activity by first-principle calculations. For practical application, we performed Zn–air flow batteries, which could effectively remove precipitated zinc oxide particles on the surface of air electrode, resulting in ...

Zn–air batteries suffer from the slow kinetics of oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER). Thus, the bifunctional electrocatalysts are required for the practical application of rechargeable Zn–air batteries. In terms of the catalytic activity and structural stability, pyrochlore oxides (A2[B2–xAx]O7–y) have emerged as promising candidates. However, a limited use of A-site cations (e.g., lead or bismuth cations) of reported pyrochlore catalysts have hampered broad understanding of their catalytic effect and structure. More seriously, the catalytic origin of the pyrochlore structure was not clearly revealed yet. Here, we report the new nanocrystalline yttrium ruthenate (Y2[Ru2–xYx]O7–y) with pyrochlore structure. The prepared pyrochlore oxide demonstrates comparable catalytic activities in both ORR and OER, compared to that of previously reported metal oxide-based catalysts such as perovskite oxides. Notably, we first find that the catalytic activity of the Y2[Ru2–xYx]O7–y is ...

Oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts including carbon-, non-precious metal-, metal alloy-, metal oxide-, and carbide/nitride-based materials are of great importance for energy conversion and storage technologies. Among them, metal oxides (e.g., perovskite and pyrochlore) are known to be promising candidates as electrocatalysts. Nevertheless, the intrinsic catalytic activities of pyrochlore oxides are still poorly understood because of the formation of undesirable phases derived from the synthesis processes. Herein, we present highly pure single crystalline pyrochlore nanoparticles with metallic conduction (Pb2Ru2O6.5) as an efficient bi-functional oxygen electrocatalyst. Notably, it has been experimentally shown that the covalency of Ru–O bonds affects the ORR and OER activities by comparing the X-ray absorption near edge structure (XANES) spectra of the metallic Pb2Ru2O6.5 and insulating Sm2Ru2O7 for the first time. Moreover, we followed the interatomic distance changes of Ru–O bonds using in situ X-ray absorption spectroscopy (XAS) to investigate the structural stabilities of the pyrochlore catalysts during electrocatalysis. The highly efficient metallic Pb2Ru2O6.5 exhibited outstanding bi-functional catalytic activities and stabilities for both ORR and OER in aqueous Zn–air batteries.

Replacing noble-metal-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is the key to developing efficient Zn-air batteries (ZABs). Here, a homogeneous ternary Ni

Understanding the interaction between a catalyst and oxygen has been a key step in designing better electrocatalysts for the oxygen reduction reaction (ORR) as well as applying them in metal-air batteries and fuel cells. Alloying has been studied to finely tune the catalysts' electronic structures to afford proper binding affinities for oxygen. Herein, we synthesized a noble-metal-free and nanosized transition metal CuFe alloy encapsulated with a graphitic carbon shell as a highly efficient and durable electrocatalyst for the ORR in alkaline solution. Theoretical models and experimental results demonstrated that the CuFe alloy has a more moderate binding strength for oxygen molecules as well as the final product, OH(-), thus facilitating the oxygen reduction process. Furthermore, the nitrogen-doped graphitic carbon-coated layer, formed catalytically under the influence of iron, affords enhanced charge transfer during the oxygen reduction process and superior durability. These benefits were successfully confirmed by realizing the catalyst application in a mechanically rechargeable Zn-air battery.

A cable-type flexible Zn-air battery with a spiral zinc anode, gel polymer electrolyte (GPE), and air cathode coated on a nonprecious metal catalyst is designed in order to extend its application area toward wearable electronic devices.

Carboxylic functional groups were introduced on multi-walled carbon nanotubes (MWCNTs) using the Ultraviolet (UV) Ozone treatment. Three melt spinning process parameters (spinning temperature, spinning distance, and the number of spinning revolutions) were evaluated by robust design (Taguchi’s method) for a composite of fibers with the objective of enhancing the mechanical strength. The optimized melt spinning parameters were obtained. The predicted strength value of CNTs–PE fibers was determined using statistical analysis, and this value is close to the verification experiment value. Thus, robust design was successfully applied in this study. The crystallization of bulk pure PE was significantly increased by the formation of fibers through mechanical drawing of the melt spinning. The addition of CNTs in the polymer matrix accelerates the nucleation and crystal growth of the polymer. No CNT alignment in the PE matrix was observed on the sectioned surface of the fiber using Scanning Electron Microscopy (SEM). The degree of crystallization of the PE polymer plays an important role in the mechanical strength enhancement.

This article discusses the effect of shear rates on the alignment of Multi-walled Carbon Nanotubes (MWCNTs) in a polyethylene (PE) matrix. Shear forces were applied with a self-constructed controllable shear extrusion system, and the degree of orientation of the MWCNTs was analyzed through image analysis of the microtome sectioned surfaces. Partially aligned MWCNTs in a PE matrix are successful fabricated in this study. It was found that the degree of alignment was increased by increasing shear rates, and an optimal shear rate was discovered. Tensile test results indicate that the mechanical properties of composites increase with an increasing degree of CNTs alignment. A partially aligned MWCNTs PE composite exhibited greater mechanical properties than randomly oriented MWCNTs. Differential scanning calorimetry analysis revealed that MWCNTs alignment by shear flow extrusion played a major role in mechanical property enhancement as compared to the crystallization effect of the polymer.

Replacing noble-metal-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is the key to developing efficient Zn-air batteries (ZABs). Here, a homogeneous ternary Ni46 Co40 Fe14 nanoalloy with a size distribution of 30-60 nm dispersed in a carbon matrix (denoted as C@NCF-900) as a highly efficient bifunctional electrocatalyst produced via supercritical reaction and subsequent heat treatment at 900 °C is reported. Among all the transition-metal-based electrocatalysts, the C@NCF-900 exhibits the highest ORR performance in terms of half-wave potential (0.93 V) in 0.1 m KOH. Moreover, C@NCF-900 exhibits negligible activity decay after 10 000 voltage cycles with minor reduction (0.006 V). In ZABs, C@NCF-900 outperforms the mixture of Pt/C 20 wt% and IrO2 , cycled over 100 h under 58% depth of discharge condition. Furthermore, density functional theory (DFT) calculations and in situ X-ray absorption spectroscopy strongly support the active sites and site-selective reaction as a plausible ORR/OER mechanism of C@NCF-900.

This article studies about the mechanical strength of different functionalized Carbon nanotubes (CNTs) reinforced Polyethylene (PE) fiber composite fabricated by melt spinning. There are four types of CNTs used, which are called as produced, carboxylated, octadecylated, polymer wrapped CNTs . Influence of mechanical drawing (melt spinning) on the mechanical strength of fibers is measured by direct comparison with mechanical strength of bulk type functionalized CNTs polymer composites, which fabricated using hot press. Dispersion and interfacial bonding strength/adhesion of CNTs with PE matrix are investigated through fracture surfaces image analysis. Functionalized CNTs composites show a significant improvement of mechanical strength of pure polymer than non functionalized CNTs polymer composite. Whereas polymer wrapped CNTs polymer composite give the highest mechanical strength in this study. Mechanical strength of bulk composites are significantly increased after mechanical drawing process indicates that melts spinning may influence on the crystallization of polymer. Fracture surface analysis revealed that additional functionalized CNTs enhanced dispersion and interfacial bonding with polymer matrix.

Excessive heat and temperature gradient may introduce failures in the components, such as cracking, delamination and warpage, eventually causing device failure. While there has been significant research toward understanding the thermal performance of many different electronic packages, the majority of these studies do not take into account the combined effects of thermal and mechanical interactions. This paper evaluates the thermal performance of flip chip packages based on the couple-field elements available in a numerical code, ANSYS, to study the interactions between temperature and stresses generated during the manufacturing process, where both two dimensional (2D) plane strain and three dimensional (3D) models of the flip chip package are considered. Compared with the model assuming uniform temperature distribution over the entire package, the model with temperature gradient provided more accurate stress profiles in the solder interconnections and underfill fillet. Further finite element studies based on the 2D model are conducted to evaluate the effects of thermal conductivity and substrate board configuration on the overall temperature and stress distribution in the package.

The reliability and mechanical performance of electronic integrated circuit (IC) package is studied based on the finite element analysis. The flip chip on board (FCOB) package – one of the most current plastic encapsulated IC packages – consists of a die, solders, a printed circuit board and underfill resin encapsulated between the die and PCB, which is subjected to a typical thermal cycle experienced during the manufacturing process. The effects of viscoelastic properties of underfill resin on mechanical responses and residual stresses of FCOB packages are specifically studied and the results are compared with those obtained for a thermoelastic underfill resin. The viscoelastic properties of underfill resin are characterized using the time–temperature superposition (TTS) technique. Both the rigid and flexible PCB substrates are considered. It is found that the elastic model underestimates significantly both the thermal stress and the strain level in the solder joints, whereas it overestimates the stress concentrations in the underfill fillet around the die corner than the viscoelastic model. When the package is subjected to an extended dwell time at an elevated temperature, a moderate loss of mechanical coupling between the die and organic substrate is expected due to the relaxation of underfill resin. The implication is that the viscoelastic nature of underfill material should be properly taken into account if the failure of solder joints and the lifetime of the package are to be accurately estimated.

This article studies the tribological behavior of functionalized multi-walled carbon nanotubes (MWNTs) reinforced epoxy matrix composites. MWNTs reinforced epoxy composites are fabricated by an injection molding process. The effects on the tribological properties of different loading concentrations and different functional groups of MWNTs are investigated by using a linear reciprocal wear tester. As increasing the concentration of MWNTs reduces wear loss, better tribological property was attained on functionalized MWNTs than as-produced MWNTs. The changes in worn surface morphology are observed in order to investigate the wear behavior. The MWNTs in the epoxy matrix near the surface are exposed and became a lubricating working film on the worn surface. The dispersion and interfacial bonding of MWNTs in the epoxy matrix are investigated from the fracture surface. The existence of MWNT at the wear surface is verified by a Raman spectrometer.

A gyroscope-free inertial measurement unit (GF-IMU) uses only accelerometers to compute specific force and angular rate. It is a low-cost inertial system, but its measurement error diverges at a rate that is an order faster than that of a conventional inertial system equipped with gyroscopes. In this paper, a redundant accelerometer-aided gyroscope-free IMU is designed to achieve a stable and bounded system. In this system, a three-axis accelerometer is used in addition to a set of six accelerometers that is typical in a conventional gyroscope-free IMU. The linear error dynamics of this aided gyroscope-free IMU is derived, and the effects of accelerometer errors are analyzed.

A numerical analysis was conducted for the resin film infusion (RFI) process using semi-cured thermosetting resin films. Mathematical models were developed for the compression of fiber and the viscosity of resin. The force balance between the fiber preform and the resin was considered to account for the deformation of fiber preform and the swell of fiber during the infusion. In an effort to locate the optimal process conditions such as the mold temperature, the fiber volume fraction, and the infusion pressure, a parametric study was carried out for the progression of resin and the infusion time for different process conditions. The numerical code developed in this study was found to be useful in determining the maximum height of vertical sections that can be infused by squeezing the liquefied resin film from the base panel.

Electrocatalysts facilitating oxygen reduction reaction (ORR) are vital components in advanced fuel cells and metal-air batteries. Here we report Ketjenblack incorporated nitrogen-doped carbon sheets derived from gelatin and apply these easily scalable materials as metal-free electrocatalysts for ORR. These carbon nanosheets demonstrate highly comparable catalytic activity for ORR as well as better durability than commercial Vulcan carbon supported Pt catalysts in alkaline media. Physico-chemical characterization and theoretical calculations suggest that proper combination of graphitic and pyridinic nitrogen species with more exposed edge sites effectively facilitates a formation of superoxide, [O2(ad)](-), via one-electron transfer, thus increasing catalytic activities for ORR. Our results demonstrate a novel strategy to expose more nitrogen doped edge sites by irregular stacked small sheets in developing better electrocatalysts for Zn-air batteries. These desirable architectures are embodied by an amphiphlilic gelatin mediated compatible synthetic strategy between hydrophobic carbon and aqueous water.

In laminated object manufacturing process (LOM) as a rapid manufacturing technique, the key process parameters for achieving a successful prototype are the roller temperature, the roller speed, the roller indentation and the laser cutting time. In addition to these basic process parameters, the material properties and the configuration of the parts affect the internal stresses, local deformations built during the process and the bonding quality. A finite element method was adopted to simulate the thermal aspects of the bonding process along with the structural deformation of the part. Thermal and stress analysis was carried out to calculate the interlaminar shear strength between layers. Experiments were conducted to verify the simulation result for the internal temperature profiles. The finished prototype was tested mechanically to measure interlaminar shear strength to estimate the bonding quality. The calculated bonding quality was compared with the bonding strength converted from the measured interlaminar shear strength, showing a good agreement between the two. In compliance with the increasing demand for high-strength working prototypes, the developed simulation code can simulate the incorporation of new material for the LOM process.