Large Contact Area Research Articles

Combining High-Temperature Cyclic Voltammetry and Electrochemical Impedance Spectroscopy in a Setup for the Controlled Oxidation of Copper

Copper is utilized in a variety of industrial applications (e.g. heat conductors, electronic components, protective coating), where it is frequently exposed to high temperatures [1]. However, contact with the atmosphere at these high temperatures causes uncontrolled oxidation of the metal. Previous research investigated the oxidation mechanism by oxidizing at specific temperatures and then analyzing the oxide layers with a scanning electron microscope [2].This work presents a new method for the simultaneous investigation of the oxide layer formation by electrochemical impedance spectroscopy and cyclic voltammetry. The high-temperature electrochemical polarization method allows a dynamic adjustment of the oxygen partial pressure on the surface of the copper, leading to oxide layers with different compositions in respect to their thickness and defect density. The common combination of a potentiostat and a frequency response analyzer (FRA) in a three-electrode setup suffers from bandwidth limitations and artifacts [3]. Therefore, a novel method developed by Fafilek in 2009 [3] for a potential controlled electrochemical spectroscopy was adapted to our high-temperature oxidation setup. Thereby the two measuring units, potentiostat and FRA are electrically separated with regard to their grounding. Cyclic voltammograms are obtained as the result of the polarization of a sputtered copper ring versus a reference electrode, while the impedance spectra are recorded between the same copper ring (large contact area) and a copper sphere (small contact area) as shown in Figure 1. The FRA has nearly no internal resistance which ensures that both samples are adopting the same potential during the potential sweep resulting in an equal oxide formation on them. As the copper ring shows a significantly larger area than the copper sphere, the current received by the potential sweep is assumed to stem from the copper ring. Conversely, it is considered that the impedance spectra originate from the copper sphere, since the impedance of the copper ring can be neglected due to its large size. The data obtained from the potential sweep, such as the oxide structure and film thickness, are combined with the electrical properties acquired by impedance spectroscopy. This allows accurate characterization of the oxide layer that forms during electrochemically controlled oxidation.[1] Davis, J.R. ed., 2001. Copper and copper alloys. ASM international.[2] Zhu, Y., Mimura, K. and Isshiki, M., 2002. Oxidation mechanism of copper at 623-1073 K. Materials transactions, 43(9), pp.2173-2176.[3] Fafilek, G., 2009. A novel experimental method for potential controlled electrochemical impedance spectroscopy. Monatshefte für Chemie-Chemical Monthly, 140(9), pp.1121-1127. Figure 1

Proficient One-Step Heat-Up Synthesis of Manganese Sulfide Quantum Dots for Solar Cell Applications.

The necessity to develop renewable energy resources that are highly durable and flexible with superior energy density and capacitance ability has attracted considerable interest in the field of solar cell research. Semiconducting compound materials that are easily available, hazard-free and cost-effective are emerging as potential solutions to tackle this challenge. Herein, we present multiple molecular precursors used to grow manganese sulfide nanoparticles through a proficient one-step heat-up approach. For all of the tested samples, the X-ray diffraction peaks correspond to a γ-MnS hexagonal wurtzite structure. UV-Vis spectroscopy yielded absorption wavelengths of 359–420 nm and band-gap energies of 3.78–4.0 eV. Photoluminescence analysis shows characteristics of red and blue shift from 451–602 nm. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) reveal a narrow size distribution with nanosticks and large contact areas, which are critical for improved catalytic performance. The current study provides an improved pathway to a well-grown and uniform nanocrystal structure for applications in energy devices.

Investigation on performance of proton exchange membrane electrolyzer with different flow field structures

Proton exchange membrane (PEM) electrolysis provides a sustainable solution for hydrogen generation. As one of the key components, flow field should be properly designed to help distribute reactant evenly across the catalyzed reaction surface area. In this study, three-dimensional models of three flow field structures are built to simulate the internal flow velocity and pressure distribution. The electrolyzer performance of the flow fields at different operating temperature and water pressure is investigated through orthogonal experiments. The output characteristics and electrochemical behavior are investigated by measurement of polarization curves and analysis of electrochemical impedance. It is found that the flow field structure has the most considerable impact on the electrolyzer performance, followed by the operating temperature. The experimental results are consistent with the simulations, indicating that the parallel flow field has lower contact impedance and better mass transfer effect under medium and low current densities due to the large contact area of the channel and the uniform pressure distribution. PEM electrolyzer with the parallel flow field of channel width 1 mm, operating at 60 °C and 0.1 bar anode pressure has the best output performance. Under this condition, the electrolyzer’s potential reaches to 2.1 V at the current density of 1 A/cm2. This work can provide simulation and experimental support for the selection and optimization of PEM electrolyzers’ flow fields and operating conditions.

Selective solar-driven CO2 reduction mediated by 2D/2D Bi2O2SiO3/MXene nanosheets heterojunction

• An ecofriendly 2D/2D heterojunction of Bi 2 O 2 SiO 3 /Ti 3 C 2 was synthesized by a simple wet chemical process. • 2D/2D Bi 2 O 2 SiO 3 /Ti 3 C 2 heterojunction boosts the photo-reactivity of Bi 2 O 2 SiO 3 for CO 2 reduction. • The 2D/2D heterojunction own a short charge transfer distance resulting in effective charge transfer. • The enhanced photocatalytic mechanism of the system was clarified by DFT study. Photocatalytic CO 2 reduction reaction (CO 2 RR) is an environment-friendly technique for clean fuel generation. Developing low-cost and efficient photocatalyst/cocatalyst systems for boosting CO 2 RR is still a challenge. Herein, a novel Bi 2 O 2 SiO 3 /Ti 3 C 2 2D/2D heterojunction photocatalysts are successfully prepared by in situ growth of Bi 2 O 2 SiO 3 on the surface of ultrathin Ti 3 C 2 nanosheets, a kind of MXenes. The observed Bi 2 O 2 SiO 3 /Ti 3 C 2 (BOSO/TC-2) hybrids exhibit a large interface contact area companied with enhanced CO 2 adsorption capability, illustrating excellent 2D/2D interfacial charge transfer behaviors. The total yield of products obtained on the optimized BOSO/TC-2 photocatalyst is 3.8 times that of pristine Bi 2 O 2 SiO 3 nanosheets and achieve near 90% selectivity for CO over CH 3 OH without sacrificial agents, which was higher than most all inorganic Bi-based photocatalysts. Moreover, the mechanism of enhanced photocatalytic activity and reaction pathway was proposed in terms of the DFT study and in situ FTIR analysis. This work might provide new semiconductor/cocatalyst systems for selective CO 2 photoreduction to solar fuels.

A Highly Sensitive Fibrous Luminescent Probe Based on Anthracene Triarylamine for Nitroaromatic Explosives

AbstractThe rapid, sensitive, and efficient detection of nitroaromatic explosives (NAEs) is extremely important for human health and public safety; however, it is still a big challenge, especially for the detection of trace amounts of explosive vapors. In this study, a small‐molecule luminescent probe of an anthracene triarylamine derivative was synthesized and employed as a highly efficient and sensitive sensor for the detection of NAEs, including 2,4‐dinitrotoluene (DNT), 4‐nitrotoluene (4‐NT), and nitrobenzene (NB). The fluorescence intensity varied linearly along with the concentration of NAEs in the diluted tetrahydrofuran solution. The KSV values (Stern‐Volmer equation coefficient) were 2457, 1735, and 1286 M−1 for DNT, 4‐NT, and NB, respectively (DNT>4‐NT>NB). Furthermore, polystyrene/LiCl/AnPh electrospun fibrous films were manufactured and proved to be efficient fluorescence sensors for NAEs vapor. This quenching can be ascribed to the photo‐induced electron transfer (PET) process between the AnPh probe and NAEs analytes. The large contact area between the nanofibers and analytes in the film also contributed to the efficient quenching effect. This work will stimulate the design of new fluorescent probes for electrospun fibrous NAEs sensors and pave the way for their applications in future practical fields of public safety control.

Utilization of Catechol End-Functionalized PMMA as a Macromolecular Coupling Agent for Ceramic/Fluoropolymer Piezoelectric Composites

An approach based on the use of a macromolecular coupling agent and the aim to improve the interfacial adhesion between piezoelectric ceramics and piezoelectric polymer matrix in piezoelectric composites is presented. Poly(methyl methacrylate) (PMMA) bearing a catechol moiety was used as a macromolecular coupling agent, as it is known to be miscible to piezoelectric fluoropolymers and catechol groups can strongly bind to a large variety of surfaces. Thus, entanglement between the PMMA chains and the amorphous segments of the fluoropolymer would ensure the desired interfacial adhesion. Well-defined PMMA was synthesized via RAFT polymerization using 2-cyano-2-propyl dodecyl trithiocarbonate as a chain-transfer agent. The PMMA ω-chain end was then functionalized with a catechol group via a one-pot aminolysis/thia-Michael addition procedure using a dopamine acrylamide (DA) derivative as a Michael acceptor. The presence of the catechol moiety at the chain end of PMMA was controlled by 1H NMR and cyclic voltammetry measurements. The resulting PMMA-DA was then grafted onto the surface of a lead-free piezoelectric ceramic film (i.e., a thin film of H2O2-activated (Bi0.5Na0.5)TiO3 (BNT) with a large contact area). The increase of the water contact angle confirmed the efficiency of the grafting. A commercial piezoelectric copolymer P(VDF-co-TrFE) was then spin-coated onto the modified BNT surface to form a bilayer composite. The composite cross section prepared by cryofracture was examined by scanning electron microscopy and revealed that the ceramic/polymer interface of the BNT-PMMA/P(VDF-co-TrFE) bilayer composite exhibits a much better cohesion than its counterpart composite prepared from nonmodified BNT. Moreover, the grazing incidence wide-angle X-ray scattering confirmed that the copolymer crystal structure was not impacted by the presence of the PMMA-DA coupling agent. A strong piezoelectric response was locally detected by piezoresponse force microscopy. This study highlights the potential of PMMA-DA as a macromolecular coupling agent to improve the ceramic/polymer interface in piezoelectric composite materials.

Green and Scalable Template-Free Strategy to Fabricate Honeycomb-Like Interconnected Porous Micro-Sized Layered Sb for High-Performance Potassium Storage.

The tremendous volume change and severe pulverization of micro-sized Sb anode generate no stable capacity in potassium-ion batteries (PIBs). The honeycomb-like porous structure provides free spaces to accommodate its volume expansion and offers efficient ion transport, yet complex synthesis and low yield limits its large-scale application. Here, a green, scalable template-free method for designing a 3D honeycomb-like interconnected porous micro-sized Sb (porous-Sb) is proposed. Its honeycomb-like porous formation mechanism is also verified. Under hydrothermal conditions, Sb reacts with water and dissolved oxygen in water, undergoing non-homogeneous and continuous corrosion at grain boundaries, and producing soluble H2 Sb2 O6 (H2 O), which regulates the porous structure of Sb by controlling reaction time. Benefiting from its porous structure and micron size, porous-Sb anode displays large gravimetric and volumetric capacities with 655.5 mAh g-1 and 2,001.9 mAh cm-3 at 0.05 A g-1 and superior rate performance of 441.9 mAh g-1 at 2.0 A g-1 in PIBs. Furthermore, ex situ characterization and kinetic analysis uncover the small volume expansion and fast K+ reaction kinetics of porous Sb during potassiation/depotassiation, originating from its large electrolyte contact area and internal expansion mechanism. It verifies a green, scalable template-free strategy to construct honeycomb-like porous metals for energy storage and conversion.

Understanding the Origin of Low-Energy Operation Characteristics for Cr2Ge2Te6 Phase-Change Material: Enhancement of Thermal Efficiency in the High-Scaled Memory Device.

Data recording based on the phase transition between amorphous and crystalline phases in a phase-change material (PCM) generally consumes a large amount of operation energy. Heat confinement and scaling down of the contact area between the PCM and electrode are effective strategies for reducing the operation energy in the memory device. Contrary to conventional PCM, such as Ge-Sb-Te compounds (GST), Cr2Ge2Te6 (CrGT) exhibits low thermal conductivity and low-energy memory operation characteristics even in a relatively large contact area. Herein, we show that the operation energy of the CrGT-based memory device is greatly reduced by scaling down. Based on the present results, an operation energy at subpico J order, which was achieved using carbon nanotubes or graphene nanoribbon in the GST-based device, can be realized in the contact area comparable to the product level in the CrGT-based device. The numerical simulation suggests that small thermal and electrical conductivities enhance the thermal efficiency, resulting in a small operation energy for amorphization. It was also found that the residual metastable phase after the amorphization process increased the operation energy for crystallization by the simulation. In other words, these results indicate that further small operation energy can be realized in the CrGT-based device by reducing the metastable phase volume.

Metal-Free Homocoupling of Pyrene inside the Pores of Mesoporous Carbons via Electrochemical Oxidation: Application for Electrochemical Capacitors.

A pyrene dimer (PYD) is synthesized by electrochemical oxidation via homocoupling of pyrene (PY) inside the pores of MgO-templated mesoporous carbons without any metal catalysts or organic solvents. The resulting MgO-C/PYD hybrids can be used as high-performance aqueous electrochemical capacitor electrodes due to the reversible redox property of PYD and large contact area between the hybridized PYD and conductive carbon surfaces, which enable rapid charge transfer at the large contact interface. In our previous study, PY was considered to polymerize through electrochemical oxidation, and activated carbon with the pore sizes of ∼4 nm was used as a porous carbon substrate. In this study, the MgO-templated carbons have the average pore sizes of 5, 10, and 30 nm, and their large mesopore volumes can accommodate a large amount of PYD for enhancing the capacitance. To develop high-performance electrochemical capacitors, the dependence of the capacitance enhancement and the capacitance retention on the amount of PY and the pore sizes of MgO-templated carbons are studied. It is found that mesopores are necessary for fast charging/discharging, but the capacitance retention and capacitance enhancement decrease with increasing the mesopore sizes and the amount of PY due to the decreased utilization ratio of PY.

Enhanced electrochemical performance by structural design of electrolyte surface combining 3D printing technology with multi-physical modelling

Patterned electrolyte surfaces are considered an effective strategy to enhance the cell performance of solid oxide fuel cells by increasing the contact area between the electrode and electrolyte, and subsequently reducing the area specific resistance. In this study, the patterning of an 8 mol% yttria stabilised zirconia (8YSZ) electrolyte surface tailored using the stereolithography (SLA) 3D printing technology and the effects of the electrolyte surface geometry on the cell performance were investigated using multi-physical field simulation and quantitative analysis. Defect-free densified planar and concavo–convex electrolytes were successfully prepared by applying SLA, and the concavo–convex cell yielded a maximum output power density of 288.9 mW cm−2 at 850 °C, which was 46.2 % higher than that of the planar cell. The simulation results revealed significant consumption of reactants and strong electrochemical reactions at the concave surface. Moreover, the hydrogen and oxygen consumptions at the edges were greater than those at the centre of both the concave and convex surfaces, whereas the edges of the concavo–convex structure were more conducive to the electrochemical reaction. Finally, the quantitative correlation between cell performance and the influencing factors was obtained by conducting stepwise linear regression analysis. Reducing the ion transfer path length and providing a sufficiently large effective contact area proved to be a productive strategy for improving cell output performance.

Mechanical Properties of Macromolecular Separators for Lithium-Ion Batteries Based on Nanoindentation Experiment.

High tensile strength and toughness play an important role in improving the mechanical performance of separator films, such as resistance to external force, improving service life, etc. In this study, a nanoindentation experiment is performed to investigate the mechanical properties of two types of separators for LIBs based on the grid nanoindentation method. During the indentation experiment, the “sink-in” phenomenon is observed around the indenter when plastic deformation of the specimen occurs. The “sink-in” area of the polyethylene (PE) separator is larger than that of the polypropylene/polyethylene/polypropylene (PP/PE/PP) separator, i.e., the plastic area of the PE separator is larger than that of the PP/PE/PP separator. In order to select a suitable method to evaluate the hardness and elastic modulus of these separators for LIBs, three theoretical methods, including the Oliver–Pharr method, the indentation work method, and the fitting curve method, are used for analysis and comparison in this study. The results obtained by the fitting curve method are more reasonable and accurate, which not only avoids the problem of the large contact area obtained by the Oliver–Pharr method, but also avoids the influence caused by the large fitting data of the displacement–force curve and the inaccuracy of using the maximum displacement obtained by the indentation method. In addition, the obstruction ability of the PP/PE/PP separator to locally resist external load pressed into its surface and to resist micro particles, such as fine metal powder, that can enter the lithium-ion battery during the manufacturing process is greater than that of the PE separator. This research provides guidance for studying the mechanical properties and exploring the estimation method of macromolecular separators for LIBs.

In-situ processing nano-porous silicon into 3D conductive structure as high-capacity anode for lithium-ion batteries

The use of high-capacity materials in lithium-ion batteries (LIBs) is critical for achieving higher energy density. In this paper, a highly-dispersed three-dimensional (3D) graphene-wrapped porous nano-silicon composite (P-Si@rGO, where rGO is reduced graphene oxide) is synthesized from SiO2 and graphene oxide through a novel and facile approach that consists of freeze-drying and in-situ magnesium-thermal reduction. The composite is then utilized as a high-capacity anode for LIBs. A number of attractive properties are evident in this new silicon-based composite and include qualities such as individually encapsulated and highly dispersed silicon particles, close Si—O—C interactions between silicon and graphene, a porous design for the silicon structure, and a bulky porosity. These merits significantly enhance the reaction kinetics of the electrode and endow the composite with both a large electrical contact area and a sufficient buffer space to cope with the volume change during the lithiation/delithiation process. Ultimately, the P-Si@rGO sample demonstrates an excellent cycling stability, boasting a capacity of 1123 mAh g−1 at 1000 mA g−1 over 500 cycles. In this paper, materials with different morphologies are prepared by changing the magnesium-thermal reaction time, so as to study the effects of phase composition and microstructure of the composites on their electrochemical performances. Importantly, the reasons for the capacity increase seen in later stages of the cycling process are also investigated. In brief, these findings provide new insights into the future functional evolution of silicon-based anode materials.

Novel Mg-Al-Sn-Ca with enhanced mechanical properties and high corrosion rate via sub-rapid solidification for degradable magnesium alloy

Coarse eutectic phases generally exist in cast alloys and have dramatic effects on mechanical properties and corrosion behaviors. Therefore, it would be convenient and feasible to modify the mechanical properties and corrosion behaviors via tuning the eutectic phases. Herein, sub-rapid solidification (SRS) is employed to modify the microstructure, especially the eutectic phase of Mg-4.5Al-1.5Sn-0.5Ca alloy. Our results reveal that SRS followed by homogenization treatment not only reduces the grain size of α-Mg matrix, but also spheroidizes and refines the large stick-like CaMgSn phase to ~1 µm. The pronounced structure modification leads to a superior strength-ductility synergy of SRS alloy, i.e., an ultimate tensile strength (UTS) of ~236 MPa and an elongation to failure (Ɛ f ) of ~24%, in comparison to the alloy prepared via conventional solidification, with an UTS of ~220 MPa and an Ɛ f of ~21%. Moreover, the homogenized SRS alloy exhibits homogeneous corrosion with increased corrosion rates of ~145 and ~2739 mm y −1 at 25 and 93 °C, respectively. It is mainly owing to the large contact area and short distance between CaMgSn and α-Mg matrix derived from the refined CaMgSn particles in SRS alloy. Our work proposes a novel degradable magnesium alloy and a processing method to prepare degradable magnesium alloy by structure modification, which is different from conventional addition of Cu, Fe, Ni elements. The novel degradable magnesium alloy shows great advantage in avoiding the residue of large amount of insoluble coarse eutectic phases, which would block the horizontal wells. • SRS followed by T4 treatment spheroidizes and refines the large stick-like CaMgSn. • Refined grains and CaMgSn in SRS alloy contribute to strength-ductility synergy. • Refined CaMgSn in SRS alloy yields uniform corrosion with increased corrosion rate.

Ni/Co-MOF@aminated MXene hierarchical electrodes for high-stability supercapacitors

Owing to the instability and poor electronic conductivity of redox-active metal–organic frameworks (MOFs), the redox-active MOFs as a direct electrode for achieving fast and high-stability supercapacitors is a significant challenge. Herein, highly redox-active bimetallic Ni/Co metal–organic frameworks (Ni/Co-MOF) is in-situ stabilizied by 2D thin-layer aminated Ti3C2Tx to construct promising hierarchical heterostructural electrodes with superior wettability for high-performance supercapacitors. Benefitting from high conductivity and the good wettability with electrolyte of aminated MXene, the bimetallic Ni/Co-MOF can be uniformly in-situ stabilizied on the aminated MXene surface, thus guaranteeing the superior electronic and ionic transmission from the redox active center of Ni/Co-MOF, and good interfacial compatibility and large contact area. The modified MXene is beneficial to slow down the van der Waals interactions between functional groups to exfoliate the sheet-like structures. For the rapid redox reactions whereas the synergy of highly redox-active Ni/Co in bimetallic Ni/Co-MOF provides a fast redox reaction for Faradaic capacitance. Therefore, as-obtained Ni/Co-MOF@TCT-NH2 presents an ultra-high specific capacitance of 1924 F·g−1 at 0.5 A·g−1 and an ultra-long cycling stability with 10,000 cycles at 10 A·g-1 in a three-electrode system. Besides, the assembled Ni/Co-MOF@TCT-NH2//AC asymmetrical devices exhibit a maximum specific energy density of 98.1 Wh·kg−1 at 600 W·kg−1 and superior rate stability with 15,600 cycles. Such superior electrochemical performance demonstrates that the heterojunction construction of thin-layer aminated MXene to stabilize highly redox-active bimetallic MOFs is an effective strategy for MOFs as a direct electrode to enhance the energy storage.

In-Built Fabrication of MOF Assimilated Porous Hollow Carbon from Pre-Hydrolysate for Supercapacitor.

With the fast consumption of traditional fossil fuels and the urgent requirement for a low-carbon economy and sustainable development, supercapacitors are gaining more and more attention as a clean energy storage and conversion device. The research on electrode materials for supercapacitors has become a hot topic nowadays. An electrode material for a supercapacitor, comprising the ZIF-67 in-built carbon-based material, was prepared from a biomass pre-hydrolysate via a hydrothermal process. As a by-product of dissolving slurry, the pre-hydrolysate is rich in carbon, which is an excellent biomass resource. The utilization of pre-hydrolysate to prepare carbon energy materials could realize the high value utilization of pre-hydrolysate and the efficient energy conversion of biomass. Meanwhile, the cobalt-based MOF (such as ZIF-67), as a porous crystalline material, has the advantages of having a regular order, high specific surface area and controllable pore size, as well as good thermal and chemical stability. The addition of ZIF-67 modified the morphology and pore structure of the carbon, and the obtained samples showed outstanding electrochemical performance. One- and two-step synthetic processes generated specimens with a coral-like cross-linked structure and a new type of rough, hollow, dandelion-like structure, respectively, and the pore size was in the range of 2.0–5.0 nm, which is conducive to ion transport and charge transfer. In C2-ZIF-67, the hollow structures could effectively prevent the accumulation of the electrochemical active center, which could provide enough space for the shrinkage and expansion of particles to protect them from the interference of electrolytes and the formation of solid electrolyte interphase film layers. Additionally, the plush tentacle structure with low density and a large specific surface area could expose more active sites and a large electrolyte electrode contact area, and short electron and charge transport paths. Importantly, active, free electrons of small amounts of Co-MOF (1 wt%) could be stored and released through the redox reaction, further improving the electrical conductivity of Carbon-ZIF-67 materials in this work. Consequently, C2-ZIF-67 exhibited superior specific capacitance (400 F g−1, at 0.5 A g−1) and stability (90%, after 10,000 cycles).

Experimental and numerical investigation of longitudinal and annular finned latent heat thermal energy storage unit

The melting process of phase change material (PCM) in horizontal latent heat thermal energy storage (LHTES) units with longitudinal and annular fins was experimentally studied under the same fin volume condition. The PCM melting time of the annular fin unit is reduced by 13.7% compared to that of the longitudinal fin unit. The annular fins are more responsive to the increase in heat transfer fluid (HTF) inlet temperature and the longitudinal fins are more responsive to the increase in HTF flow rate. After that, numerical studies were also performed for the two LHTES units to reveal in-depth the differences in heat storage processes. The results show that the longitudinal fins perform better in the early stage due to their larger contact area with the inner tube and a denser distribution near the inner tube. But it also limits the natural convection in the latter stage. The annular fins have better natural convection performance in the latter stage and therefore have better heat storage performance. Based on the analysis, a composite fin was designed to combine the advantages of longitudinal and annular fins. Numerical results show that the newly designed fin results in a 21.6% melting time reduction compared to the longitudinal fin model and a 9.5% melting time reduction compared to the annular fin model. Finally, two principles to guide the fin design in horizontal shell-and-tube LHTES units were summarized.

Conformal BiVO4/WO3 nanobowl array photoanode for efficient photoelectrochemical water splitting

As one of the most promising photoanode candidates for photoelectrochemical (PEC) water splitting, the photocurrent density of BiVO4 still needs to be further improved in order to meet the practical application. In this work, a highly-matched BiVO4/WO3 nanobowl (NB) photoanode was constructed to enhance charge separation at the interface of the junction. Upon further modification of the BiVO4/WO3NB surface by NiOOH/FeOOH as an oxygen evolution cocatalyst (OEC) layer, a high photocurrent density of 3.05 mA cm−2 at 1.23 V vs. RHE has been achieved, which is about 5-fold higher than pristine BiVO4 in neutral medium under AM 1.5 G illumination. 5 times higher IPCE at 450 nm is also achieved compared with the BiVO4 photoanode, leading to about 95% faradaic efficiency for both H2 and O2 gas production. Systematic studies attribute the significantly enhanced PEC performance to the smaller BiVO4 particle size (< 90 nm) than its hole diffusion length (~100 nm), the improved charge separation of BiVO4 by the single layer WO3 nanobowl array and the function of OEC layers. Such WO3NB possesses much smaller interface resistance with the substrate FTO glass and larger contact area with BiVO4 nanoparticles. This approach provides new insights to design and fabricate BiVO4-based heterojunction photoanode for higher PEC water splitting performance.

CMP에서 디바이스 패턴의 실 접촉 면적 측정을 통한 평탄화 규명

Chemical Mechanical Planarization (CMP) is an essential process for device integration and planarization in a semiconductor manufacturing process. The most critical function in the CMP process, is to predict and cover the geometrical characteristics of various sizes and densities, of patterned wafers for local and global planarization. To achieve the wafer-level and die-level planarization, it is necessary to understand the contact mechanism between the CMP pads and the macro-scale patterns. In the macro-scale pattern, pad deformation is divided into two layers: an asperity layer and a bulk pad layer. Through bulk pad deformation, asperity contact distribution within the pattern is predicted. In this paper, the distribution of asperity contact according to the pattern geometrical characteristics was analyzed, through large-area real contact area (RCA) measurement. Bulk pad deformation was predicted by analyzing RCA distribution according to pattern geometry such as pattern size and density, pattern shape and step height according to the polishing time, and applied pressure. Additionally, through the distribution of the contact area and the number of contact points, the rounding phenomenon and planarization characteristics in the pattern CMP were predicted.

Analysis of Thermomechanical Cracks of Disc Brake Used in Heavy Trucks

In the present work, the study of fatigue failure of the disc brake of Volvo truck under thermomechanical effects across the disc thickness is reported. Both analytical and numerical approaches have been used. In the analytical approach, flat rigid asymmetric punch contact behavior was assumed at surface interaction, while in the numerical approach, the 3D finite element model of the vented disc type is subjected to thermomechanical cycles using ABAQUS software. Linear elastic material models were used to simulate the material's behavior under the applied pad pressure on the disc. Surface-to-surface type of contact was used for bodies that have arbitrary shapes with relatively large contact areas at disc pad interfaces. The crack initiated due to hydraulic pressure of 1.47 MPa on the disc was analyzed under mixed-mode (mode I and II) conditions. This analysis has shown that the crack propagated up to critical length of 6.02 mm and finally, failure of the disc brake was observed.

Kinetic characteristics and mechanism of copper leaching from waste printed circuit boards by environmental friendly leaching system

Copper is one of the most important valuable elements in waste printed circuit boards (WPCBs), which can be finally recovered by hydrometallurgy. Environmentally-friendly copper leaching technology has become critical. In this study, two environmentally friendly leaching systems, namely ammonia-ammonium chloride leaching system and glycine-hydrogen peroxide leaching system, on copper leaching behavior was concerned, the influence of leaching time and leaching agent concentration on leaching rate of copper concentrate with different size was revealed. In addition, a simple but effective leaching kinetics model were proposed. The results show that with the extension of time, the leaching rate increases rapidly at first (0–10 min) and then slowly (10–25 min) until stable. The optimum leaching concentration of ammonia is 3 mol/L. For ammonia leaching system, the leaching rate increased from 76.92% to 90.05% with the decrease of particle size. Meanwhile, the leaching rate increased from 77.32% to 87.93% in the glycine leaching system. Finer particles have a larger contact area, resulting in higher leaching rates. The simple leaching kinetics model proposed in this study can accurately describe the leaching process of copper. These two environmentally friendly leaching systems can be used as substitutes for traditional inorganic acids.