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NaCl-induced enhancement of thermodynamic and kinetic CO2 selectivity in CO2 + N-2 hydrate formation and its significance for CO2 sequestration
No full textThe importance of carbon capture and storage (CCS) has recently been emphasized owing to the ever-increasing global warming. Direct CO2 sequestration in marine sediments is an attractive option for CO2 storage, and some amount of injected CO2 can be stored in the form of solid gas hydrates. In this study, the effects of NaCl on the hydrate phase equilibria, thermodynamic and kinetic CO2 selectivity, and time-dependent growth behaviors of CO2 + N-2 hydrates were experimentally investigated to elucidate their implications for hydrate-based CO2 sequestration. The presence of NaCl shifted the equilibrium conditions of CO2 + N-2 hydrates to the higher -pressure or lower-temperature region, whereas it increased thermodynamic CO2 selectivity at a specified temperature and pressure, which was also confirmed by the pressure-composition diagram. As revealed by powder X-ray diffraction analysis, the conversion into CO2 + N-2 hydrate was lower in the saline water system because of the lower initial driving force and gradual salt enrichment in the residual solution during hydrate growth. In situ Raman spectroscopic measurements demonstrated that CO2 was kinetically selective at the early stage of CO2 + N-2 hydrate formation and that kinetic CO2 selectivity was more noticeable in the saline water system. The overall results provide an in-depth understanding of the role of salts in CO2 + N-2 hydrate formation and thus offer valuable insights into hydrate-based CO2 storage and geological CO2 sequestration
Distributed Estimation of Stochastic Multiagent Systems for Cooperative Control With a Virtual Network
No full textThis article proposes a distributed estimation algorithm that uses local information about the neighbors through sensing or communication to design an estimation-based cooperative control of the stochastic multiagent system (MAS). The proposed distributed estimation algorithm solely relies on local sensing information rather than exchanging estimated state information from other agents, as is commonly required in conventional distributed estimation methods, reducing communication overhead. Furthermore, the proposed method allows interactions between all agents, including non-neighboring agents, by establishing a virtual fully connected network with the MAS state information independently estimated by each agent. The stability of the proposed distributed estimation algorithm is theoretically verified. Numerical simulations demonstrate the enhanced performance of the estimation-based linear and nonlinear control. In particular, using the virtual fully connected network concept in the MAS with the sensing/communication range, the flock configuration can be tightly controlled within the desired boundary, which cannot be achieved through the conventional flocking methods
Immobilizing Low-Cost Metal Nitrides in Electrochemically Reconstructed Platinum Group Metal (PGM)-Free Oxy-(Hydroxides) Surface for Exceptional OER Kinetics in Anion Exchange Membrane Water Electrolysis
No full textA highly efficient and platinum group metal (PGM)-free oxygen evolution reaction (OER) electrode is developed by immobilizing Ni3N particles on the electrochemically reconstructed amorphous oxy-hydroxides surface, resulting in a twofold higher industrial relevance current density of 1 A cm(geo)(-2) at an ultra-small overpotential eta(O-2) of 271 mV, with a high turnover frequency of 2.53 s(-1), high Faradic efficiency of 99.6 % and exceptional OER stability of 1000 h in continuous electrolysis. Such a unique amorphous-crystalline interface with enriched active sites greatly facilitates electron transport and OER kinetics at the electrode-electrolyte interface. Further, combined with an efficient PGM-free cathode (MoNi4/MoO2@Ni), this electrode demonstrates a current density of 685 mA cm(geo)(-2) at 1.85 V-cell at 70 degrees C in an anion exchange membrane water electrolyzer (AEMWE) operated with ultra-pure water-electrolyte. These findings highlight the design of highly-efficient oxygen-evolving catalysts and significant advancement in the practical implementation of AEMWEs for grid-scale hydrogen production
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No full textVisible-Light-Curable Acrylic Resins toward UV-Light-Blocking Adhesives for Foldable Displays
No full textCurrent technological advances in the organic light-emitting diode panel design of foldable smartphones demand advanced adhesives with UV-blocking abilities, beyond their conventional roles of bonding objects and relieving deformation stress. However, optically clear adhesives (OCAs) with UV-blocking ability cannot be prepared using conventional UV-curing methods relying on a photoinitiator. Herein, a new acrylic resin that can be efficiently cured using visible light without oxygen removal is presented, which may be used to develop UV-blocking OCAs for use in current flexible displays. A novel photocatalyst and a specific combination of additives facilitate sufficiently rapid curing under visible light in the presence of UV-absorbers. Only a very small amount of the highly active photocatalyst is required to prepare UV-blocking OCA films with very high transparency in the visible region. Using this system, a UV-blocking OCA that nearly meets the specifications of an OCA used in commercialized foldable smartphones is realized. This technology can also be utilized in other applications that require highly efficient visible light curing, such as optically clear resins, dental resins, and 3D/4D-printable materials
Synthesis of dithioacetals via gold-catalysed hydrothiolation of vinyl sulfides
No full textThe synthesis of unsymmetrical dithioacetals based on gold catalysis is described. Although many approaches to the preparation of symmetrical dithioacetals have been developed, the methods to access unsymmetrical ones remain limited. In this regard, we report a mild synthetic method with a broad substrate scope. Screening of various gold catalysts identified a catalyst, which allows the hydrothiolation of both activated and unactivated vinyl sulfides with high efficiency. Moreover, the reaction displays broad compatibility for both aryl and aliphatic thiols
Meniscus-Guided Micro-Printing of Prussian Blue for Smart Electrochromic Display
Get PDFUsing energy-saving electrochromic (EC) displays in smart devices for augmented reality makes cost-effective, easily producible, and efficiently operable devices for specific applications possible. Prussian blue (PB) is a metal-organic coordinated compound with unique EC properties that limit EC display applications due to the difficulty in PB micro-patterning. This work presents a novel micro-printing strategy for PB patterns using localized crystallization of FeFe(CN)(6) on a substrate confined by the acidic-ferric-ferricyanide ink meniscus, followed by thermal reduction at 120 degrees C, thereby forming PB. Uniform PB patterns can be obtained by manipulating printing parameters, such as the concentration of FeCl3 center dot K3Fe(CN)(6), printing speed, and pipette inner diameter. Using a 0.1 M KCl (pH 4) electrolyte, the printed PB pattern is consistently and reversibly converted to Prussian white (CV potential range: -0.2-0.5 V) with 200 CV cycles. The PB-based EC display with a navigation function integrated into a smart contact lens is able to display directions to a destination to a user by receiving GPS coordinates in real time. This facile method for forming PB micro-patterns could be used for advanced EC displays and various functional devices
Negative thermal expansion behaviour of graphdiyne
No full textNegative thermal expansion (NTE) is an effect of a material contracting upon heating, and NTE materials are useful for the preparation of zero thermal expansion (ZTE) composite materials for applications in energy conversion and electronic devices. In this work, the NTE behaviour of graphdiyne (GDY) was observed and studied by temperature-dependent Raman spectroscopy. The characteristic Y mode in Raman spectra of GDY film exhibit blueshift with increasing temperature, in contrast to the redshift of positive thermal ex-pansion materials. Our theoretical calculations show that the dimension of GDY decreases when the temperature is elevated, and the blueshift of the Y mode is due to the contraction of GDY. The thermal expansion coefficient (TEC) of GDY in the temperature range of 180-420 K was found to be negative, - 7.18 x 10(-6) K-1 at room temperature. Our results provide a measure of the thermal property of GDY and indicate promising applications of GDY in NTE composite materials. (C) 2022 Elsevier Ltd. All rights reserved
Effects of English proficiency on motivational regulation in a videoconference-based EFL speaking class
No full textDespite the significance of motivational regulation in the development of second language speaking skills, few studies have scrutinized its relationship with an emergent learning context. This study investigates how differently tertiary level English as a foreign language (EFL) learners exert autonomy and regulate motivation by proficiency levels to acquire speaking skills in the target language via a videoconference platform. Specifically, it contrastively examines student and instructor responses to several contextual factors specific to EFL speaking class, including synchronous online video platforms, native English-speaking instructors, and an English-medium instruction (EMI) policy. Employing a mixed method, it analyzes questionnaire responses of 340 students from two Korean universities and subsequent interviews with students and their instructors. These analyses reveal that the learners employed instructor feedback and motivational self-talk most commonly to regulate their motivation while acquiring EFL speaking skills. Although students across all three levels of proficiency showed increased vulnerability to the learning context, those of the lower two were found to be less aware of the significance of the imminent context created by EMI and videoconferencing. They also sowed stronger tendency to the strategies depending on their perceptions of the contextual factors than the advanced group. These overt differences in motivational regulation among proficiency levels were hardly problematized by the instructors. Notably, their views on peer interaction via videoconference were distinctly positive, displaying a clear difference from those of the students. A discussion of these findings follows to give insight into EFL speaking instruction in the emerging higher education context
Analyses of Pore-Size-Dependent Ionic Transport in Nanopores in the Presence of Concentration and Temperature Gradients
No full textMass transport through nanopores occurs in various natural systems, including the human body. For example, ion transport across nerve cell membranes plays a significant role in neural signal transmission, which can be significantly affected by the electrolyte and temperature conditions. To better understand and control the underlying nanoscopic transport, it is necessary to develop multiphysical transport models as well as validate them using enhanced experimental methods for facile nanopore fabrication and precise nanoscale transport characterization. Here, we report a nanopore-integrated microfluidic platform to characterize ion transport in the presence of electrolyte and temperature gradients; we employ our previous self-assembled particle membrane (SAPM)-integrated microfluidic platform to produce various nanopores with different pore sizes. Subsequently, we quantify pore-size-dependent ionic transport by measuring the short circuit current (SCC) and open circuit voltage (OCV) across various nanopores by manipulating the electrolyte and temperature gradients. We establish three simple theoretical models that heavily depend on pore size, electrolyte concentration, and temperature and subsequently validate them with the experimental results. Finally, we anticipate that the results of this study would help clarify ion transport phenomena at low-temperature conditions, not only providing a fundamental understanding but also enabling practical applications of cryo-anesthesia in the near future