56016 research outputs found
Sort by
Engineering Pt Coordination Environment with Atomically Dispersed Transition Metal Sites Toward Superior Hydrogen Evolution
No full textMetal single-atom (SA) catalysts have attracted immense attention due to the high catalytic efficiency given by the desired coordination environment of each metal atom. Yet, engineering the local electronic structure of SAs and multi-atoms (MAs) still remains a challenge. Herein, an atomically dispersed catalyst comprised of Pt SAs, Pt-Pt/V dual-atoms, and small clusters supported on a vanadium and nitrogen co-doped carbon (VNC) (denoted as Pt@VNC) surface is synthesized. In the Pt@VNC, both V and Pt atoms are evenly distributed on the surface of N-doped carbon, while a few Pt atoms are linked to other Pt atoms via V, forming Pt clusters. The coordination structures of Pt atoms are modulated upon introducing atomically dispersed V sites (which generate small-sized Pt clusters) and V2O5 clusters, showing extraordinary activity for the hydrogen evolution reaction (HER). Benefiting from the low charge transfer resistance, i.e., fast reaction kinetics, due to the synergistic effect of SAs and clusters, the Pt@VNC demonstrates superior catalytic efficiency and robust durability for the HER. It requires an overpotential of only 5 mV at a current density of 10 mA cm(-2) and shows 15 times larger mass activity than the commercial 20 wt.% Pt/C catalyst. This novel catalyst-design strategy paves a new way for maximizing catalytic efficiency by optimizing the coordination structure of metal atoms
Organic-Additive-Derived Cathode Electrolyte Interphase Layer Mitigating Intertwined Chemical and Mechanical Degradation for Sulfide-Based Solid-State Batteries
No full textKeeping both the chemical and physical state of the electrode-electrolyte interface intact is one of the greatest challenges in achieving solid-state batteries (SSBs) with longer cycle lives. Herein, the use of organic electrolyte additives in the cathode electrolyte interphase (CEI) layer to mitigate the intertwined chemical and mechanical degradation in sulfide-based SSBs is demonstrated. Lithium difluorobis(oxalato)phosphate (LiDFBOP) and argyrodite (Li6PS5Cl) are used as a model system, with the LiDFBOP-derived CEI layer induced by irreversible oxidation above 4.12 V (vs Li+/Li) during the formation cycle exhibiting dual functions. This CEI layer retards the rate of chemical degradation between the cathode active particles and solid electrolytes at high charging potential and helps maintain intimate physical contact even at a low stack pressure of 0.75 MPa. The improved physical contact enables delivery of a high initial capacity, while chemical stability suppressing the sulfite or sulfate formation has a more dominant effect on the long-term cycle stability. This study presents a new perspective and strategies for designing cathode coating materials for sulfide-based SSBs beyond the typically used inorganic oxide materials
On the Brezis-Nirenberg problem for the (p, q)-Laplacian
No full textWe prove some existence and nonexistence results for a class of critical (p, q)-Laplacian problems in a bounded domain. Our results extend and complement those in the literature for model cases
Quantitative Determination of Charge Transport Interface at Vertically Phase Separated Soluble Acene/Polymer Blends
No full textInterfacial structure is critical for optimizing the electrical properties of organic field-effect transistors. In this study, the interfacial structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/polymer blends are nondestructively determined by the complementary neutron and X-ray reflectivity. The TIPS-pentacene/deuterated poly(methylmethacrylate) (d-PMMA) blends exhibit a vertically phase-separated structure with a molecularly sharp interface (interfacial roughness approximate to 5 angstrom), whereas the TIPS-pentacene/d-polystyrene (d-PS) blend intermix near the interface. Ultrahigh molecular weight d-PMMA leads to the formation of surface-segregated hexagonal spherulites of TIPS-pentacene owing to the thermodynamic factors (e.g., surface/interface energy, polarity, and viscosity) of the blending materials. The well-developed hexagonal spherulites of TIPS-pentacene on molecularly sharp d-PMMA interface result in higher field-effect mobility as compared to the dendritic crystals from d-PS blends because of the higher perfectness, coverage, and interfacial roughness of the TIPS-pentacene crystals. The approach used in this study facilitates the understanding of the charge transport mechanism at the phase-separated interfaces in soluble acene/polymer blends
Remarkably Enhanced Lattice Oxygen Participation in Perovskites to Boost Oxygen Evolution Reaction
No full textEnhancing the participation of the lattice oxygen mechanism (LOM) in several perovskites to significantly boost the oxygen evolution reaction (OER) is daunting. With the rapid decline in fossil fuels, energy research is turning toward water splitting to produce usable hydrogen by significantly reducing overpotential for other half-cells' OER. Recent studies have shown that in addition to the conventional adsorbate evolution mechanism (AEM), participation of LOM can overcome their prevalent scaling relationship limitations. Here, we report the acid treatment strategy and bypass the cation/anion doping strategy to significantly enhance LOM participation. Our perovskite demonstrated a current density of 10 mA cm(-2) at an overpotential of 380 mV and a low Tafel slope (65 mV dec(-1)) much lower than IrO2 (73 mV dec(-1)). We propose that the presence of nitric acid-induced defects regulates the electronic structure and thereby lowers oxygen binding energy, allowing enhanced LOM participation to boost OER significantly
Novel Strategy To Inhibit Transthyretin Amyloidosis via the Synergetic Effect of Chemoselective Acylation and Noncovalent Inhibitor Release
No full textStrategies for developing targeted covalent inhib-itors (TCIs), which have the advantages of a prolonged duration of action and selectivity toward a drug target, have attracted great interest in drug discovery. Herein, we report chemoselective covalent inhibitors that specifically target lysine e-amine groups that conjugate with an endogenous protein to prevent disease -causing protein misfolding and aggregation. These TCIs are unique because the benzoyl group is preferentially conjugated to Lys15 at the top of the T4 binding site within transthyretin (TTR) while simultaneously releasing a potent noncovalent TTR kinetic stabilizer. The potency of these covalent inhibitors is superior to tafamidis, the only FDA-approved drug for the treatment of hereditary TTR amyloidosis. In addition to investigations into the covalent modification of TTR via reverse-phase high-performance liquid chromatography, direct methods are performed to confirm and visualize the presumed covalent interaction via mass spectrometry and X-ray crystallography
Turbulent characteristics in complex coastal areas assessed using BSWO observations and WRF-LES simulation results
No full textStudies exploring the turbulent structure of the planetary boundary layer (PBL) over complex topographies are very limited, especially at night, because of the lack of available observations and difficulty of highly resolved simulation. In this study, micro-meteorological and turbulent characteristics over complex coastal areas were investigated based on high spatial-temporal resolution by using the Weather Research and Forecasting???Large Eddy Simulation (WRF-LES) model. Then, the simulations were compared to comprehensive observations obtained at the Boseong Standard Weather Observatory (BSWO), which is equipped with various observation facilities, such as a meteorological observation tower with a height of 307 m, and aiding ground-based remote sensing measurements used for PBL research. The comparison between the WRF-LES model results and the measurements by the wind lidar system at the BSWO showed that the LES approach in this study reproduced the spatial/vertical wind field structure and land-sea wind circulation distinctly better than the conventional PBL schemes. High turbulent kinetic energy (TKE) was observed near the surface level at night due to the increased nocturnal shear production following the evolution of land and mountain breezes. The calculated TKE from WRF-LES model was applied to identify the mixing intensity based on the mixing length and eddy diffusion coefficient within the boundary layer, and then those were evaluated with the observed extinction coefficient from the aerosol Micro-Pulse Lidar system (MPL). In addition, the planetary boundary layer height (PBLH) at night was explored by using the TKE threshold method combined with the bulk Richardson number threshold method for the daytime PBLH. Compared with the observed value from a ceilometer at the BSWO, we found that the TKE threshold method proposed in this study could yield highly accurate PBLH values, especially at night. It is also expected that the enhanced application of WRF-LES like to this study can lead to understanding and prediction with the high confidence for much detail and accurate spatiotemporal turbulent structure over complex coastal areas, which will contribute to more comprehensive air quality modeling studies
A Tractable Approach to Coverage Analysis in Downlink Satellite Networks
No full textSatellite networks are promising to provide ubiquitous and high-capacity global wireless connectivity. Traditionally, satellite networks are modeled by placing satellites on a grid of multiple circular orbit geometries. Such a network model, however, requires intricate system-level simulations to evaluate coverage performance, and analytical understanding of the satellite network is limited. Continuing the success of stochastic geometry in a tractable analysis for terrestrial networks, in this paper, we develop novel models that are tractable for the coverage analysis of satellite networks using stochastic geometry. By modeling the locations of satellites and users using Poisson point processes on the surfaces of concentric spheres, we characterize analytical expressions for the coverage probability of a typical downlink user as a function of relevant parameters, including path-loss exponent, satellite height, density, and Nakagami fading parameter. Then, we also derive a tight lower bound of the coverage probability in tractable expression while keeping full generality. Leveraging the derived expression, we identify the optimal density of satellites in terms of the height and the path-loss exponent. Our key finding is that the optimal average number of satellites decreases logarithmically with the satellite height to maximize the coverage performance. Simulation results verify the exactness of the derived expressions
Sensitivity of Real-Time Forecast for Typhoons Around Korea to Cumulus and Cloud Microphysics Schemes
No full textIn numerical weather prediction models, the typhoon track and intensity forecast performances are highly sensitive to physics parameterization schemes. To investigate the impact of physics parameterization schemes on the real-time short-term forecasts, we simulated six typhoons which directly/indirectly affected the South Korea region in recent years using the Weather Research and Forecasting (WRF) model. Three cumulus parameterization schemes (CPSs) of Kain-Fritsch (KF), Betts-Miller-Janjic (BMJ), modified Tiedtke (TDK), and two cloud microphysics parameterization schemes (MPSs) of WRF-single-moment-microphysics class 6 (WSM6), Predicted Particle Properties (P3) 1-category were selected for the sensitivity experiment. The results showed that there was a significant difference in simulated typhoon track and intensity performances depending on the physics schemes. On average, the typhoon forecast performances were improved when applying the KF scheme for CPS and WSM6 scheme for MPS in our experimental setup. The BMJ-applied runs showed the worst performances, which simulated westward shifted typhoon tracks compared to other runs. Overall, the typhoon track and intensity spreads tended to be more sensitive to CPSs and MPSs, respectively. We conducted additional sensitivity experiments using the BMJ scheme with modified reference and temperature profiles. The result showed that the overactivity of the BMJ scheme at low latitudes was reasonably reduced, leading to the improved simulation of typhoons and synoptic fields