56016 research outputs found
Sort by
Morphologically Controlled Efficient Air-Processed Organic Solar Cells from Halogen-Free Solvent System
No full textPower conversion efficiencies (PCEs) of glove-box (GB) processed, two-component, single-junction organic solar cells (OSCs) have recently exceeded 18%. However, their mass-scale manufacture using roll-to-roll (R2R) coating techniques is impracticable if they must be fabricated in an air-free environment. From a commercialization perspective, efficient air-processed OSCs are of much greater interest than GB-processed devices since the vast majority of R2R-manufacturing infrastructure is designed to operate in the air. Herein, it is reported that controlling the crystallinity of non-fullerene acceptors plays a key role in determining the properties of blend films. Notably, Y6-hu (a Y6-derivative) is shown to exhibits a higher degree of crystallinity when processed in air. Air-processed OSCs show an outstanding PCE of 17.38%, which, to the best of the authors' knowledge, is the highest PCE yet reported for two-component-based OSCs processed in air using halogen-free solvents. Moreover, opaque large-area OSC sub-modules with PCEs of 12.44%, and red-green-blue colored semi-transparent OSC sub-modules with PCEs of >10% are demonstrated. By understanding how morphological features relate to the charge-generation dynamics of air-processed OSCs, a new window is opened for the fabrication of efficient and stable air-processable organic electronics
Controlled synthesis of highly active bifunctional electrocatalysts for overall water splitting using coal-based activated carbons
No full textWe report a facile approach for the synthesis of highly active bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), by simply annealing mixtures of cheap coal-based activated carbons (CACs), ruthenium chloride and nickel chlorides in ammonia. The electrocatalysts consist of nitrogen doped CACs (NCACs), which are uniformly decorated with ruthenium (Ru) (with a low content of 0.3 wt%) and nickel nitride (Ni3N) nanoparticles (Ni3N/Ru/NCAC composites). The Ni3N/Ru/NCAC composites have a large surface area (853 m(2) g(-1)), which is proven to be attributable to the inherent large surface area of the CACs and the easy etching of CACs during an annealing process in ammonia. Electrochemical measurements reveal that OER electrocatalytic activities of the Ni3N/Ru/NCAC composites remarkably outperform those of the state-of-the-art IrO2 catalysts, and their HER activities were comparable to those of the benchmark Pt/C catalysts. Moreover, when the Ni3N/Ru/NCAC composites are used as both anodes and cathodes of electrolyzers for overall water splitting (OWS), they delivered a lower voltage of 1.55 V at a current density of 10 mA cm(-2) and better durability than Pt/C(-)//IrO2(+) electrodes. These outstanding OER/HER bifunctional activities and OWS performances of the Ni3N/Ru/NCAC composites are ascribed to the collaborative contributions of N, Ru, Ni3N and their large surface areas
Improvement in Acid Resistance of Polyimide Membranes: A Sustainable Cross-Linking Approach via Green-Solvent-Based Fenton Reaction
Get PDFIn this study, we present a facile surface modification method using green solvents for a commercial polyimide (PI) nanofiltration membrane to exhibit good acid stability. To enhance acid stability, the PI organic solvent nanofiltration membrane was modified using Fenton???s reaction, an oxidative cross-linking process, using environmentally friendly solvents: water and ethanol. The surface properties of the pristine and modified PI membranes were investigated and compared using various analytical tools. We studied the surface morphology using scanning electron microscopy, performed elemental analysis using X-ray photoelectron spectroscopy, investigated chemical bonds using attenuated total reflectance-Fourier transform infrared spectroscopy, and studied thermal stability using thermogravimetric analysis. The acid resistances of the pristine and modified membranes were confirmed through performance tests. The pristine PI nanofiltration membrane exposed to a 50 w/v% sulfuric acid for 4 h showed an increase in the normalized water flux to 205% and a decrease in the MgSO4 normalized rejection to 44%, revealing damage to the membrane. The membrane modified by the Fenton reaction exhibited a decline in flux and improved rejection, which are typical performance changes after surface modification. However, the Fenton-modified membrane exposed to 50 w/v% sulfuric acid for 4 h showed a flux increase of 7% and a rejection increase of 4%, indicating improved acid resistance. Furthermore, the Fenton post-treatment enhanced the thermal stability and organic solvent resistance of the PI membrane. This study shows that the acid resistance of PI membranes can be successfully improved by a novel and facile Fenton reaction using green solvents
MoDEMS: Optimizing Edge Computing Migrations for User Mobility
No full textEdge computing capabilities in 5G wireless networks promise to benefit mobile users: computing tasks can be offloaded from user devices to nearby edge servers, reducing users??? experienced latencies. Few works have addressed how this offloading should handle long-term user mobility: as devices move, they will need to offload to different edge servers, which may require migrating data or state information from one edge server to another. In this paper, we introduce MoDEMS, a system model and architecture that provides a rigorous theoretical framework and studies the challenges of such migrations to minimize the service provider cost and user latency. We show that this cost minimization problem can be expressed as an integer linear programming problem, which is hard to solve due to resource constraints at the servers and unknown user mobility patterns. We show that finding the optimal migration plan is in general NP-hard, and we propose alternative heuristic solution algorithms that perform well in both theory and practice. We finally validate our results with real user mobility traces, ns-3 simulations, and an LTE testbed experiment. Migrations reduce the latency experienced by users of edge applications by 33% compared to previously proposed migration approaches
Relative Status and Dyadic Help Seeking and Giving: The Roles of Past Helping History and Power Distance Value
No full textEmployees may not always seek and give help when needed in the dyadic context due to status disparity. Drawing on the cost and benefit framework in social exchange, we examine the effects of relative status on help seeking and giving willingness and behaviors among dyads. We argue that low-status individuals tend to provide more help but seek less help from their high-status counterparts. We further consider two moderators that can help restore the balance in cross-status helping relationships: employees??? past helping history and low power distance value. Additionally, we investigate the mediating roles of perceived entitlement and perceived obligation in the relationships between relative status and help seeking and giving, respectively. We tested our hypotheses in three studies using both dyadic field studies and experiments with employee participants. Our findings consistently demonstrate that low-status employees had a disadvantage in dyadic help-seeking and help-giving relationships. We also find that past helping history mitigated the effects of relative status in predicting help giving, whereas low power distance value attenuated the effects of relative status in predicting help seeking. Finally, we find support for the mediated effects of perceived entitlement and obligation in the hypothesized relationships
Effects of water vapor addition on downstream interaction in CO/O2 counterflow premixed flames
No full textThe effects of H2O addition on downstream interaction in counterflow premixed CO/O2 flames are investigated by varying the global strain rate (ag) and CO mole fractions (XCO,L, XCO,U) in the lower and upper nozzles, respectively. For interacting premixed CO/O2 flames, the flammable region is very narrow such that the flames cannot be sustained for ag > 11.75 s???1
When 1.0% vol H2O is added to O2/CO2 mixtures, the flammable region is appreciably extended. At low strain rate, the lean-lean and rich-rich extinction boundaries show strong and weak interactions similar to those observed previously in hydrocarbon fuels. The flammable lean-lean and rich-rich regions gradually shrink with the increase of ag. When XCO,U is small for asymmetric lean double flames at low strain rate, the extinction boundary exhibits weak interaction behavior, where the weaker flame is parasitic to the stronger flame by XCO,L. The stronger flame experiences heat loss to the weaker flame. As the strain increases, the reaction cannot be completed due to the reduction in the flow time. The thermal energy loss by incomplete reaction leads to the flame extinction. This effect changes the qualitative nature of extinction boundary as strain rate increases, resulting in the extinction boundary having only the strong interaction mode having near constant (XCO,L + XCO,U) and bending toward larger XCO,L, and eventually forming an island shape at higher strain rate. The local equilibrium temperature (LET) concept is introduced to explain these flame extinction mechanisms. Local temperature behaviors are well explained by investigating major reaction contributions to heat release rate. In all cases, LET decreases by the effect of preferential diffusion because of the Lewis number of deficient reactant being larger than unity. For asymmetric double flames, conductive heat transfer (CHT) from the stronger to weaker flame reduces the LET of the stronger flame. Flame extinction mechanism can be explained by introducing a loss ratio. For CO/O2 flames, the effects of incomplete reaction as well as preferential diffusion and CHT lead to flame extinction. For (CO/O2 + 1.0% H2O) flames with the increase of strain rate, thermal energy loss by incomplete reaction becomes appreciable, as compared with the effects of preferential diffusion and CHT
Tuning functionalized hexagonal boron nitride quantum dots for full visible-light fluorescence emission
No full textTunable photoluminescence has been observed in hexagonal boron nitride quantum dots (BNQDs), but the underlying luminescence mechanism remains elusive. In this study, we examine excited-state properties of several functionalized BNQDs models using density functional theory (DFT), time-dependent DFT, and multistate complete active space second-order perturbation theory (MS-CASPT2) methods. Unlike reported graphene quantum dots, photoluminescence of BNQDs is not affected by their sizes (<2.5 nm). Instead, the embedded single sp(3) carbon atom connecting different functional groups can tune emission colors of BNQDs, whose emission wavelength cover full range of visible light and even extend toward near-infrared region. Further analysis reveals that both exciton self-trapping and electron-hole separation decrease HOMO-LUMO energy gaps, leading to large Stokes shifts. Moreover, uneven and even hybridizations induce blue- and red-shifted emission spectra. These findings provide novel insights into full-spectrum emission of BNQDs modified with functional groups
Precursor silanization assisted synthesis and optical tuning of dual-phase perovskite nanocrystals embedded in silica matrix with high environmental stability
No full textLigand-assisted re-precipitation (LARP) is one of the most practicing techniques for synthesizing colloidal nanocrystals (NCs). But due to its fast reaction kinetics, it offers limited synthesis control. In the present study, we report a novel, precursor silanization-based room temperature technique unveiling slow crystallization of Cs4PbBr6/CsPbBr3 dual-phase nanocrystals (DPNCs) protected with a dense silica cloud-like matrix. Unlike conventional LARP, we can observe the tuneable optical bandgap of the DPNCs as a function of reaction time because of the slow reaction kinetics. The as-synthesized DPNCs exhibit a high photoluminescence quantum yield (PLQY) of 76% with ultrahigh stability while retaining similar to 100% of their initial PLQY in an ambient environment with a relative humidity of 55% for more than 1 year. DPNCs demonstrates ambient photostability of 560 h, and water stability of 25 days. This interesting precursor silanization technique developed here can be extended for the synthesis of other nanomaterials. (c) 2022 Elsevier Inc. All rights reserved
A newly designed benzodithiophene building block: tuning of torsional barrier for non-halogenated and non-aromatic solvent-processible photovoltaic polymers
No full textA new benzodithiophene (BDT) building block, 4,8-bis(5-(2-ethylhexyl)-3-fluoro-4-hexylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (3-FBDT), was designed by tailoring the positions and numbers of alkyl and F substituents by adjusting the torsional energy barrier. The incorporation of 3-FBDT into a representative BDT-based polymer donor (PBDB-T-2F) yielded a new photovoltaic copolymer (PBDB-T-2F(3/4)) with a decreased valence band level and considerably improved solubility in non-halogenated and non-aromatic solvents such as tetrahydrofuran (THF). Side-chain engineering has been widely studied to control solution processability in eco-friendly solvents, but the torsional property control of conjugated main chains has rarely been attempted. Although PBDB-T-2F showed a significant drop in power conversion efficiencies (PCEs: 17.46 to 9.73%) owing to serious aggregation caused by replacing chloroform with THF as a processing solvent, a THF-processed PBDB-T-2F(3/4) device maintained a high PCE (14.3 to 13.86%) with little detrimental effect. Charge carrier dynamics and film morphology analyses suggested that the electronic and morphological properties of PBDB-T-2F(3/4) are mainly governed by the majority moiety of the PBDB-T-2F blocks. Owing to its high solubility and outstanding photoelectrical properties, PBDB-T-2F(3/4) was successfully employed to fabricate flexible, semi-transparent, and large-area THF-processed devices. The incorporation of the 3-FBDT building block into various BDT-based photovoltaic polymers can be an effective strategy to improve the solution processability and broaden the solvent selection for fabricating eco-friendly solar cells without significantly disrupting their photoelectrical properties
Highly selective and real-time detection of 5-hydroxymethylcytosine in genomic DNA using a carbon nitride-modified gold transducer-based electrochemical sensor
No full textCancer biomarkers are crucial indicators of cancer status and progression that aid in early detection and more effective treatment of the disease. The loss of 5-hydroxymethylcytosine (5hmC), an oxidation product of 5-methylcytosine (5mC), is a recurrent epigenetic biomarker across various types of cancers. Therefore, accurately quantifying 5hmC holds great potential for various clinical applications. However, distinguishing 5hmC from 5mC using conventional methods is challenging. In this study, we developed a rapid and highly selective electrochemical sensor for label-free detection of 5hmC-enriched DNAs using a graphitic carbon nitride (g-C3N4)-modified gold transducer. Two-dimensional g-C3N4 sheets were synthesized via direct pyrolysis of urea under ambient or nitrogen atmospheres and drop-cast onto the gold electrode. Subsequently, 5hmC-containing DNAs were immobilized onto g-C3N4 via hydrogen bonding between the ???OH of 5hmC and the -NH2 of g-C3N4. The developed sensor demonstrated high sensitivity, selectivity, remarkable reproducibility, and stability, with a low oxidation potential (0.23 V) and an extremely low limit of detection (0.316 pM) for 5hmC. The sensor was also tested for its applicability to real samples using primary liver samples from mouse models, in which 5hmC levels were diminished due to either Tet gene knockout or hepatocellular carcinogenesis. The sensor effectively detected reduced genomic 5hmCs in TET-deficient livers and hepatocellular carcinomas compared to controls. Thus, this novel sensing strategy has the potential to develop clinically applicable sensors for early cancer diagnosis and prognosis evaluation by rapidly quantifying genomic 5hmC