Efficient Transport Pathways Research Articles

The thermal properties of a UV curable acrylate composite prepared by digital light processing 3D printing

Digital light processing (DLP) 3D printing is a potential alternative to traditional thermal curing due to its short curing time and free design customization in the absence of a mold. With this in mind, the present work is aimed at identifying the optimum composition of a printable photopolymer resin with butyl acrylate as the main-chain monomer and diurethane dimethacrylate as a crosslinker to generate a thermal interface material. In particular, the influence of the crosslinker-to-monomer ratio upon the mechanical properties of the printed material is investigated. In addition, aluminum nitride (AlN) is used as the filler due to its excellent thermal conductivity, electrical insulation, and cost effectiveness. The thermal conductivity of the printed material with 30 wt% AlN is shown to be 1.43 W/mK in the in-plane direction and 0.35 W/mK in the through-plane direction. These values are respectively 477 and 350% higher than those of pure acrylate resins, and are attributed to the creation of an efficient thermal transport pathway via dispersion of the AlN particles throughout the layered acrylate resin.

Interfacial engineering Co and MnO within N,S co-doped carbon hierarchical branched superstructures toward high-efficiency electrocatalytic oxygen reduction for robust Zn-air batteries

Electronic regulation via interfacial formation is identified as a versatile strategy to improve the electrocatalytic activity. Herein, we report a feasible electrospinning-pyrolysis approach for the in-situ immobilization of Co/MnO hetero-nanoparticles onto N,S co-doped carbon nanotubes/nanofiber-integrated hierarchical branched superstructures (abbreviated as Co/MnO@N,S-C NT/CNFs hereafter). The simultaneous realization of interfacial engineering and nanocarbon hybridization renders the fabricated Co/MnO@N,S-C NT/CNFs with abundant firmly anchored active sites, modified electronic configuration, improved electric conductivity, efficient mass transport pathways, and significantly reinforced stability. Profiting from the compositional synergy and architectural advantages, the Co/MnO@N,S-C NT/CNFs exhibit outstanding ORR activity, superior tolerance to methanol, and excellent long-term stability in KOH electrolyte. More encouragingly, as a proof-of-concept demonstration, the rechargeable aqueous and flexible all-solid-state Zn-air batteries using Co/MnO@N,S-C NT/NFs + RuO2 as the air-cathode afford higher power densities, larger specific capacities and superb cycling stability, outperforming the state-of-the-art Pt/C + RuO2 counterparts. This work demonstrates the great contribution of heterointerfaces for oxygen electrocatalysis.

Facile synthesis of aminophenylboronic decorated electrospun CoFe2O4 spinel nanofibers with enhanced electrocatalytic performance for glucose electrochemical sensor application

CoFe2O4 nanoparticles uniformly decorated on the carbon nanofibers have been fabricated via electrospinning and subsequent calcination process. Aminophenylboric acid (APBA), as a glucose specific molecule, was modified on the surface of CoFe2O4@N-CNFs via the vapor chemical crosslinking approach. The fabricated APBA@CoFe2O4@N-CNFs hybrids were explored as electrocatalyst for the non-enzymatic electrochemical determination of glucose. Because of the synergistic effect of various materials, APBA@CoFe2O4@N-CNFs exhibits excellent non-enzymatic glucose detection properties involving sensitivity, selectivity, response time and linear correction. The remarkable electrocatalytic capability was mainly ascribed to the fact that N-CNFs with excellent electrical conductivity acted as a matrix guided the growth of CoFe2O4 nanoparticles, thus improving the dispersibility of CoFe2O4 and providing an enhanced efficient electron transport pathway. The spinel-type CoFe2O4 nanoparticles provided enhanced conductivity, while the porous structure of N-CNFs supplied the abundant active sites, which further improved the electrocatalysis. Besides, aminophenylboric acid, as a recognition molecule, was beneficial to the specific recognition of glucose molecules. Therefore, APBA@CoFe2O4@N-CNFs is promising as an important candidate material for glucose sensors due to its excellent performance, high efficiency and simple manufacturing process.

Enhancing the performances of all-small-molecule ternary organic solar cells via achieving optimized morphology and 3D charge pathways

With the emergence of non-fullerene acceptors (NFAs), the power conversion efficiencies (PCEs) of all-small-molecule organic solar cells (ASM-OSCs) have been significantly improved. However, due to the strong crystallinities of small molecules, it is much more challenging to obtain the ideal phase separation morphology and efficient charge transport pathways for ASM-OSCs. Here, a high-efficiency ternary ASM-OSC has been successfully constructed based on H11/IDIC-4F system by introduction of IDIC with a similar backbone as IDIC-4F but weak crystallinity. Notably, the addition of IDIC has effectively suppressed large-scale phase aggregation and optimized the morphology of the blend film. More importantly, the molecular orientation has also been significantly adjusted, and a mixed face-on and edge-on orientation has formed, thus establishing a more favorable three-dimensional (3D) charge pathways in the active layer. With these improvements, the enhanced short-circuit current density (JSC) and fill factor (FF) of the ternary system have been achieved. In addition, because of the high lowest unoccupied molecular orbital (LUMO) energy level of IDIC as well as the alloyed structure of the IDIC and IDIC-4F, the promoted open circuit voltage (VOC) of the ternary system has also been realized.

Charge Trapping in a Low-Crystalline High-Mobility Conjugated Polymer and Its Effects on the Operational Stability of Organic Field-Effect Transistors.

The effects of the microstructure of conjugated polymer thin films on charge trapping and operational stability of organic field-effect transistors (OFETs) are investigated. Device characteristics of OFETs based on two model conjugated polymers, poly(3-hexylthiophene) (P3HT) and a random 3-hexylthiophene-thiophene copolymer (RP33), are compared. P3HT films have high crystallinity and long-range molecular order, whereas RP33 films have low crystallinity and short-range molecular order as well as enhanced polymer backbone planarity. Experimental evidence shows that although the microstructure of the RP33 film provides efficient charge transport pathways, its high degree of structural disorder causes severe shallow trapping of charge carriers, which results in its inferior stability under bias stress. This study demonstrates that low-crystalline conjugated polymers with short-range order can provide a high charge-carrier mobility but at the same time be inappropriate for practical OFETs because of their poor intrinsic operational stability.

Identifying Efficient Transport Pathways in Early-Wood Timber: Insights from 3D X-ray CT Imaging of Softwood in the Presence of Flow

Wider use of timber has the potential to greatly reduce the embodied carbon of construction. Improved chemical treatment could help overcome some of the barriers to wider application of timber, by furthering the durability and/or mechanical properties of this natural material. Improving timber treatment by treating the whole volume of a piece of timber, or tailored sections thereof, requires sound understanding and validated modelling of the natural paths for fluid flow through wood. In this study we carry out a robust analysis of three-dimensional X-ray CT measurements on kiln-dried softwood in the presence of flow and identify small portions of early-wood which are uniquely capable of transporting fluids—herein ‘efficient transport pathways’. We successfully model the effects of these pathways on the liquid uptake by timber by introducing a spatial variability in the amount of aspiration of the bordered pits following kiln drying. The model demonstrates that fluid advances along these efficient transport paths between 10 and 30 times faster than in the remainder of the timber. Identifying these efficient transport pathways offers scope to improve and extend the degree to which timber properties are enhanced at an industrial scale through processes to impregnate timber.

Strategies for Controlling Through-Space Charge Transport in Metal-Organic Frameworks via Structural Modifications.

In recent years, charge transport in metal-organic frameworks (MOFs) has shifted into the focus of scientific research. In this context, systems with efficient through-space charge transport pathways resulting from π-stacked conjugated linkers are of particular interest. In the current manuscript, we use density functional theory-based simulations to provide a detailed understanding of such MOFs, which, in the present case, are derived from the prototypical Zn2(TTFTB) system (with TTFTB4− corresponding to tetrathiafulvalene tetrabenzoate). In particular, we show that factors such as the relative arrangement of neighboring linkers and the details of the structural conformations of the individual building blocks have a profound impact on bandwidths and charge transfer. Considering the helical stacking of individual tetrathiafulvalene (TTF) molecules around a screw axis as the dominant symmetry element in Zn2(TTFTB)-derived materials, the focus, here, is primarily on the impact of the relative rotation of neighboring molecules. Not unexpectedly, changing the stacking distance in the helix also plays a distinct role, especially for structures which display large electronic couplings to start with. The presented results provide guidelines for achieving structures with improved electronic couplings. It is, however, also shown that structural defects (especially missing linkers) provide major obstacles to charge transport in the studied, essentially one-dimensional systems. This suggests that especially the sample quality is a decisive factor for ensuring efficient through-space charge transport in MOFs comprising stacked π-systems.

Unraveling the influence of non-fullerene acceptor molecular packing on photovoltaic performance of organic solar cells

In non-fullerene organic solar cells, the long-range structure ordering induced by end-group π–π stacking of fused-ring non-fullerene acceptors is considered as the critical factor in realizing efficient charge transport and high power conversion efficiency. Here, we demonstrate that side-chain engineering of non-fullerene acceptors could drive the fused-ring backbone assembly from a π–π stacking mode to an intermixed packing mode, and to a non-stacking mode to refine its solid-state properties. Different from the above-mentioned understanding, we find that close atom contacts in a non-stacking mode can form efficient charge transport pathway through close side atom interactions. The intermixed solid-state packing motif in active layers could enable organic solar cells with superior efficiency and reduced non-radiative recombination loss compared with devices based on molecules with the classic end-group π–π stacking mode. Our observations open a new avenue in material design that endows better photovoltaic performance.

Nitrogen-rich graphene aerogel with interconnected thousand-layer pancake structure as anode for high performance of lithium-ion batteries

Nitrogen-rich graphene aerogel with interconnected thousand-layer pancake structure (NTLP) was designed and fabricated through hydrothermal template self-assembly method using polystyrene (PS) nanospheres as structural guiding templates and ethylenediamine (EDA) as a nitrogen resource for in-situ N-doping. NTLP exhibits significantly improved electrochemical performance of lithium-ion storage including a highly reversible capacity of 1147 ​mA ​h g−1 at 0.1 ​A ​g−1, and favorable rate capability of 258 ​mA ​h g−1 even at a large current density of 5 ​A ​g−1. Moreover, the reversible capacity is retained at 501 ​mA ​h g−1 after 1100 cycles at 1 ​A ​g−1. PS template effectively alleviates the aggregation of graphene membrane, meanwhile forms peculiar thousand-layered cake structure with high specific surface area and well-controlled pores. Precisely owing to the unique structure with three-dimensionally (3D) interconnected holey graphene network and the introduction of abundant N-doping (about 7 atom%) into the graphene walls, NTLP significantly enhances the electrochemical activity and effectively accelerates the diffusions of both lithium-ions and electrons. The high performance strongly indicates that NTLP possesses a promising perspective for lithium-ion batteries with excellent electronic conductivity, efficient transport pathways of electrons and ions as well as superior reversible lithium storage capacity.

Composite polymer electrolytes reinforced by hollow silica nanotubes for lithium metal batteries

Herein, a series of one-dimensional silica nanotubes (SNts) with hollow nanostructures and high uniformity are synthesized by etching the rod-shaped nickel-hydrazine complex, and composite polymer electrolytes (CPEs) are prepared by introducing SNts and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into poly(ethylene oxide) (PEO) skeleton. The CPEs obey Vogel-Tamman-Fulcher empirical equation and the ionic conductivity is demonstrated to be maximum of 4.35 × 10−4 S cm−1 with the longest SNts (270 nm) as fillers at 30 °C, which is significantly higher than that of PEO/LiTFSI (6.13 × 10−8 S cm−1) and PEO/LiTFSI/silica nanoparticles (SNps) (1.07 × 10−6 S cm−1). The connection between SNts among the whole composite contributes the efficient transport pathway to lithium ions. Furthermore, the fabricated cell exhibits good cyclability and rate capability. The SNts based CPEs represent a new design idea for solid-state electrolytes and offers opportunities for lithium metal batteries in the future.

Synthesis and property of novel gas mixed-matrix membrane with carbon nanotubes

Mixed matrix membranes (MMMs) were fabricated by incorporating carboxylated multi-walled carbon nanotubes (MWCNTs) into a poly (arylene fluorene ether ketone) that contained amino groups (Am-PAFEK) matrix to improve CO2 separation performance. The combination of MWCNTs and Am-PAFEK exerted a favorable synergistic effect on the permeability and selectivity of membranes. The extraordinary smooth wall of MWCNTs acts as a highway through which gas passes, providing better permeability. The Am-PAFEK matrix itself has a dense internal structure that provides high gas selectivity. MWCNTs particles evenly distributed among the Am-PAFEK membrane due to the non-covalent bond interaction between the amino and carboxyl group. Efficient CO2 transport pathways were constructed by homogeneous dispersion of MWCNTs with in MMMs, leading to maintained good selectivity and enhanced permeability. When the amount of carbon nanotubes added was 3 wt.%, that increased by above 60% in comparison to the Am-PAFEK membrane permeability, the CO2/CH4 and CO2/N2 selectivity of the Am-PAFEK/MWCNTs-3% membrane achieved 35.02 and 30.09, respectively. Therefore, the strategy of blending MWCNTs with Am-PAFEK exhibited a promising approach for improving gas permeability.

High-Performance Ultraviolet Photodetector Based on a Zinc Oxide Nanoparticle@Single-Walled Carbon Nanotube Heterojunction Hybrid Film.

A hybrid film consisting of zinc oxide nanoparticles (ZnO NPs) and carbon nanotubes (CNTs) is formed on a glass substrate using a simple and swift spin coating process for the use in ultraviolet photodetectors (UV PDs). The incorporation of various types of CNTs into ZnO NPs (ZnO@CNT) enhances the performance of UV PDs with respect to sensitivity, photoresponse, and long-term operation stability when compared with pristine ZnO NP films. In particular, the introduction of single-walled CNTs (SWNTs) exhibits a superior performance when compared with the multiwalled CNTs (MWNTs) because SWNTs can not only facilitate the stability of free electrons generated by the O2 desorption on ZnO under UV irradiation owing to the built-in potential between ZnO and SWNT heterojunctions, but also allow facile and efficient transport pathways for electrons through SWNTs with high aspect ratio and low defect density. Furthermore, among the various SWNTs (arc-discharged (A-SWNT), Hipco (H-SWNT), and CoMoCat (C-SWNT) SWNTs), we demonstrate the ZnO@A-SWNT hybrid film exhibits the best performance because of higher conductivity and aspect ratio in A-SWNTs when compared with those of other types of SWNTs. At the optimized conditions for the ZnO@A-SWNT film (ratio of A-SWNTs and ZnO NPs and electrode distance), ZnO@A-SWNT displays a sensitivity of 4.9 × 103 % with an on/off current ratio of ~104 at the bias of 2 V under the UV wavelength of 365 nm (0.47 mW/cm2). In addition, the stability in long-term operation and photoresponse time are significantly improved by the introduction of A-SWNTs into the ZnO NP film when compared with the bare ZnO NPs film.

Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

AbstractThis study identifies the fast (i.e., days–weeks) transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) during northern summer by integrating a large (90 member) ensemble of Boundary Impulse Response tracers in the Whole Atmosphere Community Climate Model version 5. We show that there is a fast transport pathway that occurs over the southern slope of the Tibetan Plateau, northern India, the Arabian Sea, and Saudi Arabia; furthermore, we show that during July this pathway connects the Northern Hemisphere surface to the UTLS on a modal time scale of 5–10 days. A less efficient transport pathway is also identified over the western Pacific. A detailed budget analysis reveals that, while convective processes are responsible for transport to 200–300 hPa, the resolved dynamics, specifically the vertical eddy flux, dominate at 100–150 hPa. Transport variations are analyzed on weekly, monthly, and interannual time scales and are largely related to differences in the resolved dynamics in the UTLS.

A facile biotemplate-assisted synthesis of mesoporous V2O5 microtubules for high performance asymmetric supercapacitors

Mesoporous V2O5 microtubules are synthesized using a biotemplate-assisted method and evaluated for using as supercapacitor electrode materials. The preparation process is facilely associated with the pyrolysis of cotton fiber, adsorbed with the vanadium pentoxide hydrates. The obtained microtubular V2O5 shows highly mesoporous merits and hollow interiors, leading to better electrolyte/electrode contact and more efficient transport pathways. Compared with bulk V2O5 prepared without using cotton as biotemplate, microtubular V2O5 displays the excellent electrochemical performance with a specific capacitance of 680 F g−1 at 1.0 A g−1 in 1 M LiNO3 aqueous electrolyte and a high capacity retention of 70% over 10,000 cycles at 3 A g−1 in LiClO4/ propylene carbonate organic electrolyte. Moreover, the asymmetric supercapacitors based on microtubular V2O5 exhibit a high energy density of 58 Wh kg−1 at a power density of 0.46 kW kg−1 in 1 M LiClO4/propylene carbonate organic electrolyte, which further indicates that the great potential of the microtubular V2O5 as high-performance energy storage devices.

Three-dimensional TiNb2O7 anchored on carbon nanofiber core-shell arrays as an anode for high-rate lithium ion storage.

The control of structure and morphology in an electrode design for the development of large-power lithium ion batteries is crucial to create efficient transport pathways for ions and electrons. Herein, we report a powerful combinational strategy to build omnibearing conductive networks composed of titanium niobium oxide nanorods and carbon nanofibers (TNO/CNFs) via an electrostatic spinning method and a hydrothermal method into free-standing arrays with a three-dimensional heterostructure core/shell structure. TNO/CNF electrode exhibits significantly superior electrochemical performance and high-rate capability (241 mA h g−1 at 10C, and 208 mA h g−1 at 20C). The capacity of the TNO/CNF electrode is 257 mA h g−1 after 2000 cycles at 20C, which is much higher than that of the TNO electrode. In particular, the TNO/CNF electrode delivers a reversible capacity of 153.6 mA h g−1 with a capacity retention of 95% after 5000 cycles at ultrahigh current density. Superior electrochemical performances of the TNO/CNF electrode are attributed to the unique composite structure.

Fabrication of porous NiMn2O4 nanosheet arrays on nickel foam as an advanced sensor material for non-enzymatic glucose detection

In this work, porous NiMn2O4 nanosheet arrays on nickel foam (NiMn2O4 NSs@NF) was successfully fabricated by a simple hydrothermal step followed by a heat treatment. Porous NiMn2O4 NSs@NF is directly used as a sensor electrode for electrochemical detecting glucose. The NiMn2O4 nanosheet arrays are uniformly grown and packed on nickel foam to forming sensor electrode. The porous NiMn2O4 NSs@NF electrode not only provides the abundant accessible active sites and the effective ion-transport pathways, but also offers the efficient electron transport pathways for the electrochemical catalytic reaction by the high conductive nickel foam. This synergy effect endows porous NiMn2O4 NSs@NF with excellent electrochemical behaviors for glucose detection. The electrochemical measurements are used to investigate the performances of glucose detection. Porous NiMn2O4 NSs@NF for detecting glucose exhibits the high sensitivity of 12.2 mA mM−1 cm−2 at the window concentrations of 0.99–67.30 μM (correlation coefficient = 0.9982) and 12.3 mA mM−1 cm−2 at the window concentrations of 0.115–0.661 mM (correlation coefficient = 0.9908). In addition, porous NiMn2O4 NSs@NF also exhibits a fast response of 2 s and a low LOD of 0.24 µM. The combination of porous NiMn2O4 nanosheet arrays and nickel foam is a meaningful strategy to fabricate high performance non-enzymatic glucose sensor. These excellent properties reveal its potential application in the clinical detection of glucose.

Efficient and tunable one-dimensional charge transport in layered lanthanide metal-organic frameworks.

The emergence of electrically conductive metal-organic frameworks (MOFs) has led to applications in chemical sensing and electrical energy storage, among others. The most conductive MOFs are made from organic ligands and square-planar transition metal ions connected into two-dimensional (2D) sheets stacked on top of each other. Their electrical properties are thought to depend critically on the covalency of the metal-ligand bond, and less importance is given to out-of-plane charge transport. Here, we report a series of lanthanide-based MOFs that allow fine tuning of the sheet stacking. In these materials, the Ln3+ ions lie between the planes of the ligands, thus connecting organic layers into a 3D framework through lanthanide-oxygen chains. Here, efficient charge transport is found to occur primarily perpendicular to the 2D sheets. These results demonstrate that high conductivity in layered MOFs does not necessarily require a metal-ligand bond with highly covalent character, and that interactions between organic ligands alone can produce efficient charge transport pathways.

Engineering of Co9S8–CoS nanoparticles encapsulated into N-doped graphitic carbon tubes for high-performance lithium storage

Sulfide/carbon composites are promising anode candidates for lithium-ion batteries owing to the synergy of the two components. Their electrochemical performances are highly dependent on their structures. Herein, Co9S8–CoS nanoparticles encapsulated into N-doped graphitic carbon tubes (Co9S8–CoS/NGCT) are synthesized by a controllable in-situ self-assembly method assisted by a freeze-drying process. The hollow carbon tubes with a thin wall have an enough interior void space, which can effectively accommodate the volume expansion and prevent the aggregation of Co9S8–CoS nanoparticles during cycling. Moreover, benefiting from high specific surface area and efficient electron transport pathways, pseudocapacitive-controlled process accounts for a large proportion in the electrochemical lithium storage of Co9S8–CoS/NGCT. As a result, the Co9S8–CoS/NGCT shows a high specific capacity (1004 mAh g−1 at 0.1 A g−1 after 150 cycles), good cycling stability (517 mAh g−1 at 1 A g−1 after 1000 cycles) and excellent rate capability (410 mAh·g−1 at 5 A g−1).

Mesocrystalline Ta3N5 superstructures with long-lived charges for improved visible light photocatalytic hydrogen production

Highly ordered mesocrystalline semiconductors often indicate tremendous prospects in the clean energy production and environmental photocatalysis mainly because of their unique superstructure for efficient charge transport pathways and long-lived charges. Here, superstructure Ta3N5 mesocrystals with the high-energy surface {2 0 0} planes exposed were the first time to be successfully fabricated by topological transformation of Ta2O5 mesocrystals. The prepared Ta3N5 mesocrystals showed enhanced visible-light photocatalytic hydrogen production activity of 98.67 μmol g−1 for 180 min irradiation, which was approximately 5.28 times that of comm-Ta3N5 prepared with commercial Ta2O5 as the starting material, mainly due to the formation of long-distance electron conduction pathways and long-lived charges. The detailed electronic band structures of the prepared Ta3N5 mesocrystals were also investigated by electrochemical method. Finally, possible visible-light photocatalytic mechanisms of Ta3N5 mesocrystals for enhanced hydrogen production was also proposed in detail. Current work also indicates that tantalum-based mesocrystals show great potential to enhance the charge separation for efficient photocatalytic water splitting.

Repurposing DNA-binding agents as H-bonded organic semiconductors

Organic semiconductors are usually polycyclic aromatic hydrocarbons and their analogs containing heteroatom substitution. Bioinspired materials chemistry of organic electronics promises new charge transport mechanism and specific molecular recognition with biomolecules. We discover organic semiconductors from deoxyribonucleic acid topoisomerase inhibitors, featuring conjugated backbone decorated with hydrogen-bonding moieties distinct from common organic semiconductors. Using ellipticine as a model compound, we find that hydrogen bonds not only guide polymorph assembly, but are also critical to forming efficient charge transport pathways along π−conjugated planes when at a low dihedral angle by shortening the end-to-end distance of adjacent π planes. In the π−π stacking and hydrogen-bonding directions, the intrinsic, short-range hole mobilities reach as high as 6.5 cm2V−1s−1 and 4.2 cm2V−1s−1 measured by microwave conductivity, and the long-range apparent hole mobilities are up to 1.3 × 10–3 cm2V−1s−1 and 0.4 × 10–3 cm2V−1s−1 measured in field-effect transistors. We further demonstrate printed transistor devices and chemical sensors as potential applications.