Efficient Transport Pathways Research Articles

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.

Cu3Se2 nanomeshes constructed by enoki-mushroom-like Cu3Se2 and their application to quantum dot-sensitized solar cells

Novel copper selenide (Cu3Se2) nanomeshes are synthesized on F-doped SnO2 (FTO) glass substrates via a facile single-step potentiodynamic electrodeposition method for efficient counter electrode (CE) in quantum dot-sensitized solar cells (QD-SSCs). The electrodeposited FTO/Cu3Se2 films consist of vertically standing Cu3Se2 nanomeshes, constructed by vertically and laterally grown enoki-mushroom-like Cu3Se2. The FTO/Cu3Se2 electrodes exhibit excellent electrocatalytic activity and good electrochemical stability for the S2−/Sn2− redox couple, even better than those of FTO/Cu2S and FTO/Pt. This is because the vertically standing Cu3Se2 nanomeshes provide not only high electrochemical active sites but also efficient charge transport pathways. Besides, high crystalline Cu3Se2 phase and widened pores between nanomeshes improve the electronic conduction and make ionic transport more efficient into and out of the film. As a result, the CdSe-based QD-SSC containing the optimized FTO/Cu3Se2 CE achieves a significantly increased power conversion efficiency of 5.5%, compared to those containing FTO/Cu2S and FTO/Pt CEs (4.52 and 2.62%, respectively).

One-dimensional mesoporous Co3O4 tubules for enhanced performance supercapacitor and enzymeless glucose sensing

One-dimensional hollow Co3O4 tubules have been synthesized by using a template method followed by a simple thermal annealing treatment. The obtained hollow Co3O4 nanomaterial displays one-dimensional architecture with a highly mesoporous nature and hollow interiors, leading to better electrolyte/electrode contact and more efficient transport pathways. Our experimental results demonstrate that the hollow Co3O4 nanostructures exhibit enhanced electrochemical performance for charge storage and enzymeless glucose sensing applications. Supercapacitor electrodes employing mesoporous hollow Co3O4 tubules exhibit specific capacitance of 326 F g−1 at a current density of 1 A g−1, a high capacity retention of 73.6% at 10 A g−1, and a long stable cycling performance of retaining ~ 91.6% after 5000 cycles. Compared with the bulk Co3O4, it also has good sensing ability for glucose with high sensitivity of 994.6 μA mM−1 cm−2 and 369.7 μA mM−1 cm−2 for the lower and higher concentration of glucose, fast response time of 5 s, detection limit as low as 0.84 μM, good selectivity, stability, and reproducibility. These results show that the hollow Co3O4 tubules is a versatile material for various applications.

Preciously Determining Energy Levels and Screening Extraction Medium to Design Highly Efficient Carriers Transport Pathways for Zn‐CuInS2 Quantum Dots Based H2 Generation Application

AbstractWith the creation of long‐lived defect states‐related donor‐acceptor pair (DAP) recombination pathway, the Zn doped CuInS2 quantum dots (CIZS QDs) sensitized TiO2 photoelectrode displayed a good photocurrent response ability with a density of 2.7 mA/cm2. Further introduction Au nanoparticles (NPs) between CIZS and TiO2, and the outermost layer CdS, the photocurrent of CdS‐CIZS−Au‐TiO2 reached 7.5 mA/cm2 with an increase of 75% and 175%, respectively. The enhancements both in photo‐conversion ability and photoelectrochemical hydrogen generation reactivity can be mainly attributed to the functions of Au NPs acting as electron traps to help separate the long‐lived carriers of CIZS QDs and subsequently improve interfacial charge transfer, as well as CdS's ability to enhance holes extraction.

One Dimensional Nanomaterials for Emerging Energy Storage

One-dimensional nanomaterials can offer large surface area, facile strain relaxation upon cycling and efficient electron transport pathway to achieve high electrochemical performance. Hence, nanowires have attracted increasing interest in energy related fields. We designed the single nanowire electrochemical device for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode to understand intrinsic reason of capacity fading. The results show that during the electrochemical reaction, conductivity of the nanowire electrode decreased, which limits the cycle life of the devices. We have developed a facile and high-yield strategy for the oriented formation of CNTs from metal−organic frameworks (MOFs). The appropriate graphitic N doping and the confined metal nanoparticles in CNTs both increase the densities of states near the Fermi level and reduce the work function, hence efficiently enhancing its oxygen reduction activity. In addition, we demonstrated the critical role of structural H2O. The results suggest that the H2O-solvated Zn2+ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V2O5 framework, effectively promoting its diffusion. We also identified the exciting electrochemical properties (including high electric conductivity, small volume change and self-preserving effect) and superior sodium storage performance of alkaline earth metal vanadates through preparing CaV4O9 nanowires. Furthermore, a novel assembled nanoarchitecture was also presented, which consists of V2O3 nanoparticles embedded in amorphous carbon nanotubes that are then coassembled within a reduced graphene oxide network. The naturally integrated advantages of each subunit exhibit highly stable and ultrafast sodium-ion storage. Our work presented here can inspire new thought in constructing novel one-dimensional structures and accelerate the development of energy storage applications.