Showing papers in "Advanced Functional Materials in 2013"
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TL;DR: In this paper, the status of ambient temperature sodium ion batteries is reviewed in light of recent developments in anode, electrolyte and cathode materials, including high performance layered transition metal oxides and polyanionic compounds.
Abstract: The status of ambient temperature sodium ion batteries is reviewed in light of recent developments in anode, electrolyte and cathode materials. These devices, although early in their stage of development, are promising for large-scale grid storage applications due to the abundance and very low cost of sodium-containing precursors used to make the components. The engineering knowledge developed recently for highly successful Li ion batteries can be leveraged to ensure rapid progress in this area, although different electrode materials and electrolytes will be required for dual intercalation systems based on sodium. In particular, new anode materials need to be identified, since the graphite anode, commonly used in lithium systems, does not intercalate sodium to any appreciable extent. A wider array of choices is available for cathodes, including high performance layered transition metal oxides and polyanionic compounds. Recent developments in electrodes are encouraging, but a great deal of research is necessary, particularly in new electrolytes, and the understanding of the SEI films. The engineering modeling calculations of Na-ion battery energy density indicate that 210 Wh kg−1 in gravimetric energy is possible for Na-ion batteries compared to existing Li-ion technology if a cathode capacity of 200 mAh g−1 and a 500 mAh g−1 anode can be discovered with an average cell potential of 3.3 V.
3,776 citations
TL;DR: In this article, a method of fabricating ultrathin (22-53 nm thick) graphene nanofiltration membranes (uGNMs) on microporous substrates is presented for efficient water purification using chemically converted graphene (CCG).
Abstract: A method of fabricating ultrathin (≈22–53 nm thick) graphene nanofiltration membranes (uGNMs) on microporous substrates is presented for efficient water purification using chemically converted graphene (CCG). The prepared uGNMs show well packed layer structure formed by CCG sheets, as characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The performance of the uGNMs for water treatment was evaluated on a dead end filtration device and the pure water flux of uGNMs was high (21.8 L m−2 h−1 bar−1). The uGNMs show high retention (>99%) for organic dyes and moderate retention (≈20–60%) for ion salts. The rejection mechanism of this kind of negatively charged membranes is intensively studied, and the results reveal that physical sieving and electrostatic interaction dominate the rejection process. Because of the ultrathin nature of uGNMs, 34 mg of CCG is sufficient for making a square meter of nanofiltration membrane, indicating that this new generation graphene-based nanofiltration technology would be resource saving and cost-effective. The integration of high performance, low cost, and simple solution-based fabrication process promises uGNMs great potential application in practical water purification.
1,366 citations
TL;DR: In this article, the formation and electronic properties of various MXene systems, M 2 C (M = Sc, Ti, V, Cr, Zr, Nb, Ta), M 2 N (M 2 N), with surfaces chemically functionalized by F, OH, and O groups, are examined.
Abstract: Layered MAX phases are exfoliated into 2D single layers and multilayers, so-called MXenes. Using fi rst-principles calculations, the formation and electronic properties of various MXene systems, M 2 C (M = Sc, Ti, V, Cr, Zr, Nb, Ta) and M 2 N (M = Ti, Cr, Zr) with surfaces chemically functionalized by F, OH, and O groups, are examined. Upon appropriate surface functionalization, Sc 2 C, Ti 2 C, Zr 2 C, and Hf 2 C MXenes are expected to become semiconductors. It is also derived theoretically that functionalized Cr 2 C and Cr 2 N MXenes are magnetic. Thermoelectric calculations based on the Boltzmann theory imply that semiconducting MXenes attain very large Seebeck coeffi cients at low temperatures.
1,288 citations
TL;DR: In the past decade, surface plasmon resonance of Ag and Au nanoparticles has been investigated to improve the efficiency of photocatalytic processes as discussed by the authors, which is particularly interesting for its ability to store the sun's energy in chemical bonds that can be released later without producing harmful byproducts.
Abstract: In the past decade, the surface plasmon resonance of Ag and Au nanoparticles has been investigated to improve the efficiency of photocatalytic processes. The photocatalytic production of fuels is particularly interesting for its ability to store the sun's energy in chemical bonds that can be released later without producing harmful byproducts. This Feature Article reviews recent work demonstrating plasmon-enhanced photocatalytic water splitting, reduction of CO2 with H2O to form hydrocarbon fuels, and degradation of organic molecules. Focus is placed on several possible mechanisms that have been previously discussed in the literature. A particular emphasis is given to several aspects of these mechanisms that are not fully understood and will require further investigation.
1,269 citations
TL;DR: In this article, a review of recent progress in the research and development of redox flow battery technology, including cell-level components of electrolytes, electrodes, and membranes, is reviewed.
Abstract: With the increasing need to seamlessly integrate renewable energy with the current electricity grid, which itself is evolving into a more intelligent, efficient, and capable electrical power system, it is envisioned that energy-storage systems will play a more prominent role in bridging the gap between current technology and a clean sustainable future in grid reliability and utilization. Redox flow battery technology is a leading approach in providing a well-balanced solution for current challenges. Here, recent progress in the research and development of redox flow battery technology, including cell-level components of electrolytes, electrodes, and membranes, is reviewed. The focus is on new redox chemistries for both aqueous and non-aqueous systems.
1,216 citations
TL;DR: A controllable one-pot method to synthesize ordered mesoporous carbons (NMC) with a high N content by using dicyandiamide as a nitrogen source via an evaporation-induced self-assembly process is reported in this article.
Abstract: A controllable one-pot method to synthesize N-doped ordered mesoporous carbons (NMC) with a high N content by using dicyandiamide as a nitrogen source via an evaporation-induced self-assembly process is reported. In this synthesis, resol molecules can bridge the Pluronic F127 template and dicyandiamide via hydrogen bonding and electrostatic interactions. During thermosetting at 100 °C for formation of rigid phenolic resin and subsequent pyrolysis at 600 °C for carbonization, dicyandiamide provides closed N species while resol can form a stable framework, thus ensuring the successful synthesis of ordered N-doped mesoporous carbon. The obtained N-doped ordered mesoporous carbons possess tunable mesostructures (p6m and Imm symmetry) and pore size (3.1–17.6 nm), high surface area (494–586 m2 g−1), and high N content (up to 13.1 wt%). Ascribed to the unique feature of large surface area and high N contents, NMC materials show high CO2 capture of 2.8–3.2 mmol g−1 at 298 K and 1.0 bar, and exhibit good performance as the supercapacitor electrode with specific capacitances of 262 F g−1 (in 1 M H2SO4) and 227 F g−1 (in 6 M KOH) at a current density of 0.2 A g−1.
845 citations
TL;DR: A composite made from the assembly of graphene oxide (GO) and copper-centered metal organic framework (MOF) shows good performance as a tri-functional catalyst in three important electrocatalysis reactions, namely: the hydrogen evolution reaction (HER), oxygen evolution reaction, and oxygen reduction reaction (ORR) as discussed by the authors.
Abstract: A composite made from the assembly of graphene oxide (GO) and copper-centered metal organic framework (MOF) shows good performance as a tri-functional catalyst in three important electrocatalysis reactions, namely: the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). One of the challenges in the area of electrocatalysis is to find an effective catalyst that will reduce, as well as generate, oxygen at moderate temperatures. The enhanced electrocatalytic properties and stability in acid of the GO-MOF composite is due to the unqiue porous scaffold structure, improved charge transport and synergistic interactions between the GO and MOF. In polymer electrolyte membrane fuel cell testing, the GO-incorporated Cu-MOF composite delivers a power density that is 76% that of the commercial Pt catalyst.
808 citations
TL;DR: In this article, a hybrid material consisting of MnO nanocrystals grown on conductive graphene nanosheets was used for lithium ion batteries with a reversible capacity as high as 14.1 mAh g−1 with only 0.01% capacity loss per cycle.
Abstract: To tackle the issue of inferior cycle stability and rate capability for MnO anode materials in lithium ion batteries, a facile strategy is explored to prepare a hybrid material consisting of MnO nanocrystals grown on conductive graphene nanosheets. The prepared MnO/graphene hybrid anode exhibits a reversible capacity as high as 2014.1 mAh g−1 after 150 discharge/charge cycles at 200 mA g−1, excellent rate capability (625.8 mAh g−1 at 3000 mA g−1), and superior cyclability (843.3 mAh g−1 even after 400 discharge/charge cycles at 2000 mA g−1 with only 0.01% capacity loss per cycle). The results suggest that the reconstruction of the MnO/graphene electrodes is intrinsic due to conversion reactions. A long-term stable nanoarchitecture of graphene-supported ultrafine manganese oxide nanoparticles is formed upon cycling, which yields a long-life anode material for lithium ion batteries. The lithiation and delithiation behavior suggests that the further oxidation of Mn(II) to Mn(IV) and the interfacial lithium storage upon cycling contribute to the enhanced specific capacity. The excellent rate capability benefits from the presence of conductive graphene and a short transportation length for both lithium ions and electrons. Moreover, the as-formed hybrid nanostructure of MnO on graphene may help achieve faster kinetics of conversion reactions.
758 citations
TL;DR: In this paper, a facile synthesis of mesoporous g-CN using molecular cooperative assembly between triazine molecules is reported, which is a promising heterogeneous metal-free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants.
Abstract: Graphitic carbon nitride (g-CN) is a promising heterogeneous metal-free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants. Its catalytic performance is easily adjustable by modifying texture, optical, and electronic properties via nanocasting, doping, and copolymerization. However, simultaneous optimization has yet to be achieved. Here, a facile synthesis of mesoporous g-CN using molecular cooperative assembly between triazine molecules is reported. Flower-like, layered spherical aggregates of melamine cyanuric acid complex (MCA) are formed by precipitation from equimolecular mixtures in dimethyl sulfoxide (DMSO). Thermal polycondensation of MCA under nitrogen at 550 °C produces mesoporous hollow spheres comprised of tri-s-triazine based g-CN nanosheets (MCA-CN) with the composition of C3N4.14H1.98. The layered structure succeeded from MCA induces stronger optical absorption, widens the bandgap by 0.16 eV, and increases the lifetime of photoexcited charge carriers by twice compared to that of the bulk g-CN, while the chemical structure remains similar to that of the bulk g-CN. As a result of these simultaneous modifications, the photodegradation kinetics of rhodamine B on the catalyst surface can be improved by 10 times.
691 citations
TL;DR: In this article, a highly active and stable electrocatalyst for hydrogen evolution is developed based on the in situ formation of MoS2 nanoparticles on mesoporous graphene foams (MoS2/MGF).
Abstract: A highly active and stable electrocatalyst for hydrogen evolution is developed based on the in situ formation of MoS2 nanoparticles on mesoporous graphene foams (MoS2/MGF). Taking advantage of its high specific surface area and its interconnected conductive graphene skeleton, MGF provides a favorable microenvironment for the growth of highly dispersed MoS2 nanoparticles while allowing rapid charge transfer kinetics. The MoS2/MGF nanocomposites exhibit an excellent electrocatalytic activity for the hydrogen evolution reaction with a low overpotential and substantial apparent current densities. Such enhanced catalytic activity stems from the abundance of catalytic edge sites, the increase of electrochemically accessible surface area and the unique synergic effects between the MGF support and active catalyst. The electrode reactions are characterized by electrochemical impedance spectroscopy. A Tafel slope of ≈42 mV per decade is measured for a MoS2/MGF modified electrode, suggesting the Volmer-Heyrovsky mechanism of hydrogen evolution.
654 citations
TL;DR: In this article, a new approach assisted by hydrogen plasma to synthesize unique H-doped black titania with a core/shell structure was presented, superior to the high H-2-pressure process (under 20 bar for five days).
Abstract: Black TiO2 attracts enormous attention due to its large solar absorption and induced excellent photocatalytic activity. Herein, a new approach assisted by hydrogen plasma to synthesize unique H-doped black titania with a core/shell structure (TiO2@TiO2-xHx) is presented, superior to the high H-2-pressure process (under 20 bar for five days). The black titania possesses the largest solar absorption (approximate to 83%), far more than any other reported black titania (the record (high-pressure): approximate to 30%). H doping is favorable to eliminate the recombination centers of light-induced electrons and holes. High absorption and low recombination ensure the excellent photocatalytic activity for the black titania in the photo-oxidation of organic molecules in water and the production of hydrogen. The H-doped amorphous shell is proposed to play the same role as Ag or Pt loading on TiO2 nanocrystals, which induces the localized surface plasma resonance and black coloration. Photocatalytic water splitting and cleaning using TiO2-xHx is believed to have a bright future for sustainable energy sources and cleaning environment.
TL;DR: In this paper, a self-assembled reduced graphene oxide (RGO)/MnO2/GrMoO(2) composite was used as a positive electrode and a RGO/MoO3 composite as a negative electrode in safe aqueous Na2SO4 electrolyte.
Abstract: Asymmetric supercapacitors with high energy density are fabricated using a self-assembled reduced graphene oxide (RGO)/MnO2 (GrMnO(2)) composite as a positive electrode and a RGO/MoO3 (GrMoO(3)) composite as a negative electrode in safe aqueous Na2SO4 electrolyte. The operation voltage is maximized by choosing two metal oxides with the largest work function difference. Because of the synergistic effects of highly conductive graphene and highly pseudocapacitive metal oxides, the hybrid nanostructure electrodes exhibit better charge transport and cycling stability. The operation voltage is expanded to 2.0 V in spite of the use of aqueous electrolyte, revealing a high energy density of 42.6 Wh kg(-1) at a power density of 276 W kg(-1) and a maximum specific capacitance of 307 F g(-1), consequently giving rise to an excellent Ragone plot. In addition, the GrMnO(2)//GrMoO(3) supercapacitor exhibits improved capacitance with cycling up to 1000 cycles, which is explained by the development of micropore structures during the repetition of ion transfer. This strategy for the choice of metal oxides provides a promising route for next-generation supercapacitors with high energy and high power densities.
TL;DR: In this paper, a GQDs/GQDs symmetric micro-supercapacitor is prepared using a simple electrodeposition approach, and its electrochemical properties in aqueous electrolyte and ionic liquid electrolyte are systematically investigated.
Abstract: Graphene quantum dots (GQDs) have attracted tremendous research interest due to the unique properties associated with both graphene and quantum dots. Here, a new application of GQDs as ideal electrode materials for supercapacitors is reported. To this end, a GQDs//GQDs symmetric microsupercapacitor is prepared using a simple electro-deposition approach, and its electrochemical properties in aqueous electrolyte and ionic liquid electrolyte are systematically investigated. The results show that the as-made GQDs micro-supercapacitor has superior rate capability up to 1000 V s − 1 , excellent power response with very short relaxation time constant ( τ 0 = 103.6 μ s in aqueous electrolyte and τ 0 = 53.8 μ s in ionic liquid electrolyte), and excellent cycle stability. Additionally, another GQDs//MnO 2 asymmetric supercapacitor is also built using MnO 2 nanoneedles as the positive electrode and GQDs as the negative electrode in aqueous electrolyte. Its specifi c capacitance and energy density are both two times higher than those of GQDs//GQDs symmetric micro-supercapacitor in the same electrolyte. The results presented here may pave the way for a new promising application of GQDs in micropower suppliers and microenergy storage devices.
TL;DR: In this article, the status and challenges of large-scale electrical energy storage have been reviewed from the perspective of materials science and materials chemistry in electrochemical energy storage technologies, such as Li-ion batteries, sodium (sulfur and metal halide) batteries, Pb-acid battery, redox flow batteries, and supercapacitors.
Abstract: Large-scale electrical energy storage has become more important than ever for reducing fossil energy consumption in transportation and for the widespread deployment of intermittent renewable energy in electric grid. However, significant challenges exist for its applications. Here, the status and challenges are reviewed from the perspective of materials science and materials chemistry in electrochemical energy storage technologies, such as Li-ion batteries, sodium (sulfur and metal halide) batteries, Pb-acid battery, redox flow batteries, and supercapacitors. Perspectives and approaches are introduced for emerging battery designs and new chemistry combinations to reduce the cost of energy storage devices.
TL;DR: In this article, a few-layered WS2 is synthesized by chemical vapor deposition on quartz, which is successfully used as light sensors and the results indicate that the electrical response strongly depends on the photon energy from the excitation lasers.
Abstract: Few-layered films of WS2, synthesized by chemical vapor deposition on quartz, are successfully used as light sensors. The film samples are structurally characterized by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The produced samples consist of few layered sheets possessing up to 10 layers. UV–visible absorbance spectra reveals absorption peaks at energies of 1.95 and 2.33 eV, consistent with the A and B excitons characteristic of WS2. Current–voltage (I–V) and photoresponse measurements carried out at room temperature are performed by connecting the WS2 layered material with Au/Ti contacts. The photocurrent measurements are carried out using five different laser lines ranging between 457 and 647 nm. The results indicate that the electrical response strongly depends on the photon energy from the excitation lasers. In addition, it is found that the photocurrent varies non-linearly with the incident power, and the generated photocurrent in the WS2 samples varies as a squared root of the incident power. The excellent response of few-layered WS2 to detect different photon wavelengths, over a wide range of intensities, makes it a strong candidate for constructing novel optoelectronic devices.
TL;DR: In this paper, an organic host-guest material with efficient persistent RT phosphorescence (RTP) was developed by minimizing the nonradiative deactivation pathway of triplet excitons.
Abstract: Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at room-temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host-guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red-green-blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.
TL;DR: The state‐of‐the‐art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators.
Abstract: Hydrogels find widespread applications in biomedical engineering due to their hydrated environment and tunable properties (e.g., mechanical, chemical, biocompatible) similar to the native extracellular matrix (ECM). However, challenges still exist regarding utilizing hydrogels in applications such as engineering 3D tissue constructs and active targeting in drug delivery, due to the lack of controllability, actuation, and quick-response properties. Recently, magnetic hydrogels have emerged as a novel biocomposite for their active response properties and extended applications. In this review, the state-of-the-art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed. The applications of magnetic hydrogels in biomedical engineering are also reviewed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators. Concluding remarks and perspectives for the future development of magnetic hydrogels are addressed.
TL;DR: In this article, an ideal dielectric thermally conductive epoxy nanocomposite is successfully fabricated using polyhedral oligosilsesquioxane (POSS) functionalized boron nitride nanotubes (BNNTs) as fillers.
Abstract: Dielectric polymer composites with high thermal conductivity are very promising for microelectronic packaging and thermal management application in new energy systems such as solar cells and light emitting diodes (LEDs). However, a well-known paradox is that conventional composites with high thermal conductivity usually suffer from the high dielectric constant and high dielectric loss, while on the other hand, composite materials with excellent dielectric properties usually possess low thermal conductivity. In this work, an ideal dielectric thermally conductive epoxy nanocomposite is successfully fabricated using polyhedral oligosilsesquioxane (POSS) functionalized boron nitride nanotubes (BNNTs) as fillers. The nanocomposites with 30 wt% fraction of POSS modified BNNTs exhibit much lower dielectric constant, dielectric loss tangent, and coefficient of thermal expansion in comparison with the pure epoxy resin. As an example, below 100 Hz, the dielectric loss of the nanocomposites with 20 and 30 wt% BNNTs is reduced by one order of magnitude in comparison with the pure epoxy resin. Moreover, the nanocomposites show a dramatic thermal conductivity enhancement of 1360% in comparison with the pristine epoxy resin at a BNNT loading fraction of 30 wt%. The merits of the designed composites are suggested to originate from the excellent intrinsic properties of embedded BNNTs, effective surface modification by POSS molecules, and carefully developed composite preparation methods.
TL;DR: In this paper, the maximum external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs) doped with Ir(ppy)2(acac) [bis(2-phenylpyridine)iridium(III)-acetylacetonate] in an exciplex forming co-host has been optically analyzed.
Abstract: High-efficiency phosphorescent organic light-emitting diodes (OLEDs) doped with Ir(ppy)2(acac) [bis(2-phenylpyridine)iridium(III)-acetylacetonate] in an exciplex forming co-host have been optically analyzed. This emitter has a preferred orientation with the horizontal to vertical dipole ratio of 0.77:0.23 as compared to 0.67:0.33 in the isotropic case. Theoretical analysis based on the orientation factor (Θ, the ratio of the horizontal dipoles to total dipoles) and the photoluminescence quantum yield (qPL) of the emitter predicts that the maximum external quantum efficiency (EQE) of the OLEDs with this emitter is about 30%, which matches very well with the experimental data, indicating that the electrical loss of the OLEDs is negligible and the device structure can be utilized as a platform to demonstrate the validity of optical modeling. Based on the results, the maximum EQE achievable for a certain emitting dye in a host can be predicted by just measuring qPL and Θ in a neat film on glass without the need to fabricate devices, which offers a universal plot of the maximum EQE as a function of qPL and Θ.
TL;DR: In this paper, the status and materials challenges for nonaqueous rechargeable Li-air batteries are reviewed, including electrolytes, cathode (electrocatalysts), lithium metal anodes and oxygen-selective membranes (oxygen supply from air).
Abstract: A Li-air battery could potentially provide three to five times higher energy density/specific energy than conventional batteries and, thus, enable the driving range of an electric vehicle to be comparable to gasoline vehicles. However, making Li-air batteries rechargeable presents significant challenges, mostly related to the materials. Here, the key factors that influence the rechargeability of Li-air batteries are discussed with a focus on nonaqueous systems. The status and materials challenges for nonaqueous rechargeable Li-air batteries are reviewed. These include electrolytes, cathode (electrocatalysts), lithium metal anodes, and oxygen-selective membranes (oxygen supply from air). A perspective for the future of rechargeable Li-air batteries is provided.
TL;DR: In this paper, a facile method is proposed to fabricate polyurethane foam with simultaneous super-hydrophobicity and superoleophilicity, which demonstrates super-repellency towards corrosive liquids, self-cleaning, and oil/water separation properties.
Abstract: Oil/water separation is a worldwide challenge. Learning from nature provides a promising approach for the construction of functional materials with oil/water separation. In this contribution, inspired by superhydrophobic self-cleaning lotus leaves and porous biomaterials, a facile method is proposed to fabricate polyurethane foam with simultaneous superhydrophobicity and superoleophilicity. Due to its low density, light weight, and superhydrophobicity, the as-prepared foam can float easily on water. Furthermore, the foam demonstrates super-repellency towards corrosive liquids, self-cleaning, and oil/water separation properties, possessing multifunction integration. We expect that this low-cost process can be readily and widely adopted for the design of multifunctional foams for large-area oil-spill cleanup.
TL;DR: In this article, a material concept is reported, which yields an average piezoelectric coefficientd33 of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature.
Abstract: The development of lead-free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead-free (K,Na)NbO3 (KNN)-based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd33 of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field-induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field-induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature-dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature-insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.
TL;DR: The proper selection of substrate concentration and buffer is proposed as a practical means of tailoring polydopamine functionality via control of competing pathways downstream of dopamine quinone.
Abstract: Rational approaches to engineering polydopamine films with tailored properties for surface coating and functionalization are currently challenged by the lack of detailed information about the polymer structure and the mechanism of buildup. Using an integrated chemical and spectroscopic approach enables the demonstration of: a) a three-component structure of polydopamine, comprising uncyclized (catecholamine) and cyclized (indole) units, as well as novel pyrrolecarboxylic acid moieties; b) remarkable variations in the relative proportions of the cyclized and uncyclized units with starting dopamine concentration; c) the occurrence of oligomer components up to the tetramer level; d) the covalent incorporation of Tris buffer; and e) the role of dopamine quinone as a crucial control point for directing the buildup pathways and tuning the properties. The importance of the uncyclized amine-containing units in polydopamine adhesion is also highlighted. The proper selection of substrate concentration and buffer is thus proposed as a practical means of tailoring polydopamine functionality via control of competing pathways downstream of dopamine quinone.
TL;DR: In this article, a detailed characterization of solution-derived nickel (II) oxide (NiO) hole-transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported.
Abstract: The detailed characterization of solution-derived nickel (II) oxide (NiO) hole-transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non-stoichiometric NiO. Specifically, the [Ni(MEA)2(OAc)]+ ion is found to be the most prevalent species in the precursor solution. The defect-induced Ni3+ ion, which is present in non-stoichiometric NiO and signifies the p-type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X-ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly-dithienogermole-thienopyrrolodione (pDTG-TPD) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are fabricated using these solution-processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.
TL;DR: In this article, a flexible transparent electrode was fabricated on a non-flat surface to demonstrate the possibility of cost-effective mass production as well as the applicability to the unconventional arbitrary soft surfaces.
Abstract: As an alternative to the brittle and expensive indium tin oxide (ITO) transparent conductor, a very simple, room-temperature nanosoldering method of Ag nanowire percolation network is developed with conducting polymer to demonstrate highly flexible and even stretchable transparent conductors. The drying conducting polymer on Ag nanowire percolation network is used as a nanosoldering material inducing strong capillary-force-assisted stiction of the nanowires to other nanowires or to the substrate to enhance the electrical conductivity, mechanical stability, and adhesion to the substrate of the nanowire percolation network without the conventional high-temperature annealing step. Highly bendable Ag nanowire/conducting polymer hybrid films with low sheet resistance and high transmittance are demonstrated on a plastic substrate. The fabricated flexible transparent electrode maintains its conductivity over 20 000 cyclic bends and 5 to 10% stretching. Finally, a large area (A4-size) transparent conductor and a flexible touch panel on a non-flat surface are fabricated to demonstrate the possibility of cost-effective mass production as well as the applicability to the unconventional arbitrary soft surfaces. These results suggest that this is an important step toward producing intelligent and multifunctional soft electric devices as friendly human/electronics interface, and it may ultimately contribute to the applications in wearable computers.
TL;DR: In this article, the fundamental properties and promising electrochemical performance of titanium-based anode materials for applications in hybrid electric vehicles are discussed for the purpose of evaluating the performance of hybrid vehicles.
Abstract: Lithium-ion batteries have been long considered a promising energy storage technology for electrification of the transportation system. However, the poor safety characteristics of lithium-ion batteries is one of several technological barriers that hinder their deployment for automobile applications. Within the field of battery research and development, titanium-based anode materials have recently attracted widespread attention due to their significantly better thermal stability than the conventional graphite anode. In this chapter, the fundamental properties and promising electrochemical performance of titanium-based anode materials will be discussed for applications in hybrid electric vehicles.
TL;DR: In this article, the fabrication and characterization of fi bers that are ultrastretchable and have metallic electrical conductivity are described, and they are used as stretchable wires for earphones and for a battery charger.
Abstract: The fabrication and characterization of fi bers that are ultrastretchable and have metallic electrical conductivity are described. The fi bers consist of a liquid metal alloy, eutectic gallium indium (EGaIn), injected into the core of stretchable hollow fi bers composed of a triblock copolymer, poly[styreneb -(ethylene- co -butylene)- b -styrene] (SEBS) resin. The hollow fi bers are easy to mass-produce with controlled size using commercially available melt processing methods. The fi bers are similar to conventional metallic wires, but can be stretched orders of magnitude further while retaining electrical conductivity. Mechanical measurements with and without the liquid metal inside the fi bers show the liquid core has a negligible impact on the mechanical properties of the fi bers, which is in contrast to most conductive composite fi bers. The fi bers also maintain the same tactile properties with and without the metal. Electrical measurements show that the fi bers increase resistance as the fi ber elongates and the cross sectional area narrows. Fibers with larger diameters change from a triangular to a more circular cross-section during stretching, which has the appeal of lowering the resistance below that predicted by theory. To demonstrate their utility, the ultrastretchable fi bers are used as stretchable wires for earphones and for a battery charger and perform as well as their conventional parts.
TL;DR: A comprehensive review of the fundamental properties, synthesis techniques and applications of layered and planar MoO 3, MoS 2, MoSe 2, and MoTe 2 along with their future prospects is presented in this article.
Abstract: In the quest to discover the properties of planar semiconductors, two-dimensional molybdenum trioxide and dichalcogenides have recently attracted a large amount of interest. This family, which includes molybdenum trioxide (MoO 3 ), disulphide (MoS 2 ), diselenide (MoSe 2 ) and ditelluride (MoTe 2 ), possesses many unique properties that make its compounds appealing for a wide range of applications. These properties can be thickness dependent and may be manipulated via a large number of physical and chemical processes. In this Feature Article, a comprehensive review is delivered of the fundamental properties, synthesis techniques and applications of layered and planar MoO 3 , MoS 2 , MoSe 2 , and MoTe 2 along with their future prospects.
TL;DR: In this article, the fabrication and design principles for using silver-nanowire (AgNW) networks as transparent electrodes for flexible film heaters are described, and a transparent film heater is constructed based on uniformly interconnected AgNW networks, which yields an effective and rapid heating of the film at low input voltages.
Abstract: The fabrication and design principles for using silver-nanowire (AgNW) networks as transparent electrodes for flexible film heaters are described. For best practice, AgNWs are synthesized with a small diameter and network structures of the AgNW films are optimized, demonstrating a favorably low surface resistivity in transparent layouts with a high figure-of-merit value. To explore their potential in transparent electrodes, a transparent film heater is constructed based on uniformly interconnected AgNW networks, which yields an effective and rapid heating of the film at low input voltages. In addition, the AgNW-based film heater is capable of accommodating a large amount of compressive or tensile strains in a completely reversible fashion, thereby yielding an excellent mechanical flexibility. The AgNW networks demonstrated here possess attractive features for both conventional and emerging applications of transparent flexible electrodes.
TL;DR: In this paper, an exciplex-forming co-host system enables efficient singlet and triplet energy transfers from the host to the phosphorescent dopant, and the system has low probability of direct trapping of charges at the dopant molecules and no charge-injection barrier from the chargetransport layers to the emitting layer.
Abstract: Phosphorescent organic light-emitting diodes (OLEDs) with ultimate efficiency in terms of the external quantum efficiency (EQE), driving voltage, and efficiency roll-off are reported, making use of an exciplex-forming co-host. This exciplex-forming co-host system enables efficient singlet and triplet energy transfers from the host exciplex to the phosphorescent dopant because the singlet and triplet energies of the exciplex are almost identical. In addition, the system has low probability of direct trapping of charges at the dopant molecules and no charge-injection barrier from the charge-transport layers to the emitting layer. By combining all these factors, the OLEDs achieve a low turn-on voltage of 2.4 V, a very high EQE of 29.1% and a very high power efficiency of 124 lm W−1. In addition, the OLEDs achieve an extremely low efficiency roll-off. The EQE of the optimized OLED is maintained at more than 27.8%, up to 10 000 cd m−2.