Optimized La0.6Sr0.4CoO3–δ Thin‐Film Electrodes with Extremely Fast Oxygen‐Reduction Kinetics

La_0.6Sr_0.4CoO_3–δ (LSC) thin‐film electrodes are prepared on yttria‐stabilized zirconia (YSZ) substrates by pulsed laser deposition at different deposition temperatures. The decrease of the film crystallinity, occurring when the deposition temperature is lowered, is accompanied by a strong increase of the electrochemical oxygen exchange rate of LSC. For more or less X‐ray diffraction (XRD)‐amorphous electrodes deposited between ca. 340 and 510 °C polarization resistances as low as 0.1 Ω cm² can be obtained at 600 °C. Such films also exhibit the best stability of the polarization resistance while electrodes deposited at higher temperatures show a strong and fast degradation of the electrochemical kinetics (thermal deactivation). Possible reasons for this behavior and consequences with respect to the preparation of high‐performance solid oxide fuel cell (SOFC) cathodes are discussed.     

MEL‐type Pure‐Silica Zeolite Nanocrystals Prepared by an Evaporation‐Assisted Two‐Stage Synthesis Method as Ultra‐Low‐k Materials

A MEL‐type pure‐silica zeolite (PSZ), prepared by spin‐on of nanoparticle suspensions, has been shown to be a promising ultra‐low‐dielectric‐constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two‐stage synthesis method was used to synthesize a MEL‐zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63%, the particle size is 80 nm, which has proved to be too large because it introduces a number of problems for the spin‐on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two‐stage synthesis method is modified into an evaporation‐assisted two‐stage method by adding a solvent‐evaporation process between the two thermal‐treatment steps. The modified method can yield much smaller particle sizes (e.g., 14 vs. 80 nm) while maintaining the same nanocrystal yields as the two‐stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation‐assisted two‐stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14 nm in size and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin‐on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67 ± 1.48 GPa vs. 7.82 ± 1.30 GPa), as well as a similar k value (1.91 ± 0.09 vs. 1.89 ± 0.08) to the previous two‐stage synthesized films.     

In Situ Preparation of Sandwich MoO3/C Hybrid Nanostructures for High‐Rate and Ultralong‐Life Supercapacitors

This work presents a design of sandwich MoO₃/C hybrid nanostructure via calcination of the dodecylamine‐intercalated layered α‐MoO₃, leading to the in situ production of the interlayered graphene layer. The sample with a high degree of graphitization of graphene layer and more interlayered void region exhibits the most outstanding energy storage performance. The obtained material is capable of delivering a high specific capacitance of 331 F g^?1 at a current density of 1 A g^?1 and retained 71% capacitance at 10 A g^?1. In addition, nearly no discharge capacity decay between 1000 and 10 000 continuous charge–discharge cycles is observed at a high current density of 10 A g^?1, indicating an excellent specific capacitance retention ability. The exceptional rate capability endows the electrode with a high energy density of 41.2 W h kg^?1 and a high power density of 12.0 kW kg^?1 simultaneously. The excellent performance is attributed to the sandwich hybrid nanostructure of MoO₃/C with broad ion diffusion pathway, low charge‐transfer resistance, and robust structure at high current density for long‐time cycling. The present work provides an insight into the fabrication of novel electrode materials with both enhanced rate capability and cyclability for potential use in supercapacitor and other energy storage devices.     

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Interdependence of chemical structure, thin‐film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high‐mobility, solution‐processed polymers for large‐area and flexible electronics applications. There is a specific need to achieve >1 cm² V^?1 s^?1 field‐effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron‐transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene‐diimide based donor–acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field‐effect transistors show maximum μ of 2.4 cm² V^?1 s^?1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface‐segregated prevalently edge‐on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high‐electron‐mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure–property nexus in semiconducting polymer thin films.     

Fabrication of Metal Oxides Occluded in Ordered Mesoporous Hosts via a Solid‐State Grinding Route: The Influence of Host–Guest Interactions

Solid‐state grinding is a simple and effective method to include guest species into the channels of ordered mesoporous materials with a different degree of filling. After calcination, a monolayer or several monolayers of guest species can not only form highly dispersed oxide species and other surface species on the hosts whether the template is occluded in the channels or not, but the guest species can also fill the mesoporous channels in the host and thus lead to nanowires or nanoarrays. Solid‐state salt inclusion is faster and more convenient than other inclusion routes. The absence of a solvent not only saves the time otherwise needed for evaporation but also leads to a higher degree of filling through a simple inclusion step as the void space in the pores is not occupied by the solvent. Also, the lack of competitive adsorption of solvent molecules enhances the interaction between the guest species included and the silica wall, which facilitates the high dispersion of oxide species. However, host–guest interactions that are too strong may disturb the self‐crystallization of guest species in the mesopores leading to imperfect nanocasting of the mesostructure.     

Highly Efficient Orange and Green Solid‐State Light‐Emitting Electrochemical Cells Based on Cationic IrIII Complexes with Enhanced Steric Hindrance

Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂ sb]PF₆ in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W^–1) at 2.5 V, and 7.1 % and 26.2 lm W^–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.     

Nanocomposite Hybrid Molecular Materials for Application in Solid‐State Electrochemical Supercapacitors

Molecular hybrid materials formed from polyoxometalates dispersed in conducting polymers represent an innovative concept in energy storage. This work reports in detail the first practical realization of electrodes based on these materials for energy storage in electrochemical supercapacitors. The molecular hybrids PAni/H₄SiW₁₂O₄₀, PAni/H₃PW₁₂O₄₀, and PAni/H₃PMo₁₂O₄₀ (PAni: polyaniline) have been prepared electrochemically on platinum or carbon substrates, with PAni/H₃PMo₁₂O₄₀ being the prototypical example presenting the best energy‐storage performance in the series. This hybrid displays the combined activity of its organic and inorganic components to store and release charge in solid‐state electrochemical capacitor cells, leading to a promising value of 120 F g^–1 and good cyclability beyond 1000 cycles.     

Electrochemical and Top‐Down 3D Ion‐Carving to Change Magnetic Properties

It is challenging to develop new top‐down approaches to tailor particles into subnanometer size structures on a large scale to further reveal their structure‐dependent physicochemical properties. Here, we demonstrate a non‐conventional, electrochemical, 3D ion‐carving process to tailor particles into subscale flower‐like nanostructures at room temperature. The technology is based on the electrochemical insertion/extraction of lithium ions as a carving “knife” to carve the single‐crystalline particle precursor into higher‐order, flower‐like nanostructures with hexagonal nanopetals as the building units. Our study demonstrates that the morphology of the as‐carved, flower‐like nanostructures can be controlled by the electrochemical parameters, such as the current density and the number of cycles. Particularly interesting is that dramatically different magnetic properties can be achieved depending on the morphology through careful tuning by the electrochemical ion‐carving process. The as‐carved, flower‐like particles may find many important applications, including magnetic nanodevices. Our approach, in principle, is applicable to prepare various kinds of 3D‐structured materials with different compositions.     

A Unified View on Nanoscale Packing,Connectivity, and Conductivity of CNT Networks

The design of functional structures from primary building blocks requires a thorough understanding of how size, shape, and particle–particle interactions steer the assembly process. Specifically, for electrically conductive networks build from carbon nanotubes (CNTs) combining macroscopic characterization and simulations shows that the achievable conductivity is mainly governed by CNT aspect ratio, length dispersity and attractive interactions. However, a direct link between the actual 3D network topology that leads to the observed electrical conductivity has not been established yet due to a lack in nanoscale experimental approaches. Here it is shown experimentally for randomly packed (jammed) CNT networks that the CNT aspect ratio determines, as theoretically predicted, the contact number per CNT which in turn scales linearly with the resulting electrical conductivity of the CNT network. Furthermore, nanoscale packing density, contact areas, contact distribution in random and nonrandom configurations, and least resistance pathways are quantified. The results illustrate how complex nanoscale networks can be imaged and quantified in 3D to understand and model their functional properties in a bottom‐up fashion.     

Morphology Control in Solution‐Processed Bulk‐Heterojunction Solar Cell Mixtures

The efficiency of bulk‐heterojunction solar cells is very sensitive to the nanoscale structure of the active layer. In the past, the final morphology in solution‐processed devices has been controlled by varying the casting solvent and by curing the layer using heat tempering or solvent soaking. A recipe for making the “best‐performing” morphology can be achieved using these steps. This article presents a review of several new techniques that have been developed to control the morphology in polymer/fullerene heterojunction mixtures. The techniques fall into two broad categories. First, the morphology can be controlled by preparing nanoparticle suspensions of one component. The size and shape of the nanoparticles in solution determine the size and shape of the domain in a mixed layer. Second, the morphology can be controlled by adding a secondary solvent or an additive that more strongly affects one component of the mixture during drying. In both cases, the as‐cast efficiency of the solar cell is improved with respect to the single‐solvent case, which strongly argues that morphology control is an issue that will receive increasing attention in future research.     

Capacitive Enhancement Mechanisms and Design Principles of High‐Performance Graphene Oxide‐Based All‐Solid‐State Supercapacitors

Graphene oxide (GO)‐based all‐solid‐state supercapacitors (GO‐A3Ss) are superior over liquid electrolyte‐based supercapacitors and capable of being integrated on a single chip in various geometry shapes for the use of future smart wearable electronics field as a fast energy storage device, but their capacitance need to be improved. Here, a new approach has been developed for enhancing the capacitive capability of the supercapacitors through molecular dynamics simulations with the first‐principle input. A theoretical model of charge storage is developed to understand the unique capacitive enhancement mechanism and to predict the capacitance of the GO‐A3Ss, which agrees well with the experimental observations. A novel supercapacitor with GO and reduced graphene oxide (rGO) alternatively layered structures is designed based on the model, and its energy density is the highest among conventional supercapacitors using liquid electrolytes and all‐solid‐state supercapacitors using aerogels or hydrogels as the solid‐state electrolyte. Based on the predictions, two new types of high‐performance GO/rGO multilayered capacitors are proposed to meet different practical applications. The results of this work provide an approach for the design of high‐performance all‐solid‐state supercapacitors based on GO and rGO materials.     

Enhancement of Thermoelectric Figure‐of‐Merit by a Bulk Nanostructuring Approach

Recently a significant figure‐of‐merit (ZT) improvement in the most‐studied existing thermoelectric materials has been achieved by creating nanograins and nanostructures in the grains using the combination of high‐energy ball milling and a direct‐current‐induced hot‐press process. Thermoelectric transport measurements, coupled with microstructure studies and theoretical modeling, show that the ZT improvement is the result of low lattice thermal conductivity due to the increased phonon scattering by grain boundaries and structural defects. In this article, the synthesis process and the relationship between the microstructures and the thermoelectric properties of the nanostructured thermoelectric bulk materials with an enhanced ZT value are reviewed. It is expected that the nanostructured materials described here will be useful for a variety of applications such as waste heat recovery, solar energy conversion, and environmentally friendly refrigeration.     

Excitons and Electron–Hole Liquid State in 2D γ‐Phase Group‐IV Monochalcogenides

Different dispersion near the electronic band edge of a semiconductor can have great influence on its transport, thermoelectric, and optical properties. Using first‐principles calculations, it is demonstrated that a new phase of group‐IV monochalcogenides (γ‐MX, M = Ge, Sn; X = S, Se, or Te) can be stabilized in monolayer limit. γ‐MXs are shown to possess a unique band dispersion—that is, camel's back like structure—in the top valence band. The band nesting effect near the camel's back region induces a large excitonic absorbance and significantly different exciton behaviors from other 2D materials. Importantly, the small effective mass and the indirect characteristics of lowest‐energy exciton render it advantageous for the generation of electron–hole liquid state. After careful evaluation of the electron–hole dissociation temperature and the Mott critical density, it is predicted that a high‐temperature exciton gas to electron–hole liquid phase transition can be achieved in these materials with a low excitation power density. The findings open up new opportunities for both the fundamental research on exciton physics and design of excitonic devices based on 2D materials with distinct band dispersion.     

Solid‐State NMR Investigations of the Unusual Effects Resulting from the Nanoconfinement of Water within Amphiphilic Crosslinked Polymer Networks

Two types of solid‐state ¹⁹F NMR spectroscopy experiments are used to characterize phase‐separated hyperbranched fluoropolymer–poly(ethylene glycol) (HBFP–PEG) crosslinked networks. Mobile (soft) domains are detected in the HBFP phase by a rotor‐synchronized Hahn echo under magic‐angle spinning conditions, and rigid (hard) domains by a solid echo with no magic‐angle spinning. The mobility of chains is detected in the PEG phase by ¹H → ¹³C cross‐polarization transfers with ¹H spin‐lock filters with and without magic‐angle spinning. The interface between HBFP and PEG phases is detected by a third experiment, which utilized a ¹⁹F → ¹H–(spin diffusion)–¹H → ¹³C double transfer with ¹³C solid‐echo detection. The results of these experiments show that composition‐dependent PEG inclusions in the HBFP glass rigidify on hydration, consistent with an increase in macroscopic tensile strength.     

Solution‐Processed Bulk‐Heterojunction Solar Cells Based on Monodisperse Dendritic Oligothiophenes

A novel family of soluble conjugated dendritic oligothiophenes (DOTs) as monodisperse 3D macromolecular architectures was characterized with respect to optical and redox properties in solution and in solid films. Band gaps of 2.5–2.2 eV, typical for organic semiconductors, were determined as well as HOMO/LUMO energy levels ideal for efficient electron transfer to acceptors such as [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) identifying them as suitable materials for solar cell applications. Solution‐processed bulk‐heterojunction solar cells using DOTs as electron donor and PCBM as acceptor were prepared and investigated. High open‐circuit voltages V_OC of 1.0 V and power‐conversion efficiencies up to 1.72% were obtained for the DOT‐based devices. The higher generations DOTs provide the highest efficiencies. Based on the monodispersity of the DOTs, an analysis of the molar ratio between donor and acceptor in the blended film was possible leading to an optimal value of five to six thiophene units per PCBM.     

Flame‐Synthesized Ceria‐Supported Copper Dimers for Preferential Oxidation of CO

Rapid synthesis of Cu? CeO₂ catalysts by flame spray pyrolysis produces highly active Cu dimer morphologies without the need for additional catalyst pretreatment. The active Cu component is enriched onto the CeO₂ surface at concentrations higher than the nominal loading with no evidence of amorphous or crystalline CuO phase. Increasing the Cu content results in a morphological transition from isolated Cu monomers to oxygen‐bridged dimers and an associated increase in oxygen vacancy concentration. Dimer‐containing Cu? CeO₂ catalysts display high levels of activity and selectivity in the low‐temperature preferential oxidation of CO. Experimental measurements and simulations suggest that the geometry of the dimer presents a comparatively ionic Cu? O bond at the catalyst surface. Further studies indicate that these ionic dimer species promote preferential CO oxidation at lower temperatures than observed for monomeric Cu species. This is the first report to explicitly propose and demonstrate that the structural distortion associated with the formation of Cu dimers directly induces increased bond ionicity at the catalyst surface and that these changes are responsible for improved catalytic activity.     

High Electroactive Material Loading on a Carbon Nanotube@3D Graphene Aerogel for High‐Performance Flexible All‐Solid‐State Asymmetric Supercapacitors

Freestanding carbon‐based hybrids, specifically carbon nanotube@3D graphene (CNTs@3DG) hybrid, are of great interest in electrochemical energy storage. However, the large holes (about 400 µm) in the commonly used 3D graphene foams (3DGF) constitute as high as 90% of the electrode volume, resulting in a very low loading of electroactive materials that is electrically connected to the carbon, which makes it difficult for flexible supercapacitors to achieve high gravimetric and volumetric energy density. Here, a hierarchically porous carbon hybrid is fabricated by growing 1D CNTs on 3D graphene aerogel (CNTs@3DGA) using a facile one‐step chemical vapor deposition process. In this architecture, the 3DGA with ample interconnected micrometer‐sized pores (about 5 µm) dramatically enhances mass loading of electroactive materials comparing with 3DGF. An optimized all‐solid‐state asymmetric supercapacitor (AASC) based on MnO₂@CNTs@3DGA and Ppy@CNTs@3DGA electrodes exhibits high volumetric energy density of 3.85 mW h cm^?3 and superior long‐term cycle stability with 84.6% retention after 20 000 cycles, which are among the best reported for AASCs with both electrodes made of pseudocapacitive electroactive materials.     

Oxygen Vacancies and Ordering of d‐levels Control Voltage Suppression in Oxide Cathodes: the Case of Spinel LiNi0.5Mn1.5O4‐δ

This study presents a microscopic model for the correlation between the concentration of oxygen vacancies and voltage suppression in high voltage spinel cathodes for Li‐ion batteries. Using first principles simulations, it is shown that neutral oxygen vacancies in LiNi_0.5Mn_1.5O_4‐δ promote substitutional Ni/Mn disorder and the formation of Ni‐rich and Ni‐poor regions. The former trap oxygen vacancies, while the latter trap electrons associated with these vacancies. This leads to the creation of deep and shallow Mn³⁺ states and affects the stability of the lattice Li ions. Together, these two factors result in a characteristic profile of the voltage dependence on Li content. This insight provides guidance for mitigating the voltage suppression in LiNi_0.5Mn_1.5O₄ and other cathodes.     

The Performance of Small‐Pore Microporous Aluminophosphates in Low‐Temperature Solar Energy Storage: The Structure–Property Relationship

The utilization of the reversible chemical and physical sorption of water on solids provides a new thermal energy storage concept with a great potential for lossless long‐term storage. The performance of microporous aluminophosphates in heat storage applications is highlighted by a comparative thermogravimetric and calorimetric study of three known materials (SAPO‐34, AlPO₄‐18, APO‐Tric) and is correlated with their structural features. The maximum water sorption capacity is similar for all three samples and results in a stored energy density of 240 kWh m^?3 in the 40–140 °C range. The elemental composition influences the gradual (silicoaluminophosphate SAPO‐34) or sudden (aluminophosphates AlPO₄‐18, APO‐Tric) water uptake, with the latter being favourable in storage systems. The driving force for the determined sorption process is the formation of highly ordered water clusters in the pores, which is enabled by rapid and reversible changes in the Al coordination and optimal pore diameters. The ease with which changes in the Al coordination can occur in APO‐Tric is related to the use of the fluoride route in the synthesis. The understanding of these fundamental structure/sorption relationships forms an excellent basis for predicting the storage potential of numerous known or new microporous aluminophosphates and other porous materials from their crystal structures.