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This study investigates the electrical properties of electrospun ceramic fiber mats based on potassium sodium niobate ((K,Na)NbO3;KNN) for potential applications in soft‐robotic tactile sensors. The rheological studies of electrospinning solutions exhibit shear thinning behavior, with a viscosity plateau between shear rates of 1–100 s−1. The thermal decomposition behavior of the KNN samples is analyzed using thermogravimetric analysis; the samples show multistep decomposition processes leading into a phase pure perovskite structure. For the electrospun KNN fiber mats, the electrical characterization reveals ferroelectric hysteresis loops with a high leakage current of ≈270 nA at 20 kV cm−1 and switching current behavior. The ferroelectric results indicate that a full polarization of KNN‐fiber mats is not possible due to their electrical breakdown at high electrical fields. The integration of KNN short fibers into a soft‐bending actuator demonstrates successful tactile sensing capabilities. The experimental findings reported here highlight the potential of electrospun KNN fiber mats for flexible and autonomous device applications in soft robotics. [ABSTRACT FROM AUTHOR]

Bismuth ferrite (BiFeO3, BFO) has found application in a wide range of fields owing to its fascinating multiferroic properties. Herein, the interplay between the piezoelectric properties and morphology of BFO nanostructures is exploited for vibrational energy harvesting application by tailoring BFO to a high aspect ratio and high surface area nanofiber morphology. This work demonstrates a facile pathway for the fabrication of high‐performance flexible nanogenerators, based on BFO nanofibers, from a cost‐effective and energy‐efficient electrospinning technique. The X‐ray diffraction data of calcined fibers confirm the formation of noncentrosymmetric crystalline perovskite phase. The morphological characterization by scanning electron microscopy shows a compact anisotropic nanofibrous morphology. For the fabrication of nanogenerators, BFO nanofibers are embedded in a piezoactive polymer matrix (polyvinylidenfluoride [PVDF]). As‐fabricated BFO/PVDF composite nanogenerators produce a high peak‐to‐peak voltage output of 7.6 V, with an average output power density of 185 ± 106 nW cm−2 upon periodic application of force through finger knocking. [ABSTRACT FROM AUTHOR]

The synthesis of a novel air-stable molecular precursor (LiSC2H4)2NMe enables the formation of the desired 1D lithium sulfide (Li2S) via the electrospinning method under ambient conditions. The solubility of the precursor in polar solvents combined with a common polymer (PVP) allowed a suitable spinning solution to obtain ideal green Li2S loaded fibers. 3D fiber mats of the calcined homogeneous 1D electrospun Li2S/C fibers were characterized by electron microscopy and X-ray powder diffraction analysis. Direct integration of Li2S in an electronically conductive carbon matrix as the cathode obviates the need of elemental lithium as the anode, which is a great advantage against the reported lithium-sulfur batteries. An initial capacity of about 870 mA h g1 at C/20, a capacity retention of 73% after 100 cycles at C/10 and a capacity of about 400 mA h g1 at 1C were observed for the presented system. [ABSTRACT FROM AUTHOR]

Electromechanical energy demands on homogenous thick films of piezoceramics with sufficiently large piezoelectric constant and reproducible performance. Single‐phase LiTaO3 films deposited by sol‐gel processing have been fabricated as cantilevers to investigate the interdependence of dielectric and piezoelectric properties as a function of film thickness. Phase pure LiTaO3 films with varying thickness in the range of 2.07‐4.37 µm on stainless steel substrates were obtained after calcination of samples at 650°C. The relative permittivity of optimized spin‐coated films peaked at 479.73 (1 kHz), whereas the piezoelectric coefficient (d33 mode) determined by piezoresponse force microscopy was in the range of 21‐24 pm/V. The effect of poling was studied through the butterfly and phase curves. A figure of merit (FOM) up to 3.29 (10−18 m2/V2) was determined for cantilever devices, which were able to generate a peak‐to‐peak voltage of 0.046‐0.15 V using a 1 MΩ resistor as an impedance load at a fixed acceleration of 1.5 m/s2. While the power density was in the range of ~4‐20 × 10−9 W/m3, which increased with the increasing film thickness. The leakage current density decreased in the range of 4 × 10−5‐6 × 10−7 A/m2 in the same direction. As both ferroelectric and piezoelectric properties of LiTaO3 films are dependent on film thickness, an optimal energy conversion efficiency was obtained for a thickness of ~3 µm. Furthermore, these devices were tested up to a temperature of 150°C for voltage generation. Given the need for lead‐free piezoelectric materials for environmental applications, these LiTaO3 cantilevers are very promising for vibrational energy harvester (VEH) applications especially due to their cost effectiveness, small size, stability at higher temperatures, and repeatable properties, which makes them suitable for MEMS devices for industrial applications. [ABSTRACT FROM AUTHOR]

Crystalline and amorphous organic materials are an emergent class of heterogeneous photocatalysts for the generation of hydrogen from water, but a direct correlation between their structures and the resulting properties has not been achieved so far. To make a meaningful comparison between structurally different, yet chemically similar porous polymers, two porous polymorphs of a triazine‐based graphdiyne (TzG) framework are synthesized by a simple, one‐pot homocoupling polymerization reaction using as catalysts CuI for TzGCu and PdII/CuI for TzGPd/Cu. The polymers form through irreversible coupling reactions and give rise to a crystalline (TzGCu) and an amorphous (TzGPd/Cu) polymorph. Notably, the crystalline and amorphous polymorphs are narrow‐gap semiconductors with permanent surface areas of 660 m2 g−1 and 392 m2 g−1, respectively. Hence, both polymers are ideal heterogeneous photocatalysts for water splitting with some of the highest hydrogen evolution rates reported to date (up to 972 μmol h−1 g−1 with and 276 μmol h−1 g−1 without Pt cocatalyst). Crystalline order is found to improve delocalization, whereas the amorphous polymorph requires a cocatalyst for efficient charge transfer. This will need to be considered in future rational design of polymer catalysts and organic electronics. Polymeric polymorphs: Triazine‐based graphdiyne polymers are obtained as crystalline and amorphous polymorphs. These polymers are indirect band‐gap semiconductors with permanent porosity and, hence, of interest as photocatalysts. The crystalline polymorph has efficient charge carrier mobility, owing to an ordered π‐aromatic backbone. The amorphous polymorph confines charge carriers locally and is highly fluorescent. [ABSTRACT FROM AUTHOR]

Water splitting using polymer photocatalysts is a key technology to a truly sustainable hydrogen‐based energy economy. Synthetic chemists have intuitively tried to enhance photocatalytic activity by tuning the length of π‐conjugated domains of their semiconducting polymers, but the increasing flexibility and hydrophobicity of ever‐larger organic building blocks leads to adverse effects such as structural collapse and inaccessible catalytic sites. To reach the ideal optical band gap of about 2.3 eV, A library of eight sulfur and nitrogen containing porous polymers (SNPs) with similar geometries but with optical band gaps ranging from 2.07 to 2.60 eV was synthesized using Stille coupling. These polymers combine π‐conjugated electron‐withdrawing triazine (C3N3) and electron donating, sulfur‐containing moieties as covalently bonded donor–acceptor frameworks with permanent porosity. The remarkable optical properties of SNPs enable fluorescence on‐off sensing of volatile organic compounds and illustrate intrinsic charge‐transfer effects. [ABSTRACT FROM AUTHOR]

Light-driven water splitting is a potential source of abundant, clean energy, yet efficient charge-separation and size and position of the bandgap in heterogeneous photocatalysts are challenging to predict and design. Synthetic attempts to tune the bandgap of polymer photocatalysts classically rely on variations of the sizes of their π-conjugated domains. However, only donor-acceptor dyads hold the key to prevent undesired electron-hole recombination within the catalyst via efficient charge separation. Building on our previous success in incorporating electron-donating, sulphur-containing linkers and electron-withdrawing, triazine (C 3 N 3 ) units into porous polymers, we report the synthesis of six visible-light-active, triazine-based polymers with a high heteroatom-content of S and N that photocatalytically generate H 2 from water: up to 915 μmol h -1  g -1 with Pt co-catalyst, and-as one of the highest to-date reported values -200 μmol h -1  g -1 without. The highly modular Sonogashira-Hagihara cross-coupling reaction we employ, enables a systematic study of mixed (S, N, C) and (N, C)-only polymer systems. Our results highlight that photocatalytic water-splitting does not only require an ideal optical bandgap of ≈2.2 eV, but that the choice of donor-acceptor motifs profoundly impacts charge-transfer and catalytic activity., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Donor-acceptor dyads hold the key to tuning of electrochemical properties and enhanced mobility of charge carriers, yet their incorporation into a heterogeneous polymer network proves difficulty owing to the fundamentally different chemistry of the donor and acceptor subunits. A family of sulfur- and nitrogen-containing porous polymers (SNPs) are obtained via Sonogashira-Hagihara cross-coupling and combine electron-withdrawing triazine (C 3 N 3 ) and electron-donating, sulfur-containing linkers. Choice of building blocks and synthetic conditions determines the optical band gap (from 1.67 to 2.58 eV) and nanoscale ordering of these microporous materials with BET surface areas of up to 545 m 2  g -1 and CO 2 capacities up to 1.56 mmol g -1 . Our results highlight the advantages of the modular design of SNPs, and one of the highest photocatalytic hydrogen evolution rates for a cross-linked polymer without Pt co-catalyst is attained (194 μmol h -1  g -1 )., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)