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Abstract With the huge variety of wearable/stretchable electronic devices that require materials with different properties depending on the applications, securing the large reserves of stretchable material systems is crucial. In this study, trimethylolpropane formal acrylate (TFA)-based polymer films are explored to develop stretchable composite electrodes. The TFA resin containing 1-hydroxycyclohexyl phenyl ketone as a photoinitiator is UV curable and shows a high optical transmittance of ∼93.0 ± 0.3% and a low haze of ∼0.29 ± 0.03%. The TFA films can withstand a tensile strain up to 100% and show excellent mechanical reliability during 30 cycles of tensile tests. Furthermore, the elastomeric TFA films are attachable to polymer or glass substrates, and during multiple adhesion tests, show a lower degradation of the adhesion properties than that showed by typical adhesive materials such as scotch tapes. The electrodes fabricated by embedding Ag nanowires in the surface of the TFA films (TFA/Ag nanowire electrodes) function as stretchable/patchable conductors under severe mechanical deformation such as stretching and crumpling. Furthermore, a patchable/stretchable supercapacitor comprising the TFA/Ag nanowire electrodes as a current collector is demonstrated that shows a reliable electrochemical performance under bending, stretching, and twisting conditions. [ABSTRACT FROM AUTHOR]

In this study, we explored the facile and quick dry transfer method to fabricate a paper-based electrode for flexible printed energy storage system. The conventional Ag nanoparticle suspension with high solid contents above ~50 wt% was confirmed to be deposited on a super hydrophobic polyethylene terephthalate (SHP-PET) substrate without a special ink formulation or surface treatment of substrate. The silver nanoparticle (AgNP) layer on the SHP-PET was able to be transferred only onto the toner-printed region of the paper substrate during a simple lamination process, thereby realizing the patterned AgNP conductive lines on the paper substrates. The AgNP/toner/paper electrodes were highly robust, showing no deterioration in conductivity after taping for 100 times. Moreover, the AgNP/toner/paper electrodes successfully functioned as flexible electrodes; thus, light emitting diodes connected to the AgNP/paper electrodes could be operated under folding deformation without significant loss of brightness. As a potential application in flexible energy storage systems, a flexible supercapacitor based on the AgNP/toner/paper electrodes as the current collector was also demonstrated; it showed an excellent power density of 10.79–16.64 kW/kg and energy density of 1.85–4.65 Wh/kg. [ABSTRACT FROM AUTHOR]

Micro-architectures, such as cellular truss structures, enhance the mechanical properties of structural materials while ensuring that they are lightweight in nature. Among others, stretching-dominated truss structures are known for their high modulus and yield strength, which makes them the best choice for lightweight structural applications. Finite element analysis of octahedral vs. octet structures is used to compare the differences in stress distribution in the stretching-dominated deformation of such trusses. Both octahedral and octet stretching-dominated structures were fabricated by fused deposition modeling (FDM)-based three-dimensional (3D) printing. These micro-architectures are printed with different polymeric materials, such as polylactic acid or polylactide (PLA), nylon 618, and a carbon fiber reinforced composite of PLA (CFRPLA). In addition, the CFRPLA filament with randomly suspended carbon fibers in PLA undergoes shear-induced alignment along the strut direction of the 3D printed micro-trusses, which leads to an improved Young's modulus as compared to the other materials. The properties of the 3D printed stretching-dominated micro-trusses are evaluated by compression testing, finite element analysis (FEA), and thermal analysis. The 3D printed octet structure of CFRPLA with fiber alignment exhibits the highest modulus and yield strength of 0.6 GPa and 17 MPa, respectively. [ABSTRACT FROM AUTHOR]

Hydro-electric technology has gathered much attention by the virtue of water as the energy source. However, the low energy density of this technology severely limits its practical use. Here, we demonstrate a PEDOT:PSS-based transpiration-driven electrokinetic power generator (p-TEPG) that enables the utilization of a wider variety of real-world water resources for maximizing energy generation efficiencies. In addition to the conventional electrical double layer on the material surface, the p-TEPG builds an additional potential difference in the polymer matrix by the selective penetration of cations into the matrix that contains sulfonate functional groups. p-TEPG exhibits 80–250% higher energy density than carbon-based TEPG at the same resistance. Moreover, seawater produced enhanced volumetric energy/power densities (34.36 mJ cm−3 and 44.70 μW cm−3) and areal energy/power densities (410 μJ cm−2 and 0.45 μW cm−2), respectively, compared to DI water on a single p-TEPG device, which is sufficient to charge electrical energy storage systems and directly operate low-powered electronic. • p-TEPG maximizes energy harvesting efficiency by ion-permselective PEDOT:PSS. • Green water resources improve performance of p-TEPG. • p-TEPG adsorbs more cations into its polymer matrix by sulfonate groups. • p-TEPG can increases energy harvesting efficiency by using anions and cations with smaller radii. • p-TEPG can be fueled with seawater, demonstrating its potential for blue energy generating system. [ABSTRACT FROM AUTHOR]

Wearable energy storage system must maintain robust electrochemical performance under severe mechanical and chemical deformations. Here, we demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. The carbonized mulberry paper (MP) was used as an electrode to achieve improved volumetric energy density as well as mechanical-chemical reliability (e.g. mechanical toughness and acid resistance). Rationally designed active materials composed of vertically grown WO 3 NRs and reduced graphene oxide (rGO) anchored on MP, were employed for developing organism epidermis based supercapacitor. Such electrode exhibits high volumetric energy and power densities of 30.28 mWh cm−3 and 7.67 W cm−3, retaining the volumetric capacitance of 96.0% even after 110,000 charge-discharge cycles. As the final step, we employed the gelatin based electrolyte with high ionic conductivity to solve evaporation and leakage problems of conventional electrolytes. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its gareat suitability as a large-scale wearable energy storage system. We demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its great suitability as a large-scale wearable energy storage system. [Display omitted] • We maximized areal and volumetric electrochemical performance (energy & power densities) and mechanical/chemical toughness through carbonized mulberry paper integrated with reduced graphene oxide (rGO) layer. Mulberry fibers inherently show excellent mechanical flexibility and acid resistance, since they have lower portion of lignin cellulose (~40%) compared with conventional paper fiber. However, electrochemically inactive mulberry fiber exhibits still low areal/volumetric energy densities and electrochemical reliability. Thus, we used carbonized mulberry paper as a substrate and electrode in this study, which was maximized for volumetric energy/power densities and mechanical/chemical toughness. • We have designed the plant-root inspired active materials structure with excellent electrochemical reliability and performances. Inspired from plant-root, we synthesized active materials structure by one-step reduction heat treatment, where WO 3 nanorods (NRs) vertically grow within the spaces of rGO and are anchored as strongly as plant-root on the carbonized mulberry fibers. The anchored structure can effectively maintain electrochemical performance and flexibility of carbonized paper by preventing delamination of WO 3 NRs even without protection layer. WO 3 NRs anchored carbonized mulberry paper (thickness 110 µm) with rGO layer exhibits volumetric capacitance retention of 96% for 110,000 cycles. In addition, maximum volumetric energy and power densities were increased to 30.28 mWh cm−3 and 7.67 W cm−3 (improvement of 220%). • Conventional liquid and gel-type electrolyte have critical issues including evaporation under ambient condition and leakage under mechanical bending-twisting deformation. Such problems are main causes of rapid electrochemical performance degradation. In our work, gelatin based hydrogel electrolyte extracted from porcine skin was integrated with electrode, in order to fabricate wearable energy storage system that is capable of operating in ambient conditions. The gelatin based hydrogel electrolyte can retain water contents and high ionic conductivity under ambient condition over 2 weeks. Ionic conductivity maintained 90.3% (228 mS cm−1) after two weeks of exposure to ambient condition, and the moisture content was maintained 98.0%. • We further extended organism epidermis based supercapacitor to large-scale application capable of operation in ambient condition. High hydrophilicity of mulberry paper enables the uniform deposition of precursor material for growth of WO 3 , i.e, WO 3 precursor, that is dispersed in the aqueous solution. As a result, GO and WO 3 precursor were uniformly deposited on large-area electrode with 9, 25, 49 cm2 followed by carbonization, resulting in the fabrication of large-scale organism epidermis based supercapacitor. [ABSTRACT FROM AUTHOR]

The development of highly stable and efficient oxide-based red phosphors is urgently required for next-generation lighting devices. Herein, we report the micro/crystal structures and luminescent properties of single-phase Eu 2 (WO 4) 3 and Eu3+-doped WO 3 -Eu 2 (WO 4) 3 composite phosphors prepared by a one-step conventional solid-state reaction method in air atmosphere. As increasing Eu contents in the mixtures of WO 3 and Eu 2 O 3 , the intensities of the X-ray diffraction peaks of Eu 2 (WO 4) 3 increased while that of WO 3 decreased. The photoluminescence intensity of the synthesized phosphors increased with increase in the Eu content when calcined at 900 °C, while it degraded at a higher temperature. Red-emitting single-phase Eu 2 (WO 4) 3 powders were successfully obtained when the WO 3 and Eu 2 O 3 powders were calcined in the ratio of 3:1. The intensity of the red emission spectra of the Eu 2 (WO 4) 3 phosphor was higher than those of the 6, 12, and 24 at.% Eu-added WO 3 composites at excitation wavelengths of 394 and 465 nm. On the other hand, the intensity of emission from the single-phase phosphor was lower than that of the Eu-doped WO 3 -Eu 2 (WO 4) 3 composites under excitation of UV light at 254 nm. Thus, we propose two prospective phosphors for application as red phosphors at various wavelengths. [ABSTRACT FROM AUTHOR]

• Synthesis of MFC from low-grade gum wastes. • The synthesized MFC possesses high tap density (1.4–1.7 g cm−3). • High tap density leads to outstanding volumetric capacity at 3.0 A g−1. • MFC also exhibits ultra-stable high-rate cyclability (0.001881% decrease per cycle). • Structural integrity was well maintained even after cycling. Among various natural wastes, gum wastes pose major issues, as they are unusable and hard to be disposed due to their acidic and sticky nature. Herein, a rational synthetic strategy is employed to transform various kinds of gum wastes into micron-sized carbon, which also exhibit high tap density (1.4–1.7 g cm−3) desirable for practical application in lithium-ion batteries (LIBs). Gum karaya (GK) micron-size functional carbon (GKMFC) exhibits the most outstanding electrochemical performance, with a volumetric capacity of 175.4 mAh cm−3 at a current density of 3000 mA g−1 for 5000 cycles, and possesses ultra-stable high-rate cyclability (a capacity decay of only 0.001881% per cycle). Additional electrochemical analyses reveal that GKMFC exhibits stable structural integrity as well as minimal cell resistance even after cycling, showing its practical application as viable electrode for LIBs. This work sheds light on utilizing high tap density carbon from gum wastes for LIBs, which can also be applicable to other natural wastes and carbon. Image, graphical abstract [ABSTRACT FROM AUTHOR]