Conductive-Polymer-Based Double-Network Hydrogels for Wearable Supercapacitors.

Enhanced strength and toughness of κ-carrageenan/polyacrylic acid physical double-network hydrogels by dual cross-linking of the first network

• Innovative fabrication method The study introduces a novel approach for fabricating flexible, freestanding UV sensors using additive manufacturing, specifically Direct Ink Writing (DIW), integrating tetrapodal zinc oxide (t-ZnO) particles and carbon nanotubes (CNTs) in a polyvinyl butyral (PVB) matrix. • Laser milling for functionality A selective laser milling process is employed to expose the semi-embedded t-ZnO particles, enabling effective UV sensing while preserving the flexibility and structural integrity of the printed sensor. • Enhanced adaptability The flexible sensors can be attached to a wide variety of surfaces and surface geometries, enabling potential applications in wearable electronics, soft robotics, and the Internet of Things (IoT). • Robust mechanical performance The sensor demonstrates robust mechanical stability, retaining its UV sensing capabilities under cyclic stretching and compression, with only minor current fluctuations, indicating excellent structural integrity of the particle network and polymer matrix. The fabrication of microelectronics via additive manufacturing holds previously inaccessible potential compared to cleanroom-based technologies. Printing electronics is comparably simple and cost-efficient. The main advantage, however, lies in the choice of materials. While cleanroom-based fabrication always has a two-dimensional topology, printed electronics can involve inherently complex-shaped micro- and nanoparticles with outstanding functionalities. This work reports on an approach for the assembly of flexible, ultraviolet light (UV) sensors involving complex-shaped tetrapodal zinc oxide (t-ZnO) particles and carbon nanotubes via direct ink writing (DIW). The morphology of these particles eliminates the need for traditional methods of processing; instead, they can be processed through printing a particle-laden polymer solution. This approach enables to shape the functional t-ZnO particles in a facile and fast manner. A subsequent laser milling process removes the binder polymer from the top layers and exposes the semi-embedded particles, effectively forming a UV sensor. This sensor then exhibits a UV responsivity of 0.29 ± 0.01 µA/(W/cm 2 ) and an UV on off current ratio of over 500 in a span of 10 s while maintaining the flexibility of the binder polymer. This flexibility also allows the attachment of the sensor to a great variety of surfaces and surface geometries and facilitates the formation of free-standing structures. The sensors flexibility and I on /I off ratios are maintained up to a bending radius of 5 mm and also under cyclic mechanical deformation, which tested up to 1000 cycles.

Flexible pressure sensors have received wide attention because of their potential applications in wearable electronics and electronic skins (e-skins). However, the high performance of the pressure sensors relies principally on the introduction of complex surface microstructures, which often involves either complicated procedures or costly microfabrication methods. Moreover, these devices predominantly use synthetic polymers as flexible substrates, which are generally nonbiodegradable or not ecofriendly. Here, we report a facile and scalable processing strategy to convert naturally rigid wood into reduced graphene oxide (rGO)-modified flexible wood (FW/rGO) via saw cutting, chemical treatment, and rGO coating, resulting in high-performance wood-based flexible piezoresistive pressure sensors. Benefiting from the largely deformable ribbon-like surface microstructures, the obtained wood-based pressure sensor displayed a high sensitivity of 1.85 kPa-1 over a broad linear range up to 60 kPa and showed high stability over 10 000 cyclic pressings. The favorable sensing performance of the pressure sensor allows for accurate recognition of finger movements, acoustic vibrations, and real-time pulse waves. Moreover, a large-area pressure sensor array has been successfully assembled on one piece of flexible wood for spatial pressure mapping. The proposed strategy of directly using natural wood for high-performance flexible pressure sensors is simple, low-cost, sustainable, and scalable, opening up a new avenue for the development of next-generation wearable electronics and e-skins.

High-performance and flexible solid-state supercapacitors based on high toughness and thermoplastic poly(vinyl alcohol)/NaCl/glycerol supramolecular gel polymer electrolyte

A series of polylactic acid-polyethylene glycol-polylactic acid diacrylate macromers (PEGLM) were synthesized, and a novel chitosan-PEGLM double network (DN) hydrogel was further successfully fabricated by the sequential interpenetrating technology with highly cross-linked chitosan as the rigid component and PEGLM as the flexible component. Their structures and components were characterized by 1H NMR, FTIR, and XRD. Their fracture morphology was investigated by SEM. It was interesting to found that the compressive strength of hydrogel wound reach its maximum value when the chitosan content was 10%, no matter what the molecular weight of PEGLM component was. What’s more, we found that the compressive strength of 6KL7 could reach 1.07 MPa at gel state, whose PEG segment molecular weight was 6,000, and polymerization degree of PLA was 7. The effects of glutaraldehyde ratio, polymerization degree of PLA, and molecular weight of PEG segment on the mechanical strength of DN hydrogels were also discussed in this article. To further strengthen DN hydrogels, the double network-linear (DNL) hydrogels were fabricated by introducing linear poly(vinyl alcohol) (PVA) into the DN hydrogels. The DN-L hydrogels exhibited better mechanical properties, with the compressive strength up to 1.45 MPa. These hydrogels may have prospective applications in the fields of wound dressing, artificial cartilage and tissue engineering scaffold materials which require high mechanical properties. Open image in new window

LaMnO3 nanocomposite double network hydrogel electrodes with enhanced electrochemical and mechanical performance for flexible supercapacitors

Fiber-based inorganic thermoelectric (TE) devices, owing to the small size, light-weight, flexibility, and high TE performance, are promising for applications in flexible thermoelectrics. Unfortunately, current inorganic TE fibers are strictly constrained by limited mechanical freedom because of the undesirable tensile strain, typically limited to a value of 1.5%, posing a strong obstacle for further application in large-scale wearable systems. Here, a superflexible Ag2 Te0.6 S0.4 inorganic TE fiber is demonstrated that provides a record tensile strain of 21.2%, such that it enables various complex deformations. Importantly, the TE performance of the fiber shows high stability after ≈1000 cycles of bending and releasing processes with a small bending radius of 5mm. This allows for the integration of the inorganic TE fiber into 3D wearable fabric, yielding a normalized power density of 0.4µWm-1 K-2 under the temperature difference of 20 K, which is approaching the high-performance Bi2 Te3 -based inorganic TE fabric and is nearly two orders of magnitude higher than the organic TE fabrics. These results highlight that the inorganic TE fiber with both superior shape-conformable ability and high TE performance may find potential applications in wearable electronics.

Elastic Cu@PPy sponge for hybrid device with energy conversion and storage

Colloidal quantum dots (QDs) have garnered significant interest in optoelectronics, with notable progress in material design and device engineering, leading to high-performance light-emitting diodes, solar cells, and photodetectors. Looking ahead, QDs also promise next-generation mechanically robust optoelectronics, where devices maintain reliable functionality under strain or deformation. In this talk, I will discuss the fundamental challenges of integrating mechanical resilience into QD solids without compromising their optical quality or charge transport. I will highlight strategies we have developed to address these challenges, including the design of QD–polymer hybrid heterostructures and rethinking device architectures and their processing conditions. These approaches have enabled the realization of intrinsically stretchable QD-based LEDs, with potential applications in wearable electronics and healthcare. I will conclude by discussing future opportunities for lightweight and robust QD photovoltaics.

Conductive cotton fabrics were obtained via in situ aniline polymerization by laccase from Myceliophthora thermophila under mild reaction conditions without the addition of strong proton acids. The reactions were conducted using two types of reactors, namely a water bath (WB) and an ultrasonic bath (US), and the role of a mediator, 1-hydroxybenzotriazol (HBT), on the laccase-assisted polymerization of aniline was investigated. A similar polymerization degree was obtained when using both reactors—however, the ultrasonic bath allowed the experiments to be conducted in shorter periods of time (24 h for WB vs. 2 h for US). The data obtained also revealed that the mediator (1-hydroxybenzotriazol-HBT) played a crucial role in aniline oxidation. A higher conversion yield and polymerization degree were obtained when the reaction was conducted in the presence of this compound, as confirmed by MALDI-TOF analysis. The cotton fabrics coated with polyaniline presented deep coloration and conductivity, especially when the mediator was included on the reactional system. The results obtained are a step forward in the enzymatic polymerization of aniline with the purpose of obtaining coloured conductive textile surfaces, with potential applications in wearable electronics.

The V-VI binary chalcogenide, Sb2Se3, has attracted considerable attention for its applications in thin film optoelectronic devices because of its unique 1D structure and remarkable optoelectronic properties. Herein, we report an Sb2Se3 thin film epitaxially grown on a flexible mica substrate through a relatively weak (van der Waals) interaction by vapor transport deposition. The epitaxial Sb2Se3 thin films exhibit a single (120) out-of-plane orientation and a 0.25° full width at half-maximum of (120) rocking curve in X-ray diffraction, confirming the high crystallinity of the epitaxial films. The Sb2Se3(120) plane is epitaxially aligned on mica(001) surface with the in-plane relationship of Sb2Se3[2̅10]//mica[010] and Sb2Se3[001]//mica[100]. Compared to the photodetector made of a nonepitaxial Sb2Se3 film, the photocurrent of the epitaxial Sb2Se3 film photodetector is almost doubled. Furthermore, because of the flexibility and high sensitivity of the epitaxial Sb2Se3 film photodetector on mica, it has been successfully employed to detect the heart rate of a person. These encouraging results will facilitate the development of epitaxial Sb2Se3 film-based devices and potential applications in wearable electronics.

Aqueous sodium‐ion battery of low cost, inherent safety, and environmental benignity holds substantial promise for new‐generation energy storage applications. However, the narrow potential window of water and the enlarged ionic radius because of hydration restrict the selection of electrode materials used in the aqueous electrolyte. Here, inspired by the efficient redox reaction of biomolecules during cellular energy metabolism, a proof of concept is proposed that the redox‐active biomolecule alizarin can act as a novel electrode material for the aqueous sodium‐ion battery. It is demonstrated that the specific capacity of the self‐assembled alizarin nanowires can reach as high as 233.1 mA h g−1, surpassing the majority of anodes ever utilized in the aqueous sodium‐ion batteries. Paired with biocompatible and biodegradable polypyrrole, this full battery system shows excellent sodium storage ability and flexibility, indicating its potential applications in wearable electronics and biointegrated devices. It is also shown that the electrochemical properties of electrodes can be tailored by manipulating naturally occurring 9,10‐anthroquinones with various substituent groups, which broadens application prospect of biomolecules in aqueous sodium‐ion batteries.

With the swift advancement of wearable electronics and artificial intelligence, the integration of electronic devices with the human body has advanced significantly, leading to enhanced real-time health monitoring and remote disease diagnosis. Despite progress in developing stretchable materials with skin-like mechanical properties, there remains a need for materials that also exhibit high optical transparency. Supercapacitors, as promising energy storage devices, offer advantages such as portability, long cycle life, and rapid charge/discharge rates, but achieving high capacity, stretchability, and transparency simultaneously remains challenging. This study combines the stretchable, transparent polymer PEDOT:PSS with MnO2 nanoparticles to develop high-performance, stretchable, and transparent supercapacitors. PEDOT:PSS films were deposited on a PDMS substrate using a spin-coating method, followed by electrochemical deposition of MnO2 nanoparticles. This method ensured that the nanosized MnO2 particles were uniformly distributed, maintaining the transparency and stretchability of PEDOT:PSS. The resulting PEDOT:PSS/MnO2 nanoparticle electrodes were gathered into a symmetric device using a LiCl/PVA gel electrolyte, achieving an areal capacitance of 1.14 mF cm-2 at 71.2% transparency and maintaining 89.92% capacitance after 5000 cycles of 20% strain. This work presents a scalable and economical technique to manufacturing supercapacitors that combine high capacity, transparency, and mechanical stretchability, suggesting potential applications in wearable electronics.

Supercapacitors are known to have superior power densities over batteries due to their surface-centered charge-discharge processes. Recently, increasing attention has accumulated in the fiber or yarn shaped supercapacitor (FSC) systems, mainly due to their high flexibility and pliable nature, leading to potential applications in wearable electronics, microrobots, medical implants, and smart textiles. However, one of the major limitations that occurs when supercapacitors are made into fiber/yarn shapes, is the increased equivalent series resistance (ESR) due to the fibrous geometry adopted here. For instance, even the best FSC reported will exhibit several hundred ohms of resistance at one-meter length, which however is usually neglected by researchers in their publication. To directly tackle this issue, here we report our strategies of using a metallic core filament in the yarn supercapacitors development in our lab. With detailed materials and process engineering, we are able to boost the power density by one order of magnitude. Sealing strategies and other alternative solutions for this issue will also be discussed.

To address the resource-competing issue between high sensitivity and wide working range for a stand-alone sensor, development of capacitive sensors with an adjustable gap between two electrodes has been of growing interest. While several approaches have been developed to fabricate tunable capacitive sensors, it remains challenging to achieve, simultaneously, a broad range of tunable sensitivity and working range in a single device. In this work, a 3D capacitive sensor with a seesaw-like shape is designed and fabricated by the controlled compressive buckling assembly, which leverages the mechanically tunable configuration to achieve high-precision force sensing (resolution ~5.22 nN) and unprecedented adjustment range (by ~33 times) of sensitivity. The mechanical tests under different loading conditions demonstrate the stability and reliability of capacitive sensors. Incorporation of an asymmetric seesaw-like structure design in the capacitive sensor allows the acceleration measurement with a tunable sensitivity. These results suggest simple and low-cost routes to high-performance, tunable 3D capacitive sensors, with diverse potential applications in wearable electronics and biomedical devices.