Ultrastretchable and Self-Healing Conductors with Double Dynamic Network for Omni-Healable Capacitive Strain Sensors.

Skin-mountable capacitive-type strain sensors with great linearity and low hysteresis provide inspiration for the interactions between human and machine. For practicality, high sensing performance, large stretchability, and self-healing are demanded but limited by stretchable electrode and dielectric and interfacial compatibility. Here, we demonstrate an extremely stretchable and self-healing conductor via both hard and soft tactics that combine conductive nanowire assemblies with double dynamic network based on π-π attractions and Ag-S coordination bonds. The obtained conductor outperforms the reported stretchable conductors by delivering an elongation of 3250%, resistance change of 223% at 2000% strain, high durability, and multiresponsive self-healability. Especially, this conductor accommodates large strain of 1500% at extremely knotted and twisted deformations. By sandwiching hydrogel conductors with a newly developed dielectric, ultrahigh stretchability and omni-healability are simultaneously achieved for the first time for a capacitive strain sensor inspired by metal-thiolate coordination chemistry, showing great potentials in wearable electronics and soft robotics.

Autonomous Self-Healing of Highly Stretchable Supercapacitors at All Climates.

Realizing autonomous self-healing and high stretchability of flexible supercapacitors over a wide temperature range remains a big challenge because of simultaneous incorporation of self-healing, stretchable and temperature-tolerant elements into a device as well as unfavorable electrochemical kinetics in harsh conditions. Here, we demonstrate for the first time an autonomous self-healing and intrinsically stretchable supercapacitor that can work at all-climate environments assembled by universally self-healing and highly stretchable organohydrogel electrodes with record-high temperature-invariant conductivity of ∼965 S/cm. Benefiting from multiple hydrogen bonding and dynamic metal coordination combined with electrochemistry-favorable components and integrated device configuration, the supercapacitor exhibits outstanding long-term stability, high stretchability, instantaneous and complete capacitive self-healability, and real-time mechanical healing at harsh temperatures from -35 to 80 °C. The superiorities in stretchability, self-healability, and all-climate tolerance enable the supercapacitor presented here as the best performer among the flexible supercapacitors reported to date.

Rapid Printing and Patterning of Tough, Self-Healable, and Recyclable Hydrogel Thin-Films toward Flexible Sensing Devices.

Direct and rapid printing and surface patterning of hydrogel thin films are of great significance in the construction of advanced electronic devices, yet they are greatly underdeveloped due to the intrinsic contradiction between mechanical strength and self-healability as well as recyclability. Here, we present a universal and rapid slipping-directed route with a newly developed water-soluble star polymer hydrogel for direct and reproducible printing and patterning of freestanding functional thin films with precisely controlled thicknesses, components, and surface structures on a large scale. The resulting thin films combine the features of large transmittance (93%), tough mechanical strength (114 MPa), multiresponsive self-healability, recyclability, and remarkable multifunctionality. With the unique humidity-sensitive properties as motivation, diverse humidity-sensing devices including an actuating switch, a supercapacitive sensor, and a noncontact electronic skin are facilely constructed through the humidity-induced transverse, longitudinal, and patterning assembly techniques, respectively. The method presented here is universal and efficient in the fabrication and assembly of thin films with controlled configuration and functionality for advanced flexible electronics.

Double Confinement Hydrogel Network Enables Continuously Regenerative Solar-to-Hydrogen Conversion.

Soft matter catalyst system allowing controllable manipulation of the organized nanostructure and surface property holds the potential for renewable energy. Here we demonstrate the construction of a continuously regenerative hydrogel photocatalyst that confines the metal-thiolate coordination induced nanocavity into robust micro-sized spongy network for water splitting. Thanks to low vaporization enthalpy and fast proton mobility of water molecules confining in nanocavities, the composite delivers outstanding photocatalytic H2 production (TOF of 4568 H2 h-1 ), nearly 4.5 times higher than that on the catalyst without confinements. Incorporating with conductive polymers, the TOF is substantially improved to 7819 H2 h-1 . Impressively, continuous regeneration is for the first time achieved with H2 production retention improved from 24 % to 72 % by regulating optically-active catalyst surfaces. This optical regeneration method provides new avenues for sustainable solar energy conversion.

Highly Tough Bioinspired Ternary Hydrogels Synergistically Reinforced by Graphene/Xonotlite Network.

The application fields of hydrogels are often severely limited by their weak mechanical performance. It is therefore highly demanded to develop an effective strategy to fabricate mechanically strong hydrogels. Herein, a kind of bioinspired ternary hydrogel consisting of graphene oxide (GO) nanosheets, xonotlite nanowires, and polyacrylamide (PAM) is constructed under the synergy of hydrogen bonding-induced GO/xonotlite network and the penetrated PAM chain network. Benefiting from the effective energy dissipation mechanism caused by double-network structural design and the strong hydrogen bonding interaction between two nanobuilding blocks, the gel exhibits a high toughness of 22 MJ m-3 at an elongation of 2750%. Even notched with 1/4 size, it still holds a large extensibility of 2180% its initial length. These high-performance hydrogels could be of great interest in the fields of tissue engineering and biomedical areas.

Templating Synthesis of Mesoporous Fe3C-Encapsulated Fe-N-Doped Carbon Hollow Nanospindles for Electrocatalysis.

Developing cost-efficient alternatives to the noble metal catalysts toward oxygen reduction reaction (ORR) has attracted much attention. Herein, a kind of mesoporous hollow spindlelike Fe-N-C electrocatalysts with iron carbide nanoparticles encased in the N-doped graphitic layers has been synthesized by a novel "reactive hard template" strategy through the Fe3+-assisted polymerization of dopamine on the Fe2O3 cores and the following calcinations. The Fe2O3 nanospindles not only as the hard template guide the formation of well-defined shape and structure of the catalyst but also as the reactive template provide Fe reservoir to generate Fe3C nanoparticles in the catalyst during the thermochemical process. The superiority in accessible active sites of Fe-N x species, Fe3C nanoparticles in graphenelike layers, and highly mesoporous hollow structure enables the catalysts to exhibit excellent ORR performances including high catalytic activity, outstanding long-term cycling stability, and good tolerance to methanol.

The Electrochemistry with Lithium versus Sodium of Selenium Confined To Slit Micropores in Carbon.

Substitution of selenium for sulfur in the cathode of a rechargeable battery containing Sx molecules in microporous slits in carbon allows a better characterization of the electrochemical reactions that occur. Paired with a metallic lithium anode, the Sex chains are converted to Li2Se in a single-step reaction. With a sodium anode, a sequential chemical reaction is characterized by a continuous chain shortening of Sex upon initial discharge before completing the reduction to Na2Se; on charge, the reconstituted Sex molecules retain a smaller x value than the original Sex chain molecule. In both cases, the Se molecules remain almost completely confined to the micropore slits to give a long cycle life.

Iron Oxide with Different Crystal Phases (α- and γ-Fe2O3) in Electroanalysis and Ultrasensitive and Selective Detection of Lead(II): An Advancing Approach Using XPS and EXAFS.

Iron oxide with different crystal phases (α- and γ-Fe2O3) has been applied to electrode coatings and been demonstrated to ultrasensitive and selective electrochemical sensing toward heavy metal ions (e.g., Pb(II)). A range of Pb(II) contents in micromoles (0.1 to 1.0 µM) at α-Fe2O3 nanoflowers with a sensitivity of 137.23 µA µM(-1) cm(-2) and nanomoles (from 0.1 to 1.0 nM) at γ-Fe2O3 nanoflowers with a sensitivity of 197.82 µA nM(-1) cm(-2) have been investigated. Furthermore, an extended X-ray absorption fine structure (EXAFS) technique was applied to characterize the difference of local structural environment of the adsorbed Pb(II) on the surface of α- and γ-Fe2O3. The results first showed that α- and γ-Fe2O3 had diverse interaction between Pb(II) and iron (hydro)oxides, which were consistent with the difference of electrochemical performance. Determining the responses of Cu(II) and Hg(II) as the most appropriate choice for comparison, the stripping voltammetric quantification of Pb(II) with high sensitivity and selectivity at γ-Fe2O3 nanoflower has been demonstrated. This work reveals that the stripping performances of a nanomodifier have to be directly connected with its intrinsic surface atom arrangement.

Combining Nitrogen-Doped Graphene Sheets and MoS2 : A Unique Film-Foam-Film Structure for Enhanced Lithium Storage.

With a notable advantage in terms of capacity, molybdenum disulfide has been considered a promising anode material for building high-energy-density lithium-ion batteries. However, its intrinsically low electronic conductivity and unstable electrochemistry lead to poor cycling stability and inferior rate performance. We herein describe the scalable assembly of free-standing MoS2 -graphene composite films consisting of nitrogen-doped graphene and ultrathin honeycomb-like MoS2 nanosheets. The composite has a unique film-foam-film hierarchical top-down architecture from the macroscopic to the microscopic and the nanoscopic scale, which helps rendering the composite material highly compact and leads to rapid ionic/electronic access to the active material, while also accommodating the volume variation of the sulfide upon intercalation/deintercalation of Li. The unique structural merits of the composite lead to enhanced lithium storage.

Thermoresponsive poly(N-isopropylacrylamide)/graphene/Au nanocomposite hydrogel for water treatment by a laser-assisted approach.

The thermoresponsive poly(N-isopropylacrylamide)/graphene/Au multicomponent hydrogel is prepared by the simultaneous in-situ formation of Au nanoparticles and the reduction of graphene oxide, assisted by NIR laser irradiation of a prefabricated PNIPAM/GO hydrogel with auric acid precursor, showing great potential for water treatment owing to the excellent photothermal effect.

Bioinspired, Ultrastrong, Highly Biocompatible, and Bioactive Natural Polymer/Graphene Oxide Nanocomposite Films.

Tough and biocompatible nanocomposite films: A new type of bioinspired ultrastrong, highly biocompatible, and bioactive konjac glucomannan (KGM)/graphene oxide (GO) nanocomposite film is fabricated on a large scale by a simple solution-casting method. Such KGM-GO composite films exhibit much enhanced mechanical properties under the strong hydrogen-bonding interactions, showing great potential in the fields of tissue engineering and food package.

Graphene-based macroscopic assemblies and architectures: an emerging material system.

Due to the outstanding physicochemical properties arising from its truly two-dimensional (2D) planar structure with a single-atom thickness, graphene exhibits great potential for use in sensors, catalysts, electrodes, and in biological applications, etc. With further developments in the theoretical understanding and assembly techniques, graphene should enable great changes both in scientific research and practical industrial applications. By the look of development, it is of fundamental and practical significance to translate the novel physical and chemical properties of individual graphene nanosheets into the macroscale by the assembly of graphene building blocks into macroscopic architectures with structural specialities and functional novelties. The combined features of a 2D planar structure and abundant functional groups of graphene oxide (GO) should provide great possibilities for the assembly of GO nanosheets into macroscopic architectures with different macroscaled shapes through various assembly techniques under different bonding interactions. Moreover, macroscopic graphene frameworks can be used as ideal scaffolds for the incorporation of functional materials to offset the shortage of pure graphene in the specific desired functionality. The advantages of light weight, supra-flexibility, large surface area, tough mechanical strength, and high electrical conductivity guarantee graphene-based architectures wide application fields. This critical review mainly addresses recent advances in the design and fabrication of graphene-based macroscopic assemblies and architectures and their potential applications. Herein, we first provide overviews of the functional macroscopic graphene materials from three aspects, i.e., 1D graphene fibers/ribbons, 2D graphene films/papers, 3D network-structured graphene monoliths, and their composite counterparts with either polymers or nano-objects. Then, we present the promising potential applications of graphene-based macroscopic assemblies in the fields of electronic and optoelectronic devices, sensors, electrochemical energy devices, and in water treatment. Last, the personal conclusions and perspectives for this intriguing field are given.

One-pot colloidal chemistry route to homogeneous and doped colloidosomes.

Colloidosomes are usually produced from a series of building blocks with different sizes ranging from several nanometers to micrometers or various shapes, such as particles, microrods, and quantum dots. Colloidosomes can possess a variety of characteristics in terms of photics, electrology, mechanical strength, and selective permeability, derived from their building blocks. However, poor mechanical stability and complicated synthesis processes have limited the applications of colloidosomes. Here, we report a new one-pot colloidal chemistry route to synthesize phenol formaldehyde resin (PFR), Ag@PFR, and Au@PFR colloidosomes with high yields. The method can be modified to synthesize different kinds of doped colloidosomes with different components, which will provide a new approach to design colloidosomes with different functions.

Nanocomposite Hydrogel Actuators with Ordered Structures: From Nanoscale Control to Macroscale Deformations.

Flexible intelligent actuators with the characteristics of flexibility, safety and scalability, are highly promising in industrial production, biomedical fields, environmental monitoring, and soft robots. Nanocomposite hydrogels are attractive candidates for soft actuators due to their high pliability, intelligent responsiveness, and capability to execute large-scale rapid reversible deformations under external stimuli. Here, the recent advances of nanocomposite hydrogels as soft actuators are reviewed and focus is on the construction of elaborate and programmable structures by the assembly of nano-objects in the hydrogel matrix. With the help of inducing the gradient or oriented distributions of the nanounits during the gelation process by the external forces or molecular interactions, nanocomposite hydrogels with ordered structures are achieved, which can perform bending, spiraling, patterned deformations, and biomimetic complex shape changes. Given great advantages of these intricate yet programmable shape-morphing, nanocomposite hydrogel actuators have presented high potentials in the fields of moving robots, energy collectors, and biomedicines. In the end, the challenges and future perspectives of this emerging field of nanocomposite hydrogel actuators are proposed.

Controlled assemblies of gold nanorods in PVA nanofiber matrix as flexible free-standing SERS substrates by electrospinning.

Under control: Controlled assemblies of gold nanorods in a poly(vinyl alcohol) (PVA) nanofiber matrix with tunable optical properties can be achieved by using electrospinning. The resultant assemblies can be used as substrates for surface-enhanced Raman spectroscopy (SERS). This work provides a facile way to control alignment of anisotropic nanostructures in a polymer nanofiber matrix and generates new assemblies with interesting properties.

A multi-responsive healable supercapacitor.

Self-healability is essential for supercapacitors to improve their reliability and lifespan when powering the electronics. However, the lack of a universal healing mechanism leads to low capacitive performance and unsatisfactory intelligence. Here, we demonstrate a multi-responsive healable supercapacitor with integrated configuration assembled from magnetic Fe3O4@Au/polyacrylamide (MFP) hydrogel-based electrodes and electrolyte and Ag nanowire films as current collectors. Beside a high mechanical strength, MFP hydrogel exhibits fast optical and magnetic healing properties arising from distinct photothermal and magneto-thermal triggered interfacial reconstructions. By growing electroactive polypyrrole nanoparticles into MFP framework as electrodes, the assembled supercapacitor exhibits triply-responsive healing performance under optical, electrical and magnetic stimuli. Notably, the device delivers a highest areal capacitance of 1264 mF cm-2 among the reported healable supercapacitors and restores ~ 90% of initial capacitances over ten healing cycles. These prominent performance advantages along with the facile device-assembly method make this emerging supercapacitor highly potential in the next-generation electronics.

Anisotropic and self-healing hydrogels with multi-responsive actuating capability.

Inspired by smart biological tissues, artificial muscle-like actuators offer fascinating prospects due to their distinctive shape transformation and self-healing function under external stimuli. However, further practical application is hindered by the lack of simple and general routes to fabricate ingenious soft materials with anisotropic responsiveness. Here, we describe a general in situ polymerization strategy for the fabrication of anisotropic hydrogels composed of highly-ordered lamellar network crosslinked by the metal nanostructure assemblies, accompanied with remarkably anisotropic performances on mechanical, optical, de-swelling and swelling behaviors. Owing to the dynamic thiolate-metal coordination as healing motifs, the composites exhibit rapid and efficient multi-responsive self-healing performance under NIR irradiation and low pH condition. Dependent on well-defined anisotropic structures, the hydrogel presents controllable solvent-responsive mechanical actuating performance. Impressively, the integrated device through a healing-induced assembly way can deliver more complicated, elaborate forms of actuation, demonstrating its great potentials as superior soft actuators like smart robots.

A Highly Stretchable and Real-Time Healable Supercapacitor.

In addition to a high specific capacitance, a large stretchability and self-healing properties are also essential to improve the practicality and reliability of supercapacitors in portable and wearable electronics. However, the integration of multiple functions into one device remains challenging. Here, the construction of a highly stretchable and real-time omni-healable supercapacitor is demonstrated by sandwiching the polypyrrole-incorporated gold nanoparticle/carbon nanotube (CNT)/poly(acrylamide) (GCP@PPy) hydrogel electrodes with a CNT-free GCP (GP) hydrogel as the electrolyte and chemically soldering an Ag nanowire film to the hydrogel electrode as the current collector. The newly developed dynamic metal-thiolate (M-SR, M = Au, Ag) bond-induced integrated configuration, with an intrinsically powerful electrode and electrolyte, enables the assembled supercapacitor to deliver an areal capacitance of 885 mF cm-2 and an energy density of 123 µWh cm-2 , which are among the highest-reported values for stretchable supercapacitors. Notably, the device exhibits a superhigh stretching strain of 800%, rapid optical healing capability, and significant real-time healability during the charge-discharge process. The exceptional performance combined with the facile assembly method confirms this multifunctional device as the best performer among all the flexible supercapacitors reported to date.