Material extrusion 3D printing has received enormous attention to potentially overcome its limits by tailoring and designing thick electrodes. In this work, we prepared a thick reduced graphene oxide/carbon nanotube-reduced graphene oxide/carbon nanotubes/manganese oxide@carbon nanotubes (rGC-rGCMC) electrode with controlled lattice architectures, core-sheath structure, and hierarchical porosity by material coaxial extrusion 3D printing, freeze-drying, and thermal treatment. The volume ratios of core to sheath, including 100%-0%, 0%-100%, 20%-80%, 30%-70%, 40%-60%, and 50%-50%, were designed to investigate the influences of the core-sheath structure on thick electrodes. The electrodes with a core-sheath volume ratio of 30%-70% electrodes exhibited an enhanced areal specific capacitance of 588.27 mF cm-2 (39.48 F g-1) at a scan rate of 0.5 mA cm-2. All capacitance decays from core-sheath electrodes (20%-80%, 30%-70%, 40%-60%, and 50%-50%) were smaller than those from rGCMC (0%-100%) electrodes, indicating the improved rate capability from the core-sheath structure. On comparison of 30%-70% core-sheath electrodes with electrodes made of a homogeneous 30% rGC and 70% rGCMC mixture (30%+70%), lower capacitance (382.27 mF cm-2 and 25.66 F g-1 at 0.5 mA cm-2) of the 30%+70% mixture electrode without a core-sheath structure suggested less efficiency to harvest electrons from the redox reactions. Electrochemical impedance spectroscopy (EIS) data further supported and explained the resistances of thick electrodes with different volume ratios.

Flexible electronics have become increasingly important with growing market demands. Fiber-shaped supercapacitors and batteries are promising options for developing commercial applications due to their high power density, energy density, and mechanical properties. The bottlenecks of developing fiber-shaped supercapacitors and batteries include the inherent high resistance of electrode materials, low-yield manufacturing processes, and robustness of the fiber-shaped devices. Numerous studies on electrode materials, fiber structures, and manufacturing processes promote the electrical conductivity, surface area, and flexibility for high-performance fiber-shaped energy storage devices by extrusion-based manufacturing. This review provides an overview of the state-of-the-art of fiber-shaped supercapacitors and batteries including the electrode materials, fiber structures, and the extrusion-based manufacturing processes and highlight the research trend in the emerging field. The novel designs and manufacturing methods for fiber-shaped supercapacitors and batteries are also discussed to broaden the perspective in the emerging field.

High capacitance and good rate performance supercapacitors are needed to power sensors and miniaturized electrical devices. Thick electrodes are promising to increase the mass loading of active materials in supercapacitors, but the 3D geometries and microstructures in thick electrodes still hinder the development with high electron and ion exchange rate and accessible active sites. The scaffold 3D electrodes of reduced graphene oxide:manganese oxide/carbon nanotube (rGO:MnO x /CNT) are manufactured by material extrusion 3D printing (ME3DP), where the mass ratio of rGO to MnO x /CNT composites, thickness, and mass loading per unit area are controllable. The increasing amount of MnO x /CNT composites boosts the areal capacitance. Although the rate capability decays fast with the increasing of MnO x /CNT, it remains stable at different thicknesses (1.2, 1.6, and 2 mm). 2 mm thick rGO:MnO x /CNT (weight ratio 5:3) electrode exhibits an area capacitance of 302.13 mF cm −2 at a current density of 0.5 mA cm −2 , due to the highly ordered rGO networks. Compared to the casted electrodes, the microstructures in the 3D printed electrode contribute to lower resistances for the charge and ion transportation.

The compressive strain sensor is widely used as stretchable electronic, human motion detector, and health monitor due to its ability to convert large-scale mechanical deformation to the electrical signal. Carbon material reinforced polymer matrix composites are extensively studied to fabricate the strain sensor. However, there is a challenge to tune the performance of the strain sensor due to the fixed composition of the composite. In this work, we fabricated a carbon nanotube (CNT)/ polydimethylsiloxane (PDMS) compressive strain sensor with tunable mechanical and electrical performance. CNT was used as the reinforcement material due to its excellent electrical conductivity. PDMS was used as the matrix material because of its non-toxicity and flexibility. The foam structure created by the sacrificial sodium chloride (NaCl) allowed the compressive strain sensor to obtain at least 50% strain deformation. The material extrusion 3D printing (ME3DP) method was used to fabricate the complex scaffold structure due to its advantage of free design. The compressive strain sensor had a maximum gauge factor of 17.4 and work stably for at least 10000 cycles. The strain sensor was used to detect both large- and small-scale human motions due to its adjustable composition and sensitivity. We believe our method of building CNT/PDMS strain sensor with tunable performance broadens the potential on the fabrication of flexible electronic devices. Our method of using additive manufacturing to form the model also expends the routes of fabrication in a more flexible design and cost-saving method.

The compressive strain sensor is an extensively used flexible electronic device because of its capability to convert mechanical deformation to an electrical signal. However, the difficulty in tuning the performance of the strain sensor limits its further applications. Herein, the approach of fabricating a carbon nanotube (CNT)/polydimethylsiloxane (PDMS) compressive strain sensor, which has both tunable mechanical and electrical performances, is presented. CNT plays the role of reinforcement due to its outstanding mechanical strength and electrical conductivity. PDMS is a widely used matrix because of its softness and nontoxicity. The material extrusion 3D printing method is used to fabricate the composites, due to its advantages of design flexibility and compatibility with liquid‐based materials. The foam microstructure formed by removing sodium chloride provides a large‐scale deformation of at least 50% compressive strain and excellent elasticity. The strain sensor works durably over 10 000 cycles, with a gauge factor (GF) of 17.4. The compressive strain sensor in detecting both large‐ and small‐scale human motions due to the tunability of CNT/PDMS composites is also tested.

Polydimethylsiloxane (PDMS) has been broadly exploited because of its advantages of biocompatibility, flexibility, and transparency. However, the low mechanical strength constraints its further applications. An approach to improve its mechanical properties is to reinforce the PDMS matrix with high mechanical strength reinforcements. Carbon materials, such as carbon fiber (CF) and carbon nanotube (CNT), are widely applied as reinforcement to enhance the mechanical performance of PDMS. 3D printing is a promising rapid prototyping method to manufacture carbon material/PDMS composites. Herein, we 3D printed CF/PDMS and CNT/PDMS lines, essential elements for printing 3D structures, to study the 3D printing process and mechanical performance of carbon material/PDMS composites. The rheological analysis indicated the adding of CF did not affect the printability of CF/PDMS inks. The tensile modulus of printed CF/PDMS lines was improved by 52.4% compared to pure PDMS lines with 4 wt% CF reinforced PDMS. The agglomeration of CNT in PDMS limited the improvement of Young’s modulus of printed CNT/PDMS lines as the CNT concentration increased. This work analyzed the influence of 3D printing parameters on the carbon material/PDMS lines. It also provided an approach to study the extrusion 3D printing process by analyzing the essential lines.

Fiber-shaped supercapacitors are attractive as an energy storage unit due to their excellent flexibility. However, fabricating robust fibers with large yields remains a challenge. In this work, we prepare flexible core-sheath fibers via coaxial extrusion printing. Carboxymethylcellulose sodium salt (CMC) slurry with controlled rheological properties is extruded from the outer channel, while the graphene oxide (GO) slurry is extruded from the inner channel simultaneously. The followed freeze-drying process protects GO sheets from agglomeration, providing more efficient chemical reduction. The reduced GO (rGO) sheets are separated and expanded to fill in the CMC sheath, which eliminates the delamination between the CMC sheath and rGO core. We study the influences of the freeze-drying process on the fiber microstructures, and explore the slurry design, fiber quality, reduction condition, and electrochemical performance. The fabrication method allows scalable manufacturing of the core-sheath electrodes and fiber-shaped supercapacitors with more efficient conductive networks.

Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride, transition metal dichalcogenides, and MXenes, have become the leading topics in recent years due to their excellent physiochemical properties. Further innovations based on these 2D materials have been geared toward synthesizing heterostructures for the purpose of obtaining optimal material properties that satisfy the needs for applications that are heavily dependent on electrical, photoelectric, biosensing field, etc. via a combination of advantages offered by multiple 2D materials. A number of researches focus on improving the traditional strategies, including mechanical exfoliation, molecular-beam epitaxy, chemical vapor deposition, etc. to obtain the heterostructures with high quality and yield. Herein, we primarily review the synthesis procedures, including the mechanisms and comparison of advantages and disadvantages of distinct methods, and present the succinct, extended applications recently for various heterostructures.

Suppressing the crystallization of polyether-based solid electrolytes is a widely sought-after strategy to improve ionic conductivity. We report the effects of nanoconfinement on polyethylene oxide electrolytes. We find that neat polyethylene oxide responds to nanoconfinement by adopting a preferred orientation yet is able to crystallize even in nanoconfinement volumes with widths as small as 8 nm. However, the combination of nanoconfinement and salt addition does suppress polymer crystallization at room temperature even though either factor alone cannot. Such synergistic suppression of crystallization has implications for polymer electrolytes since amorphous rather than crystalline domains predominantly contribute to ionic conduction. Our results suggest that salts previously discounted due to their inability to suppress crystallinity in bulk materials could be made viable when combined with nanoconfinement, thereby opening new possibilities for high-performance solid polymer electrolytes.

Alumina has been extensively used due to its high toughness and hardness, low bulk density, and thermal stability without interaction with the matrix at high temperature. However, the non-conductivity at room temperature narrows its broader applications. Carbon nanotube (CNT) is a suitable candidate to adjust the electrical property of alumina matrix composites due to its high electrical conductivity. By using material extrusion 3D printing (ME3DP), we fabricated 3D CNT/alumina green bodies using inks with controlled rheological properties for high printability. The printed green bodies with CNT loading from 3 wt% to 10 wt% were thermally treated to remove binders and sinter the 3D parts at temperatures from 900 to 1400 °C. The sintered samples showed a good dispersion of CNT in the alumina matrix and improved electrical conductivity. The electrical conductivity of the composites measured up to 10-1 S/m at 7 wt.% CNT loading, compared to the electrical conductivity of 10-13 S/m of pure alumina.

In this work, a three-dimensional (3D) ceramic scaffold of barium titanate (BaTiO3) is realized by stereolithographic (SLA) of BaTiO3 powder and photopolymer with a high resolution and followed by a controlled thermal treatment. The photosensitive polymer in the resin mixture plays a vital role in dispersing ceramic powders and supporting complex structures cured by ultraviolet (UV) laser. The fabricated BaTiO3 and photopolymer composite part shows homogeneous dispersion of BaTiO3 microparticles. With a controlled thermal treatment, the photopolymer was carefully removed from the composite during the debinding process. Further sintering of the debinded ceramic parts at 1100 ℃, 1200 ℃, and 1300 °C shows a huge-volume shrinkage of up to 98.25% at a low concentration of ceramic powders (10 wt%). The sintered BaTiO3 ceramic parts are structurally intact with SEM images showing uniform microstructures with a relative density of 73.48%. The ultra-high shrinkage rate in this process provides a way to create complex 3D ceramic scaffolds with higher resolution than the SLA printing resolution. With the success of sintering ultralow solid loading ceramic-polymer composites, low-cost SLA 3D printers could be used to manufacture various ceramic parts with an improved resolution. This process allows widely application of 3D printed ceramics parts in the area of biomedical, aerospace, automotive, and energy fields.

5 ABSTRACT: Suppressing the crystallization of polyether-based solid electrolytes is a widely sought6 after strategy to improve ionic conductivity. We report the effects of nanoconfinement on polyethylene 7 oxide electrolytes. We find that neat polyethylene oxide responds to nanoconfinement by adopting a 8 preferred orientation yet is able to crystallize even in nanoconfinement volumes with widths as small as 9 8 nm. However, the combination of nanoconfinement and salt addition does suppress polymer 10 crystallization at room temperature even though either factor alone cannot. Such synergistic suppression of crystallization has 11 implications for polymer electrolytes since amorphous rather than crystalline domains predominantly contribute to ionic conduction. 12 Our results suggest that salts previously discounted due to their inability to suppress crystallinity in bulk materials could be made 13 viable when combined with nanoconfinement, thereby opening new possibilities for high-performance solid polymer electrolytes.

Over the past decades, porous gold has been used in plenty of applications such as catalysis or sensor detection. However, the nanoscale size of both the ligaments and pores makes such material very sensible to temperature. Indeed, the increase in temperature induces coarsening of the structure which can be detrimental for various applications. In this context, understanding of the coarsening on nanoporous gold (NPG) is crucial. In this communication, in situ scanning transmission electron microscopy (STEM) analysis of coarsening is reported by considering the nanosize of the dealloyed sample in dependence on the annealing of NPG nanowire. This study is performed by the in situ STEM of NPG nanowires after annealing between 25 and 600 degrees C with two different feature ratios (i.e., ligament/pore size) of 0.6 and 1.4. Herein, for the first time, an experimental demonstration is carried out for the two different behaviors of morphology evolution with temperature, corresponding to ligament pinch-off and collapsing of nanoporous materials, which have been highlighted by simulations in the literature.

Recently, PDMS has been widely used because of its outstanding properties, such as its biocompatibility, moldability, and Mechanical Flexibility. However, the low mechanical strength hinders its ability for further applications. The Addition of graphene oxide (GO) into Polydimethylsiloxane (PDMS) matrices as a reinforcement is a reasonably simple way to improve its mechanical properties. Direct ink writing (DIW) is an ideal method for printing viscous materials which provides useful advantages for fabrication, such as higher design freedom, as well as having no requirement for a castable mold, compared to conventional PDMS processing methods. Herein, we demonstrate the DIW 3D printing of GO reinforced PDMS matrix composites. PDMS SE 1700 and Sylgard 184 were mixed in 4:1 and 7:3 ratios as matrix materials with controlled rheological properties. GO, synthesized by modified Hummer's method, was loaded into PDMS at various weight ratios (0.5%, 1%, 2%, 3% and 4%) to fabricate GO/PDMS composites. The GO dispersed uniformly throughout the PDMS matrix with no visible aggregation during the mixing and printing processes. Tensile tests were performed using 3D printed dog-bone shape GO/PDMS bars to evaluate the enhancement of the GO reinforcement. The results showed that the Young's modulus of PDMS increased by 58.7% with 1% GO reinforcement.

Flexible energy-storage devices increasingly attract attention owing to their advantages of providing lightweight, portable, wearable, or implantable capabilities. Many efforts are made to explore the structures and fabrication processes of flexible energy-storage devices for commercialization. Here, the most recent advances in flexible energy-storage devices based on graphene, graphene oxide (GO), and carbon nanotubes (CNTs), are described, including flexible supercapacitors and batteries. First, properties, synthesis methods, and possible applications of those carbon-based materials are described. Then, the development of carbon-nanotube-based flexible supercapacitors, graphene/graphene-oxide-based flexible supercapacitors, and graphene- and carbon-nanotube-based flexible battery electrodes are discussed. Finally, the future trends and perspectives in the development of flexible energy-storage devices are highlighted.

The 3D printing technologies can produce objects with a very complex shape or geometry nowadays thanks to the advanced researches in their precision, repeatability, material ranges, etc. The size of 3D printed objects also varies. The Oak Ridge National Lab printed a 17.5 feet long, 5.5 feet wide and 1.5 feet tall tool for Boeing that weights 1,650 lbs. On the other hand, using Two Photon Polymerization, sub-mu m structures can be produced. The majority of current 3D printers design resembles the traditional FDM 3D printer. The printer is stationary during the printing period, limiting the print zone by the size of the robots, regardless as to the printer designs (Cartesian, polar, delta or articulated robots). In addition, all current 3D printers work as stand-alone equipment, which prevents the possibility of further speeding up the fabrication by using multiple collaborating 3D printers. Using mobile robots as a 3D printer could eliminate the size limit of the print zone and enable collaboration among different mobile robots to speed up the printing process. However, major problems are remaining unsolved in the current mobile 3D printer research, such as the precise localization of the robot, material slipping, accumulative printing error, etc. In this paper, a vision-based feedback control system is presented as a solution to these problems in mobile 3D printers. The system is equipped a single camera as sensory input. Using Simultaneous Localization and Mapping (SLAM) methods, the mobile 3D printer could potentially achieve sub-millimeter accuracy for localization. The slipping and accumulative error could also be mediated using image processing and object recognition. The system also enables the possibility for multiple 3D printers to work simultaneously. It is believed that mobile 3D printers equipped with vision-based feedback control system could have a great potential in the future.

Metal materials structured at nanoscale are extensively used in a variety of applications, including molecular sensing, nanoscale heaters for photothermal therapy, etc. These applications depend on the strong absorption and electric field enhancements associated with localized surface plasmon resonance (LSPR). Despite multiple investigations of LSPR relaxation dynamics in plasmonic metallic nanoparticles (i.e. nanospheres, nanocubes, etc), no detailed studies of porous thin films or nanowires have been reported so far. In this paper, LSPR relaxation dynamics of nanoporous gold thin film, gold nanowires, and nanoporous gold nanowires (structures with the potential for a vast range of sensing and optical applications) were studied by means of transient absorption spectroscopy (TAS). Au and Au/Cu thin films produced by magnetron sputtering deposition over a nanograted silicon substrate enabled the creation of highly organized nanowire arrays of centimetres length. Nanoporous structures were created by the dealloying of Au/Cu alloy. We found that formation of such a subwavelength period grating structure in gold increases the efficiency of hot electron relaxation compared to continuous film, while the porosity of gold nanostructures has the opposite effect. The results also expressed a clear dependence of the TAS signal on the polarization (i.e. orientation of the electric field with respect to the nanoporous gold nanowires) of the pump and probe pulses, compared to non-porous gold nanowires.

Complex fluids near interfaces or confined within nanoscale volumes can exhibit substantial shifts in physical properties compared to bulk, including glass transition temperature, phase separation, and crystallization. Because studies of these effects typically use thin film samples with one dimension of confinement, it is generally unclear how more extreme spatial confinement may influence these properties. In this work, we used x-ray photon correlation spectroscopy and gold nanoprobes to characterize polyethylene oxide confined by nanostructured gratings (<100nm width) and measured the viscosity in this nanoconfinement regime to be ∼500 times the bulk viscosity. This enhanced viscosity occurs even when the scale of confinement is several times the polymer's radius of gyration, consistent with previous reports of polymer viscosity near flat interfaces.

In this paper, we present an optofluidic waveguide platform consisting of liquid as a core material and air as cladding, enabled by using a superhydrophobic channel featured with hydrophobized high-aspect-ratio sharp-tip nanostructures. The contact of the liquid core with the superhydrophobic channel wall is minimized with an air layer retained between them so that the effective refractive index of the cladding layer is close to that of air. Thus, when light is introduced through the core liquid having a higher refractive index than that of the cladding air at the incident angle parallel to the channel direction less than a critical angle, it is reflected at the liquid-gas interface by the total internal reflection. When the cladding layer is filled with water (i.e., Wenzel state), the waveguide losses for the incident angles of 0 and 10° were ∼3.9 and ∼6.8 dB/cm, respectively. In contrast, when the cladding layer is retained with air (i.e., Cassie-Baxter state), the waveguide losses for the same incident angles were as low as ∼0.1 and ∼1.8 dB/cm, respectively. The significantly lowered waveguide losses at the Cassie-Baxter state indicate that superhydrophobic channels can provide the effective waveguide platform for optofluidics, exploiting the air layer as the cladding material.

We present flexible and stretchable supercapacitors composed of interwoven carbon nanotubes (CNTs) embedded in polydimethylsiloxane (PDMS) substrates. CNTs are grown using atmospheric-pressure chemical vapor deposition (APCVD) on a Si/SiO2 substrate and then partially embedded into PDMS. This unique process permits a rapid and facile integration of the interwoven CNT-PDMS structure as a flexible and stretchable supercapacitor electrode with a high level of integrity under various strains. The electrochemical properties of the supercapacitors are measured in 30% KOH solution and with a poly(vinyl alcohol) (PVA)-KOH gel electrolyte (i.e., all -solid-state flexible supercapacitor). The measured capacitance of the supercapacitor is 0.6 mF/cm(2) in 30% KOH solution and is 0.3 mF/cm(2) with a PVA-KOH gel electrolyte at a scan rate of 100 mV/s, showing a consistent performance under stretching from 0% to 200% and bending/twisting angles from 0 degrees to 180 degrees. The stretching test is performed for 200 cycles from 0% to 100%, after which its capacitance is attenuated by 25%. The all-solid-state stretchable supercapacitors show a stable galvanostatic performance during and after 10 000 charge/discharge cycles with its capacitance maintained.