Showing papers by "Joselito M. Razal published in 2019"

Textile Strain Sensors: A Review of the Fabrication Technologies, Performance Evaluation and Applications

Abstract: The recent surge in using wearable personalized devices has made it increasingly important to have flexible textile-based sensor alternatives that can be comfortably worn and can sense a wide range of body strains. Typically fabricated from rigid materials such as metals or semiconductors, conventional strain sensors can only withstand small strains and result in bulky, inflexible, and hard-to-wear devices. Textile strain sensors offer a new generation of devices that combine strain sensing functionality with wearability and high stretchability. In this review, we discuss recent exciting advances in the fabrication, performance enhancement, and applications of wearable textile strain sensors. We describe conventional and novel approaches to achieve textile strain sensors such as coating, conducting elastomeric fiber spinning, wrapping, coiling, coaxial fiber processing, and knitting. We also discuss how important performance parameters such as electrical conductivity, mechanical properties, sensitivity, sensing range, and stability are influenced by fabrication strategies to illustrate their effects on the sensing mechanism of textile sensors. We summarize the potential applications of textile sensors in structural health monitoring, wearable body movement measurements, data gloves, and entertainment. Finally, we present the challenges and opportunities that exist to date in order to provide meaningful guidelines and directions for future research.

Knittable and Washable Multifunctional MXene-Coated Cellulose Yarns

Abstract: Textile-based electronics enable the next generation of wearable devices, which have the potential to transform the architecture of consumer electronics. Highly conductive yarns that can be manufactured using industrial-scale processing and be washed like everyday yarns are needed to fulfill the promise and rapid growth of the smart textile industry. By coating cellulose yarns with Ti3C2Tx MXene, highly conductive and electroactive yarns are produced, which can be knitted into textiles using an industrial knitting machine. It is shown that yarns with MXene loading of ≈77 wt% (≈2.2 mg cm−1) have conductivity of up to 440 S cm−1. After washing for 45 cycles at temperatures ranging from 30 to 80 °C, MXene-coated cotton yarns exhibit a minimal increase in resistance while maintaining constant MXene loading. The MXene-coated cotton yarn electrode offers a specific capacitance of 759.5 mF cm−1 at 2 mV s−1. A fully knitted textile-based capacitive pressure sensor is also prepared, which offers high sensitivity (gauge factor of ≈6.02), wide sensing range of up to ≈20% compression, and excellent cycling stability (2000 cycles at ≈14% compression strain). This work provides new and practical insights toward the development of platform technology that can integrate MXene in cellulose-based yarns for textile-based devices.

Highly Conductive Ti 3 C 2 T x MXene Hybrid Fibers for Flexible and Elastic Fiber-Shaped Supercapacitors

Abstract: Fiber-shaped supercapacitors (FSCs) are promising energy storage solutions for powering miniaturized or wearable electronics. However, the scalable fabrication of fiber electrodes with high electrical conductivity and excellent energy storage performance for use in FSCs remains a challenge. Here, an easily scalable one-step wet-spinning approach is reported to fabricate highly conductive fibers using hybrid formulations of Ti3 C2 Tx MXene nanosheets and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate. This approach produces fibers with a record conductivity of ≈1489 S cm-1 , which is about five times higher than other reported Ti3 C2 Tx MXene-based fibers (up to ≈290 S cm-1 ). The hybrid fiber at ≈70 wt% MXene shows a high volumetric capacitance (≈614.5 F cm-3 at 5 mV s-1 ) and an excellent rate performance (≈375.2 F cm-3 at 1000 mV s-1 ). When assembled into a free-standing FSC, the energy and power densities of the device reach ≈7.13 Wh cm-3 and ≈8249 mW cm-3 , respectively. The excellent strength and flexibility of the hybrid fibers allow them to be wrapped on a silicone elastomer fiber to achieve an elastic FSC with 96% capacitance retention when cyclically stretched to 100% strain. This work demonstrates the potential of MXene-based fiber electrodes and their scalable production for fiber-based energy storage applications.

Reverse synthesis of star anise-like cobalt doped Cu-MOF/Cu2+1O hybrid materials based on a Cu(OH)2 precursor for high performance supercapacitors

Abstract: Metal–organic frameworks (MOFs) have attracted increasing attention due to their high specific area and abundant redox sites for application in energy storage devices. However, the non-ideal capacity, poor mechanical/chemical stability, random arrangement and low conductivity of most MOFs largely thwart their extensive applications. Hence, designing an easily operated and highly efficient strategy to address these issues has realistic meanings. Herein, a vertically oriented Cu(OH)2 nanorod array was selected as both the template and precursor to synthesize highly oriented star anise-like Co-doped Cu-MOF/Cu2+1O (Cu2+1O refers to the Cu2O with metal excess defects) nanohybrid materials, where the MOF structure is formed through an in situ reverse transformation process. Due to the high conductivity resulting from the presence of “excess copper” and doped cobalt ions, as well as the intimate connection between the Cu-MOF and Cu2+1O, the optimized (0.1Co/Cu-MOF/Cu2+1O) electrode delivers a high areal capacity of 1.548 F cm−2 (518.58 F g−1) and remarkable cycling stability (97.26% after 5000 cycles). Meanwhile, the assembled 0.1Co/Cu-MOF/Cu2+1O//activated carbon hybrid supercapacitor shows an outstanding energy density up to 25.67 W h kg−1 at a power density of 740.44 W kg−1. Therefore, the proposed strategy may open a new avenue to unlock the inherent advantages of MOFs for application in the electrochemical energy storage field.

Fast and scalable wet-spinning of highly conductive PEDOT:PSS fibers enables versatile applications

Abstract: Highly conductive, strong and flexible fibers are important for the realization of many high technological applications including smart textiles, flexible electrodes, and fast-response sensors and actuators. Here, we report a facile one-step method to produce highly conducting poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) fibers that effectively removes the insulating PSS component within seconds, thereby enabling their fabrication in a fast one-step process. The highest electrical conductivity for a ∼15 micron fiber (3828 S cm−1) is comparable to that for very thin PEDOT:PSS film produced to date (4380 S cm−1 for 100 nm film). These fibers can withstand mechanical mistreatment – testing has been conducted in various environments including sonication and exposure to boiling water for extended periods. The study on the mechanism of conductivity enhancement shows that our spinning method efficiently removes the PSS component during fiber formation and improves orientation of the PEDOT chains, which facilitates efficient intramolecular and intermolecular charge transport, leading to the enhancement in electrical properties. We demonstrate that these highly conducting fibers can be used for fast response and highly sensitive touch sensors, body moisture monitoring, and long fiber-shaped supercapacitors. These results provide a scalable platform for the fabrication of highly conductive fibers with excellent mechanical properties, which are essential characteristics required for many advanced applications.

Facile Solution Processing of Stable MXene Dispersions towards Conductive Composite Fibers.

Abstract: 2D transition metal carbides and nitrides called “MXene” are recent exciting additions to the 2D nanomaterials family. The high electrical conductivity, specific capacitance, and hydrophilic nature of MXenes rival many other 2D nanosheets and have made MXenes excellent candidates for diverse applications including energy storage, electromagnetic shielding, water purification, and photocatalysis. However, MXene nanosheets degrade relatively quickly in the presence of water and oxygen, imposing great processing challenges for various applications. Here, a facile solvent exchange (SE) processing route is introduced to produce nonoxidized and highly delaminated Ti3C2Tx MXene dispersions. A wide range of organic solvents including methanol, ethanol, isopropanol, butanol, acetone, dimethylformamide, dimethyl sulfoxide, chloroform, dichloromethane, toluene, and n‐hexane is used. Compared to known processing approaches, the SE approach is straightforward, sonication‐free, and highly versatile as multiple solvent transfers can be carried out in sequence to yield MXene in a wide range of solvents. Conductive MXene polymer composite fibers are achieved by using MXene processed via the solvent exchange (SE) approach, while the traditional redispersion approach has proven ineffective for fiber processing. This study offers a new processing route for the development of novel MXene‐based architectures, devices, and applications.

Ti3C2 MXene as a new nanofiller for robust and conductive elastomer composites.

Abstract: Ti3C2 MXene with a layered 2D structure was applied as a novel functional filler in rubber for the first time. A facile and green method was proposed to fabricate rubber/Ti3C2 nanocomposites via a freeze-drying & mechanical mixing process. It was found that Ti3C2 with ∼1 nm thickness fabricated by etching Al from Ti3AlC2 phases can be dispersed in styrene-butadiene rubber (SBR) evenly in a single-layered state. Mechanical strength and electrical and thermal conductivities of the rubber nanocomposites were remarkably enhanced by the incorporation of Ti3C2, showing dramatic improvement compared with reduced graphene oxide (rGO) reinforced rubber composites. For example, the thermal conductivity of SBR nanocomposites with 3 wt% rGO was 0.265 W m-1 k-1, while that of SBR nanocomposites with only 1.96 wt% Ti3C2 reached 0.477 W m-1 k-1. Meanwhile, the resistance of rubber/Ti3C2 nanocomposites was stable under complex deformation and their sensitivity was well recovered during stretching/shrinking cycles under large strain. Moreover, it was discovered that incorporating Ti3C2 in rubber nanocomposites dramatically improved the wet skid resistance and thermal stability without increasing the rolling resistance. Ti3C2 MXene with a distinctive structure and properties as well as uniform dispersion will have more potential for the preparation of high-performance rubber nanocomposites, especially for green tires and flexible sensors.

Shape-tailorable high-energy asymmetric micro-supercapacitors based on plasma reduced and nitrogen-doped graphene oxide and MoO₂ nanoparticles

Abstract: Asymmetric micro-supercapacitors (AMSCs) are considered to be highly competitive miniaturized energy-storage units for wearable and portable electronics. However, the energy density, voltage output and fabrication technology for AMSCs remain challenges for practical applications. Herein, we adopt plasma reduced and nitrogen-doped graphene oxide with a high nitrogen content of 8.05% and ultra-fine MoO2 nanoparticles with a diameter of 5–10 nm as electrode materials for high-energy flexible all-solid-state AMSCs. The AMSCs based on plasma reduced and nitrogen-doped graphene oxide (PNG) and plasma reduced and nitrogen-doped graphene oxide–MoO2 composite films (PNG–MoO2) can be integrated on diverse substrates (e.g., cloth, glass, leaves, and polyethylene terephthalate (PET) films) and tailored into microelectrodes with various planar geometries by accurate laser cutting. The resulting PNG//PNG–MoO2-AMSCs exhibit a high working voltage of 1.4 V, a significant areal capacitance of 33.6 mF cm−2 and an outstanding volumetric capacitance of 152.9 F cm−3 at 5 mV s−1, and offer an exceptionally high energy density of 38.1 mW h cm−3, outperforming most reported AMSCs. Furthermore, the microdevices demonstrate electrochemical performance with excellent stability under various bending conditions up to 180° and without obvious capacitance degradation even after being bent at 60° for 1000 times. Furthermore, PNG//PNG–MoO2-AMSCs displayed exceptional serial and parallel integration to boost the output of voltage and capacitance. This work demonstrates the great potential of such AMSCs for practical application in miniaturized, wearable, and flexible electronics.

Unimpeded migration of ions in carbon electrodes with bimodal pores at an ultralow temperature of −100 °C

Abstract: The ability to rapidly charge (and discharge) energy storage devices at extremely low temperature (down to −100 °C) is critical for low-temperature applications such as high altitude exploration and space missions. Electric double-layer supercapacitors (EDLCs) are promising energy storage devices under these conditions. However, it is still a great challenge to obtain EDLCs with both high gravimetric/volumetric capacitance and good rate performance at such low temperatures. We found that, in carbon-based EDLCs, the poor performance at low temperature was mainly caused by the sluggish desolvation of ions at the pore openings and low ion migration within pores. Further, we discovered that there exists a minimum pore opening size for ion adsorption and an effect of pore size on rate performance. These findings enable us to envisage a rational pore structure with a special bimodal distribution of micropores and mesopores. In this work, we successfully synthesized high surface area activated carbon (AC) with a similar structure. Based on this AC, record gravimetric/volumetric capacitance (173 F g−1 and 66 F cm−3 at 10 mV s−1 scan rate) and good rate performance (157 F g−1 and 60 F cm−3 at 100 mV s−1 scan rate) were obtained at a temperature of −100 °C.