Environment-Adaptable Rotational Energy Harvesters Based on Nylon-core Coiled Carbon Nanotube Yarns.

Owing to increasing amount of research on energy harvesting, studies on harvesters for practical application and their performance are attracting attention. Therefore, studies on the use of continuous energy as an energy source for energy-harvesting devices are being conducted, and fluid flows, e.g., wind, river flow, and sea wave, are widely used as input energy sources for continuous energy harvesting. A new energy-harvesting technology has emerged based on the mechanical stretch and release of coiled carbon nanotube (CNT) yarns, which generate energy based on the change in the electrochemical double-layer capacitance. First, this CNT yarn-based mechanical energy harvester is demonstrated, which is applicable to various environments where fluid flow exists. This environment-adaptable harvester uses rotational energy as the mechanical energy source and is tested in river and ocean environments. Moreover, an attachable-type harvester for the application of the existing rotational system is devised. In the case of a slow rotational environment, a square-wave strain-applying harvester has been implemented, which can convert sinusoidal strain motion into square-wave strain motion for high output voltages. To achieve high performance of practical harvesting applications, a scale-up method for powering signal-transmitting devices has been implemented.

More Powerful Twistron Carbon Nanotube Yarn Mechanical Energy Harvesters.

Stretching a coiled carbon nanotube (CNT) yarn can provide large, reversible electrochemical capacitance changes, which convert mechanical energy to electricity. Here, it is shown that the performance of these "twistron" harvesters can be increased by optimizing the alignment of precursor CNT forests, plastically stretching the precursor twisted yarn, applying much higher tensile loads during precoiling twist than for coiling, using electrothermal pulse annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power for a 1 and a 30 Hz sinusoidal deformation are 0.73 and 3.19 kW kg-1 , respectively, which are 24- and 13-fold that of previous twistron harvesters at these respective frequencies. This performance at 30 Hz is over 12-fold that of other prior-art mechanical energy harvesters for frequencies between 0.1 and 600 Hz. The maximum energy conversion efficiency is 7.2-fold that for previous twistrons. Twistron anode and cathode yarn arrays are stretched 180° out-of-phase by locating them in the negative and positive compressibility directions of hinged wine-rack frames, thereby doubling the output voltage and reducing the input mechanical energy.

Enhancing the Work Capacity of Electrochemical Artificial Muscles by Coiling Plies of Twist-Released Carbon Nanotube Yarns.

Twisted-yarn-based artificial muscles can potentially be used in diverse applications, such as valves in microfluidic devices, smart textiles, air vehicles, and exoskeletons, because of their high torsional and tensile strokes, high work capacities, and long cycle life. Here, we demonstrate electrochemically powered, hierarchically twisted carbon nanotube yarn artificial muscles that have a contractile work capacity of 3.78 kJ/kg, which is 95 times the work capacity of mammalian skeletal muscles. This record work capacity and a tensile stroke of 15.1% were obtained by maximizing yarn capacitance by optimizing the degree of inserted twist in component yarns that are plied until fully coiled. These electrochemically driven artificial muscles can be operated in reverse as mechanical energy harvesters that need no externally applied bias. In aqueous sodium chloride electrolyte, a peak electrical output power of 0.65 W/kg of energy harvester was generated by 1 Hz sinusoidal elongation.

Carbon nanotubes-elastomer actuator driven electrothermally by low-voltage.

Electroactive polymers (EAPs) have attracted attention in many fields such as robotics, sensors devices and biomedical devices. However, the practical application of these actuators has still problems due to incomplete reversibility and high applied voltage. In order to overcome these problems, in this study, we have shown actuator based on phase transition that is consisted of the carbon nanotubes yarn infiltrated with the mixture of elastomer and methanol. Our electrothermally driven hybrid coiled yarn muscle provides a work capacity of 0.49 kJ kg-1 and a tensile contraction of 30.5% within ∼3 s on an applied stress of 3.1 MPa at an applied DC voltage of 5 V. The maximum work capacity is under isobaric 23.4 MPa, which is 110 times that of typical mammalian skeletal muscles. This actuator may serve as a promising candidate for the practical use in soft robotics.

Thermally Responsive Torsional and Tensile Fiber Actuator Based on Graphene Oxide.

Graphene-based actuators are of practical interest because of their relatively low cost compared with other nanocarbon materials, such as carbon nanotubes. We demonstrate the simple fabrication of graphene oxide (GO)-based fibers with an infiltrated nylon-6,6 polymer by wet spinning. These fibers could be twisted to form torsional actuators and further coiled to form tensile actuators. By controlling the relative twisting and coiling direction of the GO/nylon fiber, we were able to realize reversible contraction or elongation actuation with strokes as high as -80 and 75%, respectively, when the samples were heated to 200 °C. The tensile actuation showed a remarkably little hysteresis. Moreover, this GO/nylon actuator could lift loads over 100 times heavier than itself and generate a stable actuation at high temperatures over the melting point of the polymer. This novel kind of GO-based actuator, which has a multidirectional actuation, has potential for a wide range of applications such as artificial muscles, robotics, and temperature sensing.

Harvesting electrical energy from carbon nanotube yarn twist.

Mechanical energy harvesters are needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. We report carbon nanotube yarn harvesters that electrochemically convert tensile or torsional mechanical energy into electrical energy without requiring an external bias voltage. Stretching coiled yarns generated 250 watts per kilogram of peak electrical power when cycled up to 30 hertz, as well as up to 41.2 joules per kilogram of electrical energy per mechanical cycle, when normalized to harvester yarn weight. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a light-emitting diode and to charge a storage capacitor.

Bio-inspired, Moisture-Powered Hybrid Carbon Nanotube Yarn Muscles.

Hygromorph artificial muscles are attractive as self-powered actuators driven by moisture from the ambient environment. Previously reported hygromorph muscles have been largely limited to bending or torsional motions or as tensile actuators with low work and energy densities. Herein, we developed a hybrid yarn artificial muscle with a unique coiled and wrinkled structure, which can be actuated by either changing relative humidity or contact with water. The muscle provides a large tensile stroke (up to 78%) and a high maximum gravimetric work capacity during contraction (2.17 kJ kg(-1)), which is over 50 times that of the same weight human muscle and 5.5 times higher than for the same weight spider silk, which is the previous record holder for a moisture driven muscle. We demonstrate an automatic ventilation system that is operated by the tensile actuation of the hybrid muscles caused by dew condensing on the hybrid yarn. This self-powered humidity-controlled ventilation system could be adapted to automatically control the desired relative humidity of an enclosed space.