A new material could help harvest the energy from ocean waves or even human movement. The material, a carbon nanotube yarn, generates electricity when stretched or twisted.
An international team, led by Seon Jeong Kim of Hanyang University and Ray H. Baughman of the University of Texas, Dallas, made the materials by twisting multiwalled carbon nanotube yarns until they became tightly coiled. Stretching decreases the ability of the yarn to store electrical charge, which increases its voltage, leading to an electrical current (Science 2017, DOI: 10.1126/science.aam8771).
The scientists also coated the yarns with a gel electrolyte and then interwove the fibers with fabric in a shirt, allowing the researchers to monitor a person’s breathing from the current generated as the person’s chest expanded and contracted. According to Baughman, the team’s “twistrons” generate more than 100 times as much power as similar electricity-generating materials that can be woven into fabric. The twistrons provide enough power to transmit up to 2 kilobytes of data over 100 meters every 10 seconds.
To harvest electricity from near-shore ocean waves, the research team suspended a 10-cm-long twistron weighing only 1 mg between a weight and a balloon in the Gyeongpo Sea, just off the coast of South Korea. The weight anchored one end to the seafloor, and each passing wave pulled the balloon, stretching the coiled nanotube, generating an average of about 2 µW of power.
Large-scale harvesting of ocean wave energy would be limited by the manufacturing cost of these nanotube yarns, however. An important next step “is to take what we’ve learned from these carbon nanotube harvesters and apply it to less expensive materials that are commercially available,” Baughman says.
John A. Rogers, of Northwestern University, calls the twistron technology “a clever type of platform” and adds that it provides a variety of technological opportunities, particularly for powering biomedical monitoring devices.