Mechanical energy harvesters with tensile efficiency of 17.4 percent and torsional efficiency of 22.4 percent based on homochirally plied carbon nanotube yarns

Improved methods are needed for harvesting mechanical energy. Coiled carbon nanotube yarns, termed twistrons, use stretch-induced changes in electrochemical capacitance to convert mechanical energy to electricity. Elongation of the yarn produces such large lateral Poisson's ratios that the yarns are highly stretch densified, which contributes to harvesting. Here we report plied twistrons, instead of coiled, which increase the energy conversion efficiency of the yarns from 7.6 percent to 17.4 percent for stretch and to 22.4 percent for twist. This is attributed to additional harvesting mechanisms by yarn stretch and lateral deformations. For harvesting between 2 and 120?Hz, our plied twistron has higher gravimetric peak power and average power than has been reported for non-twistron, material-based mechanical energy harvesters. We sew the twistrons into textiles for sensing and harvesting human motion, deploy them in salt water for harvesting ocean wave energy and use them to charge supercapacitors.