Scientists from Tokyo Metropolitan University have used aligned “metallic” carbon nanotubes to create a device which converts heat to electrical energy (a thermoelectric device) with a higher power output than pure semiconducting carbon nanotubes (CNTs) in random networks. The new device bypasses the troublesome trade-off in semiconductors between conductivity and electrical voltage, significantly outperforming its counterpart. High power thermoelectric devices may pave the way for more efficient use of waste heat, like wearable electronics.

Thermoelectric devices can directly convert heat to electricity. When we think about the amount of wasted heat in our environment like in air conditioning exhausts, vehicle engines or even body heat, it would be revolutionary if we could somehow scavenge this energy back from our surroundings and put it to good use. This goes some way to powering the thought behind wearable electronics and photonics, devices which could be worn on the skin and powered by body heat. Limited applications are already available in the form of body heat powered lights and smartwatches.

The power extracted from a thermoelectric device when a temperature gradient is formed is affected by the conductivity of the device and the Seebeck coefficient, a number indicating how much electrical voltage is generated with a certain difference in temperature. The problem is that there is a trade-off between the Seebeck coefficient and conductivity: the Seebeck coefficient drops when the device is made more conductive. To generate more power, we ideally want to improve both.