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Power with a twist: Twisted ropes made from single-walled carbon nanotubes could store enough energy to power sensors within the human body while avoiding the chemical hazards associated with batteries. (Courtesy: Shigenori UTSUMI)

Topics: Applied Physics, Battery, Carbon Nanotubes, Chemistry, Materials Science, Nanoengineering

Mechanical watches and clockwork toys might seem like relics of a bygone age, but scientists in the US and Japan are bringing this old-fashioned form of energy storage into the modern era. By making single-walled carbon nanotubes (SWCNTs) into ropes and twisting them like the string on an overworked yo-yo, Katsumi Kaneko, Sanjeev Kumar Ujjain , and colleagues showed that they can store twice as much energy per unit mass as the best commercial lithium-ion batteries. The nanotube ropes are also stable at a wide range of temperatures, and the team says they could be safer than batteries for powering devices such as medical sensors.

SWCNTs are made from sheets of pure carbon just one atom thick that have been rolled into a straw-like tube. They are impressively tough – five times stiffer and 100 times stronger than steel – and earlier theoretical studies by team member David Tománek and others suggested that twisting them could be a viable means of storing large amounts of energy in a compact, lightweight system.

Twisted carbon nanotubes store more energy than lithium-ion batteries, Margaret Harris, Physics World.

Stored energy: a rendition of a system that combines polymeric nitrogen (blue chain) and carbon nanotube (clear spheres). (Courtesy: Heba Megahd)

Topics: Carbon Nanotubes, Materials Science, Nanotechnology

From TNT to nitro-glycerine, nitrogen-rich compounds are known for packing an explosive punch. When these materials explode, bonds between atoms in the compounds are broken, which gives a chance for two nitrogen atoms to form very strong triple bonds with each other. This releases an enormous amount of chemical energy due to the high strength of the triple bond, which is almost six times stronger than its single-band counterpart. In fact, the strength of nitrogen-nitrogen triple bonds is one of the reasons that the stable nitrogen gas dominates Earth’s atmosphere.

This chemical property of nitrogen is encouraging scientists to develop new nitrogen-rich compounds for use as high-energy-density materials that can be used as explosives or propellants. Polymeric nitrogen exists in the form of chains and tubes of linked nitrogen atoms with a high number of single or double bonds that can break and form triple bonds, releasing a large amount of energy and no dangerous by-products.

Several types of these polymers have been made at high temperatures and pressures, but they have been notoriously difficult to stabilize under ambient conditions. However, the electrochemical pressure inside the confined walls of carbon nanotubes may be the key to realizing these structures under more practical conditions. In a paper, published in Chinese Physics Letters, a team of scientists led by Jian Sun at Nanjing University provides a theoretical map of the process and the resulting compounds.

Carbon nanotubes could stabilize energy-rich nitrogen chains, Heba Megahd, Physics World