Researchers from the Indian Institute of Technology (IIT) Mandi have recently developed aligned carbon nanotube-based electrodes that could enable high energy supercapacitors. The research papers by Dr. Viswanath Balakrishnan and his research scholar, Piyush Avasthi has been published in Advanced Materials Interfaces and ACS Applied Nanomaterials.

Supercapacitors can charge and discharge instantly and can ideally last across millions of charge-discharge cycles without performance degradation.  They also have a higher power density than batteries. But, where they have fallen short so far, is in the area of energy density. Supercapacitors have forty times less ability to store energy than the state-of-art lithium-ion battery. Carbon nanotubes are tiny tubes of carbon, a hundred thousand times thinner than the human hair. These materials, when used as electrodes, have the potential to considerably increase the energy density of supercapacitors.  But typically high surface area carbon nanotube and fibres are hydrophobic, which means they cannot be ‘wetted’ by the electrolyte.

Piyush Avasthi, Research Scholar, Indian Institute of Technology Mandi, used a process called Chemical Vapor Deposition to produce ‘forests’ of vertically aligned carbon nanotubes that are wettable (hydrophilic) by the electrolyte. The perfectly aligned nanotubes, that were a few micrometres in height, were grown on a stainless-steel mesh and treated with two different ways to enhance their hydrophilic properties – in one, the forests were treated with potassium hydroxide (KOH), and in the other, they were coated with an ultrathin layer of titanium dioxide (titania), which made the nanotubes superhydrophilic.  While KOH treatment resulted in better energy density than randomly oriented carbon nanotubes, treating with titania resulted in a 102-fold increase in energy density, 20-fold increase in specific capacitance, and 13-fold increase in power density. With that kind of improvement, supercapacitors can certainly give lithium-ion batteries a run for their voltage.

“A promising route to improving the performance of energy storage devices, especially in terms of cycling life and charging times, is to move away from batteries towards supercapacitors,” says Dr. Viswanath Balakrishnan, Associate Professor, School of Engineering, Indian Institute of Technology Mandi.  

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