By EurekAlert
Thursday, November 19, 2009
Most people would like to be able to charge their cell phones
and other personal electronics quickly and not too often. A recent
discovery made by UC San Diego engineers could lead to carbon
nanotube-based supercapacitors that could do just this.
In recent research, published in Applied Physics Letters,
Prabhakar Bandaru, a professor in the UCSD Department of Mechanical
and Aerospace Engineering, along with graduate student Mark Hoefer,
have found that artificially introduced defects in nanotubes can
aid the development of supercapacitors.
"While batteries have large storage capacity, they take a long
time to charge; while electrostatic capacitors can charge quickly
but typically have limited capacity. However,
supercapacitors/electrochemical capacitors incorporate the
advantages of both," Bandaru said.
Carbon nanotubes (CNTs) have been generally hailed as one of the
wonder materials of the 21st century and have been widely
recognized as ushering in the nanotechnology revolution. They are
cylindrical structures, with diameters of 1 to 100 nanometers, that
have been suggested to have outstanding structural, chemical, and
electrical, characteristics based on their atomically perfect
structures with a large surface area-to-volume ratio. However,
defects are inevitable in such a practical structure, an aspect
that was first investigated by UCSD engineering graduate student
Jeff Nichols and then substantially extended by Hoefer in Bandaru's
lab.
"We first realized that defective CNTs could be used for energy
storage when we were investigating their use as electrodes for
chemical sensors," Hoefer said. "During our initial tests we
noticed that we were able to create charged defects that could be
used to increase CNT charge storage capabilities."
Specifically, defects on nanotubes create additional charge
sites enhancing the stored charge. The researchers have also
discovered methods which could increase or decrease the charge
associated with the defects by bombarding the CNTs with argon or
hydrogen.
"It is important to control this process carefully as too many
defects can deteriorate the electrical conductivity, which is the
reason for the use of CNTs in the first place. Good conductivity
helps in efficient charge transport and increases the power density
of these devices," Bandaru added.
"At the very outset, it is interesting that CNTs, which are
nominally considered perfect, could be useful with so many
incorporated defects," he added.
The researchers think that the energy density and power density
obtained through their work could be practically higher than
existing capacitor configurations which suffer from problems
associated with poor reliability, cost, and poor electrical
characteristics.
Bandaru and Hoefer hope that their research could have major
implications in the area of energy storage, a pertinent topic of
today. "We hope that our research will spark future interest in
utilizing CNTs as electrodes in charge storage devices with greater
energy and power densities," Hoefer said.
While more research still needs to be done to figure out
potential applications from this discovery, the engineers suggest
that this research could lead to wide variety of commercial
applications, and hope that more scientists and engineers will be
compelled to work in this area, Bandaru said.
Meanwhile, Hoefer said this type of research will help fuel his
future engineering career.
"It is remarkable how current tools and devices are becoming
increasing more efficient and yet smaller due to discoveries made
at the nanoscale," he said. "My time spent investigating CNTs and
their potential uses at the Jacobs School will prepare me for my
career, since future research will continue the trend of
miniaturization while increasing efficiency."
SOURCE