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Saturday, April 28, 2012
Nanotube Arrays Alternative to platinum
It appears that a carpet of nanotubes can be used to replace platinum
in situations needing catalytic activity.
Early days of course but still very promising.
Over the past few years, physics has been winkling out a whole new tool
box that while once only imagined was also pretty unattainable but
imaginable. Now the tricks keep coming
and the promise keeps expanding.
I had anticipated rapid knowledge expansion after the advent of the
internet but no one can ever imagine the details. A lot of it is expanding slowly but generally
every hand on board is continuing to find ample work.
This will be known as the golden age of physics.
Nanotube electrodes improve
by Staff Writers
Houston TX (SPX) Apr 18, 2012
Pei Dong, a graduate student
at Rice University, holds a lab-built solar cell that combines a carbon
nanotube current collector and a sulfide-based electrolyte. The combination
could make such solar cells more efficient and less expensive than current
dye-sensitized units. (Credit: Jeff Fitlow/Rice University).
Forests of carbon nanotubes
are an efficient alternative for platinum electrodes in dye-sensitized solar
cells (DSC), according to new research by collaborators at Rice University and
The single-wall nanotube
arrays, grown in a process invented at Rice, are both much more electroactive
and potentially cheaper than platinum, a common catalyst in DSCs, said Jun Lou,
a materials scientist at Rice. In combination with newly developed sulfide
electrolytes synthesized at Tsinghua, they could lead to more efficient and
robust solar cells at a fraction of the current cost for traditional
silicon-based solar cells.
Lou and co-lead investigator
Hong Lin, a professor of materials science and engineering at Tsinghua,
detailed their work in the online, open-access Nature journal Scientific Reports
DSCs are easier to manufacture
than silicon-based solid-state photovoltaic cells but not as efficient, said
Lou, a professor of mechanical engineering and materials science.
“DSCs are sensitized with
dyes, ideally organic dyes like the juices from berries - which some students
have actually used in demonstrations."
Dyes absorb photons from
sunlight and generate a charge in the form of electrons, which are captured
first by a semiconducting titanium oxide layer deposited on a current collector
before flowing back to the counter electrode through another current collector.
Progress has been made in the
manufacture of DSCs that incorporate an iodine-based electrolyte, but iodine
tends to corrode metallic current collectors, which "poses a challenge for
its long-term reliability," Lou said.
Iodine electrolyte also has
the unfortunate tendency to absorb light in the visible wavelengths,
"which means fewer photons could be utilized," Lou said.
So Tsinghua researchers
decided to try a noncorrosive, sulfide-based electrolyte that absorbs little
visible light and works well with the single-walled carbon nanotube carpets
created in the Rice lab of Robert Hauge, a co-author of the paper and a
distinguished faculty fellow in chemistry at Rice's Richard E. Smalley
Institute for Nanoscale Science and Technology .
"These are very versatile
materials," Lou said. "Single-walled carbon nanotubes have been
around at Rice for a very long time, and people have found many different ways
to use them. This is another way that turns out to be very well-matched to a
sulfid-based electrolyte in DSC technology."
Both Rice and Tsinghua built
working solar cells, with similar results. They were able to achieve a power
conversion efficiency of 5.25 percent - lower than the DSC record of 11 percent
with iodine electrolytes a platinum electrode, but significantly higher a
control that combined the new electrolyte with a traditional platinum counter
electrode. Resistance between the new electrolyte and counter electrode is "the
lowest we've ever seen," Lou said.
There's much work to be done,
however. "The carbon nanotube-to-current collector still has a pretty
large contact resistance, and the effects of structural defects in carbon
nanotubes on their corresponding performance are not fully understood, but we
believe once we optimize everything, we're going to get decent efficiency and
make the whole thing very affordable," Lou said. "The real attraction
is that it will be a very low-cost alternative to silicon-based solar cells."
Pei Dong, a graduate student
in Lou's lab, and Feng Hao, a graduate student at Tsinghua, are lead authors of
the paper. Co-authors include Rice graduate students Jing Zhang and Philip
Loya, Yongchang Zhang of Tsinghua and Professor Jianbao Li of Hainan
The project was supported by
the National High Technology Research and Development Program of China, the
Welch Foundation and the Faculty Initiative Fund at Rice. Read the