| |
 |
|
|
Science Forum Index » Energy - Hydrogen Forum » A Boost for Hydrogen Fuel Cell Research
Page 1 of 1
|
| Author |
Message |
| awe |
 Posted: Thu Feb 01, 2007 9:10 am |
|
|
|
Guest
|
http://www.physorg.com/news88953630.html
The green dots in this Low Energy Electron Diffraction pattern for a single
crystal of Pt3Ni(111) reveal a tightly packed arrangement of surface atoms
that wards off platinum-grabbing hydroxide ions and boosts catalytic
performance. Credit: Berkeley Lab
The development of hydrogen fuel cells for vehicles, the ultimate green
dream in transportation energy, is another step closer. Researchers with the
U.S. Department of Energy's Lawrence Berkeley National Laboratory and
Argonne National Laboratory have identified a new variation of a familiar
platinum-nickel alloy that is far and away the most active oxygen-reducing
catalyst ever reported.
The slow rate of oxygen-reduction catalysis on the cathode - a fuel cell's
positively charged electrode - has been a primary factor hindering
development of the polymer electrolyte membrane (PEM) fuel cells favored for
use in vehicles powered by hydrogen.
"The existing limitations facing PEM fuel cell technology applications in
the transportation sector could be eliminated with the development of stable
cathode catalysts with several orders of magnitude increase in activity over
today's state-of-the-art catalysts, and that is what our discovery has the
potential to provide," said Vojislav Stamenkovic, a scientist with dual
appointments in the Materials Sciences Division of both Berkeley Lab and
Argonne.
Stamenkovic and Argonne senior scientist Nenad Markovic are the
corresponding authors of a study whose results are now available online from
the journal Science. The paper, entitled Improved Oxygen Reduction Activity
on Pt3Ni(111) via Increased Surface Site Availability, reports a
platinum-nickel alloy that increased the catalytic activity of a fuel cell
cathode by an astonishing 90-fold over the platinum-carbon cathode catalysts
used today.
"This surface sets a new bar for catalytic activity in PEM fuel cells and
makes it feasible to meet U.S. Department of Energy (DOE) targets for
platinum-specific power densities without a loss in cell voltage,"
Stamenkovic said.
Other authors of the Science paper in addition to Stamenkovic and Markovic
were Philip Ross and Bongjin Mun of Berkeley Lab, Ben Fowler and Christopher
Lucas of England's University of Liverpool, and Guofeng Wang, of the
University of South Carolina.
By converting chemical energy into electrical energy without combustion,
fuel cells represent perhaps the most efficient and clean technology for
generating electricity. This is especially true for fuel cells designed to
directly run off hydrogen, which produce only water as a byproduct. The
hydrogen-powered fuel cells most talked about for use in vehicles are PEM
fuel cells (also known as "proton exchange membrane fuel cells") because
they can deliver high power in a relative small, light-weight device. Unlike
batteries, PEM fuel cells do not require recharging, but rely on a supply of
hydrogen and access to oxygen from the atmosphere.
PEM fuel cells have admirably served NASA's space program, but they remain
far too expensive for use in cars or most other Earth-bound applications.
The biggest cost factor is their dependency on platinum, which is used as
the cathode catalyst. A PEM fuel cell consists of a cathode and an anode
(the negatively charged electrode) that are positioned on either side of a
polymer electrolyte membrane, which is a specially treated substance that
conducts positively charged protons and blocks negatively charged electrons.
Like other types of fuel cells, PEM fuel cells carry out two reactions, an
oxidation reaction at the anode and an oxygen reduction reaction (ORR) at
the cathode. For PEMs, this means that hydrogen molecules are split into
pairs of protons and electrons at the anode. While the protons pass through
the membrane, the blocked electrons are conducted via a wire (the electrical
current), through a load and eventually onto the cathode. At the cathode,
the electrons combine with the protons that passed through the membrane plus
atoms of oxygen to produce water. The oxygen (O) comes from molecules in the
air (O2) that are split into pairs of O atoms by the cathode catalyst.
"Massive application of PEM fuel cells as the basis for a renewable
hydrogen-based energy economy is a leading concept for meeting global energy
needs," said Stamenkovic.
"Since the only byproduct of PEM fuel cell exploitation is water vapor,
their widespread use should have a tremendously beneficial impact on
greenhouse gas emissions and global warming."
A challenge has been the platinum. While pure platinum is an exceptionally
active catalyst, it is quite expensive and its performance can quickly
degrade through the creation of unwanted by-products, such as hydroxide
ions. Hydroxides have an affinity for binding with platinum atoms and when
they do this they take those platinum atoms out of the catalytic game. As
this platinum-binding continues, the catalytic ability of the cathode
erodes. Consequently, researchers have been investigating the use of
platinum alloys in combination with a surface enrichment technique. Under
this scenario, the surface of the cathode is covered with a "skin" of
platinum atoms, and beneath are layers of atoms made from a combination of
platinum and a non-precious metal, such as nickel or cobalt. The subsurface
alloy interacts with the skin in a way that enhances the overall performance
of the cathode.
For this latest study, Stamenkovic and Markovic and their colleagues created
pure single crystals of platinum-nickel alloys across a range of atomic
lattice structures in an ultra-high vacuum (UHV) chamber. They then used a
combination of surface-sensitive probes and electrochemical techniques to
measure the respective abilities of these crystals to perform ORR catalysis.
The ORR activity of each sample was then compared to that of platinum single
crystals and platinum-carbon catalysts.
The researchers identified the platinum-nickel alloy configuration
Pt3Ni(111) as displaying the highest ORR activity that has ever been
detected on a cathode catalyst - 10 times better than a single crystal
surface of pure platinum(111), and 90 times better than platinum-carbon. In
this (111) configuration, the surface skin is a layer of tightly packed
platinum atoms that sits on top of a layer made up of equal numbers of
platinum and nickel atoms. All of the layers underneath those top two layers
consist of three atoms of platinum for every atom of nickel.
According to Stamenkovic, the Pt3Ni(111) configuration acts as a buffer
against hydroxide and other platinum-binding molecules, blunting their
interactions with the cathode surface and allowing for far more ORR
activity. The reduced platinum-binding also cuts down on the degradation of
the cathode surface.
"We have identified a cathode surface that is capable of achieving and even
exceeding the target for catalytic activity, with improved stability for the
cathodic reaction in fuel cells," said Stamenkovic. "Although the
platinum-nickel alloy itself is well-known, we were able to control and tune
key parameters which enabled us to make this discovery. Our study
demonstrates the potential of new analytical tools for characterizing
nanoscale surfaces in order to fine-tune their properties in a desired
direction."
The next step, Stamenkovic said, will be to engineer nanoparticle catalysts
with electronic and morphological properties that mimic the surfaces of pure
single crystals of Pt3Ni(111).
Source: Lawrence Berkeley National Laboratory |
|
|
| Back to top |
|
| Eeyore |
| Posted: Thu Feb 01, 2007 11:38 am |
|
|
|
Guest
|
awe wrote:
Quote: The development of hydrogen fuel cells for vehicles, the ultimate green
dream in transportation energy, is another step closer.
What's green about an energy carrier that's barely 25% efficient ?
Graham |
|
|
| Back to top |
|
| Bob Eld |
| Posted: Thu Feb 01, 2007 12:09 pm |
|
|
|
Guest
|
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:45C2096D.48583AA@hotmail.com...
Quote:
awe wrote:
The development of hydrogen fuel cells for vehicles, the ultimate green
dream in transportation energy, is another step closer.
What's green about an energy carrier that's barely 25% efficient ?
Graham
Or comes from natural gas or coal? |
|
|
| Back to top |
|
| Don Lancaster |
| Posted: Thu Feb 01, 2007 12:41 pm |
|
|
|
Guest
|
Bob Eld wrote:
Quote: "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:45C2096D.48583AA@hotmail.com...
awe wrote:
The development of hydrogen fuel cells for vehicles, the ultimate green
dream in transportation energy, is another step closer.
What's green about an energy carrier that's barely 25% efficient ?
Graham
Or comes from natural gas or coal?
Well, an energy carrier that's barely 25% efficient would be a damn site
more green than hydrogen, which currently has a negative efficiency.
http://www.tinaja.com/glib/energfun.pdf
--
Many thanks,
Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com |
|
|
| Back to top |
|
| |
|
Page 1 of 1
All times are GMT - 5 Hours
The time now is Sat Oct 11, 2008 5:28 pm
|
|