There has been a lot of talk in the mainstream media regarding fuel cell
powered vehicles as a greener and cleaner alternative to petrol engines over the
past few years. A major obstacles to this revolution is the cost of hydrogen
fuel cell power plants. A fuel cell is a device that converts fuel, normally in
the form of a gas such as hydrogen or oxygen, into electricity. For road
vehicles, proton exchange membrane (PEM) cells are widely seen as the most
Proton exchange membrane (PEM) fuel cells provide high power density and the
advantages of low weight and volume compared to other types of fuel cells. In a
PEM cell, hydrogen and oxygen gas are fed to catalytic electrodes at opposite
sides of a special membrane. This special membrane is porous to protons but not
electrons. The protons and electrons are separated by the action of a platinum
catalyst in the electrodes. The protons can diffuse directly through the
membrane but the electrons have to make their way through an external circuit to
reach the other side, providing power for an electric motor in the process.
Proton Exchange Membrane Fuel Cell. (Source:
Dept. of Energy)
Professor Rod Boswell and the Space Plasma, Power &
Propulsion Group at ANU have been working with plasmas for many years and
recently became interested in the possibility using plasma deposition technology
to dramatically reduce the cost of making fuel cells.
Professor Boswell also commented "Production of current cells
frequently relies on wet chemical stages which are messy, inefficient and
consume large amounts of expensive materials. Our aim is to develop plasma based
techniques to create both the membranes and the catalytic electrodes needed in
Proton exchange membrane fuel cells (PEM), also known as polymer electrolyte membrane fuel cells, deliver
high-power density and offer the advantages of low weight and volume, compared
with other fuel cells. PEM fuel cells operate at relatively low temperatures,
around 80°C (176°F). Low-temperature operation allows them to start quickly
(less warm-up time) and results in less wear on system components, resulting in
The manufacture of electrodes starts with a substrate of carbon paper. Carbon
paper is chosen because it is both porous to the gaseous fuels used in the final
cells and is also an excellent conductor of electricity. This is loaded into the
plasma reactor chamber and a very fine layer of nickel is deposited on the
surface. Under the right conditions the nickel forms nanoscale droplets all over
the carbon surface.
The next stage is to introduce methane and hydrogen into the plasma chamber.
Many complex reactions ensue leading to a very surprising situation where carbon
complexes diffuse through the nickel seeds to form multi-carbon complexes below.
The highly reactive hydrogen protons in the chamber etch away any carbon atoms
that aren't strongly bonded to each other. The practical upshot of this is that
carbon nano fibres grow below the nickel droplets lifting them from the
substrate as they extend. The result is a carpet-like covering of carbon
nanofibres on the paper.
Once the forest of nanofibres has been created the next step is to sputter
coat the surface with platinum. Professor
Boswell explains: "During the sputtering process the nanofibre tips get
thickly coated with platinum with the droplets becoming progressively sparser
further down the fibre. It's very much like snow falling in a forest, a lot gets
deposited on the tree tops which greatly reduces the amount on the ground."
The tremendous advantage of this nanotechnology electrode is that its vast
surface area and microscopically thin platinum coat reduce the amount of
platinum required to about 15% of that in a conventional electrode of the same
To make the finished fuel cell, the membrane is sandwiched between the hairy
sides of two of the carbon catalytic electrode sheets and the whole assembly is
hot pressed into a single sheet.
The new fuel cell technology is exciting stuff and may well be a key part of
the transition to clean transport. "It has to be a holistic approach to clean
transport. If you buy a cylinder of hydrogen today, chances are it was made from
fossil fuels - it would be better to just burn the fossil fuel directly. What we
need are fuel cell vehicles running on hydrogen that is in turn generated by
clean electricity from solar or hydro. Then we'd be getting ahead" Professor
Boswell warns. At the moment it costs about six times as much to run on
hydrogen as petrol. However, with petrol costs continuing to climb and the
possibility of economies of scale in hydrogen production and distribution, it
may not be all that long before that economic balance shifts.
Copyright AZoNano.com, Prof. Rod Boswell (Australian National
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