Raytheon Technology Today 2011 Issue 1

SOFC systems run at high internal temperatures
(500–1,000°C), improving electrical
efficiency and more easily accommodating
the use of alternative fuels. Higher temperature
operation, however, increases start-up
time and drives material costs. For these
reasons SOFCs are currently a less favored
solution for certain applications, such as
automotive, where lower temperature fuel
cell technology is dominant.
Powering automobiles is a much-discussed
application of fuel cells. The first fuel-cell
vehicle offerings utilize proton exchange
membrane (PEM) — also known as polymer
electrolyte membrane — solid fuel cells with
compressed hydrogen fuel.
PEM fuel cells differ from SOFCs in that
they operate at lower temperatures,
typically 50 to 100 degrees Celsius. The
principal fuel choice is pure hydrogen
(although other fuels, including hydrocarbons,
have been used). The electrolyte in
this type of fuel cell is a polymer membrane
that is electrically insulating, but that
allows for the flow of protons, which are
generated by the interaction of hydrogen
fuel with the anode. The anode, typically
consisting of a platinum catalyst, ionizes the
hydrogen to generate hydrogen ions
(i.e., protons) and electrons. Electrons are
free to flow in the external load circuit
and power the vehicle or other device,
and combine with the hydrogen ions and
oxygen at the cathode to form water as a
waste byproduct of the PEM fuel cell. While
the detailed engineering and materials
challenges for constructing a PEM versus
an SOFC fuel cell differ, the basic concept
holds: Hydrogen/hydrocarbon fuel plus
oxygen generates electrical power plus
water/carbon dioxide and heat as byproducts.
According to the U.S. Department of
Energy, the appeal of PEMs for automotive
applications is that they hold the promise of
clean, reliable power; hydrogen production
to power a PEM is typically greener than
The Battlefield Game Changer:
Portable and Wearable Soldier Power
Feature
a gasoline or diesel internal combustion
engine. Hydrogen can also be produced domestically,
reducing dependence on
imported oil. Challenges in producing
economically viable PEMs include on-board
hydrogen storage; total cost of the fuel cell
stack; durability, reliability and life cycle of
the fuel cell, including ability to perform in
sub-freezing temperatures; and the need
for a consumer hydrogen fuel distribution
network.
The fuel cell examples cited here are
representative of the type of research,
development and product creation that is
occurring in this rapidly evolving field to
provide new types of clean, reliable power
solutions. Raytheon’s continued pursuit of
advances in this area ensures that our
customers have access to the best technology
in the marketplace, whether developed
in-house or through partnerships with
industry and academia. •
Steve Klepper and Tony Marinilli
Imagine that you have a 100-pound load on your back for the next 72 hours, and you’re hiking on rough terrain where there are likely to
be many life-threatening dangers in your path. You can’t abandon your load, because it holds life-saving necessities. This is a 72-hour
mission in Afghanistan.
Of the 100 pounds in the load, approximately 25 percent is from batteries, which power all electronic devices a soldier carries. If the
battery load can be decreased, while still allowing the devices to be powered, the soldier could carry more ammunition, water and other
warfighting gear. Or it will simply help the soldier feel less fatigued when on the battlefield.
In order to remove battery weight from our soldiers, Raytheon is developing an efficient, portable/wearable fuel cell that can either supply
power directly or charge batteries anywhere, any time. Comparing this to the standard BA-5290 military lithium ion battery (880cc and
1300g) with the same volume or form factor, the fuel cell can provide four times more run-time with a half of the BA-5290 weight.
Revisiting the 72-hour mission, a soldier needs to carry seven different battery types weighing about 25 pounds. The battery cost per
soldier, per day is approximately $40 to $50. Using this alternative fuel cell technology, a soldier could potentially drop portable power
weight by more than 11 pounds (a weight savings of more than 40 percent). The savings become even more dramatic when considering
next-generation, soldier-borne power management schemes where the fuel cell directly powers all equipment. In this example, no batteries
would be needed, and no recharging would be required. A fuel cell with three cartridges of fuel could last 72 hours and weigh only
about 5 pounds. The cost of this system would be about $5 per soldier, per day.
Howard Choe
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