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Fuel Cells Possible For Portable Power

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by Brad Amburn
Washington DC (UPI) Aug 2, 2004
U.S. researchers are refining a type of fuel cell to be smaller, less costly and more efficient than traditional models and could provide reliable, clean sources of energy for portable devices such as laptop computers or spacesuits for astronauts.

Solid-oxide fuel cells -- which use hydrogen and oxygen to produce an electric current that give off only water vapor and heat as byproducts -- traditionally have been adapted to provide power for larger facilities, such as homes, buildings and spacecraft.

Now, researchers at the University of Houston's Texas Center for Superconductivity and Advanced Materials are developing a solid-oxide fuel cell ideally no bigger than a sugar cube to power portable devices at lower costs and increased durability, they said.

In solid-oxide fuel cells, the major benefit is that it is very efficient, on the order of 60 percent efficiency or sometimes even higher, whereas other fuel cells are usually on the order of 25 percent to 30 percent efficiency, Alex Ignatiev, director of TcSAM, told United Press International.

But for the solid-oxide fuel cell, the problem is it works at typically 900 degrees or 1,000 degrees Centigrade (1,650 degrees to 1,830 degrees Fahrenheit). So you need very exotic materials to work with -- very expensive materials -- and so it becomes a challenge in terms of cost and longevity.

Traditional solid-oxide fuel cells run similar to a battery by converting the energy from chemical reactions directly into electrical energy. Unlike batteries, which eventually die out, fuel cells are continually powered by sources such as hydrogen and oxygen to produce a constant, clean source of electricity.

Current, non-hydro powerplants must convert chemical energy -- from coal, oil, natural gas or uranium -- into mechanical energy -- driving a turbine -- before turning it into electricity. This indirect process cuts efficiency levels to only 30 percent to 35 percent and emits greenhouse gases, Ignatiev explained.

Ignatiev and colleagues think they can beat both methods by reducing the thickness of the current-carrying region in solid-oxide fuel cells, called the electrolyte, to the size of 1 micron -- roughly one-hundredth the size of a human hair. Past efforts have managed only to reduce it to perhaps 10 microns, he said.

If 1 micron is achieved, it would be about 1,000 times thinner than the standard fuel cell, Ignatiev continued. Electrolytes that thin would allow oxygen ions -- atoms with a gain or loss of electrons that feed the electric current -- to move faster and easier through a fuel cell vs. a cell that is a few fractions of a centimeter thick.

With a shorter distance to travel, these thin-film fuel cells can operate at much lower temperatures, providing 10 watts to 20 watts of power per cubic centimeter when linked together at nearly 450 degrees Celsius (840 degrees F), half of what is normally required, with over 55 percent efficiency, Ignatiev said.

It's very exciting because now we have efficiency, we have much lower temperatures of operation and therefore less costly materials and a very high power density, so using these in small form can give you a large power output, he said.

A new, thin layer of nickel foil also improves energy efficiency by causing oxygen atoms to break down without the need of a catalyst, which would increase the cell's size.

Ignatiev said they have not had sufficient time to test the longevity of the new cells, because solid-oxide units traditionally are short-lived at extreme temperatures. Nevertheless, Debbie Myers, leader of the Hydrogen and Fuel Cell Materials group at Argonne National Laboratory in Illinois, said preliminary data seem positive.

There is a fairly stable power output for a test that lasted 350 minutes, Myers told UPI. Many solid-oxide fuel cells only last for a few hours.

The technology could go beyond just powering homes and laptops.

We're talking to NASA right now, which has a large need for electrical energy for spacesuits and for exploration projects and wants to have small size ... because of the cost of working in space -- so it would be ideal for them, Ignatiev said.

We're also addressing the Department of Defense and talking about the all-electric soldier, so to speak, and that soldier needs a lot of energy to run all the sensors and devices and computers, et cetera, that are needed for military purposes, he added.

The project has refined the size and design of a single fuel cell, but the stacking process that links these units together to produce a higher energy output remains in the design stages, Ignatiev said.

Each cell gives about a volt or nine-tenths of a volt of output, he said, so say we want 50-volt output we would stack 50 of these layers together, but we have not done that yet. We have a preliminary design for it and now we're going to be working with the Department of Energy laboratories to try and bring the design to final form and put together a stack.

Ignatiev said a final stacking design should be in operation by next spring with a fully operational fuel system available as an industrial product in about a year and a half, but Myers noted the cost of producing these types of cells lags behind its goal.

A present, solid-oxide cells have a unit cost of $2,000 per kilowatt. The goal is to reduce this to $400 per kilowatt, Myers said.

Neither Myers nor Ignatiev was able to provide precise predictions for operational costs.

The University of Houston work is interesting and novel and they are achieving high power densities at low operating temperatures, Myers said. However, they are not alone in achieving these power densities.

Myers also cited research at Northwestern University that has found new materials to build solid-oxide fuel cells comparable to those at the University of Houston.

We have to go to new materials to push temperatures down and also get good power densities, said Northwestern professor Scott A. Barnett, who has published several reports on thin film solid oxide fuel cells. We think we have developed a material set that can put temperatures down to 400 degrees Centigrade (750 degrees F) and produce really good power densities up to 400 milliwatts per square centimeter.

Myers also spoke of a colleague who previously had manufactured fuel cells with an output of 330 milliwatts at 550 degrees Centigrade (1,025 degrees F), but she would not elaborate because he is in private communication with the laboratory.

Myers also said the small size of the University of Houston's fuel cell system could be exaggerated.

In between each of these cells there is a gas flow that constitutes a large fraction of the thickness of the cell. So a system going from, say, 200 microns down to 120 microns -- which is just 60 percent of the size -- is bit of an exaggeration.

All rights reserved. Copyright 2004 by United Press International. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by United Press International. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of by United Press International.

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