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Q: Direct Carbon Fuel Cells ( Answered,   0 Comments )
Subject: Direct Carbon Fuel Cells
Category: Science > Technology
Asked by: joy677-ga
List Price: $50.00
Posted: 25 Sep 2006 08:24 PDT
Expires: 25 Oct 2006 08:24 PDT
Question ID: 768240
What energy conversion efficiency can the present DCFCs in  labs
demonstrate on a continuous basis (electrical energy output as a
percentage of the energy contained in the carbon fuel input)?
Subject: Re: Direct Carbon Fuel Cells
Answered By: keystroke-ga on 26 Sep 2006 10:59 PDT
Hello joy677,

The current direct carbon fuel cell energy efficiency rate is about 80
percent over repeated tests, compared to 40 percent for coal and other
natural resources that are currently utilized for energy.

Lawrence Livermore National Laboratory
"Carbon Conversion Fuel Cell"

"[Lawrence Livermore Laboratory researcher John] Cooper explains that
direct carbon conversion requires a unique kind of fuel cell. A fuel
cell is an electrochemical device that efficiently converts a fuel?s
chemical energy directly to electrical energy without burning the
fuel. However, instead of using gaseous fuels, as is typically done,
the new technology uses aggregates of extremely fine (10- to
1,000-nanometer-diameter) carbon particles distributed in a mixture of
molten lithium, sodium, or potassium carbonate at a temperature of 750
to 850C. The overall cell reaction is carbon and oxygen (from ambient
air) forming carbon dioxide and electricity.

The reaction yields 80 percent of the carbon?oxygen combustion energy
as electricity. It provides up to 1 kilowatt of power per square meter
of cell surface area?a rate sufficiently high for practical
applications. Yet no burning of the carbon takes place."

"In repeated tests, the cells deliver up to 0.1 watt continuously per
square centimeter and are 80-percent efficient at 80 milliwatts per
centimeter. Recently, using a new cell design that automatically
regulates the amount of molten salt, the team has operated cells for
days, simply by adding more carbon fuel."

This is much greater than hydrogen fuel cells, which many people have
trumpeted as a solution to the world's energy problems. They have an
efficiency of below 50 percent.

"'Realistically, we can get out a maximum of about 80- to 85-percent
efficiency, based on the heating value of the carbon, when the cell is
operated at a practical rate, which is about 100 milliamperes per
square centimeter,' says Cooper. 'The losses are primarily those
associated with the sluggishness of electrode reactions and the
electrical resistance of the cell. It was the two thermodynamic
properties?zero entropy change and constant electromotive force?that
first drew our attention to carbon as an attractive electrochemical
fuel.' In contrast, the entropy decrease for the hydrogen?oxygen
reaction in high-temperature fuel cells limits conversion efficiency
to 70 percent of the fuel?s HHV, while electrical efficiencies (about
80 percent) and practical fuel use (about 80 percent) further reduce
the total efficiency to below 50 percent."

Lawrence Livermore National Laboratory
"Carbon Conversion Fuel Cell"

Search terms:
"direct carbon fuel cell" + "energy conversion efficiency"

If you need any additional help or clarification, feel free to ask and
I'll be happy to help.

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