NEW FUEL
CELL TECHNOLOGY
RUNS ON SOLID CARBON
Advancements in a fuel cell
ADVANCEMENTS IN A FUEL CELL TECHNOLOGY POWERED BY SOLID CARBON COULD MAKE ELECTRICITY
GENERATION FROM COAL AND BIOMASS CLEANER AND MORE EFFICIENT. INNOVATIONS IN THE ANODE, THE
ELECTROLYTE AND THE FUEL ALLOW THE FUEL CELL TO UTILISE MORE CARBON, OPERATE AT LOWER TEMPERATURES
AND SHOW HIGHER MAXIMUM POWER DENSITIES THAN EARLIER DIRECT CARBON FUEL CELLS (DCFCS).
technology powered by solid
carbon could make electricity
generation from resources
such as coal and biomass
cleaner and more efficient, according to a new
paper published by Idaho National Laboratory
researchers.
The fuel cell design incorporates innovations in
three components: the anode, the electrolyte
and the fuel. Together, these advancements allow
the fuel cell to utilise about three times as much
carbon as earlier direct carbon fuel cell (DCFC)
designs.
The fuel cells also operate at lower temperatures
and showed higher maximum power densities
than earlier DCFCs, according to INL materials
engineer Dong Ding.
Whereas hydrogen fuel cells (eg, proton exchange
membrane (PEM) and other fuel cells) generate
electricity from the chemical reaction between
pure hydrogen and oxygen, DCFCs can use any
number of carbon-based resources for fuel,
including coal, coke, tar, biomass and organic
waste.
Because DCFCs make use of readily available
fuels, they are potentially more efficient than
conventional hydrogen fuel cells. "You can
skip the energy-intensive step of producing
hydrogen," Ding says.
But earlier DCFC designs have several drawbacks:
they require high temperatures - 700 to 900
degrees Celsius - which makes them less efficient
and less durable. Further, as a consequence
of those high temperatures, they're typically
constructed of expensive materials that can
handle the heat.
Also, early DCFC designs aren't able to effectively
utilise the carbon fuel.
Ding and his colleagues addressed these
challenges by designing a true direct carbon
fuel cell that's capable of operating at lower
temperatures - below 600 degrees Celsius. The
fuel cell makes use of solid carbon, which is finely
ground and injected via an airstream into the
cell. The researchers tackled the need for high
temperatures by developing an electrolyte using
highly conductive materials - doped cerium oxide
and carbonate. These materials maintain their
performance under lower temperatures.
Next, they increased carbon utilisation by
developing a 3-D ceramic textile anode design
that interlaces bundles of fibres together like a
piece of cloth. The fibres themselves are hollow
and porous. All of these features combine to
maximise the amount of surface area that's
available for a chemical reaction with the carbon
fuel.
Finally, the researchers developed a composite
fuel made from solid carbon and carbonate. "At
the operating temperature, that composite is
fluidlike," Ding says. "It can easily flow into the
interface."
The molten carbonate carries the solid carbon
into the hollow fibres and the pinholes of the
anode, increasing the power density of the fuel
cell.
The resulting fuel cell looks like a green, ceramic
watch battery that's about as thick as a piece
of construction paper. A larger square is 10
centimetres on each side. The fuel cells can be
stacked on top of one another depending on the
application.
The technology has the potential for improved
utilisation of carbon fuels, such as coal and
biomass, because direct carbon fuel cells
produce carbon dioxide without the mixture of
other gases and particulates found in smoke from
coal-fired power plants, for example. This makes it
easier to implement carbon capture technologies,
Ding says.
Caption: Research scientist Dong Ding is developing direct carbon fuel cells at INL's
Energy Innovation Laboratory. Credit: Idaho National Laboratory
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