US engineers have developed a direct carbon fuel cell that runs at relatively lower temperatures and higher maximum power densities and offers a much cleaner way to generate electricity from fossil fuels.
Direct carbon fuel cells (DCFC) run off carbon-based resources, such as coal, coke, tar, biomass or organic waste. Most fuel cells run off hydrogen, generating electricity from the chemical reaction between pure hydrogen and oxygen.
However, DCFC fuel cells normally require high temperatures to work, 700 to 900°C, making them less efficient and durable and requiring the use of expensive materials in their design.
The researchers at the Idaho National Laboratory (INL) improved on the design of previous carbon fuel cells in several ways, enabling their fuel cell to use about three times as much carbon as earlier designs and reducing the operating temperature to below 600°C.
The fuel cells also showed higher maximum power densities than earlier DCFCs, according to INL materials engineer Dong Ding. The results appear in this week’s edition of the journal Advanced Materials.
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.
They increased carbon utilization by developing a 3D 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 maximize 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. 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.
“At the operating temperature the composite is fluid-like,” said Ding. “It can easily flow into the interface.”
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 centimeters on each side. The fuel cells can be stacked on top of one another depending on the application. The Advanced Materials journal posted a video abstract here.
Direct carbon fuel cells make use of readily available fuels and are therefore potentially more efficient than conventional hydrogen fuel cells. “You can skip the energy-intensive step of producing hydrogen,” Ding said.
DCFCs also produce carbon dioxide without the mixture of other gases and particulates found in smoke from coal-fired power plants, making it easier to implement carbon capture technologies.
Idaho National Laboratory is partnering with Salt Lake City-based Storagenergy to further develop the fuel cell using government funding. A Canadian energy-related company has also shown interest in these DCFC technologies.