Self-cleaning Anodes Could Facilitate Cost-effective Coal-powered Fuel Cells

Using barium oxide nanoparticles, researchers have developed a self-cleaning technique that could allow solid oxide fuel cells to be powered directly by coal gas at operating temperatures as low as 750 degrees Celsius. The technique could provide a cleaner and more efficient alternative to conventional power plants for generating electricity from the nation's vast coal reserves. Solid oxide fuel cells can operate on a wide variety of fuels, and use hydrocarbons gases directly – without a separate reformer. The fuel cells rely on anodes made from nickel and a ceramic material known as yttria-stabilized zirconia. Until now, however, carbon-containing fuels such as coal gas or propane could quickly deactivate these Ni-YSZ anodes, clogging them with carbon deposits in a process known as "coking" – especially at lower operating temperatures.

To counter this problem, researchers have developed a technique for growing barium oxide nanostructures on the anodes. The structures adsorb moisture to initiate a water-based chemical reaction that oxidizes the carbon as it forms, keeping the nickel electrode surfaces clean even when carbon-containing fuels are used at low temperatures.

"This could ultimately be the cleanest, most efficient and cost-effective way of converting coal into electricity," said Meilin Liu, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "And by providing an exhaust stream of pure carbon dioxide, this technique could also facilitate carbon sequestration without the separation and purification steps now required for conventional coal-burning power plants."

The water-mediated carbon removal technique was reported June 21 in the journal Nature Communications. The research was supported by the U.S. Department of Energy's Office of Basic Energy Sciences, through the HeteroFoaM Center, an Energy Frontier Research Center. The work also involved researchers from Brookhaven National Laboratory, the New Jersey Institute of Technology and Oak Ridge National Laboratory.

Conventional coal-fired electric generating facilities capture just a third of the energy available in the fuel they burn. Fuel cells can convert significantly more of the energy, approximately 50 percent. If gas turbines and fuel cells could be combined into hybrid systems, researchers believe they could capture as much as 80 percent of the energy, reducing the amount of coal needed to produce a given amount of energy, potentially cutting carbon emissions.

But that would only be possible if the fuel cells could run for long periods of time on coal gas, which now deactivates the anodes after as little as 30 minutes of operation.

The carbon removal system developed by the Georgia Tech-led team uses a vapor deposition process to apply barium oxide nanoparticles to the nickel-YSZ electrode. The particles, which range in size from 10 to 100 nanometers, form "islands" on the nickel that do not block the flow of electrons across the electrode surface.