PORTLAND, Ore. Solid-oxide fuel cells offer high efficiency--80 percent compared to 50 percent for hydrogen fuel cells--and can utilize a wider variety of fuels, including hydrogen, natural gas or propane. But they also are easily contaminated by sulfur and carbon build-up on anodes that reduce these advantages.
A new kind of electrode material could overcome contamination problems using an auto-cleaning process that could also lower their cost. "Our new material gives us very high tolerance to contaminant poisoning--the critical problem holding back the development of solid-oxide fuel cells," said Georgia Tech professor Meilin Liu. "Our ceramic anode electrode oxidizes sulfur and carbon so that they do not poison the solid-oxide fuel cells."
Traditional anode electrodes can be fouled by as little as 1 part per million of sulfur in the fuel, according to Liu, requiring the costly step of purifying fuel before it is used. The ceramic electrode material can tolerate sulfur contaminants in concentrations as high as 50 ppm.
The ceramic material, which was discovered after extensive experimentation, is composed of five different elements: barium, zirconium, cerium, yttrium and ytterbium. Despite the complex formulation, it can be cast into relatively inexpensive anode electrodes, the researchers said.
The ceramic electrodes also permit the fuel cell to operate at lower temperatures, thereby lowering the cost of packaging a solid-oxide fuel cell. Ordinary fuel cells require temperatures as high as 1,000 degrees C, but the new ceramic electrode material permits operation below 500 degrees C.
"Higher temperatures increase the output current from a solid-oxide fuel cell, but our electrode reduces the required operating temperature, which should translate into lower cost," Liu claimed.
So far, the Georgia Tech team has only tested their ceramic electrode in a small laboratory prototype for 1,000 hours at a time. They next want to build a full-sized prototype to demonstrate that the ceramic electrode formulation can be scaled up. They also plan to test the design to ensure that it can last about five years, the desired minimum lifetime for the fuel cell technology to reach volume production.
The team also wants to reduce operating temperature to as little 300 degrees C.
Liu contended that despite being less advanced than competing fuel cell designs, solid-oxide fuel cells could eventually dominate the industry since they are not only more efficient but require no precious metals such as the platinum used for electrodes in traditional fuel cells.
Funding for the fuel cell research was provided by the U.S. Energy Department's Basic Energy Science Catalysis Science Program.