Low Temperature Fuel Cells Can Run on Biomass

Until recently, fuel cells were unable to use biomass as a fuel because scientists lacked an effective catalyst system for the polymeric material (the biomass). Low temperature fuel cells that use methanol or hydrogen to produce energy have been well studied, but a low temperature biomass fuel cell would create a new realm of alternative energy sources.

Researchers at the Georgia Institute of Technology recently developed low temperature fuel cells that use solar or thermal energy to catalyze the conversion of biomass to electricity. These fuel cells can run on starch, cellulose, lignin or even materials such as switchgrass, powdered wood, algae and waste from poultry processing.

The technology is scalable and can be utlizied in small operations in developing nationals or in large facilities where biomass is abundant.

"We have developed a new method that can handle the biomass at room temperature, and the type of biomass that can be used is not restricted - the process can handle nearly any type of biomass," said Yulin Deng, a professor in Georgia Tech's School of Chemical and Biomolecular Engineering and the Institute of Paper Science and Technology. "This is a very generic approach to utilizing many kinds of biomass and organic waste to produce electrical power without the need for purification of the starting materials."

Deng noted that the major barrier to biomass fuel cells is the inability to easily break down the carbon to carbon bonds of the biomass. To overcome that obstacle, researchers have used microbes or enzymes to break down the biomass. However, this process is unstable, the power output is limited and the number of compatible types of biomass is low.

To expand on the power, stability and versatility of the fuel cells, Deng altered the chemistry to use outside energy input to activate the cells oxidation-reduction reaction.

In Deng's model, the biomass is mixed with a polyoxometalate (POM) catalyst and then exposed to light or heat. The outside energy activates POM, which functions as both an oxidation agent and a charge carrier. After oxidizing the biomass, the POM helps electrons reach the cathode, where they are oxidized and produce electricity.

"If you mix the biomass and catalyst at room temperature, they will not react," Deng said. "But when you expose them to light or heat, the reaction begins. The POM introduces an intermediate step because biomass cannot be directly accessed by oxygen."

The maximum power density was reported by the researchers as "0.72 milliwatts per square centimeter, which is nearly 100 times higher than cellulose-based microbial fuel cells, and near that of the best microbial fuel cells." Deng believes the output can be further increased through optimization, according to a statement.

"I believe this type of fuel cell could have an energy output similar to that of methanol fuel cells in the future," he said. "To optimize the system, we need to have a better understanding of the chemical processes involved and how to improve them."

The study was published in Nature Communications.