A fuel cell that uses microorganisms to break down organic matter could help provide additional fuel for a hydrogen economy, a new report suggests. The novel design, with energy requirements amounting to less than 5 percent of those of a cell phone, can coax pure hydrogen out of biomass that is not suitable for natural fermentation processes.

For conventional fermentation to yield hydrogen, the process must use carbohydrate-based biomass. But the reaction also produces other end products, such as acetic acid and butyric acid, that bacteria cannot break down further into hydrogen. Bruce E. Logan and his colleagues at Penn State University modified a version of a microbial fuel cell (MFC) that they had conceived of to clean wastewater. "However," Logan explains, "to produce hydrogen, we keep oxygen out of the MFC and add a small amount of power into the system." By applying a boost of just 0.25 volt, the researchers succeeded in generating four times as much hydrogen as conventional fermentation does. What is more, the cell can be used with any biodegradable dissolved organic matter.

"While there is likely insufficient waste biomass to sustain a global hydrogen economy, this form of renewable energy production may help offset the substantial costs of wastewater treatment as well as provide a contribution to nations able to harness hydrogen as an energy source," Logan says. The results will be published in a forthcoming issue of the Journal of Environmental Science and Technology.