US Researchers said Friday in Los Angeles that they have developed a new electrically-assisted microbial fuel cell that does not require oxygen, enabling bacteria to produce four times as much hydrogen directly out of biomass than can be generated typically by fermentation alone.
This process is not limited to using only carbohydrate-based biomass for hydrogen production like conventional fermentation processes. Theoretically, it yields hydrogen from any biodegradable, dissolved, organic matter and cleans the waste water,according to Bruce Logan, a professor at Pennsylvania State University who led the study.
“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 said.
The researchers described their findings in a paper “Electrochemically Assisted Microbial Production of Hydrogen from Acetate.” The paper is published in the online issue of journal Environmental Science and Technology.
In their paper, the researchers explain that hydrogen production by bacterial fermentation is currently limited by the “fermentation barrier,” the fact that bacteria, without a power boost, can only convert carbohydrates to a limited amount of hydrogen and a mixture of “dead end” fermentation end products such as acetic and butyric acids.
However, giving the bacteria a small assist with a tiny amount of electricity, about 0.25 volts or a small fraction of the voltage needed to run a typical six volt cell phone, they can leap over the fermentation barrier and convert a “dead end” fermentation product, acetic acid, into carbon dioxide and hydrogen.
“Basically, we use the same microbial fuel cell we developed to clean wastewater and produce electricity. However, to produce hydrogen, we keep oxygen out of the microbial fuel cell and add a small amount of power into the system,” Logan said.
When the bacteria eat biomass, they transfer electrons to an anode. The bacteria also release protons, hydrogen atoms stripped of their electrons, which go into solution. The electrons on the anode migrate via a wire to the cathode, the other electrode in the fuel cell, where they are electrochemically assisted to combine with the protons and produce hydrogen gas.
A voltage in the range of 0.25 volts or more is applied to the circuit by connecting the positive pole of a programmable power supply to the anode and the negative pole to the cathode.
This hydrogen-producing microbial fuel cell can also simultaneously cleanse the wastewater used as its feedstock. It uses about one-tenth of the voltage needed for electrolysis, the process that uses electricity to break water down into hydrogen and oxygen.
The new process demonstrates, for the first time, that there is real potential to capture hydrogen for fuel from renewable sources for clean transportation, the researchers said.