New Device Creates Hydrogen Gas from Sun and Sewage

Using only sunlight and wastewater, researchers from the University of California, Santa Cruz have found a way to produce hydrogen gas.

The discovery could provide a sustainable energy source while simultaneously improving the efficiency of treating wastewater, according to the scientists led by Yat Li, associate professor of chemistry.

The study, published in the journal ACS Nano, hinges on a device comprised of a microbial fuel cell (MFC) and a solar cell called a photoelectrochemical cell (PEC).

Bacteria degrade organic matter in the wastewater in the MFC component, generating electricity that is then transferred to the PEC bit where it aids in the process of splitting water, resulting in hydrogen and oxygen.

While a PEC or MFC device can be used alone to produce hydrogen gas, a small voltage is required when the two are paired together. This need for an additional electricity source has long rendered similar devices complicated and costly.

However, by using both energy from the organic matter and sunlight, Li's device is self-driven and self-sustaining.

"The only energy sources are wastewater and sunlight," Li said. "The successful demonstration of such a self-biased, sustainable microbial device for hydrogen generation could provide a new solution that can simultaneously address the need for wastewater treatment and the increasing demand for clean energy."

Microbial fuel cells rely on a specific kind of bacteria known as electrogenic bacteria. Li's group teamed up with the Lawrence Livermore National Laboratory to run "proof-of-concept" tests first using a well-studied strain of electrogenic bacteria grown in the lab, and then with untreated municipal wastewater.

In the case of the latter, the PEC-MFC device was able to produce hydrogen gas at a rate of 0.05 cubic meters per day. Meanwhile, the wastewater became clearer.

According to LLNL co-author Fang Qian, the scientists are optimistic about their ability to commercialize the product and are currently developing a larger, 40-liter prototype that will be fed municipal wastewater continuously upon completion.