Hydrogen - a potential clean energy source - can be sustainably generated using just seawater, river water and bacteria, according to new research.
Hydrogen is a potentially valuable energy source but production costs and environmental concerns about using fossil fuels to produce the gas have limited its application so far.
Previous studies have shown hydrogen gas can be produced by harnessing the by-products of microbial organic matter metabolism in a device called a microbial electrolysis cell.
But the process requires an additional input of electricity to make it work effectively.
Now, according to a study published online in the Proceedings of the National Academy of Sciences, hydrogen can be produced in a single device by integrating a water-based power supply into the system.
Exoelectrogenic bacteria are found in ponds, streams, sediments and soils, as well as in waste water.
Because they metabolise organic matter, they can transfer electrical energy to conductive materials such as metal or graphite.
“[When they are used in Microbial Electrolysis Cells] bacteria produce electrical current, but not enough voltage to drive hydrogen gas production at the other electrode,” Professor Bruce Logan from Pennsylvania State University’s Hydrogen Energy (H2E) Centre said.
Salt gradient
Professor Logan and Dr Younggy Kim designed a microbial reverse electrodialysis system, containing five pairs of seawater and river water cells separated by thin membranes, which were sandwiched between an anode containing the bacteria, and a cathode.
The passage of salt through the membranes down the gradient of seawater to river water generated the additional electricity needed to produce hydrogen without the need for fossil fuels, sunlight, or wind.
“The most significant finding is that hydrogen production is possible using readily available and sustainable sources, and with no need for electricity [input],” Professor Logan said.
Because the bacteria in the device can be fed organic waste, the system may also prove useful for wastewater treatment.
“The implication of this research is that waste water can become a resource from which we can actually capture energy in the very useful form of hydrogen gas” - without any consumption of electrical grid energy,” he said.
Dr Rene Rozendal, a former research fellow at the University of Queensland’s Advanced Water Management Centre and the inventor of microbial electrolysis, says this is an interesting study.
“However, due to the large amount of membranes [and electrodes] required, it is a rather expensive method of making hydrogen gas,” he said.
“Moreover, the number of places where salt and fresh water and large amounts of biodegradable organic matter occur together are rather limited.”
“Still, it is a nice proof-of-principle that demonstrates that hydrogen can be produced from natural resources without electricity input.”
