A new study found that self-powered cells, fueled by bacteria, can produce a limitless supply of hydrogen, offering hope for the future use of this efficient energy carrier.

Hydrogen is a plentiful, potential clean energy source that produces almost no pollution, but high production costs and environmental concerns about using fossil fuels to prouce the gas has limited its application. It can be produced by a process called microbial electrolysis cell, but that requires an additional input of electricity to work effectively.

The study, published online in the Proceedings of the National Academy of Sciences, indicates that the difference between river water and seawater could be used to give the extra energy needed to produce hydrogen, and the system is completely carbon neutral.

There are bacteria that occur naturally in the environment that are able to release electrons outside of the cell, so they can actually produce electricity as they are breaking down organic matter, said the study's co-author professor Bruce Logan, of Pennsylvania State University.

Exoelectrogenic bacteria, which can transfer electrical energy to conductive materials including metal,  are found in ponds, streams, wastewater, sediments and soil.

Since the electrical current produced by the bacteria didn't provide sufficient voltage in producing hydrogen, the researchers designed a microbial reverse electrodialysis system.

By adding fresh water, salt water, and membranes to the microbial electrolysis cell, the energy gathered from the difference in salt content between seawater and freshwater could be put to work in generating hydrogen molecules.

The added voltage that we need is a lot less than the 1.8 volts necessary to hydrolyze water, said Professor Logan. Biodegradable liquids and cellulose waste are abundant and with no energy in and hydrogen out we can get rid of wastewater and by-products. This could be an inexhaustible source of energy.

If you think about desalinating water, it takes energy. If you have a freshwater and saltwater interface, that can add energy. We realized that just a little bit of that energy could make this process go on its own, he told BBC.

The new technology is still  in its infancy and remains too costly to be commercially viable. In taking the next step of developing larger-scale cells, then it will easier to evaluate the costs and investment needed to use the technology, said Logan.