A study by U.S. researchers has found an energy-efficient way to create hydrogen by just using some fresh water, salt water and membranes. Self-powered cells, fueled by bacteria, can produce an abundant supply of hydrogen.

Hydrogen can be produced by a process called microbial electrolysis cell (MEC), but that requires an additional input of electricity to work effectively.

The researchers have found 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. The study was published online in the Proceedings of the National Academy of Sciences.

Two years back, scientists figured that running a measured jolt of electricity through a battery containing these bacteria enervated the bugs, causing them to get going on breaking down the organics to release hydrogen, reports fastcompany.com

However, the team has found a way to make hydrogen without consuming that electricity.

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.

As 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 salinity 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 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.

At the moment the cost of the technology is too high for it to be used commercially.

Hydrogen has many uses- from refining crude oil to being used to hydrogenate oils or fats, which permits the production of margarine from liquid vegetable oil. Even though hydrogen is a clean source of energy, the high production costs and environmental concerns about using fossil fuels to produce the gas has restricted its application.