Put fresh water and salt water together along with some bacteria and what do you get? Perhaps the future of renewable energy. US researchers say they have demonstrated how cells fuelled by bacteria can be “self-powered” and produce a limitless supply of hydrogen.

The process is still fundamentally electrochemical. Sea water and fresh water are placed on opposite sides of a membrane that allows ions through, but prevents the passage of water molecules. The ions will move to the fresh water to balance osmotic forces, which will create a charge difference that can be harvested for various purposes. The voltage produced in a single one of these cells is small, but the source of the power is essentially unlimited and is available 24 hours a day.

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