Most of the renewable energy sources that are under consideration involve an obvious source of energy — light, heat, or motion. But this is the second time this year there has been a paper that has focused on a less obvious source: the potential difference between fresh river water and the salty oceans it flows into. But this paper doesn’t simply use the difference to produce some electricity; instead, it adds bacteria to the process and takes out a portable fuel: hydrogen.
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“Hydrogen production from inexhaustible supplies of fresh and salt water using microbial reverse-electrodialysis electrolysis cells.” (http://www.pnas.org/content/early/2011/09/12/1106335108)