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: Scientists have created the first rechargeable battery that uses seawater and freshwater to generate electricity. If installed into every ocean-discharging river in the world (that's not a realistic scenario---just a frame of reference), the process could produce 2 terawatts, or about 13% of worldwide electricity use. As the researchers write, this battery is "simple to fabricate and could contribute significantly to renewable energy in the future." How the Heck:

What's the News

Dubbed the "mixing entropy battery," this gadget generates current by harnessing the salinity difference between salt and freshwater.

Freshwater is first funneled into the battery, which houses a positive and negative electrode.

After the battery is charged by an external energy source, the freshwater is switched out for seawater, whose added ions increase "the electrical potential, or voltage, between the two electrodes. That makes it possible to reap far more electricity than the amount used to charge the battery," according to Stanford News.

What's the Context:

Not So Fast:

As a major energy source, the battery is limited by supply of and access to freshwater.

While the researchers say that the process has little environmental impact, future ocean-river batteries need to proceed with caution because estuaries, where freshwater and seawater combine, are "environmentally sensitive areas."

Another limiting factor is the negative electrode, which is made of expensive silver.

Next Up: Noting the limited supply of freshwater on Earth, lead author Yi Cui says that "we need to study using sewage water ... If we can use sewage water, this will sell really well." Reference: Fabio La Mantia et al. "Batteries for Efficient Energy Extraction from a Water Salinity Difference." Nano Letters. doi: 10.1021/nl200500sImage: Nano Letters