Researchers use the ocean to recharge their batteries
When people think of harvesting energy from the oceans, it's typically in the form of wave or tidal power, in which the motion of the water drives the production of electricity. A paper in Nano Letters suggests an alternate way to turn the ocean into power: using the fact that it's salty. There have been a few ideas about how to extract energy from the salinity difference between salt and fresh water, but the paper suggests a rather intriguing approach: treat the entire ocean a bit like a battery medium.
The battery charge cycle generally involves the exchange of electrons with ions that shuffle between a storage medium and electrodes; normally, the ions themselves remain encased within the battery. The new device takes a very different approach, allowing the ions to exchange freely with water that flows through it.
The device has electrodes that specifically react with some of the salt ions normally found in sea water. One is made of manganese dioxide, which can react with a sodium ion to form Na2Mn5O10. The material also happens to be cheap, environmentally benign, and has a high energy density. The authors weren't so careful when they chose the other electrode, as they used silver, which can react with chlorine. Thus, the two electrodes in the device can sequester the ions that form when sodium chloride—common salt—dissolves in water.
