A battery is often thought of as an energy storage device because that is how we use them on a day to day basis. A battery is basically a container of chemicals that holds on to energy for us until we need it. When called to action, the battery, through electrochemical reactions, produces electrons which we use to power all sorts of stuff. Recently, Stanford University researchers have figured out a way to use the fundamental processes behind battery technology to generate electricity in a different way. Their “battery” takes advantage of the salinity difference between freshwater and seawater to create electricity in a way that is far more efficient than previously demonstrated.
The battery itself is similar to the sort that we’re familiar with: It has a positive electrode and negative electrode immersed in liquid containing electrically charged particles, or ions. In this case, though, the liquid is water and the ions are sodium and chlorine-aka salt. The battery is first filled with fresh water and given a small electrical charge to prime things up. The freshwater is then drained and replaced with seawater. Since seawater is chock full of salt (or, ions) it boosts the electric potential between the electrodes and, zap, electricity. It turns out that the electric potential obtained by using seawater is so high that it far exceeds the amount of current that was needed to charge things up in the first place-hence an efficient system
Yi Cui, associate professor of materials science and engineering at Stanford, lead the team that has developed the new “battery” technology. To enhance the efficiency of their battery, he and his team employed the use of nanorods made from manganese dioxide for the positive electrode material. The benefit of manganese dioxide is that it is environmentally benign and increases the battery’s efficiency- 74% according to the team’s trials. Cui thinks that number can be increased to 85%, but he needs to find a suitable material to use for the negative electrode. For the purposes of their experiment, silver was used, but it is too expensive to be practical.
Applying the technology appears to be the next challenge, but the team has some pretty good ideas. The most obvious location choice for such a system would be at the point where large rivers drain into the ocean-the Amazon as it drains into the Atlantic, for instance. However, that approach presents certain environmental concerns. The team is also considering the use of storm runoff and grey water as freshwater sources, since the water doesn’t have to be particularly clean to be effective. They are even considering the use of sewage water (black water) as a viable option.
The numbers Cui and his team came up with are impressive. They estimate that power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power. That would be enough to provide electricity for about 100,000 households.