The most familiar sources of renewable energy are intermittent: They don't produce power when the sun goes down and the wind stops. Finding a way to store solar and wind energy is crucial if California is to move away from fossil fuel-based electricity. And yet while there have been advances in storing electrical power, the banks of batteries needed for grid-scale storage are prohibitively expensive.
But a team of USC researchers may have hit on a way to change all that, suggesting a future in which our grid runs on rust.
Or if not precisely rust, then on the same process by which rust forms. Batteries in their simplest form are made up of two separated elements, one of which -- the anode -- wants to give up electrons, and the other -- the cathode -- that wants more electrons. A battery's anode and cathode are usually separated by a non-conductive material. This means you have to place the battery into a closed electrical circuit, like the wiring in your smartphone, or a flashlight, or the state's electrical power grid, in order for the electrons in the battery to flow from the anode to the cathode.
The USC team, led by Sri Narayan, professor of chemistry at the USC Dornsife College of Letters, Arts and Sciences, is working with rechargeable batteries that use iron as the anode material. Iron readily gives up electrons. When exposed to air, it gives those electrons up to the oxygen in the air, forming iron oxide, or rust. So-called "iron-air" batteries have been used for years, and gained a great deal of interest in the 1970s. However, due to the iron anodes' chemical reaction with hydrogen from water vapor in the air, which counteracted the iron-oxygen reaction, the batteries had serious efficiency problems. Battery engineers ultimately looked elsewhere.
Narayan's team, aided by a $1,459,324 grant from the Department of Energy's Advance Research Projects Agency-Energy program, found that adding small amounts of the chemical bismuth sulfide to the anode suppressed the hydrogen reaction, reducing the consequent energy losses from around 50% to around 4%. The result is a battery that can store between eight and 24 hours' worth of energy, and Narayan's team is working to improve that performance.
So what's the excitement about yet another kind of rechargeable battery? Its cost. As Narayan puts it, "Iron is cheap and air is free." Iron is the fourth-most common element on the planet, and far cheaper to obtain than its major metal competitor in the battery world, lithium. If Narayan's team's research pans out, a truly affordable form of mass energy storage may make solar and wind's contribution to the California grid even more vital.