Rust-based Tech May Join Solar PV as a Source of Renewables

Move over batteries, solar photovoltaic (PV) panels and wind turbines. Rust may be the new kid in town as a source of renewable energy. Researchers have long looked for alternatives and complements to the silicon found in solar PV cells – such as graphene and solar thermal. So chalk this up to another technology that could transform how we keep the lights on in the future.

Rust, you ask? Yes, rust, according to a study published in the July 29th issue of the Proceedings of the National Academy of Sciences. Well, not exactly the kind you find on your 1974 Chevy Corvette sitting in your driveway, but, in the new study, rust produced in a lab setting was able to conduct electricity when interacting with salt water.

While more research is needed, this could be exciting news for the renewable energy sector as companies compete for cleaner energy alternatives to non-renewables. According to data compiled by BCC Research, the global market for renewable energy (excluding biofuels) should grow from $636 billion in 2018 to reach $855 billion by 2023.

So how would rust work compared to solar PV panels?

As you may recall from your high school chemistry class, combining metal compounds and salt water is a well-known way of conducting electricity, since chlorine and sodium ions can carry electrical currents. But producing electricity on a large-scale using rust is a bit more complicated than that.

The mechanism behind the electricity generation in the study was highly complex, in fact, involving ion adsorption and desorption. According to the professors behind the study from Caltech and Northwestern University, the process essentially works like this: The ions present in saltwater attract electrons in the iron beneath the layer of rust. As the saltwater flows, so do those ions, and through that attractive force, they drag the electrons in the iron along with them, generating an electrical current.

This process is more commonly known as the electro kinetic effect. According to a press statement put out by Caltech, at its best, the electro kinetic effect can generate electricity with around 30 percent efficiency. For reference, the best solar panels are only about 20 percent efficient.

Could rust really become a viable option?

Back to your Chevy Corvette (or, vehicles looking like those in the photo shown above). Unfortunately, naturally spreading rust is too thick to be mass-produced, and doesn’t spread evenly. To work, the team involved in the study created thin films of rust in their labs that were a mere 10 nanometers thick, thousands of times thinner than a human hair. When salt water flowed over their rust-coated iron, the scientists found that it generated several tens of millivolts.

"For perspective, plates having an area of 10 square meters each would generate a few kilowatts per hour—enough for a standard U.S. home," Tom Miller, Caltech professor of chemistry, told Phys.org, a leading web-based science, research and technology news service. "Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term."

Low-power devices in remote locations, you say? How about items already in the ocean?

"Tidal energy, or things bobbing in the ocean, like buoys, could be used for passive electrical energy conversion," Miller says. "You have saltwater flowing in your veins in periodic pulses. That could be used to generate electricity for powering implants."

Given that the vast majority of the planet's water is salt water, these researchers could be onto something - maybe even an entirely new form of renewable power production joining the likes of wind turbines, geothermal and of course, solar PV.

Image credit: Kevin Noble/Unsplash