In addition to being an indicator of iron corrosion and oxidation, rust can also be an agent of renewable energy production. California Institute of Technology and Northwestern University researchers have paired thin films of the degradation product with saltwater to generate electricity.

A demonstration system was prepared by physical vapor deposition to form a 10 nm thick iron layer. Iron Metal nanolayers for gravitational to electrical energy conversion. (A) Photographs of iron and aluminum nanolayers with indicated thicknesses on microscope glass slides over the Northwestern University seal. (B) Photograph of Teflon cell with flow channel. Dashed lines indicate substrate position and arrows indicate aqueous flow direction. Source: M. Boamah et al.oxide, or rust, then formed to a depth of about 2 nm, after which the iron slab was exposed to saltwater solution flows of varying concentrations. Open-circuit potentials of several tens of millivolt and current densities of several microamps/cm² were documented.

The kinetic energy of flowing saltwater was converted into electricity at an efficiency approaching 30% as 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.

The energy conversion system described in Proceedings of the National Academy of Sciences may find future application in solar photovoltaics, window coatings or medical implants.