Combo of rainwater and cheap nanometals gives rise to renewable electricity

1 Aug 2019

Water drops on metal nanolayer. Image: Northwestern University

In the quest for more sources of renewable electricity, researchers have found a rather novel method using cheap metals and water.

Hydroelectricity is perhaps one of the oldest forms of renewable electricity production, but researchers at Northwestern University have found an altogether different means of production using H20.

In a paper published to the Proceedings of the National Academy of Sciences, the researchers showed it was possible to produce electricity by simply flowing water over extremely thin layers of inexpensive metals – including iron – that have oxidised. If scaled up to an industrial size, it would represent a whole new form of sustainable power production.

The conducting metal films in question measure as thin as 10 nanometres, insulated with an oxide layer two nanometres thin. As rainwater and ocean water move across the nanolayers, a current is generated as the difference in salinity drags the electrons along in the metal below to produce a current.

The oxide layer is key to this process, the researchers explained, as, instead of corroding, the presence of oxides helps shuttle the electrons along. As the films are transparent, they could ideally be placed in solar cells as an additional method of generating electricity.

“The ease of scaling up the metal nanolayer to large areas and the ease with which plastics can be coated gets us to 3D structures where large volumes of liquids can be used,” said Franz M Geiger, the study’s corresponding author.

“Foldable designs that fit, for instance, into a backpack are a possibility as well. Given how transparent the films are, it’s exciting to think about coupling the metal nanolayers to a solar cell or coating the outside of building windows with metal nanolayers to obtain energy when it rains.”

Similar to graphene

Measurements taken of the new method show it is comparable to graphene-based devices with efficiencies of approximately 30pc. However, unlike methods involving carbon nanotubes and graphene, this new method is a single-step fabrication from Earth-abundant elements instead of multistep fabrication.

Iron, nickel and vanadium were found to work best for the method, and researchers tested a pure rust sample as a control experiment, which did not produce a current. Using a process called physical vapour deposition, the researchers could turn solid materials into a vapour that condenses on a desired surface.

Co-author of the study, Thomas Miller, said devices with this new technology generated dozens of millivolts and several microamps per sq cm.

“For perspective, plates having an area of 10 sq m each would generate a few kilowatts per hour – enough for a standard US home,” he added. “Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term.”

Colm Gorey was a senior journalist with Silicon Republic