Energy-storing walls made from ordinary red bricks

Brick walls might some day power your lights and laptop, thanks to a new technique that converts building blocks into battery-like devices (Nat. Commun. 2020, DOI: 10.1038/s41467-020-17708-1). By packing bricks’ tiny pores with conductive polymer nanofibers, researchers have made supercapacitors that can power an LED light for up to 15 min.

“Bricks have been around for thousands of years but we’ve added value and new functionality to them,” says Julio D’Arcy, a chemist at Washington University in St Louis. The proof-of-concept brick supercapacitor takes 13 min to charge fully, and can be recharged 10,000 times. Integrated into walls and coupled with solar panels, the devices could provide emergency power and lighting in case of power outages or emergencies.

Supercapacitors, like batteries, have two electrodes with an electrolyte in between. But while batteries rely on chemical reactions, supercapacitors store energy by storing charge on the surfaces of their electrodes. Ions move on and off the electrode surface much faster than the chemical reactions of a battery. So supercapacitors can recharge quickly and provide powerful bursts of energy.

The inspiration to turn bricks into supercapacitors came from D’Arcy’s work on organic supercapacitors. He makes electrodes from conductive polymer nanofibers, whose high surface area can store a relatively large amount of charge. The nanofiber synthesis method relies on ferric ions to trigger polymerization reactions. D’Arcy’s group had recently turned to rust as an iron source.

D’Arcy spotted bricks at the hardware store and was struck by their color. “Anything red in nature has the pigment iron oxide,” he says. And bricks turned out to have other advantages. “Bricks are really cool materials because they are inert, sterile when they come out of the oven, mechanically robust, and porous,” he says. So his group decided to use iron oxide in the bricks as a reactant to fill the brick pores with conductive polymer nanofibers.

They used the conductive polymer poly (3,4-ethylenedioxythiophene) (PEDOT) to make the brick electrodes. First, they pump hydrochloric acid vapors into the brick’s pores at 160°C, dissolving iron oxide to release ferric ions. Next they pump in a monomer vapor, which polymerizes in the presence of the ferric ions to create PEDOT nanofibers. To finish the supercapacitor, D’Arcy and his colleagues put two brick electrodes together with a gel electrolyte in between that also acts as mortar. Finally, they encase the device in a waterproof epoxy coating.

The device produces 3W of power and can operate over a wide range of temperatures, and can keep an LED light on for 10 minutes when immersed under water. The energy-storing bricks are strong enough to be made into decorative, but not load-bearing, walls, D’Arcy says. A coated brick costs three times the standard price of a brick, which is 65 cents. But D’Arcy says scaling up the process should bring down the cost.

“This is a clever and interesting idea,” says Manas Gartia, a mechanical engineer at Louisiana State University. He says the added cost compared to conventional bricks might be a hurdle, but that the smart bricks could nevertheless have immense practical impact, he says.

Vibha Kalra, a chemical and biomolecular engineer at Drexel University, likens the concept of the energy-storing bricks to smart fabrics where devices are embedded into wearable materials. “There is merit in integrating energy storage and smart devices into commonly used systems and materials, saving the extra volume or weight,” she says.