Usually the term “power brick” affectionately refers to the power supply of a laptop. But what if that term was quite literal and included an actual brick?
A team led by Washington University's Hongmin Wang set out to create a real power stone. Specifically, they wanted to find out if they could use a vapor deposition technique to turn ordinary red brick into part of a supercapacitor. This is actually not quite as strange as it sounds, since the red of a brick is an iron mineral, and iron is a common ingredient in some battery chemistries. Bricks are often porous too, which means there is a large surface area on which a thin coating can interact with this iron.
The process (something they had developed earlier) involves heating the brick in a casing along with hydrochloric acid and an organic compound that graciously shortens to "EDOT". The two liquid substances evaporate and condense on the winding surface of the brick. The acid dissolves part of the iron mineral and releases iron atoms, which help the organic molecules bond to form polymer chains (graduated to “PEDOT”) that cover the surface. The polymer forms microscopic, entangled fibers that form a continuous, electrically conductive layer on each side of the brick that otherwise remains. (However, this has the effect of turning the brick black.)
Scanning electron microscope image of the fibrous PEDOT layer on the surface of three different stones with different porosities.
The team tested the performance in a number of configurations, including one with a stable gel electrolyte that is placed between the bricks like mortar. Coating the whole thing with epoxy resin makes it waterproof (as in "works underwater" waterproof) and also prevents the electrolyte from ever drying out. Many combinations of bricks in series and in parallel are obviously possible, although they wired three units of tiny sugar cube size bricks in series for testing. Once fully charged in 15 seconds, this configuration powered an LED for about 11 minutes before the voltage dropped from an initial 2.7 volts to below the LED's required 2.5 volts.
Three larger brick supercapacitors in series light up an LED. The split stone on the right shows the color change of the PEDOT coating.
Even with full size bricks, the total energy storage is … less than huge. They estimate that a wall made from these bricks could hold about 1.6 watt hours per square meter of wall space. That means a three by six meter (10 by 20 foot) wall can hold about 20 watt hours of electricity. As a result, researchers' attitude towards this idea is less dramatic than "turn your house into a battery!"
“Our supercapacitor technology adds value to a“ dirt cheap ”building material and demonstrates a scalable process that provides energy storage for powering embedded micro devices in baked brick architectural applications,” they write. These powered walls are unlikely to challenge Tesla's Powerwall (13.5 kilowatt-hours in less than a square meter on the wall) anytime soon. But it's a creative concept – one super capacitor brick definitely wouldn't be just another brick in the wall.
Nature Communications, 2020. DOI: 10.1038 / s41467-020-17708-1 (About DOIs).