Mixing carbon nanopowder into cement gives a low-cost supercapacitor

Researchers have made an energy-storing supercapacitor material by mixing cement, water, and carbon black—a fine powder of tiny carbon particles (Proc. Natl. Acad. Sci. U.S.A. 2023, DOI: 10.1073/pnas.230431812). Concrete made with the material could be used in home foundations able to store renewable energy and in roads that could charge electric vehicles.

Making cement, the main ingredient of concrete, produces about 8% of global carbon dioxide emissions. By giving concrete energy-storing powers and strength, “concrete becomes part of the energy solution,” says Franz-Josef Ulm, a civil and environmental engineer at the Massachusetts Institute of Technology.

While batteries store energy via chemical reactions, conventional supercapacitors rely on physically adsorbing ions from an electrolyte solution onto electrode surfaces. Instead of using conventional metal plate electrodes, Ulm and colleagues made a network of fine wires inside cement using carbon black.

They first added water to cement, which created a branching network of pores as the two materials reacted; carbon black particles added during this process spread into those pores. As the cement absorbed water, water-repelling carbon particles self-assembled into a branched, connected mesh. “The interplay between hydrophilic cement and hydrophobic carbon black allows this nanoscopic carbon black–based wiring through the entire material,” says Admir Masic, a coauthor of the paper.

The researchers soaked two pieces of the carbon black–fortified cement with a potassium chloride electrolyte and sandwiched them together to make a supercapacitor. A 1 mm-wide device stores enough charge to generate 1 V; three of these strung together powers a light-emitting diode bulb. The team calculates that a cubic block 3.5 m per side of the material could power an average household’s daily needs.

Yat Li, a chemist at the University of California, Santa Cruz, says that this is a “new and innovative strategy for making cheap and scalable supercapacitors.” The self-assembly process should enable fast, easy fabrication, and the low cost of cement and carbon is promising for large-scale applications.