Supercapacitors provide a cement-based method of storing electricity

Supercapacitors integrated into walls and foundations could store enough renewable power to run a home or feed into the grid to support the global shift away from fossil fuels.

Engineers at Massachusetts Institute of Technology (MIT) have created a supercapacitor made from just cement, water, and carbon black (a highly conductive material resembling powdered charcoal) which could form the basis for renewable power storage systems in building walls or foundations.

The technology, described in a paper in the journal PNAS, was developed as a response to the global need for inexpensive and easily-deployable storage solutions for intermittent renewable energy sources such as wind or solar. The researchers said cement and carbon black were ‘two of humanity's most ubiquitous materials’. 

Tests showed that a 1cm-wide by 1mm-thick supercapacitor, roughly the size of a button-cell battery, could be charged to 1V. When scaled up to the size of a 45m³ block of nanocarbon-black-doped concrete, the device would have the capacity to store about 10 kW-hours of energy – enough to meet the average daily electricity usage for a household, researchers said. Furthermore, this would add little or no cost to a building’s foundations and still provide the required structural strength.

Professor Franz-Josef Ulm, one of the paper’s authors at MIT’s Department of Civil and Environmental Engineering, told RIBAJ that he envisions scalable solutions for buildings being based around the use of small sub-unit1 2V bricks, similar to car batteries.

‘These would be connected to arrive both at the desired voltage, 110V, 240V etc. and the desired power,’ he says. ‘The bricks can be built into the foundation or into the wall systems, and connected to photovoltaic cells or other renewable energy sources, in the façade and/or on the roof.’

Supercapacitors work by storing electrical energy between two electrically conductive plates, separated by a thin insulation layer, the amount of energy they can store depends on the total surface area of the plates.

The ‘secret sauce’ of MIT’s innovation is the extremely high internal surface area of the cement-based material, achieved by introducing highly conductive carbon black into a concrete mixture along with cement powder and water before curing.

The water forms a branching network of openings within the structure as it reacts with the cement, the carbon migrates into these spaces, creating wire-like structures within the hardened cement.

The project team is aiming to complete a 12V brick in the coming months, optimised with the help of electrical, structural and materials engineers and architects. ‘Then we aim at project scale implementation,’ says Ulm. ‘We have several offers from project developers to prototype a building with carbon-cement supercapacitor technology.’

Cement may be ubiquitous, but that very characteristic makes it one of the most dangerous materials on the planet, responsible for around 8 per cent of global CO₂ emissions.

According to Ulm, any low-carbon-type cement can be used with the technology, as long as it provides similar ‘connected porosity’ to regular cement-based materials. However, achieving a large-scale global implementation means focusing first on existing cements.

‘The fact that we add a new function to “classical” load-bearing concrete, in the form of energy storage capacity, should outweigh the CO₂ intensity of cement production,’ he concludes.