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Concrete has long shaped our environment, and now it’s edging closer to serving as a power source as well. Created by merging cement, water, ultra-fine carbon black (with nanoscale fragments), and electrolytes, electron-conducting carbon concrete (ec³, pronounced “e-c-cubed”) establishes a conductive “nanonetwork” within concrete that could allow everyday constructions such as walls, pathways, and bridges to accumulate and release electrical energy. In simpler terms, the concrete surrounding us may eventually function as massive “batteries.”

As MIT scholars describe in a recent PNAS publication, enhanced electrolytes and fabrication techniques have amplified the energy storage capability of the latest ec³ supercapacitors significantly. In 2023, to store enough energy for the daily requirements of an average household would have necessitated approximately 45 cubic meters of ec³, roughly equivalent to the volume of concrete in a standard basement. Now, thanks to the refined electrolyte, this same goal can be attained with around 5 cubic meters, the size of a conventional basement wall.

“A crucial element for the sustainability of concrete is the innovation of ‘multifunctional concrete,’ which incorporates capabilities such as energy storage, self-repairing, and carbon capture. Concrete already holds the title of the world’s most utilized building material, so why not leverage that scale to create additional advantages?” queries Admir Masic, the principal author of the new research, MIT Electron-Conducting Carbon-Cement-Based Materials Hub (EC³ Hub) co-director and associate professor of civil and environmental engineering (CEE) at MIT.

The heightened energy density was made achievable by a greater comprehension of how the nanocarbon black framework within ec³ operates and interacts with electrolytes. Utilizing focused ion beams for the gradual removal of thin layers of the ec³ substance, followed by high-resolution imaging of each layer with a scanning electron microscope (a process known as FIB-SEM tomography), the team from the EC³ Hub and MIT Concrete Sustainability Hub successfully reconstructed the conductive nanonetwork at unprecedented resolution. This method allowed the team to realize that the network essentially resembles a fractal-like “web” enveloping ec³ pores, facilitating electrolyte infiltration and enabling current flow throughout the system.

“Grasping how these materials ‘assemble’ at the nanoscale is fundamental to realizing these new capabilities,” Masic adds.

Armed with their newfound understanding of the nanonetwork, the team tested various electrolytes and their concentrations to determine their effects on energy storage density. Damian Stefaniuk, the principal author and EC³ Hub research scientist, emphasizes, “we discovered that there exists a broad spectrum of electrolytes that could serve as potential candidates for ec³. This even includes seawater, which might make this material suitable for usage in coastal and marine settings, perhaps as support frameworks for offshore wind farms.”

Concurrently, the team optimized the way they introduced electrolytes into the mixture. Instead of curing ec³ electrodes and subsequently soaking them in electrolyte, they incorporated the electrolyte directly into the mixing water. As electrolyte penetration was no longer an obstacle, the team could mold thicker electrodes that stored more energy.

The team reached peak performance when they transitioned to organic electrolytes, particularly those that combined quaternary ammonium salts — commonly found in everyday items like disinfectants — with acetonitrile, a clear, conductive liquid often utilized in industrial applications. A cubic meter of this variant of ec³ — approximately the dimension of a refrigerator — can store over 2 kilowatt-hours of energy. That’s enough to run an actual refrigerator for a day.

While batteries offer a higher energy density, ec³ can, in theory, be integrated directly into a variety of architectural elements — from slabs and walls to domes and vaults — and endure as long as the structure itself.

“The Ancient Romans made notable advancements in concrete construction. Monumental structures like the Pantheon remain standing today without reinforcement. If we maintain their spirit of blending material science with architectural creativity, we could be on the verge of a new architectural transformation with multifunctional concretes like ec³,” suggests Masic.

Drawing inspiration from Roman architecture, the team crafted a miniature ec³ arch to demonstrate how structural design and energy storage can harmonize. Operated at 9 volts, the arch supported its own weight along with additional load while illuminating an LED light.

However, something unusual occurred as the load on the arch increased: the light flickered. This is likely due to how stress affects electrical contacts or charge distribution. “There might be a sort of self-monitoring capability here. If we envision an ec³ arch at architectural scale, its output may fluctuate when it encounters a stressor like high winds. We could potentially use this as an indicator of when and how much stress a structure is under, or to monitor its overall health in real-time,” envisions Masic.

The recent advancements in ec³ technology move it a step closer to practical scalability. It has already been deployed to warm sidewalk slabs in Sapporo, Japan, owing to its thermally conductive characteristics, signifying a possible alternative to salting. “With these increased energy densities and proven utility across a wider range of applications, we now possess a powerful and adaptable tool that can assist in addressing a multitude of ongoing energy challenges,” Stefaniuk explains. “One of our main motivations was to facilitate the transition to renewable energy. Solar power, for instance, has made significant strides in efficiency. However, it only generates power when there is sufficient sunlight. Thus, the question arises: How do you fulfill your energy needs during the night or on overcast days?”

Franz-Josef Ulm, EC³ Hub co-director and CEE professor, continues the discussion: “The solution is that you require a method to store and discharge energy. Traditionally, this has involved a battery, which often depends on scarce or harmful materials. We believe that ec³ serves as a practical alternative, allowing our buildings and infrastructure to satisfy our energy storage requirements.” The team is progressing toward applications like parking lots and roadways capable of charging electric vehicles, as well as residences that can function entirely off the grid.

“What excites us most is that we’ve taken a material as ancient as concrete and demonstrated that it can perform something completely novel,” states James Weaver, a co-author of the publication who is an associate professor of design technology and materials science and engineering at Cornell University, along with being a former EC³ Hub researcher. “By fusing contemporary nanoscience with an ancient cornerstone of civilization, we’re opening a pathway to infrastructure that not only supports our lives but also powers them.”

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