ΒΒΚ - Our News

Developed by scientists using seawater, electricity and CO2

Using seawater, electricity and carbon dioxide (CO2), scientists at Northwestern University have developed a new carbon-negative building material, essentially offering a way to reduce the impact of the built environment on the climate crisis, while expanding the ways to capture CO2 from the atmosphere.
According to a report by Eris Driva on economix.gr, scientists at Northwestern University have managed to permanently lock in CO2 and convert it into materials useful for the production of concrete, cement, plaster and paints. The process for producing the carbon-negative materials also releases hydrogen gas – a clean fuel with various applications in sectors such as transportation.
The study, “Electrodeposition of carbon-trapping minerals in seawater for variable electrochemical potentials and carbon dioxide injections,” was published in the journal Advanced Sustainable Systems. “We developed a new approach that allows us to use seawater to create carbon-negative building materials,” said Alessandro Rotta Loria of Northwestern, who led the study, in a statement. “Cement, concrete, paints and plasters are made up of or derived from calcium and magnesium-based minerals, which are often derived from aggregates – what we call sand. Currently, sand comes from mining in mountains, riverbeds, coasts and the ocean floor. In collaboration with Cemex, we have taken an alternative approach to sand sourcing – not by digging into the earth, but by harnessing electricity and CO2 to grow sand-like materials in seawater.” In addition to the large research staff, the study also benefited from the input of key representatives from the Global R&D department of Cemex, a building materials company focused on sustainable construction. This work is part of a broader collaboration between Northwestern and Cemex.
Science inspired by shells
The new study builds on the lab’s previous work on long-term CO2 storage in concrete and electrifying seawater to cement marine soils. Now, he’s harnessing the knowledge from those two projects by injecting CO2 while applying electricity to seawater in the lab. “Our research team is trying to harness electricity to create innovative manufacturing and industrial processes,” Loria said. “We also like to use seawater because it’s a naturally abundant resource. It’s not scarce like freshwater.”
To create the carbon-negative material, the researchers started by inserting electrodes into seawater and applying an electric current. The low electrical current split the water molecules into hydrogen gas and hydroxide ions. While leaving the electricity on, the researchers bubbled CO2 gas into the seawater. This process changed the chemical composition of the water, increasing the concentration of bicarbonate ions.
Finally, the hydroxide ions and bicarbonate ions reacted with other dissolved ions, such as calcium and magnesium, that occur naturally in seawater. The reaction produced solid minerals, including calcium carbonate and magnesium hydroxide. Calcium carbonate acts directly as a carbon acceptor, while magnesium hydroxide binds the carbon through further interactions with CO2. Loria likens the process to the technique used by corals and mollusks to form their shells, which harnesses metabolic energy to convert dissolved ions into calcium carbonate. But instead of metabolic energy, the researchers applied electrical energy to start the process and increased mineralization by injecting CO2.
Double discovery
Through experimentation, the researchers made two important discoveries. Not only were they able to grow these minerals in sand, but they were also able to change the composition of these materials by controlling experimental factors, including the voltage and current of the electricity, the flow rate, timing and duration of CO2 injection, as well as the flow rate, timing and duration of seawater recirculation in the reactor. Depending on the conditions, the resulting substances were more porous or denser and harder – but they were always composed primarily of calcium carbonate and/or magnesium hydroxide. Researchers can grow the materials around an electrode or directly in solution.
“We showed that when we produce these materials, we can fully control their properties, such as their chemical composition, size, shape and pore form,” Loria said. “This gives us some flexibility to develop materials suitable for different applications.” These materials could be used in concrete as a substitute for sand and/or gravel—a critical ingredient that makes up 60-70% of this ubiquitous building material. Or they could be used to make cement, plasters, and paints—all essential finishes in the built environment.
Carbon storage in structures
Depending on the ratio of minerals, the material can hold more than half its weight in CO2. With a composition of half calcium carbonate and half magnesium hydroxide, for example, 1 metric ton of the material has the potential to store more than half a metric ton of CO2. Loria also says that the material, if used to replace sand or dust, will not weaken the strength of concrete or cement. According to the professor, the industry could apply the technique in highly scalable, modular reactors – not directly in the ocean – to avoid disturbing ecosystems and marine life. “This approach would allow for full control of the chemistry of water sources and wastewater, which would be reintroduced into open seawater only after appropriate treatment and environmental verifications,” he said.
According to the World Economic Forum, the cement industry, responsible for 8% of global CO2 emissions, is the fourth largest carbon dioxide emitter in the world. Combined with concrete production, this percentage is even higher. Loria envisions putting some of this CO2 back into concrete and cement to produce more sustainable materials for construction and manufacturing. “We could create a circularity where we capture CO2 right at the source,” he notes. “And, if concrete and cement plants are located on the coast, we could use the ocean right next to them to power special reactors where CO2 is converted through clean electricity into materials that can be used for a myriad of applications in the construction industry. Then, these materials would truly become carbon sinks.”