Garlic roots: a green solution for carbon capture

Bárbara Pinho

Garlic root electrodes show promise for efficient and cost-effective carbon capture.

Chemists worldwide have been working on electrochemical methods to capture carbon with supercapacitors. Using a new approach, researchers have increased the amount of carbon captured at a low energetic cost.

Supercapacitive swing adsorption (SSA) refers to an electrochemical method for capturing CO₂ with supercapacitors. In the process, a supercapacitor’s electrode comes into contact with a gas containing CO₂, while the other electrode is immersed in an electrolyte. Through the charging of the supercapacitor, CO₂ is adsorbed from the gas. This adsorbed CO₂ is then released as discharging occurs.

Still in its early stages, SSA has been gaining attention due to its cost-effectiveness and its potential synergy with renewable energy sources. In 2022, researchers from the University of Cambridge, UK, devised a method that improved the amount of carbon dioxide that can be captured with a supercapacitor (Nanoscale, doi: 10.1039/d2nr00748g).

Now, a team from Lehigh University, US, has explored a more sustainable approach, using garlic roots as the starting point to make the electrodes, with promising results (Small, doi: 10.1002/smll.202207834).

‘This is biomass waste; it’s widely available and we can use it if we want to scale up this technology,’ explains Muhammad Bilal, one the study’s authors.

‘We need to use materials which are environmentally friendly, cheap and which don’t produce so much waste at the end of their lifetime.’ Muhammad Bilal. Image: Lehigh University

Having assembled the system with the garlic-based electrodes, the team went on to test the adsorption and desorption of CO₂ from a gas mixture. Upon attributing voltage, thus charging the capacitors, they saw the system captured more CO₂ than previous systems.

The typical benchmark for SSA systems is around 60mmol of CO₂ captured/kg of adsorbent. In the 2022 Cambridge study, scientists achieved an impressive 112mmol, but at a relatively high energetic cost of 751kJ. The recent Lehigh study captured a record 312mmol at an energy consumption of just 72kJ.

‘As soon as we apply a small amount of voltage, we see a sharp decrease in concentration of carbon dioxide [in the gas mixture],’ Bilal adds. The results further show that the adsorption capacity can be significantly augmented by expanding the voltage window without compromising energy consumption efficiency. However, despite the positive outcomes, this is still not as effective as conventional carbon capture systems, which can capture up to 800mmol of CO₂/kg of solvent.

‘In terms of how much CO₂ we can absorb, we are still below the existing technologies,’ Bilal adds. ‘There are other research groups who have started working on these technologies. And with every new research, they show promising results in terms of how we can go above the current bottleneck,’ he explains.

But efficiency shouldn’t come at the expense of sustainability. Although it’s possible to improve carbon capture levels with other materials, Bilal is focused on environmentally friendly options.

Sustainable supercapacitors are an increasing focus in the global development of carbon capture technologies.

Talking about other electrochemistry projects around the world, he praises the potential of increasing carbon capture but believes the path forward should centre on sustainable materials. ‘We need to use materials which are environmentally friendly, cheap and which don’t produce so much waste at the end of their lifetime,’ he adds.

In terms of commercialising the technology, Bilal is positive it might not take too long. ‘There’s room for improvement. But at the same time, I believe this technology is close to being ready to be implemented.’

To Israel Temprano from the University of Cambridge, UK, this research constitutes a small step forward. ‘SSA is still a nascent field, and we don’t fully understand yet how things work and what parameters we need to prioritise to optimise these devices,’ he says.

‘This is an interesting study from the point of view of demonstrating the use of waste material to inexpensively produce well-performing electrodes. However, more fundamental research is still needed in the field to bring home the details on how to exploit this effect for technological applications,’ Temprano concludes.