A team of scientists led by Kumar Varoon Agrawal at EPFL has developed membranes that show exceptional CO₂ capture performance by incorporating pyridinic nitrogen at the edges of graphene pores. The membranes strike a remarkable balance of high CO₂ permeance and selectivity, making them highly promising for various industrial applications. The work is published in Nature Energy.

The researchers began by synthesizing single-layer graphene films using chemical vapor deposition on copper foil. They introduced pores into the graphene through controlled oxidation with ozone, which formed oxygen-atom functionalized pores. They then developed a method to incorporate nitrogen atoms at the pore edge in the form of pyridinic N by reacting the oxidized graphene with ammonia at room temperature.

The researchers confirmed the successful incorporation of pyridinic nitrogen and the formation of CO₂ complexes at the pore edges by using various techniques, such as X-ray photoelectron spectroscopy and scanning tunneling microscopy. The incorporation of pyridinic N remarkably improved the binding of CO₂ on graphene pores.

The resulting membranes showed a high CO₂/N₂ separation factor, with an average of 53 for a gas stream containing 20% CO₂. Remarkably, streams with about 1% CO₂, achieved separation factors above 1000 because of the competitive and reversible binding of CO₂ at the pore edges, facilitated by the pyridinic nitrogen.

A schematic of porous graphene hosting pyridinic N (shown as purple spheres) at the pore edges. The resulting membrane is highly selective to CO₂. Credit: Kuang-Jung Hsu (EPFL)

The scientists also showed that the membrane preparation process is scalable, producing high-performance membranes on a centimeter scale. This is crucial for practical applications, meaning that the membranes can be deployed in large-scale industrial settings.

The high performance of these graphene membranes in capturing CO₂, even from dilute gas streams, can significantly reduce the costs and energy requirements of carbon capture processes. This innovation opens new avenues in the field of membrane science, potentially leading to more sustainable and economical CCUS solutions.

The uniform and scalable chemistry used in creating the membranes means that they can be scaled-up soon. The team is now looking to produce these membranes by a continuous roll-to-roll process.

Resources

• Hsu, KJ., Li, S., Micari, M. et al. Graphene membranes with pyridinic nitrogen at pore edges for high-performance CO₂ capture. Nat Energy (2024) doi: 10.1038/s41560-024-01556-0