Atom-thin graphene membranes make carbon capture more efficient

Scientists at EPFL have developed advanced atom-thin graphene membranes with pyridinic-nitrogen at pore edges, showing unprecedented performance in CO₂ capture. It marks a significant stride toward more efficient carbon capture technologies.

As the world battles climate change, the need for efficient and cost-effective carbon capture technologies is more urgent than ever. In that vein, scientists are exploring a number of innovations to drastically reduce industrial carbon emissions, which is pivotal in mitigating global warming.

One of these is carbon capture, utilization, and storage (CCUS), a critical technology that reduces carbon dioxide (CO₂) emissions from hard-to-abate industrial sources such as power plants, cement factories, steel mills, and waste incinerators. But current capture methods rely on energy-intensive processes, which makes them costly and unsustainable.

Research now aims to develop membranes that can selectively capture CO₂ with high efficiency, thereby reducing the energy and financial costs associated with CCS. But even state-of-the-art membranes, such as polymer thin films, are limited in terms of CO₂ permeance and selectivity, which limits their scalability.

So the challenge is to create membranes that can simultaneously offer high CO₂ permeance and selectivity, crucial for effective carbon capture.

A team of scientists led by Kumar Varoon Agrawal at EPFL has now made a breakthrough in this area by developing 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 1,000 because of the competitive and reversible binding of CO₂ at the pore edges, facilitated by the pyridinic nitrogen.