Electrocatalytic CO2 upcycling excels under pressure

An electrocatalytic reactor that directly converts a high-pressure stream of captured CO₂ into a major commodity chemical could offer an economically viable option for addressing climate change.

Conventional carbon capture prevents industrial CO₂ emissions from reaching the atmosphere by trapping the greenhouse gas from factory or power plant emissions and pumping it underground for long-term geological storage. The high economic cost of this process prompted a KAUST team to consider an alternative approach. “We aimed to convert industrially captured high-pressure CO₂ directly into valuable chemicals, which would turn carbon capture into an economic opportunity,” says Xu Lu, from the Chemical Engineering programme, who led the study.

The team devised an electrocatalytic reactor that directly connects to the latest cryogenic carbon capture system^[1]. The reactor’s copper-based electrocatalyst turns the high-pressure, high-purity stream of captured CO₂ into industrial-grade ethylene.

“This commodity chemical is essential to plastics, textiles, and construction, and has a global market that exceeds US$200 billion per year,” says Liang Huang, a member of Lu’s team.

Previous attempts to electrocatalytically convert captured CO₂ into valuable chemicals, using reactors that run at ambient pressure, had limitations that prevented real-world use. These limitations have included sluggish reactivity; low reaction selectivity that then required additional steps to purify the products generated; and a buildup of salt byproducts in the reactor that choke its performance.

The new process involved operating the reactor under pressure, which significantly enhanced reactivity and selectivity for ethylene production, say the researchers. The high-pressure process had the dual benefit of significantly increasing CO₂ coverage of the electrocatalyst as well as accelerating the C–C coupling reaction required for ethylene formation. “Also, by directly using the high-pressure captured CO₂ gas stream, we avoid the energy loss of depressurizing and repressurizing the gas,” Lu explains.

The team further boosted their reactor system’s performance by systematically testing a series of copper electrocatalysts spiked with the atoms of other metals. They found that adding indium gave the best results. “Trace indium fine-tunes the adsorption of the key ‘*CO’ reaction intermediate onto the copper, promoting C–C coupling and improving product selectivity,” Lu says.

After recapturing unreacted CO₂ from the product gas stream and cycling it back into the reactor’s high-pressure CO₂ gas feed, the reactor system efficiently generated ethylene with 99.9% purity. “High-pressure operation boosted ethylene production performance,” Lu adds, “but it also helped to mitigate salt precipitation, which has been a long-standing challenge in the field.”

The team’s economic analysis showed that their new process can produce ethylene at a cost of US$1,240 per ton, a figure very close to ethylene’s current market price. “With system optimization, costs may fall further and turn carbon capture from a cost burden into a profit opportunity – as well as support Saudi Arabia’s ambition of becoming a circular economy by 2060,” Huang says.

“Overall, the study demonstrates that it is essential to co-design the catalyst and reactor system to realize practical CO₂ upcycling,” Lu explains. “Next, we will scale up our single cell reactors into a modular reactor stack, extend operational lifetime, and run in-situ connected tests with capture facilities to move toward pilot demonstrations,” he adds.