A Novel Electrochemical Reactor for Direct Air Capture

Researchers from Rice University have created an electrochemical reactor that could significantly lower the energy required for direct air capture or the extraction of carbon dioxide straight from the atmosphere. This study was published in Nature Energy.

By facilitating more flexible and scalable carbon dioxide mitigation techniques, the new reactor design could help address the urgent impact of emissions on the climate and biosphere.

The reactor features a three-chambered, modular structure with a carefully engineered porous solid electrolyte layer at its core.

“This study represents a big milestone in carbon capture from the atmosphere,” said Haotian Wang, a chemical and biomolecular engineer at Rice University, whose lab has focused on industrial decarbonization and energy conversion and storage solutions.

Our research findings present an opportunity to make carbon capture more cost-effective and practically viable across a wide range of industries.

Haotian Wang, Study Corresponding Author and Associate Professor, Chemical and Biomolecular Engineering, Rice University

The device demonstrates industrially relevant rates of carbon dioxide regeneration from carbon-containing solutions, with performance metrics indicating its potential for large-scale industrial application. These include its long-term stability and adaptability to various cathode and anode reactions.

“One of the major draws of this technology is its flexibility. Hydrogen coproduction during direct air capture could translate into dramatically lower capital and operation costs for downstream manufacturing of net-zero fuels or chemicals,” Wang added.

In direct air capture processes, which usually involve passing a mixed gas stream through high-pH liquids to capture carbon dioxide (an acidic gas), this new technology offers an alternative that avoids the need for high temperatures. During this initial step, the chemical used to trap carbon dioxide forms bonds of varying strength between carbon and oxygen atoms in the gas molecules and compounds in the liquid, depending on the trapping agent.

The next crucial step is to retrieve the carbon dioxide from these solutions, which can be achieved through heat, chemical reactions, or electrochemical methods. Traditional direct air capture technologies often rely on high-temperature processes to regenerate carbon dioxide from the sorbent, or filtering agent, according to Zhiwei Fang, a Rice postdoctoral researcher and co-first author of the study.

Our work focused on using electrical energy instead of thermal energy to regenerate carbon dioxide.

Zhiwei Fang, Study Co-First Author and Postdoctoral Researcher, Rice University

According to Fang, this method offers several advantages, including room-temperature operation, no need for additional chemicals, and the absence of unwanted byproducts.

Different types of chemicals used to trap carbon dioxide come with their own advantages and disadvantages. Amine-based sorbents, for example, form weaker bonds with carbon dioxide, requiring less energy for removal, which has made them widely used. However, they are unstable and highly toxic. In contrast, basic water-based solutions with sorbents like potassium and sodium hydroxide are a more environmentally friendly option, though they require much higher temperatures to release the captured carbon dioxide.

Wang added, “Our reactor can efficiently split carbonate and bicarbonate solutions, producing alkaline absorbent in one chamber and high-purity carbon dioxide in a separate chamber. Our innovative approach optimizes electrical inputs to efficiently control ion movement and mass transfer, reducing energy barriers.”

Wang expressed hope that the study will encourage more industries to adopt sustainable practices and accelerate progress toward a net-zero future. He added that this project, along with others conducted in his lab over the years, highlights Rice University's strategic focus on sustainable energy innovation.

Wang concluded, “Rice is the place to be if you are passionate about sustainability and energy innovation.”

Former Rice postdoctoral researcher Xiao Zhang and Rice doctoral alumni and former postdoctoral scientists Peng Zhu and Yang Xia are the other study authors.

Robert A. Welch Foundation (C-2051) and the David and Lucile Packard Foundation (2020-71371) supported the study.

Video Credit: Rice University

Journal Reference:

Zhang, X. et. al. (2024) Electrochemical regeneration of high-purity CO₂ from (bi)carbonates in a porous solid electrolyte reactor for efficient carbon capture. Nature Energy. doi.org/10.1038/s41560-024-01654-z