A team of researchers has made important strides in understanding the intricate reaction processes of carbon dioxide (CO2) when mixed with supercritical water. These breakthroughs are vital for grasping how CO2 is naturally mineralized and sequestered, and for comprehending the deep carbon cycle within the Earth. This knowledge could introduce innovative approaches to future carbon capture technologies.
Under the leadership of Associate Professor Ding PAN from both the Department of Physics and the Department of Chemistry at the Hong Kong University of Science and Technology (HKUST), and in partnership with Prof. Yuan Yao from the Department of Mathematics, a research team has uncovered important insights into the complex reaction processes of carbon dioxide (CO2) in supercritical water. These discoveries are essential for better understanding the molecular processes involved in the mineralization and storage of CO2 in both natural and engineered systems, as well as the deep carbon cycle within the Earth’s subsurface. This enhanced understanding aims to lead to new pathways for carbon sequestration technologies in the future. The results of this research were published in the Proceedings of the National Academy of Sciences (PNAS)*.
The process of CO₂ dissolving in water and its following hydrolysis reactions are critical for efficient carbon capture and mineral storage, playing a major role in carbon sequestration efforts to combat global warming. Prof. Pan’s team created and utilized first-principles Markov models to unravel the reaction mechanisms of CO₂ in supercritical water, exploring both bulk and nanoconfined settings. They identified that pyrocarbonate (C₂O₅²⁻) serves as a stable and significant intermediate in these nanoconfined conditions, a detail that was previously unnoticed due to pyrocarbonate’s typical instability and fast decomposition in water. This surprising finding regarding pyrocarbonate is tied to the superionic characteristics of confined water solutions. Furthermore, the team learned that carbonation reactions are characterized by the collective transfer of protons through temporary chains of water molecules; this process displays a unified behavior in bulk solutions, but occurs in a stepwise fashion when confined to nanoscale spaces. This study highlights how powerful first-principles Markov models can be for illuminating complex reaction kinetics in aqueous systems.
“Our innovative approach has allowed us to uncover a novel pathway for CO2 dissolution that involves pyrocarbonate ions,” explained Prof. Chu LI, a Research Assistant Professor in the Department of Physics. “Our advanced computational methods do not depend on pre-existing knowledge, enabling automatic identification of reaction pathways without human interference, which uncovers previously unknown reaction mechanisms grounded in the fundamental principles of physics.”
Prof. Ding Pan further remarked, “Our approach uses unsupervised learning techniques, highlighting the significance of large oxocarbon compounds in water reactions under extreme conditions, and shows that nanoconfinement is a viable method for controlling chemical processes. We anticipate these findings to direct future developments in carbon sequestration technologies.”
This research received funding from the Hong Kong Research Grants Council, the Croucher Foundation, and the Excellent Young Scientists Fund of the National Natural Science Foundation of China. Part of the computational work was conducted on the Tianhe-2 supercomputer located at the National Supercomputer Center in Guangzhou.
*Note: Prof. Chu Li, the Research Assistant Professor, is the lead author of the article and, along with Prof. Ding Pan, is a corresponding author.
