Recently, Professor Sun Weiwei’s team from the School of Physics at Southeast University (SEU) has made a significant breakthrough in understanding the morphological evolution and diffusion mechanisms of confined water between the layers of two-dimensional MXene materials.The research findings, entitled "Altered morphology and diffusivity of water confined in MXenes: Machine learning-accelerated computations combined with experiments," were published in the premier international academic journal, Science Advances.
The behavior of water in nanoscale confined environments differs fundamentally from that of bulk water. This phenomenon is not only ubiquitous in biological systems but also plays a critical role in fields such as energy storage and nanofluidics. As an important class of pseudocapacitive energy storage materials, low-dimensional transition metal carbonitrides (MXenes) rely heavily on the confined water, which has been proven essential for proton transport and overall energy storage performance.
Therefore, a deep understanding of confined water behavior at the interface level provides vital guidance for achieving further breakthroughs in ionic devices and energy storage technologies. Thanks to their excellent hydrophilicity and rich surface terminal groups, MXenes offer an ideal platform for exploring solid-liquid interfacial interactions and tuning the physicochemical behavior of water molecules. However, a unified understanding of the structural evolution behavior and diffusion mechanisms of confined water are still lack of deep understanding. Specifically, how the interfacial chemical environment synergistically affects water molecule orientation, hydrogen bond networks, and diffusion behavior has remained unclear.
To address these challenges, our research team combined on-the-fly machine learning-accelerated ab initio molecular dynamics simulations with multi-scale experimental characterizations to systematically study the intrinsic correlation between the morphological evolution of confined water and its diffusion characteristics.The study revealed distinct behaviors driven by different functional groups: i) -OH functional groups anchor water molecules at the interface by forming numerous stable interfacial hydrogen bonds, resulting in an extremely low diffusion rate. Ii) -F and -O functional groups, conversely, promote ultrafast transport characteristics. This is closely related to an increased interfacial electrostatic potential barrier, shortened hydrogen bond lifetimes, and disordered orientation of water molecules.
Based on these findings, the team identified three core factors determining the diffusion of confined water: interfacial electrostatic potential difference, hydrogen bond lifetime, and the proportion of water molecule orientation. Innovatively, they constructed an exponential linear combination diffusion model, providing a robust theoretical framework for regulating the behavior of nano-confined water.
This research unifies the correlation mechanism of solid-liquid interfacial interactions, confined water structure, and dynamics at the atomic level for the first time. It not only deepens the fundamental understanding of confined solid-liquid interfaces but also provides crucial design guidelines for the application of MXene materials in electrochemical energy storage, seawater desalination, and fluid sensing.
Southeast University is in the leading role of this work. Doctoral student Tang Jiawei is the first author, and Professor Sun Weiwei is the primary corresponding author.Collaborators on this paper include Professor Wang Xuehang from Delft University of Technology, Netherlands (corresponding author), and senior researchers Paul R.C. Kent, Jingsong Huang, and Naresh Osti from Oak Ridge National Laboratory, USA. The work also received valuable support from Professor Sun Litao and Professor Wang Jinlan of Southeast University.
Link: https://www.science.org/doi/10.1126/sciadv.adz1780
