Academician Wang Enge, Professor Jiang Ying, and Researcher Chen Ji of Peking University cooperated with Professor Guo Jing from the School of Chemistry of Beijing Normal University, etc.Using high-resolution qPlus atomic force microscopy technology, the atomic-level resolution images of protons in the water layer were captured for the first time, and it was found that the hydrated protons of Eigen and Zundel configurations can exist stably on the solid surface, and further confirmed that the full quantum effect caused A new configuration of hydrogen atom symmetry in surface two-dimensional ice at room temperature and atmospheric pressure.The work, titled “Visualizing Eigen / Zundel cations and their interconversion in monolayer water on metal surfaces”, was published in the top international academic journal Science on July 15.
In this work, the researchers co-deposit hydrogen atoms and water molecules on the surface of different metals (Au, Cu, Pt, Ru). The hydrogen atoms undergo charge transfer with the metal substrate to form hydrogen ions, which further combine with water molecules spontaneously. A two-dimensional hydrogen bond network is formed. In order to be able to distinguish water molecules and hydrated protons from real space, the researchers developed a new generation of qPlus non-intrusive atomic force microscopy (qPlus-AFM) based on the detection of hydrated sodium ions in 2018 (Nature 557, 701 (2018)). ), and improved its detection sensitivity and imaging resolution to ~2 pico-N and ~20 picometres (the best international level), respectively, and “see” the atomic structure of the hydrated proton monomer (H3O+) and its configuration by Eigen for the first time. A two-dimensional hexagonal hydrogen-bonding network formed by the self-assembly of hydrated protons (below).
Description: AFM experimental image of the two-dimensional hydrogen bond network formed by the self-assembly of Eigen (A) and Zundel (B) configuration hydrated protons on the surface of Au (111) (the first column of hydrated ion map; the second column of hydrogen bond network map) And the atomic structure model diagram (third column). In the model diagram, blue represents ions in Eigen/Zundel configuration, and red represents water molecules.
By increasing the hydrogen ion doping concentration, the Eigen-configuration hydrated protons are transformed into Zundel-configuration hydrated protons (Fig. 2B). High-resolution AFM images of hydrated protons in Zundel configuration can directly distinguish the protons being shared by two water molecules to form a symmetrical hydrogen bond configuration. First-principles path-integrated molecular dynamics (PIMD) simulations show that nuclear quantum effects induce quantum delocalization of hydrogen nuclei, which promotes the formation of symmetric hydrogen bonds and stabilizes the Zundel configuration at room temperature. This is also the first time that the concept of hydrated protons was proposed more than 100 years ago. The microstructure of hydrated protons was observed in real space for the first time, and a new two-dimensional ice species with a symmetrical configuration of hydrogen atoms maintained at normal pressure at room temperature was discovered. state.
On this basis, the researchers controlled the proton transfer through the AFM tip, and found that two Eigen configuration hydrated protons can be combined into a Zundel configuration hydrated proton, and an extra proton is transferred from the water layer to the solid surface ( H*), forming the Zundel+H* configuration (below). This is a novel proton co-transfer process that goes beyond the known fundamental steps of the hydrogen evolution reaction on the electrode surface. Further study found that there is a concentration-dependent Eigen-Zundel transition of hydrated protons on the Au (111) surface, while different concentrations of hydrated protons on the Pt (111) surface are more inclined to form the Zundel configuration (Fig. 3D). This means that when the hydrated proton concentration is low, the Zundel configuration hydrated protons in the Pt (111) surface water layer and the H* adsorbed on the solid surface mainly generate H2 through the Heyrovsky reaction path (H+ + e- + H* → H2); When the concentration of hydrated protons increases, the coverage of H* adsorbed on the surface increases accordingly, thereby opening a new Tafel reaction pathway (2H* → H2) for hydrogen production. These images show that the full quantum effect is helpful for understanding the microscopic mechanism of efficient hydrogen production at Pt electrodes, and also provides a new idea for improving the hydrogen production efficiency by improving electrode materials.
Description: (AC) Experimental and model schematic diagrams of tip manipulation of Eigen and Zundel configuration interconversion; (D) Correlation of Eigen and Zundel ion concentrations on Au (111) and Pt (111) surfaces under different hydrogen ion doping concentrations.
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