Visualizing Eigen/Zundel cations and their interconversion in monolayer water on metal surfaces
Ye Tian, Jiani Hong, Duanyun Cao, Sifan You, Yizhi Song, Bowei Cheng, Zhichang Wang, Dong Guan, Xinmeng Liu, Zhengpu Zhao, Xin-Zheng Li, Limei Xu, Jing Guo, Ji Chen, Enge Wang, Ying Jiang
Abstract
The nature of hydrated proton on solid surfaces is of vital importance in electrochemistry, proton channels, and hydrogen fuel cells but remains unclear because of the lack of atomic-scale characterization. We directly visualized Eigen- and Zundel-type hydrated protons within the hydrogen bonding water network on Au(111) and Pt(111) surfaces, using cryogenic qPlus-based atomic force microscopy under ultrahigh vacuum. We found that the Eigen cations self-assembled into monolayer structures with local order, and the Zundel cations formed long-range ordered structures stabilized by nuclear quantum effects. Two Eigen cations could combine into one Zundel cation accompanied with a simultaneous proton transfer to the surface. Moreover, we revealed that the Zundel configuration was preferred over the Eigen on Pt(111), and such a preference was absent on Au(111).