Coexistence of Two Types of Liquid Structures at Platinum–Water Interfaces

Platinum–water interfaces underpin many electrochemical energy conversion processes. However, despite decades of research, the real-space liquid structure at these interfaces remains elusive. Using three-dimensional atomic force microscopy (3D-AFM), we mapped the Pt–water interface in real space with angstrom-level resolution. Topographic imaging revealed atomically flat (type I) and stripe-like (type II) surface nanodomains. Force–distance profiles above type I domains exhibited oscillatory decay patterns with a periodicity of ∼0.33 nm, consistent with water. In contrast, type II domains showed stronger oscillations with a larger periodicity of ∼0.45 nm and extended decay lengths, indicative of a different liquid structure with stronger correlation and ordering. Wide-angle X-ray scattering measurements of pure water and a series of liquid n-alkanes revealed peaks at ∼0.31 nm and ∼0.46 nm, in agreement with 3D-AFM observations of type I and type II structures, respectively. Our findings uncover the coexistence of two types of liquid structures at Pt–water interfaces modulated by surface heterogeneity, enabling a new understanding and design principle for energy conversion applications.