Understanding the structure and dynamic process of water at the solid–liquid interface is an extremely important topic in surface science, energy science and catalysis^1,2,3. As model catalysts, atomically flat single-crystal electrodes exhibit well-defined surface and electric field properties, and therefore may be used to elucidate the relationship between structure and electrocatalytic activity at the atomic level^4,5. Hence, studying interfacial water behaviour on single-crystal surfaces provides a framework for understanding electrocatalysis^6,7. However, interfacial water is notoriously difficult to probe owing to interference from bulk water and the complexity of interfacial environments⁸. Here, we use electrochemical, in situ Raman spectroscopic and computational techniques to investigate the interfacial water on atomically flat Pd single-crystal surfaces. Direct spectral evidence reveals that interfacial water consists of hydrogen-bonded and hydrated Na⁺ ion water. At hydrogen evolution reaction (HER) potentials, dynamic changes in the structure of interfacial water were observed from a random distribution to an ordered structure due to bias potential and Na⁺ ion cooperation. Structurally ordered interfacial water facilitated high-efficiency electron transfer across the interface, resulting in higher HER rates. The electrolytes and electrode surface effects on interfacial water were also probed and found to affect water structure. Therefore, through local cation tuning strategies, we anticipate that these results may be generalized to enable ordered interfacial water to improve electrocatalytic reaction rates.

了解水在固液界面的结构和动态过程是表面科学、能源科学和催化^1,2,3中极其重要的课题。作为模型催化剂，原子级平面单晶电极表现出明确的表面和电场特性，因此可用于阐明原子水平^4,5结构和电催化活性之间的关系。因此，研究单晶表面的界面水行为为理解电^{催化 6,7}提供了一个框架。然而，众所周知，由于大量水的干扰和界面环境的复杂性，界面水难以探测⁸. 在这里，我们使用电化学、原位拉曼光谱和计算技术来研究原子平坦 Pd 单晶表面上的界面水。直接光谱证据表明界面水由氢键和水合 Na ⁺离子水组成。^{在析氢反应 (HER) 电位下，由于偏置电位和 Na +}的作用，观察到界面水结构从随机分布到有序结构的动态变化。离子合作。结构有序的界面水促进了跨界面的高效电子转移，从而提高了 HER 速率。还探测了电解质和电极表面对界面水的影响，发现它们会影响水的结构。因此，通过局部阳离子调节策略，我们预计这些结果可以推广到使有序界面水能够提高电催化反应速率。