近日，瑞士洛桑联邦理工学院欧洲原子与分子中心Sara Bonella团队研究了电驱动的二维离子晶体在电极/电解质界面的一阶相变。相关论文于2025年11月12日发表在《美国科学院院刊》杂志上。

吸附在金属电极表面的液态电解质会展现出多种结构，无论在组成还是局部组织上，都可能与其母体块体系统大相径庭。特别地，实验和模拟研究已越来越多地报道了无序-有序或有序-有序转变的存在，并确定了电极电势是其相应的驱动力。然而，对于这一过程的微观机制和各个阶段，人们的理解仍很有限，且转变过程中的自由能变化也未能得到充分表征。

为填补这一空白，研究组分析了一个典型的熔盐-金属界面中吸附层的结晶过程。他们证明，从无序结构到有序结构的转变分两个阶段进行。在一个宽广的电势范围内可以观察到预有序效应，它在电极表面形成多晶结构，之后才最终发生突发的有序转变。这种预有序显示出连续相变的特征。另一方面，有限尺寸效应分析证明了向单晶态的转变具有一级相变的特征。随着系统尺寸的增加，研究组观察到起始施加电压发生偏移，同时自由能垒也急剧增加。这一变化反映在界面电容上，该电容呈现一个峰值，且该峰值随系统尺寸的增大而愈发尖锐。

附：英文原文

Title: Electrically driven first-order phase transition of a 2D ionic crystal at the electrode/electrolyte interface

Author: Angiolari, Federica, Coretti, Alessandro, Salanne, Mathieu, Bonella, Sara

Issue&Volume: 2025-11-12

Abstract: Liquid electrolytes adsorbed at the surface of metallic electrodes display a multitude of structures that can largely differ from the parent bulk system, both in terms of composition and local organization. In particular, the existence of disorder–order or order–order transitions has been increasingly reported in experimental and simulation studies, and the electrode potential identified as the corresponding driving force. The microscopic mechanisms and the stages of the process are, however, poorly understood, and the free energy variation during the transition remains insufficiently characterized. To fill this gap, we investigate the crystallization of the adsorbed layer in a prototypical molten salt–metal interface. We demonstrate that the transition from the disordered to ordered structures proceeds in two stages. Preordering effects are observed across a wide range of potentials, resulting in the formation of a polycrystalline structure on the electrode surface, before an abrupt ordering transition finally occurs. The preordering displays signature of a continuous transition. On the other hand, finite-size effects analysis proves the first-order character of the transition toward the monocrystalline state. Upon increasing the system size, a shift in the onset applied voltage is observed, accompanied by a dramatic increase in the free energy barrier. The latter reflects in the interfacial capacitance, which displays a peak that sharpens with increasing system size.

DOI: 10.1073/pnas.2520026122

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2520026122