Single atoms or ions on surfaces affect processes from nucleation¹ to electrochemical reactions² and heterogeneous catalysis³. Transmission electron microscopy (TEM) is a leading approach for visualizing single atoms on a variety of substrates^4,5. It conventionally requires high vacuum conditions, but has been developed for in situ imaging in liquid and gaseous environments^6,7 with a combined spatial and temporal resolution that is unmatched by any other method —notwithstanding concerns about electron beam effects on samples. When imaging in liquid using commercial technologies, electron scattering in the windows enclosing the sample and in the liquid generally limits the achievable resolution to a few nanometres^6,8,9. Graphene liquid cells, on the other hand, have enabled atomic resolution imaging of metal nanoparticles in liquids¹⁰. Here we show that a double graphene liquid cell, comprised of a central molybdenum disulphide monolayer separated by hexagonal boron nitride spacers from the two enclosing graphene windows, makes it possible to monitor with atomic resolution the dynamics of platinum adatoms on the monolayer in an aqueous salt solution. By imaging over 70,000 single adatom adsorption sites, we compare the site preference and dynamic motion of the adatoms in both a fully hydrated and vacuum state. We find a modified adsorption site distribution and higher diffusivities for the adatoms in liquid phase compared to those in vacuum. This approach paves the way for in situ liquid phase imaging of chemical processes with single atom precision.

表面上的单个原子或离子影响从成核¹到电化学反应²和多相催化³的过程。透射电子显微镜 (TEM) 是在各种基底上可视化单个原子的领先方法^4,5。它通常需要高真空条件，但已开发用于液体和气体环境中的原位成像^6,7具有任何其他方法无法比拟的组合空间和时间分辨率——尽管担心电子束对样品的影响。当使用商业技术在液体中成像时，包围样品的窗口和液体中的电子散射通常将可实现的分辨率限制在几纳米^6,8,9。另一方面，石墨烯液体电池已经能够对液体中的金属纳米粒子进行原子分辨率成像¹⁰. 在这里，我们展示了一个双石墨烯液体电池，由一个中央二硫化钼单层组成，由六方氮化硼间隔物与两个封闭的石墨烯窗口隔开，可以用原子分辨率监测盐水溶液中单层上铂吸附原子的动力学解决方案。通过对超过 70,000 个吸附原子吸附位点进行成像，我们比较了吸附原子在完全水合和真空状态下的位点偏好和动态运动。我们发现与真空中的吸附原子相比，液相中的吸附原子具有改进的吸附位点分布和更高的扩散系数。这种方法为以单原子精度对化学过程进行原位液相成像铺平了道路。