Developments in chemistry, materials science and biology have been fuelled by our search for structure–property relationships in matter at different levels of organization. Transformations in chemical synthesis and living systems predominantly take place in solution, such that many efforts have focused on studying nanoscale systems in the liquid phase. These studies have largely relied on spectroscopic data, the assignment of which can often be ambiguous. By contrast, electron microscopy can be used to directly visualize chemical systems and processes with up to atomic resolution. Electron microscopy is most amenable to studying solid samples and, until recently, to study a liquid phase, one had to remove solvent and lose important structural information. Over the past decade, however, liquid-phase electron microscopy has revolutionized direct mechanistic studies of reactions in liquid media. Scanning electron microscopy and (scanning) transmission electron microscopy of liquid samples have enabled breakthroughs in nanoparticle chemistry, soft-matter science, catalysis, electrochemistry, battery research and biochemistry. In this Review, we discuss the utility of liquid-phase electron microscopy for studying chemical reaction mechanisms in liquid systems.

我们在不同组织级别的物质中寻求结构与性质的关系，推动了化学，材料科学和生物学的发展。化学合成和生物系统的转化主要发生在溶液中，因此许多努力都集中在研究液相中的纳米系统上。这些研究在很大程度上依赖于光谱数据，这些数据的分配通常可能是模棱两可的。相比之下，电子显微镜可用于以不超过原子分辨率的方式直接可视化化学系统和过程。电子显微镜最适合于研究固体样品，直到最近，为了研究液相，人们必须除去溶剂并丢失重要的结构信息。但是，在过去的十年中，液相电子显微镜彻底改变了液体介质中反应的直接机理研究。液体样品的扫描电子显微镜和（扫描）透射电子显微镜在纳米粒子化学，软物质科学，催化，电化学，电池研究和生物化学领域取得了突破。在这篇综述中，我们讨论了液相电子显微镜在研究液体系统中化学反应机理方面的实用性。