Optical imaging of nanoscale electrochemical interfaces in energy applications

A dynamic partnership between optical imaging and electrochemistry has generated a myriad of new opportunities in which both fields are mutually beneficial for understanding the nanoscale electrochemical interfaces. An in-depth understanding of the heterogeneity of the interfaces is crucial for determining the performance of electrochemical devices, including energy-related systems. Based on classical optical microscopies, innovative methodologies and tools such as super resolution fluorescence microscopy, electrochemiluminescence microscopy, surface plasmon resonance microscopy, dark-field microscopy, and Raman microscopy have been developed to monitor the dynamic processes of electrochemical reactions occurring on certain nanoscale interfaces, owing to their sufficient spatial and temporal resolution, diverse spectroscopic principles, excellent sensitivity, and non-invasive nature. These microscopic techniques are uniquely suited for probing the nanoscale interfaces in an operando, in situ, or in a real-time manner. Correspondingly, state-of-the-art optical microscopies and imaging are overwhelmingly utilized in nanoscale interfaces research, for example in direct visualization of nanoscale heterogeneous electrocatalytic reactions at the individual nanoparticle/molecule scale, monitoring the interfacial phenomena inside batteries, and studying electrochemical process at single entity scale. This review surveys the basic methodologies, key challenges in the field, and recent applications/ achievements of these microscopes in studying nanoscale electrochemical interfaces for energy applications. Extension to emerging optical microscopies is further discussed to promote new discoveries. Moreover, present compilation highlights the advantages and disadvantages, emerging research opportunities, and concludes in the potential future directions in advancing this field.