Optical methods for studying local electrochemical reactions with spatial resolution: A critical review

Electrochemistry has been developed toward high spatial resolution and throughput during the past decades to match the growing demands for studying heterogeneous electrodes and nanomaterials that are widely used in electrocatalysis, electroanalysis and energy conversion. Combining optical methods with electrochemistry enables us to obtain local electrochemical information via a noninvasive way. Optical methods also possess high throughput, which are beneficial to investigate large amounts of nanoelectrodes or nanocatalysts simultaneously, and to develop electrochemical multiplex sensors. This article critically reviews the optical methods that have been developed with spatial resolution for imaging electrochemical reactions and processes in the nanometer-scale. Recent development on these methods, such as plasmonics-based electrochemical current microscopy (PECM), dark field microscopy (DFM), Raman spectroscopy, fluorescence microscopy (FLM) and electrogenerated chemiluminescence (ECL), and research progress in the relevant fields, particularly nanocatalysis and single particle/molecule electrochemistry, will be briefly overviewed. Finally, current limitations and trends of these optical methods and potential strategies to further improve the spatial resolution of electrochemistry are discussed.