Abstract
In this article, we present the possibilities that STEM and electron energy loss spectroscopy (EELS) offer in terms of probing fundamental aspects of electrochemical systems by combining electron microscopy with in situ control of local electrochemical potentials by tuning the atmosphere, by biasing, or using a liquid environment. Some recent advances in electron microscopy based studies of electrochemical processes in solids and at solid-liquid and solid-gas interfaces are summarized. STEM/EELS directly probes a broad range of parameters related to the electrochemical state of the system, including local atomic configurations, bond length and angle and valence states and orbital populations of atoms on the individual column level. The challenge in the development of these techniques is twofold. The first one is the continued need for increase in resolution, both spatial (for imaging) and energy (for spectroscopy). The second challenge is related to electrochemical aspects, and consequently to the necessity to control and probe the local electrochemical potentials and ionic flows in the active region under investigation. This necessitates development of stable electrochemical cells that can support high-resolution studies, while at the same time being able to control global potential and allow local interrogation.