  Electrochemistry exploits local current heterogeneities at various scales
ranging from the micrometer to the nanometer. The last decade has witnessed
unprecedented progress in the development of a wide range of electroanalytical
techniques allowing to reveal and quantify such heterogeneity through
multiscale and multifonctionnal operando probing of electrochemical processes.
However most of these advanced electrochemical imaging techniques, employing
scanning probes, suffer from either low imaging throughput or limited imaging
size. In parallel, optical microscopies, which can image a wide field of view
in a single snapshot, have made considerable progress in terms of sensitivity,
resolution and implementation of detection modes. Optical microscopies are then
mature enough to propose, with basic bench equipment, to probe in a non
destructive way a wide range of optical (and therefore structural) properties
of a material in situ, in real time: under operating conditions. They offer
promising alternative strategies for quantitative high-resolution imaging of
electrochemistry. The first sections recall the optical properties of materials
and how they can be probed optically. They discuss fluorescence, Raman, surface
plasmon resonance, scattering or refractive index. Then the different optical
microscopes used to image electrochemical processes are examined along with
some strategies to extract quantitative electrochemical information from
optical images. Finally the last section reviews some examples of in situ
imaging, at micro- to nanometer resolution, and quantification of
electrochemical processes ranging from solution diffusion to the conversion of
molecular interfaces or solids.
