  The unique properties of graphene offer immense opportunities for
applications to many scientific fields, as well as societal needs, beyond our
present imagination. One of the important features of graphene is the
relatively simple tunability of its electronic structure, an asset which
extends the usability of graphene even further beyond present experience. A
direct injection of charge carriers into the conduction or valence bands, i.e.,
doping, represents a viable way of shifting the Fermi level. In particular, the
electrochemical doping should be the method of choice, when higher doping
levels are desired and when a firm control of experimental conditions is
needed. In this Account, we focus on the electrochemistry of graphene in
combination with in-situ Raman spectroscopy, i.e., the in-situ Raman
spectroelectrochemistry. Such a combination of methods is indeed very powerful,
since Raman spectroscopy can readily monitor not only the changes in the doping
level, but it can give information also on eventual stress or disorder in the
material. However, when employing Raman spectroscopy, one of its main strengths
lies in the utilization of isotope engineering during the chemical vapor
deposition (CVD) growth of the graphene samples. The in-situ Raman
spectroelectrochemical study of multi-layered systems with smartly designed
isotope compositions in individual layers can provide a plethora of knowledge
about the mutual interactions: (i) between the graphene layers themselves, (ii)
between graphene layers and their directly adjacent environment (e.g.,
substrate or electrolyte), and (iii) between graphene layers and their extended
environment, which is separated from the layer by a certain number of
additional graphene layers.
