Electrostatic gating using electrolytes is a powerful
approach
for controlling the electronic properties of atomically thin two-dimensional
materials such as graphene. However, the role of the ionic type, size,
and concentration and the resulting gating efficiency is unclear due
to the complex interplay of electrochemical processes and charge doping.
Understanding these relationships facilitates the successful design
of electrolyte gates and supercapacitors. To that end, we employin situRaman microspectroscopy combined with electrostatic
gating using various concentrated aqueous electrolytes. We show that
while the ionic type and concentration alter the initial doping state
of graphene, they have no measurable influence over the rate of the
doping of graphene with applied voltage in the high ionic strength
limit of 3–15 M. Crucially, unlike for conventional dielectric
gates, a large proportion of the applied voltage contributes to the
Fermi level shift of graphene in concentrated electrolytes. We provide
a practical overview of the doping efficiency for different gating
systems.