  In situ electrochemical dilatometry was used to study, for the first time,
the expansion behavior of a porous carbon electrode in a pure ionic liquid,
1-ethyl-3-methyl-imidazolium-tetrafluoroborate. For a single electrode, an
applied potential of -2 V and +2 V against the potential of zero charge
resulted in maximum strain of 1.8 % and 0.5 %, respectively. During cyclic
voltammetry, the characteristic expansion behavior strongly depends on the scan
rate, with increased scan rates leading to a decrease of the expansion.
Chronoamperometry was used to determine the equilibrium specific capacitance
and expansion. The obtained strain versus accumulated charge relationship can
be fitted with a simple quadratic function. Cathodic and anodic expansion data
collapses on one parabola when normalizing the surface charge by the ratio of
ion volume and average pore size. There is also a transient spike in the height
change when polarity is switched from positive to negative that is not observed
when changing the potential from negative to positive indicating the size and
the shape of the ion is influencing the expansion behavior.
