We also evaluated the distribution of the applied potential across the graphite/hBN/liquid heterostructure. Fig. shows the difference between the hBN and graphite half-wave potentials (E 1/2 hBN and E 1/2 gra , respectively) as a function of the hBN thickness. This difference can be thought of as the additional voltage (akin to an overpotential) that has to be applied, with the hBN barrier present, in order to achieve the same current density as that obtained on bare graphite. We further express this quantity as the fraction of the applied potential "spent" within the hBN, according to the following expression: