The electron tunneling through hBN in the graphite/hBN/liquid heterostructure was measured by voltammetry, i.e. a current-voltage measurement, and is summarized in Fig. The voltammograms of [IrCl 6 ] 3-oxidation in Fig. exhibit the steady-state sigmoidal shape expected for disk ultramicroelectrodes, for both the bare graphite (black curve) and hBN layers (green curves). However, rather than maintaining the limiting value of the potentialindependent plateau, the current density rises further at large positive potentials, owing to the graphite oxidation side-reaction delimiting the potential window. All hBN voltammograms maintain a similar shape to that of the bare graphite, but are offset to increasingly more positive potentials upon increasing N. The red curves, fitted to the voltammograms using an empirical function described in ref , allowed us to extract k 0 , j lim , and (1-α) or α. The k 0 of [IrCl 6 ] 3- oxidation on bare graphite (k 0, gra ) averaged over all the devices was (1.4 ± 0.2) × 10 -3 cm s -1 , about one order of magnitude lower than reported previously, not entirely unexpected considering the exposure of the topmost surface to PMMA during device fabrication.