where r is the electrode radius and D is the diffusion coefficient of the redox mediator. One way to approach this condition is to decrease r to units of nanometers, a feat demonstrated more than a decade ago, however, this leads to complications since r becomes comparable to the electrical double layer thickness. Basal plane graphite has long been identified as having small k 0 for outersphere redox mediators, due to its low DOS, but little effort has been expended toward employing it as an ultramicroelectrode. More crucially, very few systems have values of k 0 and λ low enough to meet the conditions imposed by Eq. ( ), since k 0 increases with decreasing λ, according to Eq. (8). Our system is unique, since λ is kept constant, whereas k 0 decreases progressively with the tunneling distance due to the weakened electronic coupling. Consequently, the combination of basal plane graphite ultramicroelectrodes with r = 2.5 µm and tunneling through hBN, which pushes the apparent k 0 to below 10 -7 -10 -5 cm s -1 , allows the conditions imposed by Eq. ( ) to be met, subject to the value of λ. In fact, we can obtain a rough estimate of λ, based on the observed deviation from the expected exponential decay between 2-3L hBN layers (Fig. ). Indeed, evaluating k 0 , r, and D values against Eq. ( ) leads to λ ≈ 1.3 eV for [IrCl 6 ] 3-and λ ≈ 0.7 eV for [Ru(NH 3 ) 6 ] 3+ , both in agreement with experimentally determined values of ~1.2 eV and ~0.6 eV , respectively, although in disagreement with theoretical predictions. This also explains why deviations in α and j lim are only seen at the largest distances for [IrCl 6 ] 3-while anomalous behavior is observed for [Ru(NH 3 ) 6 ] 3+ across the entire range of distances. We stress that the above evaluation is very approximate and does not fully explain all the aspects of the observed deviations.