where f E, 1 hBN and f E, N hBN are the fractions of E spent per hBN layer and in N layers of hBN, respectively. Fig. shows these fractions as a function of the inverse hBN thickness and, expectedly, suggests that for bulk hBN, f E, N hBN approaches unity for both mediators. However, it also shows that less of E is spent in hBN for [IrCl 6 ] 3-in comparison to [Ru(NH 3 ) 6 ] 3+ . This indicates a smaller tunneling barrier for the former, at least for the few-layer hBN measured here, which is in agreement with the differences predicted from Figs. .