Fitting a mechanism to the CV data (Figure3) c), d)) shows that the overall BTDF reduction reaction follows an ECEC type reaction (an ECE reaction followed by a second chemical step) where the second reduction step occurs at a less reductive potential than the first reduction, -0.5 V compared to -1.89 V vs F c/F c + in this case, but any value on closer to zero than -1 V vs F c/F c + fits the data quite well (Scheme 2). A key feature to getting the peak-splitting and then merging at higher acid concentrations is that the first protonation is an equilibrium that is heavily shifted towards the protonated species with reaction kinetics around or exceeding the diffusion limit at 0.1-5 * 10 10 M -1 s -1 but the back reaction (2 * 10 7 M -1 s -1 ) is still faster than the next protonation step 2 * 10 6 M -1 s -1 .