The protonation mechanism of BT unit can be extracted from the behaviour of the shift in the first reduction wave. At high concentrations (more than two equivalents) of acid, the wave is completely irreversible with a doubling in electric current. Including the positive shift, this is the mark of two consecutive follow-up reactions, a so-called EC (electrochemical step followed by a chemical step) reaction that is followed by a secondary reduction step either another electrode-based electron transfer (an ECE reaction: an EC reaction followed by a secondary electrochemical step) or an intermolecular charge transfer between the newly generated species similar to what happens in BTDN (a so-called EC-DISP reaction: an EC reaction followed by a disproportionate reaction) . To disentangle the two types of reactions, an acid titration and a scan rate dependence experiment were performed (Figure ) and d)). During the titration, it can be seen that the reduction peak splits into two different peaks at lower acid concentrations and then merge at higher concentrations. At higher scan rates a merge of the two peaks can be seen as well as a slight return of the oxidation peak showing that the irreversible nature of the reaction is dependent on the scan rate. The two data sets were then used to simulate the protonation mechanism.