b Results represent the average of three replicates for each set of conditions. With views on characterizing the chemical species responsible of the observed electrocatalytic signal, a controlled potential electrolysis at -1.65 V (vs Fc + /Fc) was monitored by LC-MS over the course of four hours. Two species were observed according to the chromatogram (Figure ), positive ionization ESI-MS detection for these two peaks confirmed the gradual consumption of BT-DCAF in solution (molecular ion m/z = 521.1, Figure ) and the conspicuous formation of BT-DCAFH4 (molecular ion m/z = 525.1, Figure ). LC-MS analysis of the 4-hour electrolyzed solution after long term storage (N2 atmosphere, 7 days) showed a decrease in the signal of BT-DCAFH4 and a small increase in the signal assigned to BT-DCAF (Figure ). This suggests that there is probably a pathway in which BT-DCAFH4 goes back to the neutral BT-DCAF form releasing H2 in the absence of an applied external potential. This pathway however, appears to be kinetically very slow. In addition, a series of controlled potential electrolysis were carried out at different potentials and sampled for 1 H NMR analysis (Figures 5d-5e and S22). After 4hour electrolysis at -1.65 V (vs Fc + /Fc), a new signal at 4.60 ppm was observed in the 1 H NMR spectra and it is assigned to the C-H hydridic species BT-DCAFH4. Chemical shifts in this region (4.30 to 5.70 ppm) are characteristic of the C-H group of imidazoline compounds. These compounds are the reduced derivatives of imidazoles where the C=N bond has reacted via a 2e -/2H + or 2e -/1H + pathway. This new signal confirms that during the electrolysis experiments in presence of TFA, the imidazole rings in the caffeine units of BT-DCAF underwent a symmetric double reduction and formed a global 4e -, 4H + reduced species. In addition, as the concentration of BT-DCAFH4 in the reaction mixture increased by the electrochemical reduction of BT-DCAF, the C-H signal corresponding to the BT core in the active species showed a small shift upfield (Figures and). This signal is therefore assigned to the presence of a mixture of BT-DCAF and BT-DCAFH4. Controlled potential electrolysis at -1.45 V (vs Fc + /Fc) and -1.25 V (vs Fc + /Fc) also lead to a mixture of BT-DCAFH4 and BT-DCAF (Figure ). Controlled potential electrolysis experiments suggest that the electrocatalytic production of H2 gas starts to take place when the applied potential is equal or lower than -1.25 V (vs Fc + /Fc) (Tables and). Interestingly, controlled potential electrolysis at -1.15 V (vs Fc + /Fc), the potential at which BTH2-DCAF is formed, also produced a mixture of BT-DCAFH4 and BT-DCAF (Figure ). However, only trace amounts of H2 were observed in this latter electrolysis experiment. This suggests that upon accumulation in solution, the species BTH2-DCAF species undergoes a disproportionation (DISP) reaction to form BT-DCAF and BT-DCAFH4. This experiment also confirmed that a lower applied potential is required in order to observe the electrocatalytic H2 production. BT-DCAFH4 is considered to be the activate species because increase of BT-DCAFH4 in the solution dose not inhibit the hydrogen production. Finally, to address the possible effect of metallic/organometallic impurities being responsible for the production of H2, BT-DCAF was analyzed by Inductively Coupled Plasma (ICP) spectroscopy and P NMR (Table and Figure ). Synthetic protocols that involve the Suzuki-Miyaura reaction employ Pd catalysts to perform C-C couplings. The ICP analysis showed that residual Pd was only 17 ppm in BT-DCAF. In the controlled potential electrolysis experiments, BT-DCAF was employed at 0.2 mM concentration, therefore the contribution of Pd originated from the BT-DCAF to the liquid mixture would fall around 1.8 ppb. This value is too low to have any significant activity in the electrocatalytic H2 evolution of the system. Also, no H2 evolution was observed in the electrolysis experiments with BT-DCAF or AcOH indicating that Pd is not the catalyst.