The dependence on proton source concentration and catalyst concentration was evaluated in order to gain insights into the undergoing electrocatalytic process. When the concentration of BT-DCAF catalyst was maintained constant (0.2 mM), first order dependence on the proton source was observed following the linear relationship between Icat/Ip (Icat= catalytic current upon addition of proton source, Ip= peak current at -1.42 V vs Fc + /Fc, the first reduction event of BT-DCAF in the absence of proton source) and the square root of the proton source concentration (Figures ). In addition, the magnitude of the associated kinetic isotope effect (KIE) was measured. TFA was substituted with the deuterated alternative CF3COOD (TFA-d) and the effect of its concentration on the electrocatalytic response was evaluated in the presence of BT-DCAF (Figures and). A KIE of 1.66 was observed for the kH/kD pair, the KIE effect is small in comparison to other small organic molecular systems. Similarly, when the concentration of TFA proton source was kept constant (15 mM), first order dependence on BT-DCAF concentration was observed following the linear relationship between the catalytic current Icat and the concentration of BT-DCAF (Figures 4c). In addition to TFA, phytic acid (PhytA, pKa = 1.92 in water) was also explored as proton source. PhytA also gives rise to an electrocatalytic wave when is incorporated into a solution of BT-DCAF as seen during CV measurements (Figures ) and is therefore interesting for H2 evolution applications. Employing a weak proton source such as AcOH (pKa = 4.76 in water) in combination with BT-DCAF did not lead to the same catalytic current during the electrochemical measurements (Figure ). The results using a series of proton sources with different acidities indicate that a strong proton source is needed to generate the electrocatalytic species derived of BT-DCAF. To verify the electrocatalytic reaction, controlled potential electrolysis was performed and gas chromatography was used to confirm the production of H2 gas. The electrocatalytic data is collected in Table . The charge passed after 4-hour electrolysis experiments with strong protons sources (Figures and) alongside with the amount of H2 gas produced during the reaction (Figures S20-S21) were significantly higher in the presence of BT-DCAF compared to control experiments in the absence of BT-DCAF. The production of H2 gas reached a maximum of 27 µmol during the electrolysis experiments. Faradaic efficiency (FE) up to 92% (±5.0) and turnover number (TON) up to 23 (± 4) were achieved in the presence of BT-DCAF. These values represent an improvement from the previous efforts of our group regarding H2 evolution with small organic system 2,1,3-benzothiadiazole-4,7-dicarbonitrile (BTDN) . These findings are also of comparable magnitude to other systems recently reported in the literature. BT-DCAF also shows satisfactory stability under controlled potential electrolysis conditions. We attribute the high stability to the molecular design of BT-DCAF, both the BT core and the caffeine motifs are electron deficient building blocks and the covalent linkage between the two enhances the stability of BT-DCAF towards any potential oxidation pathway. Furthermore, the two bulky caffeine groups provide steric hindrance that prevents dimerization reactions under electrocatalytic conditions. The molecular symmetric architecture of BT-DCAF delocalizes the electrons and also perform H2 production at mild potentials which in turn, also minimizes the possibility of catalyst decomposition. a Concentration of proton source was 100 mM.