The electrocatalytic hydrogen evolution reaction in the presence of a metal-free organic catalyst based on 1,10-phenanthroline: the first example of a reaction proceeding by an intramolecular mechanism

This article presents data on the electrocatalytic activity of new members of the metal-free electrocatalyst family, 1,10-phenathroline and N-methyl-1,10-phenathrolium iodide, for the hydrogen evolution reaction (HER) in the presence of perchloric acid (HClO4) and trifluoroacetic acid (CF3COOH). It has been shown that the efficiency and mechanism of the electrocatalytic process strongly depend on the nature of the catalyst and the pKavalue of the acids. In the presence of HClO4and 1,10-phenathroline, the cyclic voltammogram shows the appearance of two electrocatalytic waves, while in the case of N-methyl-1,10-phenathrolium iodide, only one wave is observed. In the presence of CF3COOH, only one electrocatalytic wave is observed for 1,10-phenathroline and no such waves are formed for the N-substituted salt. For the first time, the possibility of the HER occurring at different potentials, according to the same mechanism, has been shown: in the case of 1,10-phenathroline and perchloric acid, the hydrogen evolution reaction at potentials of E= −0.6 V and E= −0.25 V proceeds through the same key intermediates. Using the DFT method, the mechanisms of the occurring processes were studied, and key intermediates were identified.