Unexpected the Mechanistic Pathway of the Hydrogen Evolution Reaction in the Presence of N-Substituted Hydro-Derivatives of Ortho-Bipyridines

Abstract

Using cyclic voltammetry, the electrochemical properties and electrocatalytic activity in the reaction of molecular hydrogen formation in the presence of 2,2′-bipyridinium-1,1′-diium and 2,2′-bipyridinium-1-ium perchlorates were studied. The electrochemical reduction product of 2,2′-bipyridinium-1,1′-diium perchlorate decomposes to form molecular hydrogen, but in the case of 2,2′-bipyridinium-1-ium perchlorate, a two-electron reduction product is formed −(E)-1H,1′H-2,2′-bipyridinylidene. It has been shown that the hydrogen evolution reaction (HER) in the presence of 2,2′-bipyridinium-1,1′-diium and 2,2′-bipyridinium-1-ium perchlorates occurs at the same potentials but through different mechanisms. In both cases, the potential is −0.85 V according to the CECE mechanism, but at a potential of −1.25 V according to the ECEC mechanism. In both cases, the key intermediate, through which both mechanisms are realized, is (E)-1H,1′H-2,2′-bipyridinylidene.