Cathodic Hydrogen Evolution Reaction on Gold Catalyzed by Proton-Carriers

Several amines with aromatic and aliphatic substituents have been investigated as catalysts in the solution for the hydrogen evolution reaction, based on their ability to increase the concentration of protons in the electric double layer at the interface, by transporting protons from the bulk solution to the cathode surface. The highest electrocatalytic activity, expressed by the activation energy for hydrogen evolution reaction has been obtained for methylamine, 4-chloroaniline and aniline. In this series, the catalytic activity is primarily influenced by the molecular coverage area, which determines the number of protonated molecules that can adsorb on the cathode surface. The second factor that affects catalytic activity is the magnitude of the dipole moment, which determines a preferential orientation of the protonated molecule at the interface. As a consequence, methylamine shows the highest catalytic activity due to its low coverage area and 4-chloroaniline has a stronger effect than aniline due to its larger dipole moment induced by the electron-withdrawing inductive effect of chlorine. A mechanism for hydrogen evolution reaction in the presence of amines has been proposed, where both hydronium and ammonium ions are involved in the charge transfer process.