Investigation of electrochemical reactions at a molecular level : a combined electrochemical, infrared and DFT study

Abstract

Hydrogen evolution reaction (HER) on Ag electrode in neutral and alkaline solution is significantly accelerated by the addition of 4,4’-bipyridine (BiPy). The mechanism of the HER acceleration is discussed at a molecular level by using surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with electrochemical techniques and density functional theory (DFT) calculations. Simultaneous SEIRAS and electrochemical measurements revealed that the onset potential of the accelerated HER coincides with the 1e^- + 1H⁺ reduction potential of adsorbed BiPy to yield monohydro BiPy (BiPy-H^*) and that both BiPy and BiPy-H^* are oriented perpendicular to the electrode via one N-end. The detailed electrochemical data indicates that BiPy-H^* is further reduced via an additional 1e^- +1H⁺ step. DFT calculation showed that generated N,N-dihydro BiPy (BiPy-H₂) is unstable and easily decomposes to BiPy and H₂. Since adsorbed BiPy is readily reduced again to BiPy-H^* in the potential range of HER, the reaction process is catalytically cycled.