The Role of Surface Hydrogen Atoms in the Electrochemical Reduction of Pyridine and CO2 in Aqueous Electrolyte

The present study aims to get more insight into the role of pyridinium ions, surface H atoms and the nature of the electrode surface for the electrochemical reduction of CO2. The electrochemical activity of pyridinium ions in the absence and presence of CO2 is investigated on Ir, Pt, Au and glassy carbon electrodes. Glassy carbon and Au electrodes show irreversible reduction of pyridinium characterized by a cathodic peak potential. In the further presence of CO2, an increase of the current is noticed and the overall reduction process remains irreversible. In contrast, cyclic voltammograms recorded on an Ir electrode in a pyridine solution under nitrogen and CO2 are quasi-reversible and consistent with the participation of H atoms adsorbed onto the electrode surface. Cyclic voltammograms for Ir and Pt electrodes are similar, as expected for metals with a strong affinity for hydrogen. Our results suggest that adsorbed H atoms may play a key role in the electrochemical reduction of CO2.