Electrochemical mass spectrometry study of the pyridine/pyridinium in the CO2 electroreduction reaction on copper electrodes

Abstract

The role of pyridine and its protonated form, pyridinium, in the CO2 Electroreduction Reaction (CO2ER) is a long-discussed subject, with controversies concerning whether pyridinium act as a catalyst or is merely participating as a proton source for hydrogen evolution reaction. The pyridine electroactivity is often discussed in terms of faradaic currents from cyclic voltammetry, in which the catalytic effect of pyridine is characterized by a well-defined cathodic current peak. The analysis is not straightforward, and a deeper look is especially needed when dealing with complex systems such as CO2ER. To get further insight, we examine the electrochemical behavior of the pyridine/pyridinium pair with the aid of online mass spectrometry coupled to an electrochemical cell (EC-MS) on a polycrystalline copper electrode. Copper is a unique metal, capable to generate a variety of volatile hydrocarbons such as methane and ethylene during CO2ER. For this reason, this metal was selected to investigate the CO2ER in the presence and absence of pyridine by monitoring the mass fragments of H2 (m/z = 2), CH4 (m/z = 15), C2H4 (m/z = 26) and pyridine (m/z = 26, 52 and 79). Our findings validate the discussion of pyridine promoting the formation of dihydrogen (H2) via pyridinium deprotonation, as evidenced by ionic currents signals of both H2 and pyridine. Furthermore, clear evidence of pyridine enhancing CO2ER was not detected in the formation of any measurable product.