Electrochemical Behavior of Pyridinium and N‐Methyl Pyridinium Cations in Aqueous Electrolytes for CO₂ Reduction

Abstract

The electrochemical reduction of aqueous pyridinium and N‐methyl pyridinium ions is investigated in the absence and presence of CO2 and electrolysis reaction products on glassy carbon, Au, and Pt electrodes are studied. Unlike pyridinium, N‐methyl pyridinium is not electroactive at the Pt electrode. The electrochemical reduction of the two pyridine derivatives was found to be irreversible on glassy carbon. These results confirmed the essential role of the N−H bond of the pyridinium cation. In contrast, the electrochemical response of N‐methyl pyridinium ion at the glassy carbon electrode suggests that a specific interaction occurs between the glassy carbon surface and the aromatic ring of the pyridinium derivative. For all electrodes, an enhancement of current was observed in the presence of CO2. However, NMR spectroscopy of the solutions following electrolysis showed no formation of methanol or other possible byproducts of the reduction of CO2 in the presence of either pyridinium derivative ion.

Evaluation of Organic Hydride Donors as Reagents for the Reduction of Carbon Dioxide and Metal-Bound Formates

“…That pyridine is a catalyst for the electrochemical reduction CO 2 is controversial: First, most homogeneous catalysts do not catalyze electrochemical reduction of CO 2 beyond the two-electron level (thus carbon monoxide or formate are the normal reduction product(s)); second, pyridine is such a simple and readily accessible heterocycle. Third, several authors have found the experimental evidence suffers from a lack of reproducibility. − For noble metal electrodes, the consensus viewpoint has recently trended toward weak initial catalysis, followed by poisoning by produced carbon monoxide, which in sum leads to very poor turnovers. At semiconductor electrodes, photoelectrocatalysis of CO 2 reduction by pyridine is understood to be a heterogeneous process. ,, Other studies, however, do provide evidence that pyridine may be an important homogeneous catalyst, such as in the [Ru­(bpy) 3 ] 2+ -photosensitized production of methanol from CO 2 in the presence of pyridine catalyst without the use of electrodes, albeit with low turnover numbers. − The ongoing debate certainly indicates that simple heterocycles may possess OHD functionality useful in the electrochemical, and/or chemical, reduction of carbon dioxide.…”

Catalysis of CO2 Electrochemical Reduction by Protonated Pyridine and Similar Molecules. Useful Lessons from a Methodological Misadventure

“…−0.35 V vs SHE for the experimental value. There is no way to check experimentally the computed value because no corresponding one-electron response couple is observable on an inert electrode such as glassy carbon . However, the difference between the value and the potential where the reaction take place is so large that there is little doubt that the reaction cannot involve the intermediacy of PyH • .…”

Principal Descriptors of Ionic Liquid Co-catalysts for the Electrochemical Reduction of CO2

“…It should be noted, however, that not all ILs act as co-catalysts. Tetraalkylammonium and phosphonium salts were initially considered as co-catalysts but have since been questioned, and N -alkylpyridinium-based ILs do not function as co-catalysts. , Therefore, active non-functionalized ionic co-catalysts are currently limited to Im, pyrazolium, and pyrrolidinium ILs, each of which comprises a five-membered heterocycle.…”