Study of Pyridine‐Mediated Electrochemical Reduction of CO₂ to Methanol at High CO₂ Pressure

Abstract

The recently proposed highly efficient route of pyridine-catalyzed CO2 reduction to methanol was explored on platinum electrodes at high CO2 pressure. At 55 bar (5.5 MPa) of CO2 , the bulk electrolysis in both potentiostatic and galvanostatic regimes resulted in methanol production with Faradaic yields of up to 10 % for the first 5-10 C cm(-2) of charge passed. For longer electrolysis, the methanol concentration failed to increase proportionally and was limited to sub-ppm levels irrespective of biasing conditions and pyridine concentration. This limitation cannot be removed by electrode reactivation and/or pre-electrolysis and appears to be an inherent feature of the reduction process. In agreement with bulk electrolysis findings, the CV analysis supported by simulation indicated that hydrogen evolution is still the dominant electrode reaction in pyridine-containing electrolyte solution, even with an excess CO2 concentration in the solution. No prominent contribution from either a direct or coupled CO2 reduction was found. The results obtained suggest that the reduction of CO2 to methanol is a transient process that is largely decoupled from the electrode charge transfer.

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

“…Therefore, in our experimental electrolysis conditions either methanol is not formed or its concentration too low to be detected by 1 H NMR spectroscopy. Note that in all cases the charges passed during electrolysis (Table ) are in the same order as those reported in the literature (between 4 and 64 C cm −2 ) but without methanol formation in our conditions . Control experiments by injection of methanol (2 m m ) into a solution containing pyridine at the beginning of electrolysis revealed that the methanol concentration remained unchanged over a 25 h electrolysis (Figure S4).…”

“…The absence of a CO stripping peak by cyclic voltammetry could be explained by the low CO surface concentration owing to the decrease of CO adsorption at the profit of pyridine adsorption of pyridine on Pt . Nonetheless, CO adsorption might poison the Pt surface, as reported for Pt electrodes …”

“…For ANHs, recent investigations have mainly focused on the electrochemical behavior of pyridine toward CO 2 reduction and the role of the electrode surface in the reaction mechanisms . The pyridinium cation (PyrH + ) has been reported to be an effective catalyst for the electrochemical reduction of CO 2 at metal electrodes such as Pd and Pt .…”

“…The pyridinium cation (PyrH + ) has been reported to be an effective catalyst for the electrochemical reduction of CO 2 at metal electrodes such as Pd and Pt . Furthermore, several recent studies have discussed possible reaction mechanisms that take place on these different electrode materials and some of these are illustrated in Scheme ,. The first mechanism for the catalytic effect of pyridinium ions proposed by Bocarsly and co‐workers suggested that PyrH + reduction on a Pt electrode produced the pyridinyl radical (PyrH . )…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…In this study56 they concluded that pyridinium is reduced on a Pt electrode, including a pyridinium‐bound proton to form a surface hydride which was further supported by the work of Batista 57. Indeed, the study from Bocarsly and co‐workers55 created more controversy in the field and drove several studies 58, 59, 60, 61. Another study was conducted by Savéant and co‐workers arguing the plausibility of this catalytic process 62.…”