Study of Pyridine-Mediated Electrochemical Reduction of CO sub(2) to Methanol at High CO sub(2) Pressure

The recently proposed highly efficient route of pyridine-catalyzed CO sub(2) reduction to methanol was explored on platinum electrodes at high CO sub(2) pressure. At 55bar (5.5MPa) of CO sub(2), the bulk electrolysis in both potentiostatic and galvanostatic regimes resulted in methanol production with Faradaic yields of up to 10% for the first 5-10Ccm super(-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 CO sub(2) concentration in the solution. No prominent contribution from either a direct or coupled CO sub(2) reduction was found. The results obtained suggest that the reduction of CO sub(2) to methanol is a transient process that is largely decoupled from the electrode charge transfer. Contents under pressure! The recently proposed highly efficient route of pyridine-catalyzed CO sub(2) reduction to methanol was explored at high CO sub(2) pressure. Although the higher CO sub(2) pressure results in higher reduction current, it does not lead to an increase of the methanol yield. Nearly all passed charge is consumed in the generation of hydrogen.