Significant research efforts have been directed towards exploring electrocatalysts for the selective reduction of CO2 to fuels such as methanol. Bocarsly et al (Princeton University) have recently reported the use of aromatic amines (e.g. pyridine (C5H5N)) as electrocatalysts in aqueous electrolytes for the reduction of CO2 at low overpotentials (50-150 mV). Importantly, the CO2-pyridine reduction process was claimed to selectively produce methanol with Faradaic efficiencies of ~100% on p-GaP electrode and 22-30% on Pt and Pd electrodes. Moreover, the initially proposed mechanism based on a radical intermediate interaction with CO2 as a key step toward the production of methanol was subsequently disproved. In this project, methanol formation by the CO2-pyridine (C5H5N) system was assessed by conducting electrolysis under various conditions at platinum electrodes. High pressure CO2 was used with the aim of increasing the methanol yield. In the course of the present study, the bulk electrolysis confirmed the methanol production at 1 bar and at 55bar of CO2 in the presence of pyridine. However, the methanol yield was found to be persistently limited to sub-ppm level (< 1ppm) under all conditions investigated. The observed methanol yield limitation could not be overcome by the electrode reactivation techniques used. Moreover, the methanol formation seemed unaffected by the current density or the biasing mode. This was an indication of the independence of methanol production from the charge transfer on the electrode. In agreement with these observations, analysis of the voltammetric data supported by simulation revealed that the CO2-pyridine reduction system is mainly pyridinium assisted molecular hydrogen production under all conditions investigated. In particular, protonated pyridine (C5H5N) ‘pyridinium’ was confirmed to behave as a weak acid on platinum. It was found that CO2 is merely a proton source of pyridine reprotonation via the hydration reaction followed by carbonic acid dissociation. The reprotonation reaction coupled to the electrode reaction ultimately leads to the dihydrogen production. No direct contribution of CO2 in the reduction process was observed. The production of methanol seems to occur chemically rather than directly driven by the charge transfer on the electrode. The role of pyridine (C5H5N) appears to be restricted to assisting in the generation of the hydrogen necessary for the alcohol production.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:762064 |
| Date | January 2015 |
| Creators | Touhami, Dalila |
| Contributors | Rybchenko, S. I. ; Haywood, S. K. |
| Publisher | University of Hull |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hydra.hull.ac.uk/resources/hull:16572 |
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