Abstract
Until recently, investigations into the electrochemical reduction of CO2 have tended to focus on thereactivity of the catalyst in an electrochemical cell known as an H-cell. While H-cells are a convenient
way to screen catalysts, they also impose mass transport limitations on the reaction. The formation
of products containing multiple carbon-carbon bonds is also a great challenge with Cu and Cu-based
catalysts being the most active and selective but still exhibit insufficient performance for commercial
utilisation. In this work, the CO2 reduction behavior of a commercial benchmarked catalyst, Sn, and a
range of novel catalysts Pt1-xFex,are examined in both H-cells and gas-diffusion electrolysers (GDEs).
For Sn, the choice of ionomer was shown the be highly influential in H-cell experiments, with the
cation-exchange ionomer resulting in double the faradaic efficiency towards formate versus the
anion-exchange ionomer, however no significant difference was found between the ionomers in the
GDE, highlighting that optimisations with a H-cell do not necessarily map to GDEs.
In the case of Pt1-xFex, formate, methanol and acetate were detected using H-cells at low
overpotentials of -0.13 V vs RHE. In particular, Pt20Fe80 produced methanol with a faradaic efficiency
as high as 85% in 0.5 M KHCO3. When applied in gas-diffusion electrolysers, acetate faradaic
efficiencies reached up to 60% and the formation of C3 compounds, propanol and propanoic acid
were also detected. Pt20Fe80 produced propanol at a faradaic efficiency of 18% with an associated
partial current density of 6 mA cm-2 which places it among the best catalysts in the field.
DFT investigations were conducted with vacuum, implicit solvation and explicit solvation and found
that explicit solvent molecules were highly influential on the relative stabilities of CO2 and its
reduction intermediates via the donation of charge through their hydrogen bonding network.
Moreover, the relative adsorption energy of CO2, CO and CHO/COH was found to increase with
respect to the high Pt composition which correlates with the experimental finding that high iron
compositions were more active towards CO2 reduction
| Date of Award | 28 Sept 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David J Fermin (Supervisor) & Alberto Roldan (Supervisor) |