Electrochemical valorization of sustainable feedstocks using metal-based gas diffusion electrodes

In this thesis, we investigated the electrochemical reduction of sustainable feedstocks to utilize (a surplus of) renewable energy in synthesis of value-added chemicals.
In Chapter 1, an extensive background is provided on the motivation to employ electrochemistry as a tool to convert greenhouse gases such as CO2 and biomass-based molecules into chemicals and fuels.
In Chapter 2, we investigated the effect of the catalyst ink composition on the electrochemical reduction of CO2 towards ethylene using Cu-based gas diffusion electrodes. We conclude that aprotic solvents (DMSO and NMP) prevent ionomer polymerization, leading to a homogeneous catalyst layer and optimum performance towards ethylene (FEC2H4 = 27%), while protic solvents (IPA and EG) induce copper agglomeration and coverage of catalyst particles by the Nafion polymer, decreasing FEC2H4 to 13%, enhancing formation of CO.
In Chapter 3, we extended the use of Cu-GDEs in bicarbonate solutions to investigate the effect of the mass transport mechanism, the ionic membrane and ionomer content in the ink used to prepare the GDEs, on selectivity towards CO and catalyst stability. We reported an outstanding FECO of 85% by using convective CO2 supply (flow through), far above the FECO obtained via diffusive CO2 supply (FECO = 64%).
In Chapter 4, we addressed the effect of imidazolium-based cations when added to common bicarbonate electrolytes on Au-GDEs, in the electrochemical reduction of CO2. Surprisingly, the addition of imidazolium species to bicarbonate solution induced reduction of HCO3- to form H2. By using Raman spectroscopy, we observed an increased concentration of methyl-methylimidazolium and bicarbonate on the surface of Au in the potential region where H2 was mainly formed.
In Chapter 5, we investigated the electrochemical hydrogenation (ECH) of bio-oil model molecules (butyraldehyde and crotonaldehyde) on polycrystalline copper electrodes. We conclude that butanal species adsorb vertically on copper surfaces via formation of carboxylate, which is further reduced to 1-butanol (FE > 90%), while unsaturated aldehydes such as crotonaldehyde adsorb parallel to the copper surface, interacting through both C=C from the aliphatic chain and the C=O carbonyl group.
Finally, Chapter 6 presents an outlook and perspectives for future research in the field.