Towards renewable production of CO and H₂O₂ in flow electrolyzers

The manufacturing industry relies on fossil fuels as a source of heat, C, and H atoms. Electrochemical processes powered by renewable energy can reduce this dependence on fossil fuels if integrated properly to the existing industry. Two examples are investigated in this thesis: (i) CO₂ electro-conversion to CO directly from model carbon capture solutions in bicarbonate electrolyzers to bypass energy-intensive CO₂(g) regeneration otherwise required for gas-fed electrolyzers; and (ii) anthraquinone hydrogenation for H₂O₂ production in a membrane reactor that sources H atoms from water electrolysis instead of carbon-intensive steam methane reforming. This thesis first investigates the role of the counter alkali cation in bicarbonate electrolyzers. The selectivity for CO formation increased with the ionic radius of the cation to reach a maximum of ~80% during electrolysis of 3 M CsHCO₃ solutions at 100 mA cm⁻². The identity of the cation has no impact on in-situ generation of electrochemically active CO₂. These results demonstrate the importance of the identity of the cation to maximize activity towards CO₂ electro-reduction in bicarbonate electrolyzers. This thesis then investigates the inclusion of enzymatic carbon capture promoters to the feedstock solution of the bicarbonate electrolyzer. 16% CO selectivity was achieved in presence of the enzyme at 100 mA cm⁻². This result is 3-fold lower than without the enzyme due to enzyme chemisorption on the electrocatalyst. The addition of hydrophobic layers on the cathode prevents the enzyme from poisoning the electrocatalyst. This thesis demonstrates successful integration of enzymatic carbon capture to bicarbonate electrolysis. The last part of this thesis demonstrates the hydrogenation of anthraquinones in a membrane reactor using water and electricity instead of methane-derived H₂(g). Membrane reactors separate the electrochemical reduction of H⁺ into H atoms from the hydrogenation of anthraquinones by a H-permeable Pd membrane. This physical separation enabled a 3-fold increase in hydrogenation rates compared to the previous benchmark in the field of electrochemical-derived anthraquinone hydrogenation. This thesis demonstrates 48 h of stable production of H₂O₂ from anthraquinones hydrogenated in the membrane reactor. These results testify to the power of membrane reactors to decarbonize the manufacturing industry.Science, Faculty ofChemistry, Department ofGraduat