Selective methanol oxidation for paired electrolysis

Electrochemical processes offer promising routes to defossilize the chemical industry by integrating low-carbon electricity. Industrial application is still hindered by high costs and the challenging transition from lab-scale research to industrial maturity. Key processes, such as cathodic hydrogen evolution and CO2 reduction, are typically paired with the anodic oxygen evolution reaction (OER). However, the generated oxygen holds little value, and the electrical costs associated with energy-intensive OER pose a significant economic barrier. This thesis explores selective methanol oxidation as a less energy-intensive alternative to OER for paired electrolysis, which yield value-added products from both anodic and cathodic reactions.Two paired processes were studied in electrochemical flow cells: Methanol oxidation to formaldehyde at platinum paired with CO2 reduction, and methanol oxidation to formate at hierarchically structured copper oxide paired with hydrogen evolution. Investigating both processes at conditions significantly exceeding previous studies in terms of electrode area, current density, and product concentration allowed novel insights into selective methanol oxidation and revealed crucial interactions within the paired systems. Furthermore, methanol oxidation was employed to introduce 'feed and bleed' as a versatile alternative to conventional batch and single-pass operation of electrochemical flow cells.Methanol oxidation to formaldehyde was strongly influenced by the oxidation state of the electrode with a higher Faraday efficiency for oxidized platinum (up to 58%), but a lower anodic potential for metallic platinum. Methanol oxidation to formate at optimized conditions achieved nearly 100% Faraday efficiency and up to 70% yield. The reaction conditions, in particular the conversion, had a critical impact on the selectivity for formate. In both paired processes, methanol oxidation required less electrical energy than conventional OER and provided value-added products with substantial yields. Interactions between the anode and cathode side, such as ion transfer and the crossover of water and reactants were found to be crucial for the stability of the paired processes, especially at high product concentrations. Building on the findings on methanol oxidation, the 'feed and bleed' operating mode was established enabling the investigation of reactions in steady state at high product concentration.The present work highlights the benefits of paired electrolysis and provides valuable insights on selective methanol oxidation to formaldehyde and formate with yields and product concentrations exceeding the previous state of the art. Challenges arising from high product concentration and adverse interactions within the paired process were identified and discussed. The methodological aspects of this work can be applied to the investigation of other electrochemical processes under industrially relevant conditions and thus contribute to the overarching goal of bringing sustainable processes to industrial application.