Investigation of Gas Diffusion Electrode Systems for the Electrochemical CO2 conversion

In the context of the strategies needed to mitigate CO2 emissions and combat climate change, electrochemical CO2 reduction represents a promising alternative. This approach offers an interesting opportunity to capture and store renewable electricity and CO2 in the form of chemicals and fuels. Until some years ago, researchers focused their work observing the effects of surface modification (e.g. nano-structuring and surface tailoring) on catalyst selectivity and activity. To date, few studies have been carried out on the overall system design. In order to overcome the limitations of operation with dissolved CO2 and to pursue commercially-relevant current densities, several reactor architectures are being addressed: among those, GDE-based systems and MEA are widely studied designs. This thesis work fits in this context: a GDE-cell configuration was studied, where CO2 electroreduction was performed on integrated Cu-based electrocatalysts. Individual aspects of this challenging device were considered to understand their impact on the performance and to identify the optimal solution, specifically: catalyst loading, binder content, type of catalyst, cell configuration. With Cu-06 based GDE, the best results in terms of FE and productivity towards liquid products have been obtained: at j=4.7 mA cm-2 and at a catalyst loading of 0.4 mg cm-2, the FE to formate was 13% and its productivity 26 mmol h-1 gcat-1. Additionally, this was the only case where production of methanol was visible. An in-depth theoretical study has been carried out, focusing on frequent failure modes in flow electrolyzers and proposing solutions to improve the reduction process through (i) electrode structure, (ii) experimental layout, (iii) regulation of the operating pressure. Furthermore, the role of pH on the course of reactions was investigated noting that surface pH usually differs from its bulk value.