Investigation of Gas Diffusion Electrode systems for the electrochemical CO2 conversion

In the context of climate change and carbon management, electrochemical CO2 reduction represents a promising solution. In this study, the electrochemical conversion of CO2 under atmospheric conditions has been performed in a continuous flow gas diffusion electrode (GDE)-based cell configuration. A porous and conductive support has been employed to this end, where a Cu-based catalyst has been manually deposited in a GDE by means of an airbrusher. With the aim to increase the production of CO2 reduction liquid products, several variables of the studied system have been assessed. The most promising conditions have been explored among the applied potential, catalyst loading, Nafion content, KHCO3 electrolyte concentration and the presence of metal oxides, like ZnO or/and Al2O3. In particular, it has been found that the binder content has affected the production of CO, leading to syngas with a H2/CO ratio of ⁓1 at the lowest Nafion content (15%). In contrast, the highest Nafion content of 45% has led to an increase of C2+ products formation and a decrease of CO selectivity by 80%. The obtained results revealed that liquid crossover affects the GDE performance by severely compromising the CO2 transport to the active sites of the catalyst, thus reducing the CO2 conversion efficiency. A mathematical model confirmed the role of a high local pH, combined with electro-wetting, in promoting the formation of bi-carbonate species: salts formation may cause the catalyst deactivation and hinder the mechanisms for C2+ liquid products. The ultimate intent of this work is to direct the attention of the scientific community to other involved factors of the CO2 reduction process rather than the catalytic activity of the materials, which can impact on both kinetics and mass transport and in turns on the final efficiency of this kind of devices.