Control of the microenvironment by ionomers to increase the CO selectivity during CO2 electrolysis at Ag-based gas-diffusion electrodes

• Applicants: Professorin Dr.-Ing. Christina Roth; Professor Dr.-Ing. Thomas Turek
• Subject Area: Chemical and Thermal Process Engineering ; Technical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 547492927

The electrochemical reduction of CO2 (eCO2R) is a promising technology in the fight against climate change. It allows excess renewable energy to be used to produce valuable base chemicals from CO2, providing a process with a net negative carbon balance. Gas diffusion electrodes (GDEs) are essential to ensure efficient transport of CO2 to the catalytically active centers of the electrode. Silver-based GDEs are of particular interest in current research, as they have a very high selectivity for the formation of CO and already enable technically relevant current densities. The structure and hydrophobicity of the GDEs play a decisive role here in regard to performance. While conventional production methods such as airbrushing have limitations in terms of controlling the hydrophobic and hydrophilic areas in the GDE, dynamic gas bubble templation (DHBT) offers an alternative method for producing tailored metal foams. These structured electrodes can be adapted for use in eCO2R by specifically modifying the microenvironment, e.g. by adding ionomers. The proposed project focuses on the development of efficient GDEs for eCO2R based on this method. The main aim of the project is to investigate the influence of ion-conducting polymers on the microenvironment in silver-based GDEs and the mechanism of action in eCO2R to CO to increase selectivity and stability. Various effects are postulated as the cause of the positive influence. These include influencing the wettability of the GDE through the hydrophobicity of the ionomers, influencing the local concentration of dissolved CO2 within the GDE and influencing the local pH value. The work plan includes several steps. First, a standardized measurement environment is to be established at both project partners. This should ensure that the results obtained in the course of the project are always comparable. Subsequently, the influence of different ionomer types and ionomer concentrations will be investigated in targeted measurement programs. For this purpose, GDEs are to be produced and characterized physically and electrochemically in comprehensive experiments. In a further work package, an existing mathematical electrode model for eCO2R will be modified to accurately reflect the influence of the ionomers. Furthermore, validation data will be generated in experiments in order to be able to carry out parameter adjustments by model fitting. Ultimately, the results obtained will help to clarify the postulated effects of ionomers on the microenvironment in the GDE and the reaction mechanism of eCO2R to CO.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Ingo Manke