Production and characterization of gas diffusion electrodes for CO2 reduction to formic acid

Sustainable conversion of CO2 to formic acid by an electrochemical process, often called artificial photosynthesis due to the O2 produced at the counter electrode, can help to reduce the CO2 emission from industrial production sites. The produced formic acid can be used for a wide variety of applications in the pharmaceutical and chemical industry or it can be stored and converted back to electrical energy via a fuel-cell like device. Thus, this process can help to stabilize the power-grid during peak-times by providing control power. The basic idea of this process is the well-known concept of power to chemicals to store energy and additionally reduce CO2 emissions. By using carbon supported Sn/SnOx gas diffusion electrodes (GDE), an efficient electrochemical conversion of CO2 to formic acid can be realized. The porous structure of the GDEs strongly affects the electrochemical performance of these GDEs. In detail, the intrusion of the electrolyte and CO2 into the electrode has a considerable influence onto the cathodes physicochemical characteristics. The intrusion behaviour of the electrolyte was investigated to determine the inner hydrophobicity, by using a combination of the Lucas-Washburn and Owens-Wendt method. To further investigate the penetration behaviour a custom-made cell was used to measure the capillary pressure. Additionally iridium oxide based electrodes are used as anodes for the oxygen evolution reaction (OER) and optimized regarding their electrochemical performance. With these anodes and the above mentioned GDEs a continuous working full-cell set-up can be realized. The full-cell set-up was investigated by polarization, cyclic voltammetry and electrochemical impedance spectroscopy