Metal-based gas diffusion electrodes (GDE) are utilized to achieve high current densities during the reaction in energy conversion systems, such as chlor-alkali electrolysis or the electrochemical reduction of carbon dioxide. By intense contact between the liquid and the gas phase with the catalytically active surfaces within the metallic electrodes, industrially required current densities can be accomplished. Their almost bulk-like silver structures with the 3D porous design and the strong absorption of the extended material make radiographic measurements extremely demanding. To receive in-depth information on electrolyte intrusion into the electrode's porous structure and the distribution during electrochemical measurements, lab-based and synchrotron radiography allows for monitoring this process operando ^{1, 2}.

In this work, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the ORR and the CO₂RR as exemplary and currently very relevant examples of gas-liquid reactions. The applied half-cell set-up designed for ORR allowed for operando synchrotron radiation measurements at electrochemically stable operation at viable industrial conditions and current densities to follow the electrolyte distribution within Ag-based GDE during chlor-alkali-electrolysis. By adding one additional electrolyte compartment, extending the X-ray window, and implementing an anion exchange membrane, the in-house built half-cell set-up designed for operando synchrotron radiation measurements of ORR, was converted into a full-cell set-up for imaging CO₂RR of strongly absorbing metal-based GDEs. With the reported cell design, we were able to observe the electrolyte distribution within GDEs during cell operation at technically relevant current densities for CO₂RR up to 300 mAcm^-2 (Figure 1). By high-resolution synchrotron radiation operando measurements, we demonstrated crystallization of electrolyte caused by the hydrophobic character of the GDE. At high overpotentials, hydrogen evolution reaction caused blockade of the Ag-based GDE, resulting in declining current densities, which could be imaged and monitored during realistic potentiostatic operation.

1. M. C. Paulisch, M. Gebhard, D. Franzen, A. Hilger, M. Osenberg, S. Marathe, C. Rau, B. Ellendorff, T. Turek, C. Roth and I. Manke, ACS Appl. Energy Mater., 4(8), 7497–7503 (2021).
2. M. Gebhard, M. Paulisch, A. Hilger, D. Franzen, B. Ellendorff, T. Turek, I. Manke and C. Roth, Materials (Basel, Switzerland), 12(8) (2019).