Search

Porous gas‐diffusion electrodes (GDEs) are widely used in electrochemical applications where a gaseous reactant is converted to a target product. Important applications for silver‐based GDEs are the chlor‐alkali and the CO2 electrolysis processes in which silver catalyzes the oxygen‐ or carbon dioxide reduction reaction. The wetting of the porous GDEs is of utmost importance for the achieved performance of the electrode: a completely dry electrode will result in low current densities due to the reduced active surface area while on the other hand, a completely flooded electrode will deteriorate the access of the gaseous reactant. Therefore, we investigated silver‐based GDEs for the oxygen reduction reaction with different amounts of the hydrophobic agent polytetrafluoroethylene (PTFE) and analyzed the potential‐induced wetting behavior (electrowetting). The electrolyte breakthrough was recorded by a digital microscope and subsequently evaluated via imaging analysis of the observed breached electrolyte droplets. In order to characterize the wetting state during transition to the steady‐state, we applied electrochemical impedance spectroscopy measurements and retrieved the double‐layer capacitance. Our results indicate that a higher overvoltage facilitates the breakthrough of electrolytes through the gas‐diffusion electrode. Surprisingly, a faster breakthrough of electrolyte was observed for electrodes with higher PTFE content. Porometry measurements revealed that the GDE with low PTFE content has a monomodal pore size distribution, whereas electrodes with higher PTFE amount exhibit a bimodal pore size distribution. In GDEs with monomodal pore size distribution the time in which the double layer capacitance is leveling off correlates with the breakthrough time of the electrolyte. In summary, we emphasize that the wetting of GDEs is a complex interplay of the applied potential, electrode composition, and resulting porous structure which requires further advanced measurements and analysis considering the parameters affecting the wetting behavior as a whole. [ABSTRACT FROM AUTHOR]

The open architecture of cathodes in Li–air batteries implies the need for open porosity with adequate pore size distribution and surface energy optimization with regard to the electrolyte. The interaction of liquid and cathode material, especially the wetting properties, which depend on cathode material, roughness and porosity, and electrolyte properties, needs to be understood properly to avoid flooding and assure high active areas. In this work, contact angle goniometry, capillary rise method, and pressure saturation curves are used to investigate the wetting properties of dimethyl sulfoxide (DMSO), tetraethylene glycol dimethyl ether (Tetraglyme), a 1:1 mixture of ethylene carbonate and dimethyl carbonate (EC:DMC) and water on a gas diffusion layer (GDL) Sigracet 39BC, and a pure flat polytetrafluorethylene (PTFE) foil. Contact angle measurement shows that all three organic solvents wet the GDL hydrophobic agent PTFE. Capillary rise measurements show that all sample liquids slowly imbibe into the porous network. While for Tetraglyme an efficient penetration is limited by the high viscosity, water flow rate is slowed down by the hydrophobic pore network of the GDL. Pressure saturation curves for DMSO, Tetraglyme, and EC:DMC can be obtained for the first time and are compared with the water pressure saturation curve. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO2 to useful chemicals can change the role of CO2 from harmful waste to a valuable feedstock. Despite a lot of progress in the alkaline electrochemical conversion of CO2 to formate, there is still a lack of potential applications for the generated aqueous formate solution. Here, the general ability of formate to be used as an energy or hydrogen carrier is discussed and compared to well‐known energy storage chemicals. Concepts to employ formate solution as an energy carrier by combining CO2 electrolysis with the reconversion of formate into electricity via a direct formate fuel cell or catalytic decomposition to H2 combined with a proton exchange membrane fuel cell are demonstrated. [ABSTRACT FROM AUTHOR]