Metal-based gas diffusion electrodes are utilized in chlor-alkali electrolysis or electrochemical reduction of carbon dioxide, allowing the reaction to proceed at high current densities. In contrast to planar electrodes and predominantly 2D designs, the industrially required high current densities can be achieved by intense contact between the gas and liquid phase with the catalytically active surfaces. An essential asset for the knowledge-based design of tailored electrodes is therefore in-depth information on electrolyte distribution and intrusion into the electrode's porous structure. Lab-based and synchrotron radiography allow for monitoring this process operando. Herein, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the oxygen reduction reaction and the electrochemical reduction of CO2 as exemplary and currently very relevant examples of gas-liquid reactions by only minor modifications to the cell set-up. With the reported cell design, we were able to observe the electrolyte distribution within the gas diffusion electrode during cell operation in realistic conditions.

One of the challenges of high-temperature polymer electrolyte membrane fuel cells is the poisoning of the Pt catalyst with H3PO4. H3PO4 is imbibed into the routinely used polybenzimidazole-based membranes, which facilitate proton conductivity in the temperature range of 120–200 °C. However, when leached out of the membrane by water produced during operation, H3PO4 adsorbs on the Pt catalyst surface, blocking the active sites and hindering the oxygen reduction reaction (ORR). The reduction of H3PO4 to H3PO3, which occurs at the anode due to a combination of a low potential and the presence of gaseous H2, has been investigated as an additional important contributing factor to the observed poisoning effect. H3PO3 has an affinity toward adsorption on Pt surfaces even greater than that of H2PO4 –. In this work, we investigated the poisoning effect of both H3PO3 and H3PO4 using a half-cell setup with a gas diffusion electrode under ambient conditions. By means of in situ X-ray absorption spectroscopy, it was possible to follow the signature of different species adsorbed on the Pt nanoparticle catalyst (H, O, H2PO4 –, and H3PO3) at different potentials under ORR conditions in various electrolytes (HClO4, H3PO4, and H3PO3). It was found that H3PO3 adsorbs in a pyramidal configuration P­(OH)3 through a Pt–P bond. The competition between H3PO4 and H3PO3 adsorption was studied, which should allow for a better understanding of the catalyst poisoning mechanism and thus assist in the development of strategies to mitigate this phenomenon in the future by minimizing H3PO3 generation by, for example, improved catalyst design or adapted operation conditions or changes in the electrolyte composition.

Ag catalysts show high selectivities in the conversion of carbon dioxide to carbon monoxide during the electrochemical carbon dioxide reduction reaction (CO2RR). Indeed, highly catalytically active porous electrodes with increased surface area achieve faradaic conversion efficiencies close to 100%. To establish reliable structure-property relationships, the results of qualitative structural analysis need to be complemented by a more quantitative approach to assess the overall picture. In this paper, we present a combination of suitable methods to characterize foam electrodes, which were synthesised by the Dynamic Hydrogen Bubble Templation (DHBT) approach to be used for the CO2RR. Physicochemical and microscopic techniques in conjunction with electrochemical analyses provide insight into the structure of the carefully tailored electrodes. By elucidating the morphology, we were able to link the electrochemical deposition at higher current densities to a more homogenous and dense structure and hence, achieve a better performance in the conversion of CO2 to valuable products.

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An Mischungen aus C8F17SO3N(CH3)4 und C14H25SO4N(CH3)4 wurden thermodynamische und kinetische Messungen durchgeführt, aus denen Informationen über das dynamische Verhalten der vorliegenden Mizellen erhalten wurden. Die CMC‐Werte der beiden reinen Komponenten sind 1, 25 · 10−3 m und 1, 4 · 10−3 m. Die CMC‐Werte der Mischungen liegen höher, jedoch niedriger als zu erwarten wäre, wenn sich keine gemischten Mizellen bilden könnten. Dieses Ergebnis zeigt damit eindeutig die Existenz gemischter Mizellen an. Aus den kinetischen Daten geht hervor, daß die gemischten Mizellen wesentlich niedrigere Aggregationszahlen besitzen als die Mizellen aus den reinen Komponenten. Insbesondere sind die großen stäbchenförmigen Aggregate, die in den Lösungen der reinen Perfluortenside für das viscoelastische Verhalten verantwortlich sind, nicht mehr nachzuweisen. Die gemischten Mizellen sind auch kleiner als die Tetradecylsulfatmizellen. Die mittlere Verweilzeit der Tenside ist in den gemischten Mizellen bedeutend kürzer als in den Mizellen der reinen Verbindungen. Ähnliche Folgerungen ergeben sich auch an Mischungen der Li‐Salze der beiden Tensidionen. Aus diesen Resultaten geht weiterhin hervor, daß die Löslichkeit eines perfluorierten Tensid‐ions in einer Mizelle aus Normaltensiden größer ist als die Löslichkeit eines normalen Tensid‐ions in einer perfluorierten Mizelle.