Highly active screen-printed Ir-Ti4O7 anodes for proton exchange membrane electrolyzers.

Electroceramic support materials can help reducing the noble-metal loading of iridium in the membrane electrodes assembly (MEA) of proton exchange membrane (PEM) electrolyzers. Highly active anodes containing Ir-black catalyst and submicronic Ti4O7 are manufactured through screen printing technique. Several vehicle solvents, including ethane-1,2-diol; propane-1,2-diol and cyclohexanol are investigated. Suitable functional anodic layer with iridium loading as low as 0.4 mg cm-2 is obtained. Surface properties of the deposited layers are investigated by atomic force microscopy (AFM). The most homogeneous coating with the highest electronic conductivity is obtained using cyclohexanol. Tests in PEM electrolyzer operating at 1.7 V and 40 °C demonstrate that the CCM with anode coated with cyclohexanol presents a 1.5-fold higher Ir-mass activity than that of the commercial CCM

Influence of Platinum Precipitation on Properties and Degradation of Nafion® Membranes

In this study, the role of Pt concentration and distribution in the membrane on ionomer degradation was investigated. Nafion® membranes were impregnated with different mass fraction of Pt via ion-exchange and operated as membrane electrode assemblies (MEAs) at open circuit voltage (OCV). Various MEAs with known Pt concentration were characterized by electrochemical in-situ measurements regarding both, membrane properties and ionomer degradation. Additionally, Pt particle distribution in the membrane cross sections was analyzed. The presence of Pt precipitations was found to influence ionic conductivity and the sensitivity of cell performance for humidification. Ionomer decomposition increased with concentration and surface area of Pt deposits as well as distance between particles. The comparison between Pt precipitated artificially and during operation showed a considerable difference in particle distribution and extent of internal membrane humidification due to water formation at Pt sites

Investigation of rechargeable lithium-sulfur batteries by in-situ techniques: Insight into interfacial processes

The lithium-sulfur (Li-S) battery is currently of great interest for the research community. This battery promises with its high theoretical capacity (1675 mA h-1) and energy density (2600 Wh kg-1) to be one of the energy storage systems of the future. Nevertheless, the electrochemical processes and degradation mechanisms of the cell are still not well understood. In this work, in-situ characterization methods were applied for the characterization of reaction products and changes in the electrode properties. By means of XRD, the formation of reaction products during charging and discharging was monitored in operando. The formation of di-lithium sulfide and the recrystallization of sulfur have been semi-quantitatively determined. The electrochemical behavior of the cell was also investigated using electrochemical impedance spectroscopy (EIS) at different depths of discharge and charge; and up to 50 cycles. An electrical circuit is proposed to quantify the impedance contribution of the cell. Changes in the electrolyte resistance and charge transfer resistance due layer formation on the electrode are amongst others the analyzed processes in this research. Furthermore, ex-situ atomic force microscopy (AFM) measurements provide information about changes in the electrical conductivity of the cathode surfac

Investigation of rechargeable lithium-sulfur batteries by in-situ techniques

The lithium-sulfur (Li-S) battery is currently of great interest for the research community. This battery promises with its high theoretical capacity (1675 mA h-1) and energy density (2600 Wh kg-1) to be one of the energy storage systems of the future. Nevertheless, the electrochemical processes and degradation mechanisms of the cell are still not well understood. In this work, in-situ characterization methods were applied for the characterization of reaction products and changes in the electrode properties. By means of XRD, the formation of reaction products during charging and discharging were monitored in operando. The formation of dilithium sulfide and the recrystallization of sulfur have been semi-quantitatively determined. The electrochemical behavior of the cell was also investigated using electrochemical impedance spectroscopy (EIS) at different depths of discharge and charge; and up to 50 cycles. An electrical circuit is proposed to quantify the impedance contribution of the cell. Changes in the electrolyte resistance and charge transfer resistance due layer formation on the electrode are amongst others the analyzed processes in this research. Furthermore, ex-situ atomic force microscopy (AFM) measurements provide information about changes in the electrical conductivity of the cathode surface

Analysis of Fuel Cell and Electrolyzer Components with Nanoelectrical and Nanomechanical AFM

Electrochemical energy converters are getting more and more important in the near future since the transition to sustainable energy sources is progressing. For an improvement of these technologies a precise knowledge about their structure and functionality at the nanoscale is crucial. This talk will provide insight into the application of nanoelectrical and nanomechanical atomic force microscopy for analysis of fuel cell and electrolysis components. In particular, spatially resolved imaging of the different constituents and structural analysis of the complex catalytic layers will be discussed

Atomic Force Microscopy

Although atomic force microscopy (AFM) is an ex situ technique, the measuring conditions can be chosen rather close to operating conditions in a PEM fuel cell. The flexibility in the analyzed areas allows an overview of the sample as well as a highly resolved measurement on the nanometer scale. The signals recorded by AFM are on the one hand based on force interaction of the AFM tip with the sample surface, thereby delivering, that is, local friction, adhesion, stiffness, and energy loss. On the other hand, electrical properties such as electronic conductivity, ionic conductivity as well as surface potential, electrostatic force or reactivity can be retrieved. The AFM works in ambient air and in a humid or liquid environment, including an electrochemical cell. Hydrophilic and hydrophobic surface properties are especially important for water management in a PEM fuel cell and degradation processes can be followed by a comparison of samples in a fresh state and after operation

Für die Zukunft der E-Mobilität

Eine hohe Effizienz von Brennstoffzellen und Batterien wird weitgehend durch die Nanostruktur der Komponenten bestimmt. Ein Rasterkraftmikroskop (AFM) kann Materialeigenschaften mit einer lateralen Auflösung von wenigen Nanometern messen. Mit einer auf ihrer Resonanzfrequenz schwingenden kleinen Sonde wird die Oberfläche abgetastet. Im QNM-PeakForce Tapping Mode (Bruker Corp.) berührt die Spitze periodisch und definiert die Oberfläche. Aus dem Verlauf der Kraftkurve beim Annähern und Zurückziehen der Spitze werden außer der Oberflächentopografie die lokale Adhäsion, Deformierbarkeit, Härte und die Verformarbeit ermittelt. Mit einer leitfähigen Spitze kann zusätzlich während der Kontaktzeit der Strom, in feuchter Umgebung auch der Ionenstrom, der durch die Probe fließt, gemessen werden

Herstellung und Charakterisierung von Li-Schwefel-Kathoden durch in-situ XRD, Impedanzspektroskopie und AFM-Messungen

Derzeit ist das wissenschaftliche und kommerzielle Interesse an der Entwicklung von Lithium-Schwefel Batterien sehr groß. Besondere Eigenschaften dieser Batte-rien sind, unter anderem, die hohe theoretische Energiedichte (2600 Wh/kg bzw. 2800 Wh/l) und Kapazität des Schwefels (1675 mAh/g), sowie das geringe Gewicht und die gute Verfügbarkeit von Schwefel als Ausgangsstoff für die Batterieherstel-lung. Um diese Werte auch in der Praxis zu erreichen, wird an der Optimierung der Nutzung des Aktivmaterials und der Zyklenstabilität intensiv geforscht. Die Stabilisierung der Kathodenstruktur wurde durch den Einsatz von verschiede-nen Kompositen, bestehend aus Schwefel und Multiwall Carbon Nanotubes (MWCNT) erreicht. Die so hergestellten Kathoden wurden zu einer Li-Schwefelbatterie (Swagelock-Zelle) zusammengebaut und anschließend zyklisiert. Für die Optimierung der Lithium Schwefel Batterie wurden auch elektrochemische Impedanzspektren (EIS) bei verschiedenen Ladezuständen während des Lade- und Entladevorganges aufgenommen und mit Hilfe eines geeigneten Ersatzschaltbildes ausgewertet. Zusätzlich zu den elektrochemischen Untersuchungen wurden zur Identifizierung der verschiedenen Materialkomponenten an Hand ihrer mechanischen und elektri-schen Eigenschaften auch moderne AFM-Verfahren eingesetzt. Um in-situ Röntgenbeugungsexperimente (XRD) Lithium-Schwefel Batterien durch-führen zu können, wurde eine geeignete Messzelle gebaut und damit konnte erfolg-reich Zwischenprodukte (Polysulfide) bei verschiedenen Ladezuständen bzw Po-tenzialen und Endprodukte (Li2S bzw. S) sowie strukturelle Änderungen während des Entlade- und Ladevorganges der Lithium-Schwefelbatterie erfolgreich nachge-wiesen werden