Mehtap Oezaslan, Dr.
room: W03 1-117
fon: +49 (0)441 798 3917
fax: +49 (0)441 798 3979
...are concerned with the design of highly efficient and durable nanostructured electrocatalysts for fuel cell and electrolyzer systems.
Understanding of electrocatalytic processes occurring on the electrolyte-electrode interfaces is the key to predict and to ultimately design properties of materials and interfaces over large length and time scales.
Our research topics are:
...with well-defined Structure, Composition, Particle Size and Particle Shape
Electrocatalysis on multimetallic nanoparticles (NPs) is strongly influenced by their structure, composition, particle size and particle shape. Recently, multimetallic NPs have attracted great attention in science and industry due to their optical, magnetic or (electro)catalytic properties. For instance, their improved catalytic reactivity of Pt-based NPs is based on the modification of electronic and atomic surface structure of Pt by the presence of other metals in the sublayers. In order to establish relationships between catalytic properties, durability, structure and composition of electrocatalysts, we will prepare well-defined multimetallic nanostructured materials by using modern wet-impregnation and colloidal synthesis approaches.
In-situ high temperature X-ray diffraction (HT-XRD) is one of the powerful techniques to understand the dynamic behavior of alloy formation and particle growth at the nano scale. The influences of experimental parameters on the resulting structure and chemical homogeneity of the prepared NPs will be clarified in detail.
...for acidic and alkaline Fuel Cells.
Nowadays, the oxygen reduction reaction (ORR, O2 + 4 H+ + 4 e- -> 2 H2O) is one of most studied electrochemical reactions in the world. Due to the very sluggish kinetics of ORR, high loadings of precious metals are required for fuel cells. Our research activities are focusing on the reduction or the elimination of the costly and scarce platinum in order to meet and even to exceed the commercial targets for cost, activity and catalyst lifetime, e.g. proposed for the application of polymer electrolyte fuel cell vehicles.
Our group design highly efficient and robust nanostructured ORR electrocatalysts for acidic and alkaline fuel cells. Modern analytical tools are used here to examine the electrochemical behavior and the electrocatalytic properties of the as-prepared ORR electrocatalysts in dependence of the supporting electrolyte. So various strategies are pursued to stabilize the less noble metals inside the multimetallic Pt-based ORR electrocatalysts. The stability of the structure and chemical composition helps to maintain the high ORR activity over the time under fuel cell conditions. Therefore, the aging process of the catalysts is comprehensively investigated by utilization of in-situ high-resolution microscopic and synchrotron-based spectroscopic techniques like XAS, SAXS, XRD.
The goal is to provide a real mechanistic picture about the degradation mechanisms of catalytically active multimetallic NPs under the fuel cell conditions.
In the last decades, direct alcohol fuel cells (DAFCs) have emerged as one of the promising renewable and clean technologies for energy conversion. In particular, ethanol is an interesting fuel because it exhibits high energy density, low toxicity compared to other alcohols like methanol, ease of storage and transportation and it can be obtained largely from biomass. However, their world-wide commercialization is hindered by the very sluggish kinetics of the ethanol oxidation reaction (EOR) towards CO2 (C2H5OH + 3 H2O -> 2 CO2 + 12 H+ + 12 e-). The electrochemical oxidation of ethanol towards CO2 is associated with the cleavage of the C-H bond and C-C bond on the catalytic active electrode surface.
Currently, our group work on ternary shape-controlled Pt-Sn-based NPs to improve the reactivity and durability for the ethanol oxidation. In order to clarify the role of Sn during the oxidation reaction, in-situ electrochemical spectroscopic techniques like FT-IR, DEMS and XAS are used in our group to obtain important insights into structural and electronic effects related to the electrochemical activity and selectivity for the well-defined Pt-Sn-M nanoparticle electrocatalysts.
...on Nanostructured Copper-based Materials.
In the last three decades, large efforts have been made to directly convert CO2 as a potential resource into carbon-based chemicals and fuels. However, for a carbon neutral footprint the required energy for the CO2 reduction needs to be provided by renewable energy sources, such as sun and wind. Only polycrystalline copper electrodes are capable to form hydrocarbons with sufficient amounts. However, the overpotentials are in the range of 0.7 – 1.0 V.
In our group, Cu-based nanostructured electrocatalysts are investigated for the electrochemical CO2 reduction.
The catalyst concepts vary from simple pure Cu nanoparticles (NPs) to bimetallic NPs in form of core-shell NPs and/or multimetallic alloy NPs. In addition, nanoporous Cu materials are prepared by (electro)chemical dealloying method.
The formed products during the CO2 reduction will be in-situ monitored by Differential Electrochemical Mass Spectroscopy (DEMS), Gas Chromatography (GC), Nuclear Magnetic Resonance Spectroscopy (NMR) and Fourier-Transform Infrared Spectroscopy (FT-IR).
The goal is to adjust optimal synergy interactions of strain and electronic effects toward improved activity and selectivity.