Martin-Luther-Universität Halle-Wittenberg

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Current Projects

N-containing CNTs as catalyst supports

We are interested in the development of nitrogen-containing carbon nanotubes (NCNTs)  with different structural parameters (diameter, length, defect density, nitrogen amount) and to use these nanostructured materials as support in (electro)catalysts preparation. The NCNTs are impregnated with platinum or other metals, using a microwave‐assisted wet impregnation process, and tested in the oxidation and reduction reactions in a direct liquid fuel cell (DLFC).

The NCNTs are grown by catalysed chemical vapour deposition (CVD) and the properties of these materials can be adjusted using different variables in order to obtain nanotubes of high quality and low impurities. Acetonitrile is used as a source of nitrogen and the catalysts are composed of iron nanoparticles supported on silica.

The growth catalyst is removed by subsequent refluxing the raw product, using 1M KOH and 1M HCl, and an oxidative treatment, using air at 450 °C, to remove amorphous carbon and graphene sheets.

The materials prepared can be characterized by different physico-chemical methods: thermal analysis (DTA, DTG, DSC), temperature programmed techniques (TPD, TPR, TPO), X‐ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), scanning electrochemical microscopy (SECM), transmission electron microscopy (TEM) and Raman spectroscopy.

The electrochemical activities are measured in a three-electrode test cell at room temperature. The catalyst suspension is applied on a polished glassy carbon disk electrode and characterized by techniques as cyclic voltammetry (CV), rotating disk electrode (RDE), impedance spectroscopy (IS), CO stripping, among others. The experiments are performed in sulfuric acid solution (0.5 mol L-1), where the alcohol solutions are dissolved. A Pt wire and a reversible hydrogen electrode (RHE) are used as the counter and reference electrode, respectively.

New concepts for a controlled 3D-design of porous gas diffusion electrodes for Redox Flow Batteries

The all-Vanadium Redox Flow Battery (VRFB) is a device in which intermittent renewable energy such as solar and wind power is converted into chemical energy which is stored in electrolytes rather than in the electrodes. In this system, the reactive species used to complete the energy conversion are the VO2+/VO2+ and V3+/V2+ redox couples in sulphuric acid solution. In comparison with the rechargeable Li-ion battery and other energy storage batteries, VRFB has many superior properties such as high efficiency, long cycle life, quick response time, deep discharge capability, low running cost, independent tunability of power and capacity and is particularly suited for large-scale energy storage. Electrode, electrolyte and proton exchange membrane are the key battery materials and have been studied intensively since the VRFB was firstly proposed by Skyllas-Kazacos in the late eighties. With respect to the electrodes, improvement of stability and activity as well as fine-tuning of electrode structure and porosity is required and is mandatory to satisfy the high standards required for a large-scale commercialization. This work is part of a joint BMBF project (Flow 3D) aiming at the optimization of the 3D-structure of carbon based electrodes. Further requirements are high porosity, good permeability and high conductivity under compression.

Surface modification of carbon materials and their impact on electrocatalytic properties are investigated. The focus is laid on the effect of surface functional groups of carbon materials on the redox properties. Different carbon materials are tested particularly graphitized carbon without micro- but with a large amount of tunable meso- and macropores (Porocarb® by Heraeus). Furthermore, carbon nonwoven (Freudenberg) was used. Homogeneous distribution and good adhesion of the active carbon material towards the supporting carbon nonwoven is crucial. Oxygen (O-) and nitrogen (N-) functional groups were implemented by various techniques. Characterization of the materials was done by TEM, TG-MS and spatially-resolved Raman microscopy. Electrochemical properties were accessed by cyclic voltammetry.

Spatially-resolved Raman microscopy of carbon nonwoven impregnated with Porocarb® (top left microscopic image; top right above: Raman spectra; large figure: Distribution of Porocarb® (green) within the carbon nonwoven (red) by Raman-Mapping of a selected area. Scale bar: 10µm.

Spatially-resolved Raman microscopy of carbon nonwoven impregnated with Porocarb® (top left microscopic image; top right above: Raman spectra; large figure: Distribution of Porocarb® (green) within the carbon nonwoven (red) by Raman-Mapping of a selected area. Scale bar: 10µm.

Spatially-resolved Raman microscopy of carbon nonwoven impregnated with Porocarb® (top left microscopic image; top right above: Raman spectra; large figure: Distribution of Porocarb® (green) within the carbon nonwoven (red) by Raman-Mapping of a selected area. Scale bar: 10µm.

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