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For this experimental work gas diffusion electrodes (GDE) with low platinum loading are prepared for the application as anodes in polymer electrolyte membrane fuel cells. As catalyst support material, carbon nano fibres (CNF) are investigated due to high specific surface area as well as high graphitisation degree. Optimisation is achieved by an economic and environmental friendly pre-treatment process in oxygen plasma. For electrode preparation an ink is used containing oxygen plasma activated CNFs as well as hydrophilic polymer. After spray coating of this CNF ink on a graphitic substrate, platinum is deposited by pulse plating method. Preliminary results established that the plasma activation improves considerably CNF dispersibility as well as the amount, respectively, the morphology of the deposited platinum. Morphology and microstructure are observed by electron microscopy. Platinum loading is determined by thermogravimetric analysis to be in the range of 0.010 to 0.016 mg cm-2. Furthermore, MEAs are prepared from these GDEs and testing is performed in a novel modular test stack based on hydraulic compression. Technical information about the test stack design and functions are given in this work. In this test environment maximum specific power output of 182 mW cm-2 has been obtained under robust operation conditions.
In state of the art polymer electrolyte membrane fuel cells (PEMFC) rare and expensive platinum group metals (PGM) are used as catalyst material. Reduction of PGM in PEMFC electrodes is strongly required to reach cost targets for this technology. An optimal catalyst utilisation is achieved in the case of nano-structured particles supported on carbon material with a large specific surface area. In this study, graphitic material in form of carbon nanofibres (CNFs) is decorated with platinum (Pt) particles serving as catalyst material for PEMFC electrodes with low Pt loading. For electrode preparation CNFs have been previously activated by means of radio frequency induced oxygen plasma. This kind of treatment results in formation of functional groups on the CNF’s surface which directly influences the characteristics of subsequent Pt particle deposition. Different plasma parameters (plasma power, gas flow or exposure time) have to be set in order to achieve formation of oxygen containing functional groups (hydroxylic, carboxylic or carbonylic) on the CNF’s surface. In the frame of this experimental work, electrodes are investigated in respect of optimal morphology, microstructure as well as electrochemical properties. Therefore, samples were characterised by means of scanning electron microscopy combined with energy dispersive X-ray analysis, transmission electron microscopy, thermogravimetry, X-ray diffraction, X-ray fluorescence as well as polarisation measurements.
Efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes
(2015)
Steganography, the art of concealing information in different types of medias, is a very old practice. Yet, it only recently started being used by malware operators on a large scale. Malware programmers and operators are increasing their efforts in developing covert communication channels between infected computers and their command and control servers. In addition to steganography, recent examples include hiding communication in inconspicuous network traffic such as DNS queries or HTTP 404 error messages.
When used properly, these covert communication channels can bypass many automated detection mechanisms and render malware communication difficult to detect and block. From an attacker's perspective, covert communication channels are a valuable addition because they allow messages to blend in with legitimate traffic and thus significantly lower the chance of being detected even when inspected by a human analyst.
This presentation studies recent advances in covert communication channels used by real-world malware. First, we will show how steganography has recently been used in three different malware families (Stegoloader, Vawtrak, and Lurk). We will dive into the implementation details on how steganography is implemented and discuss the strengths and weaknesses of each approach. Furthermore, we will detail and compare the usage of inconspicuous carrier protocols for covert communication channels in malware. Examples will span commodity cybercrime as well as targeted attack malware.
The cases that are discussed in this presentation are based on real life incidents. While it is easy to speculate how covert communication channels might be used by malicious actors, documentation of real-world cases is sparse. Yet covert communication channels have arrived in both, the commodity cybercrime and targeted attack world. It is thus vital to understand the status-quo and identify current trends in cybercriminal and targeted attack malware. As such, we believe that it is mandatory to highlight what is currently being used in the wild.
In polymer electrolyte membrane fuel cells (PEMFC) noble metal nano particles are deposited on graphitic supports serving as electrocatalysts for devices with high power density. In this study anodes are analysed with low platinum loading of about 0.1 mg cm-2. These electrodes are prepared by carbon nano fibres (CNF) decorated with platinum nano particles. For electrode manufacturing two sorts of fibres, which are produced in an industrial scale, are used with different graphitisation degree and surface area. CNF layers are applied on commercially available graphitic substrate by spray coating which leads to a porous structure with high surface area. Subsequently, platinum deposition is achieved by pulsed electroplating for an improved platinum utilisation in PEMFC electrodes. Spray coating and platinum deposition are assisted by a previous oxygen plasma activation process. Prepared anode material is characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), X-ray fluorescence spectroscopy (XRF) and thermogravimetry (TGA). Electrochemical analyses (cyclic voltammetry and corrosion test) are carried out in 0.5 M sulphuric acid. The effect of graphitisation degree of carbon nano fibres on the performance of prepared electrodes is investigated in-situ in a PEM fuel cell test bench.