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Institut
- Westfälisches Energieinstitut (55) (entfernen)
Carbon Nanofibers (CNF) are considered to be a promising catalyst support material due to their unique characteristics, excellent mechanical, electrical and structural properties, high surface area and nevertheless, good interaction with metallic catalyst particles. The possibility of preparing CNF decorated with platinum by an electrochemical method was tested, using a hexachloroplatinic bath solution. The experiments were carried out with the aid of a Potentiostat/Galvanostat Ivium Technologies Vertex, in a three – electrode cell. The aim of the present work was to determine the electrochemical surface area (ECSA) of the CNF-Pt catalysts in relation to the functionalization treatment of fibers, using an electrochemical method. ECSA for different functionalized CNF-Pt catalysts was determined by cyclic voltammetry in 0.5 M H2SO4 solution. The highest active surface of platinum was obtained for the samples with CNF functionalized by plasma treatment using 80 W for 1800 s. The obtained results correlate very well with the particles size and distribution of platinum, revealed by scanning electron microscopy (SEM) and the quantity of deposited platinum determined by thermo gravimetrical analysis (TGA) respectively. Cyclic voltammetry (CV) has been proven to be a suitable method for estimation of the ECSA of the electrocatalysts.
In the polymer electrolyte membrane fuel cells (PEMFC) state of the art, rare and expensive platinum group metals (PGM) or PGM alloys are used as catalyst material. Reduction of PGMs in PEMFC electrodes is strongly required to reach cost targets for this technology. An optimal catalyst utilization is achieved in case of nano-structured particles supported on carbon material with a large specific surface area. In this study, graphitic material, in form of carbon nanofibers (CNF), is decorated with Pt particles, serving as catalyst material for PEMFC electrodes with low Pt loading. As a novelty, the effect of oxygen plasma treatment of CNFs previously to platinum particle deposition has been studied. Electrodes are investigated in respect of the optimal morphology, microstructure as well as electrochemical properties. Therefore, samples are characterized by means of scanning electron microscopy combined with energy dispersive X-ray analysis, transmission electron microscopy, thermogravimetry, X-ray diffraction as well as X-ray fluorescence analysis. In order to determine the electrochemical active surface area of catalyst particles, cyclic voltammetry has been performed in 0.5 M sulphuric acid. Selected samples have been investigated in a PEMFC test bench according to their polarization behavior.
In this experimental work polymer electrolyte membrane fuel cell (PEMFC) electrodes are analysed, which are prepared by the use of two sorts of carbon nano fibres (CNF) serving as support material for platinum nano particles. Those CNFs, which are heat treated subsequently to their production, have a higher graphitisation degree than fibres as produced. The improved graphitisation degree leads to higher electrical conductivity, which is favourably for the use in PEMFC electrodes. Samples have been analysed, in order to determine graphitisation degree, electrical conductivity, as well as morphology and loading of the prepared electro catalyst. Membrane electrode assemblies manufactured from prepared electrodes are analysed in-situ in a PEM fuel cell test environment. It has been determined that power output for samples containing CNFs with higher graphitisation degree is increased by about 13.5%.
Platinum nanoparticles electrodeposition on carbon nanofibers (CNF) support has been performed with the purpose to obtain electrodes that can be further used especially in a polymer electrolyte membrane fuel cell (PEMFC). A pretreatment of CNF is required in order to enhance the surface energy, which simultaneously improves handling and wettability as well as interaction with the platinum cations. This step was performed using oxygen plasma functionalization. To produce CNF supported Pt catalysts, an electrochemical method was applied and the deposition parameters were adjusted to obtain nanosized platinum particles with a good distribution onto the graphitic surface. The morphology and structure of the obtained particles were investigated by scanning electron microscopy combined with energy dispersive X-Ray spectroscopy. The amount of deposited platinum was established using thermogravimetrical measurements. Cyclic voltammetry performed in 0.5 M H2SO4 solution was applied for determining the electrochemical surface area (ECSA) of the obtained electrodes.The functionalization degree of the CNF outer surface has a strong influence on the structure, distribution and amount of platinum particles. Moreover, the current densities, which were set for the deposition process influenced not only the particles size but also the platinum amount. Applying an oxygen plasma treatment of 80 W for 1800 s, the necessary degree of surface functionalization is achieved in order to deposit the catalyst particles. The best electrodes were prepared using a current density of 50 mA cm-2 during the deposition process that leads to a homogenous platinum distribution with particles size under 80 nm and ECSA over 6 cm2
The technology of polymer electrolyte membrane (PEM) electrolysis provides an efficient way to produce hydrogen. In combination with renewable energy sources, it promises to be one of the key factors towards a carbon-free energy infrastructure in the future. Today, PEM electrolyzers with a power consumption higher than 1 MW and a gas output pressure of 30 bar (or even higher) are already commercially available. Nevertheless, fundamental research and development for an improved efficiency is far from being finally accomplished, and mostly takes place on a laboratory scale. Upscaling the laboratory prototypes to an industrial size usually cannot be achieved without facing further problems and/or losing efficiency. With our novel system design based on hydraulic cell compression, a lot of the commonly occurring problems like inhomogeneous temperature and current distribution can be avoided. In this study we present first results of an upscaling by a factor of 30 in active cell area.
This work deals with the preparation and investigation of polymer electrolyte membrane fuel cell (PEMFC) electrodes, which are obtained using gas diffusion layers coated with graphene related material (GRM) serving as a catalyst support for platinum nanoparticles. PEMFC electrocatalysts have been prepared by pulsed electrochemical deposition of platinum particles from hexachloroplatinic acid. Prior to GRM decoration with platinum, the graphene structures are functionalized by oxygen plasma treatment. This leads to oxygen containing functional groups on the GRM outer surface, providing an improved hydrophilic behavior, thus favoring the Pt deposition process. Membrane electrode assemblies (MEAs) with the so prepared electrodes are investigated in-situ in our fuel cell test system. Polarization plots (in-situ cell performance) using these MEAs have been tested under different operational conditions.
Gebäude sind immer auch ein Ausdruck der Zeit, in der sie erbaut wurden. Oft bleiben sie sehr lange erhalten und erfahren über die Jahrzehnte mehrfache Nutzungsänderungen. Betroffen sind alte Produktionshallen ebenso wie Verwaltungsimmobilien. Die Gebäudehülle bleibt bei einer Umnutzung meist unangetastet. Aufgabe der Technischen Gebäudeausrüstung ist es dann, das Raumklima für die Nutzer unter den geänderten Bedingungen behaglich zu gestalten und die Aspekte der Energieeffizienz und Nachhaltigkeit nicht aus den Augen zu verlieren. Insbesondere die Kühlung der Gebäude im Sommer steht aufgrund der steigenden internen Lasten und der solaren Gewinne durch große Glasfassaden im Vordergrund.
Am Beispiel eines rund 100 Jahre alten Verwaltungsgebäudes wird gezeigt, wie eine dynamischen Kühllastberechnung eine exakte Voraussage der zu erwartenden Spitzenlasten ermöglicht. Darauf basierend kann dann eine individuelle RLT-Anlagentechnik installiert wird. Die Auslegung erfolgt mit zwei Versionen der VDI 2078. Die Ergebnisse werden miteinander verglichen.
Am Beispiel eines rund 100 Jahre alten Verwaltungsgebäudes wird gezeigt, wie eine dynamische Kühllastberechnung eine exakte Voraussage der zu erwartenden Spitzenlasten ermöglicht. Darauf basierend kann dann eine individuelle RLT-Anlagentechnik installiert werden. Die Auslegung erfolgt mit zwei Versionen der VDI 2078. Die Ergebnisse werden miteinander verglichen.