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This experimental work deals with the preparation and investigation of PEM fuel cell electrodes, which are obtained using Graphene Related Material (GRM) serving as catalyst support material for platinum nanoparticles. The applied GRM belong to the group of carbon nanofibers and exhibits a helical-ribbon structure with dimensions of 50 nm in diameter and an average length up to a few µm. Furthermore, utilized GRM provide a superior graphitisation degree of about 100 %, which leads to both high corrosion resistance and low ohmic resistance. Material stability plays one of the main roles for long term fuel cell operation, whereby a great electrical catalyst contact combined with high specific surface area yields in high fuel cell performances.
Prior to GRM dispersion and deposition onto a gas diffusion layer, the graphene structures are functionalized by oxygen plasma treatment. Through this step, functional oxygen groups are generated onto the GRM outer surface providing an improved hydrophilic behaviour and facilitating the GRM suspension preparation. In addition, the oxygen groups act as anchors for platinum nanoparticles which are subsequently deposited onto the GRM surface through a pulse electrodeposition process.
Membrane electrode assemblies produced with the prepared electrodes are investigated in-situ in a PEM fuel cell test bench.
This work deals with the preparation and investigation of PEM fuel cell electrodes, which are obtained using graphene related material (GRM) serving as catalyst support for platinum nanoparticles. Applied GRM are used for the preparation of suspensions in four distinct mixing ratios. Two sorts of GRM have been investigated: carbon nanofibers (CNF) and graphene oxide (GO). Utilized CNFs provide a superior graphitization degree of about 100%, which leads to both high corrosion resistance and low ohmic resistance in PEM fuel cells.
For electrode preparation a GRM containing layer serving as catalyst support is applied onto a gas diffusion layer (GDL). Prior to GRM suspension and deposition onto a GDL, the graphene structures are functionalized by plasma treatment. Due to this step, an improved hydrophilic behavior for facilitating suspension preparation is achieved. In addition, a subsequent platinum nanoparticle deposition by pulsed electrodeposition process is optimized.
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
For this study gas diffusion electrodes (GDE) with low platinum loading are prepared for the application as anode in polymer electrolyte membrane fuel cell (PEMFC) systems based on hydraulic compression. As catalyst support material, carbon nanofibers (CNF) are investigated because of their high specific surface area and high graphitization degree. The electrode preparation is optimized by an economic and environmental friendly pre-treatment process in oxygen plasma. For GDE manufacture an ink containing oxygen plasma activated CNFs as well as hydrophilic polymer is used. After spray coating of this CNF ink on a graphitic substrate, platinum is deposited using the pulse plating technique. Preliminary results showed a considerable improvement of CNF dispersibility as well as an increased amount and an optimized morphology of the deposited platinum. Morphology and microstructure are observed by scanning electron microscopy as well as transmission electron microscopy. Platinum loading is determined by thermogravimetric analysis to be in the range of 0.01 mg cm-2 to 0.017 mg cm-2. Furthermore, MEAs are prepared from these GDEs and testing is performed in a novel modular fuel cell test stack based on hydraulic compression. Technical information about stack design and functions is given in this work.
In this experimental work we present a novel electrolyzer system for the production of hydrogen and oxygen at high pressure levels without an additional mechanical compressor. Due to its control strategies, the operation conditions for this electrolyzer can be kept optimal for each load situation of the system. Furthermore, the novel system design allows for dynamic long-term operation as well as for easy maintainability. Therefore, the device meets the requirements for prospective power-to-gas applications, especially, in order to store excess energy from renewable sources. A laboratory scale device has been developed and high-pressure operation was validated. We also studied the long-term stability of the system by applying dynamic load cycles with load changes every 30 sec. After 80 h of operation the used membrane electrode assembly (MEA) was investigated by means of SEM, EDX and XRD analysis.
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.
Hochdruck PEM-Elektrolyse
(2017)
Performance enhancing study for large scale PEM electrolyzer cells based on hydraulic compression
(2017)
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.
Die Neuberechnung der Kühllast von Gebäuden im Bestand wird immer dann nötig, wenn sich größere Nutzungsänderungen ergeben. Dabei ist die Datenlagen zur Bausubstanz und dem Aufbau der Umschließungsflächen meist unzureichend für die Eingabe in die Berechnungsalgorithmen nach VDI 2078:2015-06. Der Artikel analysiert an einem denkmalgeschützten Verwaltungsgebäude die wichtigsten Einflussfaktoren auf die Kühllast. Dabei wir auch ein Vergleich zur lange gültigen Vorgängerrichtline von 1996 durchgeführt.
Die Klimatisierung von Gebäuden gewinnt zunehmend an Bedeutung. Dies liegt zum einen an der Bauweise und Nutzung, die höhere Kühllasten mit sich bringt. Zum anderen fordern die Nutzer eine angemessene Behaglichkeit bei hoher Luftqualität.
Diese Forderungen gehen einher mit hoher Energieeffizienz und einwandfreier Hygiene der Raum-lufttechnischen Anlagen. Dieser Beitrag untersucht diese Forderungen für Nichtwohngebäude und prüft, ob Hygiene und Energieeffizienz zu Zielkonflikten führen können.
Der Mensch verbringt einen Großteil seiner Zeit in geschlossenen Räumen und erwartet, dass die Luftqualität mindestens der Außenluft entspricht. Mit Blick auf die aktuelle Feinstaubdebatte, muss die Raumluftqualität noch deutlich darüber hinaus gehen. Weiterhin soll der Aufenthalt am Arbeitsplatz nicht zu gesundheitlichen Beeinträchtigungen führen (Reizung der Schleimhäute, trockene Augen oder virale Infektionen).
Die Klimatisierung von Gebäuden benötigt einen nicht unerheblichen Teil der Primärenergie, so dass ein effizienter Anlagenbetrieb ein wichtiger Baustein der Energiewende ist. Dabei spielt die Nutzung von regenerativen Energien (Solarstrom zur Gebäudekühlung) genauso eine wichtige Rolle wie die Optimierung von Komponenten und deren Abstimmung zum „System Gebäudeklimatisierung“.
Zur Einordnung der Themengebiete werden die relevanten Normen und Regelwerke auf europäischer und deutscher Ebene kurz vorgestellt und erläutert.
Am Beispiel eines typischen RLT-Gerätes werden die Komponenten und Funktionen im Betrieb veranschaulicht. Die wichtigsten Komponenten (z. B. Filter, Wärmeübertrager, Befeuchter und Ventilatoren) werden mit Blick auf Hygiene und Energieeffizienz anschließend analysiert und verglichen. Die Vergleiche finden anhand von Fallbeispielen statt, wie sie für Nichtwohngebäude typisch sind. Zusammenfassend wird die Ausgangsfrage aus Sicht des Autors beantwortet.