Elektrospinnen als potentielle Elektrodenvorbereitungsmethode für PEM- Brennstoffzellen

In this thesis, the potential of the electrospinning technique as a tool for the preparation of fuel cell electrodes was studied. In the first part of the work, electrospinning was used to prepare porous electrode structures that allow for rapid transport of both fuel and water as well as protons and electrons to and from the electrodes. A solution containing polyacrylonitrile (10 wt.%) and a small amount of carbon nanotubes (0.25 wt.%) was electrospun to get highly porous structures. The pyrolsis of the structure results in carbon nanotube enforced carbon nanofiber networks which are freestanding. Pt was deposited on the surface of the fiber structure via impregnation of Pt precursor and successive reduction with sodium borohydride. X-ray diffractogram showed a crystal size of 5.3 nm, transmission electron micrographs showed a uniform distribution of Pt nanoparticles on the network. Electrochemical surface area (ECSA) was calculated as 30.1 m^2/g. The catalyst layer which retained its morphology, was hotpressed as cathode electrode for testing in a fuel cell test-bench. The electrospun catalyst performed better at higher potential (between 0.95 V and 0.6 V) and poorer at high currents. From the ECSA, calculated using in-situ cyclic voltammetry, a high Pt utilization of approx. 90% for a loading of 0.3 mgPt/cm2 was demonstrated. In comparison, a standard electrode prepared via the air-brush technique had a catalyst utilization of 60% for the same loading. A new technique for fabrication of catalyst layers independent of ink formulation was hence successfully developed. In the second part of the work, the role of polyacrylic acid (PAA) in enhancing the stability of the electrodes was studied. Polyacrylic acid is a common additive for electrospinning Nafion. Here, an electrode containing PAA/Nafion polymer as support for Pt nanoparticles was prepared. Pt nanoparticles were produced by photochemical reaction of the Pt precursor induced by UV light. PAA-Nafion was added to the solution covering the Pt nanoparticles and thereby separating Pt particles from carbon. By this approach, the Pt enhanced carbon corrosion was decreased. The prepared electrode was characterized by both physical and electrochemical characterization techniques. From the potential cycling experiment, it was revealed that Pt nanoparticles were indeed separated from carbon particles due to which there was no change in crystallite sizes of Pt before and after cycling. This was also confirmed by accelerated degradation studies in a fuel cell test-bench which showed that 52% of the ECSA was retained after 5000 cycles, whereas the commercial catalyst lost most of its activity in the first 2000 cycles. The results suggest use of electrospinning as an indispensable tool for designing advanced fuel cell electrodes.In dieser Arbeit wurde das Potenzial des Elektrospinnverfahrens für die Herstellung von Brennstoffzellelektroden untersucht. Im ersten Teil der Arbeit wurden poröse Elektrodenmaterialien mittels des Elektrospinnverfahrens hergestellt. Die hergestellten Materialien wiesen Strukturen auf, die sowohl eine hohe Permittivit¨at für Gase, Wasser und Protonen, als auch eine hohe Elektronenleitfähigkeit besaßen. Eine Lösung aus Polyacrylnitril (10 wt.%) und einem geringen Anteil an Kohlenstoffnanoröhren (0.25 wt.%) wurde versponnen, um hochporöse Strukturen zu erhalten. Die Pyrolyse dieses Materials ergab freistehende Kohlenstoffnanofasernetzwerke, welche durch die Kohlenstoffnanoröhren stabilisiert wurden. Das Platin wurde anschließendüber einen Pt-Precursor auf die gesponnenen Kohlenstoffstrukturen aufgebracht und anschließend mit Natriumborhydrid reduziert. Röntgenbeugungs Untersuchungen ergaben eine Platinpartikelgröße von 5,3 nm und Transmissionsmikroskopische Aufnahmen zeigten eine gleichmäßige Verteilung des Katalysators auf dem gesponnenen Material. Aus Berechnungen ging eine elektrochemisch aktive Oberfläche von 30,1 m2 g–1 hervor. Die Morphologie der Katalysatorschicht blieb erhalten, was die Herstellung einer Elektrode durch Heißpressen erlaubte. Diese Elektrode wurde anschließend auf der Kathodenseite der Brennstoffzelle untersucht. Die elektrogesponnene Elektrode wies höherer Leistung in hohen Potentialbereichen zwischen 0,95 V bis 0,6 V auf. Die Leistung bei hohen Strömen war jedoch geringer. Durch die in-situ Bestimmung der elektrochemisch aktiven Oberfläche mittels zyklovoltermmetrischer Messungen, konnte eine Platinausnutzung von ca. 90%für eine Beladung von 0,3 mgPt cm–2 nachgewiesen werden. Zum Vergleich wurde eine Standardelektrode, die mit dem Heißsprayverfahren hergestellt wurde, herangezogen. Diese wies eine Platinausnutzung von 60% für eine vergleichbare Beladung auf. Somit wurde ein neues Verfahren zur Herstellung von Brennstoffzellenkatalysatoren entwickelt, die unabhängig von der Formulierung des Tintenrezeptes ist. Im zweiten Teil dieser Arbeit wurde der Einfluss von Polyacrylsäure auf die Verbesserung der Stabilität der elektrogesponnenen Elektroden untersucht. Polyacrylsäure ist ein gängiges Additiv, dass zum Elektrospinnen von Nafion verwendet wird. Daher wurden Elektroden aus Polyacrylsäure/Nafion-Polymeren zur Stabilisierung von Platinnanopartikeln hergestellt. Die Platinnanopartikel wurden mittels einer durch UV-Licht induzierten photochemischen Reaktion des Platin-Precursors hergestellt. Polyacrylsäure/Nafion wurde hinzugegeben, wodurch die Platinpartikel umschlossen wurden und somit vom Kohlenstoffträger separiert blieben. Durch diesen Ansatz wurde die durch Platin induzierte Korrosion des Kohlenstoffträgermaterials verringert. Die hergestellten Elektroden wurden sowohl mit physikalischen, als auch mit elektrochemischen Methoden charakterisiert. Durch das Zyklieren des Potentials konnte gezeigt werden, dass die Platinpartikel tatsächlich keinen direkten Kontakt zum Kohlenstoffträger hatten, da die Partikelgröße nach dem Experiment unverändert blieb. Dies wurde zusätzlich durch beschleunigte Alterungstests in einem Brennstoffzellenteststand bestätigt. Außerdem konnte dabei nach 5000 Zyklen eine elektrochemisch aktive Oberfläche von 52% nachgewiesen werden. Im Vergleich dazu verliert ein kommerziell erhältlicher Katalysator bereits nach 2000 Zyklen den Großteil seiner Aktivität. Die Ergebnisse belegen, dass das Elektrospinnen das Potenzial besitzt zu einer unverzichtbaren Methode zur Herstellung von maßgeschneiderten Elektroden für die Brennstoffzelle zu werden

Education for Corporate Sustainability Disclosures by Higher Educational Institutions – A Quantitative ABCD Analysis

Purpose: The main aim of the paper is to administer and analyse the comprehensive analysis approach known as ABCD analysis to determine its suitability in the analysis of education for corporate sustainability disclosures. It also aims to use factor analysis and elementary analysis for further insights into the topic. Design: The study follows a systematic literature review by the way of keyword search, for factors and elementary analysis under the ABCD framework. For the quantitative analysis focus group method is adopted by assigning the weights to the factors and elements identified in the study Findings: The researcher found that the ABCD analysis framework is suitable for any business, concepts, systems, strategies, and many others. Through focus group interactions it also finds that the concept of education for corporate sustainability disclosures by higher educational institutions is quite advantageous to its stakeholders. Originality value: This paper extensively studies the corporate sustainability disclosure education by HEIs using the ABCD analysis framework. Though several ABCD analysis are published related to the higher educational institutions, this paper opens the door of new research in the area of Education for Corporate Sustainability Disclosures finding the critical constituents elements and underlining its importance in the modern education system. Paper Type: Empirical Pape

Congenital erythropoietic porphyria in an Indian Child

Congenital Erythropoetic Porphyria (CEP) also called the “Günther disease”, is a rare variant of porphyria. It is caused by the deficiency of uroporphyrinogen III synthase (URO-III-synthase), an enzyme in the heme biosynthetic pathway. Clinically, CEP presents with blistering over face and extremities, scarring, hypertrichosis and dyspigmentation. Acral blistering leads to mutilation of the fingers with acro-osteolysis of distal phalanx We, hereby, report an 8-years-old boy with classical clinical features and porphyrin assays

Excerpt of dermatopathology continuous medical education 2018 conducted by Departments of Dermatology and Pathology, Kasturba Medical College, Manipal, on September 15–16, 2018

Dermatopathology is an indispensable tool for dermatologists as well as pathologists. Hence, continuous medical education (CME) on Dermatopathology was hosted by the departments of Dermatology and Pathology on September 15-16, 2018. This program was a witness to some of the lucid presentations by distinguished faculty. Around 253 delegates attended this academic feast which was a day and a half affair

A Promising N doped Carbon Metal Oxide Hybrid Electrocatalyst Derived from Crustacean s Shells Oxygen Reduction and Oxygen Evolution

The development of both efficient and durable Pt free catalysts for oxygen reduction ORR is extremely important to realize the world wide commercialization of clean energy technologies, such as fuel cells and batteries, which is currently hindered by the exorbitant cost and scarcity of the state of the art Pt based catalysts. As a potential alternative to such expensive catalysts, this investigation addresses the facile synthesis of an efficient, durable and highly poison tolerant metal free N doped carbon Nd2O3 hybrid bifunctional electrocatalyst for ORR and water splitting, which has been derived from encapsulated Nd OH 3 in the chitosan matrix N C Nd2O3 . Chitosan, obtained from the crustacean s shells, assists to form a smaller Nd2O3 particle sizes and at the same time yields an efficiently nitrogen doped graphitic structure with outstanding activity and durability for ORR in alkaline and acidic media. N C Nd2O3 catalyst exhibits 50 mV positive shift in half wave potential with a comparable onset potential and limiting current density of ORR to that of Pt C catalyst with same loading in 0.1 M KOH. Additionally, N C Nd2O3 shows a high tolerance towards crossover of the various anodic fuels concurrent with outstanding tolerance against poisoning with various hydrocarbon impurities e.g., acetonitrile, acrylonitrile, etc in situ generated during fuel cell operation. N C Nd2O3 activity shows only a slight attenuation of 3 after 8 h of continuous ORR and 6 in the presence of 50 ppm of acetonitrile compared with 50 and 80 observed at Pt C. In a H2 air single cell a membrane electrode assembly MEA prepared from N C Nd2O3 as a cathode catalyst delivered a maximum power density of 287 mW cm2 and current density of 572 mA cm 2 at 0.6 V which is especially outstanding. The superior electrocatalytic activity and durability of the as prepared catalysts mainly originate from the synergistic effects between Nd2O3 particles and chitosan functional groups, besides the nitrogen doped nature of the as prepared catalyst. Furthermore, the as prepared catalyst shows a high activity and durability in the oxygen evolution reaction OER as well, making it an efficient non precious bifunctional catalyst. The facile preparation method with metal oxide encapsulated N doped graphitic structures from cheap, nature and ecofriendly chitosan opens up a new horizon for the world wide commercialization of fuel cells and metal air batterie