Die vorliegende Arbeit befasst sich mit synthetischen Ansätzen zur Verbesserung der Handhabung von Pd-Nanopartikeln in der heterogenen Umwelt- und Elektrokatalyse. Nanopartikuläres Pd an Magnetit sowie an Silica-Sphären mit Magnetit-Kern erreichten eine hohe Aktivität bei der Dechlorierung von Hexachlorbenzol. Im Gegensatz zu ungeträgerten Nanopartikeln gelang die Abtrennung jener mit einem Magnet aus der Reaktionslösung. Weitere Untersuchungen ergaben, dass die Shewanella oneidensis eine heterogene Keimbildung im mikrobiellen Herstellungsverfahren von Pd-Nanomaterialien vermittelte. Die Mikroorganismen waren vermutlich nicht aktiv am Elektronenübergang beteiligt. Die partiell aggregierten Produkte des mikrobiellen Verfahrens ließen sich zur Herstellung von Aerogelen durch Selbstassemblierung verwenden. Elektrodenfilme aus mikrobiell als auch chemisch synthetisiertem nanopartikulären Pd zeigten ähnliche Eigenschaften bei der elektrochemischen Oxidation von Methanol. Darüber hinaus ermöglichte die Anwendung der fraktalen Dimension strukturelle Veränderungen abhängig von Verfahrensparametern bei der Selbstassemblierung festzustellen.:Inhaltsverzeichnis i Abbildungsverzeichnis iii Tabellenverzeichnis v Einleitung 1 1. Grundlagen 5 1.1. Eigenbewegung von Nanopartikeln in Suspension 6 1.2. Die DLVO-Theorie der Stabilität von lyophoben Kolloiden 7 1.3. Aggregation und die fraktale Dimension 11 1.4. Lichtstreuung an Kolloiden 15 1.5. Transmissionselektronenmikroskopie 19 1.6. Röntgenpulverdiffraktometrie 24 2. Edelmetall-Nanopartikel 27 2.1. Synthese von Palladium-Nanopartikeln 30 2.1.1. Reduktion mit Natriumborhydrid 30 2.1.2. Reduktion mit Citrat und Dicarboxyaceton 31 2.1.3. Keimvermitteltes Wachstum 33 2.2. pH- und Temperatur-Stabilität der Suspensionen 35 2.3. Integration in Polymerbeschichtungen 37 2.4. Resümee 41 3. Mikrobiell hergestellte Pd-Nanostrukturen 43 3.1. Dissimilatorische Metall-Reduktion 44 3.2. Eigenschaften von mikrobiellem Pd 49 3.2.1. Herstellung und Präparation 49 3.2.2. Strukturelle Eigenschaften 51 3.2.3. Umsatz und chemische Zusammensetzung 56 3.2.4. Untersuchung der organischen Bestandteile 60 3.2.5. Eigenschaften der Suspensionen 64 3.3. Kontrollversuche zur mikrobiellen Herstellung 66 3.4. Dechlorierung von Hexachlorbenzol 69 3.5. Resümee 71 4. Palladium-Magnetit-Nanokatalysatoren 75 4.1. Synthese von Magnetit-Nanopartikeln 78 4.2. Kombination von Magnetit- und Pd-Nanopartikeln 81 4.3. Abscheidung von Pd an Magnetit 84 4.4. Zwischenfazit 85 4.5. Oberflächen-modifizierte Pd-Magnetit-Komposite 86 4.6. Dechlorierung von Hexachlorbenzol 89 4.7. Resümee 91 5. Selbstassemblierung von Edelmetallnanopartikeln 93 5.1. Verfahren zur Herstellung von Pd-Hydrogelen 96 5.1.1. Variation der Verfahrensparameter 97 5.1.2. Einfluss von Temperatur und Anreicherungsfaktor 99 5.2. Aerogel-Monolithe 103 5.3. Netzwerkstrukuren aus mikrobiellem Pd 105 5.4. Elektrochemische Oxidation von Methanol 106 5.5. Resümee 111 Zusammenfassung und Ausblick 113 A. Terminologie zu Kolloiden, Aggregaten, Gelen & Co. 115 B. Experimentelle Methoden 117 B.1. Synthesevorschriften 118 B.2. Charakterisierungsmethoden 128 B.3. Elektrochemische Untersuchungen an Aerogel-Elektroden 132 Literaturverzeichnis 135 / The present work deals with synthetic approaches for the implementation of Pd-based materials in environmental and electrocatalysis. Nanoparticles of Pd either coupled to magnetite or to silica-spheres with a magnetic core showed a high activity in the dechlorination of hexachlorbenzene similar to unsupported nanoparticles. However, in contrast to unsupported nanoparticles they could be separated from the reaction solution by a magnet. Structural and chemical properties of Pd nanomaterials from a microbial synthesis were comparatively investigated. The results lead to the conclusion that the Shewanella oneidensis were not actively involved into the electron transfer and the microorganisms acted more as a substrate for heterogeneous seeding. Partially nanostructured Pd-aggregates from the microbial synthesis were further subjected to self-assembly to form noble metal aerogels. Electrode films made of both microbially and synthetically produced Pd aerogels showed similar structural and electrochemical properties in the electrooxidation of methanol. Finally, the fractal dimension was implemented as a parameter allowing to monitor the evolution of both aerogel structure and its density during the process of selfassembly.:Inhaltsverzeichnis i Abbildungsverzeichnis iii Tabellenverzeichnis v Einleitung 1 1. Grundlagen 5 1.1. Eigenbewegung von Nanopartikeln in Suspension 6 1.2. Die DLVO-Theorie der Stabilität von lyophoben Kolloiden 7 1.3. Aggregation und die fraktale Dimension 11 1.4. Lichtstreuung an Kolloiden 15 1.5. Transmissionselektronenmikroskopie 19 1.6. Röntgenpulverdiffraktometrie 24 2. Edelmetall-Nanopartikel 27 2.1. Synthese von Palladium-Nanopartikeln 30 2.1.1. Reduktion mit Natriumborhydrid 30 2.1.2. Reduktion mit Citrat und Dicarboxyaceton 31 2.1.3. Keimvermitteltes Wachstum 33 2.2. pH- und Temperatur-Stabilität der Suspensionen 35 2.3. Integration in Polymerbeschichtungen 37 2.4. Resümee 41 3. Mikrobiell hergestellte Pd-Nanostrukturen 43 3.1. Dissimilatorische Metall-Reduktion 44 3.2. Eigenschaften von mikrobiellem Pd 49 3.2.1. Herstellung und Präparation 49 3.2.2. Strukturelle Eigenschaften 51 3.2.3. Umsatz und chemische Zusammensetzung 56 3.2.4. Untersuchung der organischen Bestandteile 60 3.2.5. Eigenschaften der Suspensionen 64 3.3. Kontrollversuche zur mikrobiellen Herstellung 66 3.4. Dechlorierung von Hexachlorbenzol 69 3.5. Resümee 71 4. Palladium-Magnetit-Nanokatalysatoren 75 4.1. Synthese von Magnetit-Nanopartikeln 78 4.2. Kombination von Magnetit- und Pd-Nanopartikeln 81 4.3. Abscheidung von Pd an Magnetit 84 4.4. Zwischenfazit 85 4.5. Oberflächen-modifizierte Pd-Magnetit-Komposite 86 4.6. Dechlorierung von Hexachlorbenzol 89 4.7. Resümee 91 5. Selbstassemblierung von Edelmetallnanopartikeln 93 5.1. Verfahren zur Herstellung von Pd-Hydrogelen 96 5.1.1. Variation der Verfahrensparameter 97 5.1.2. Einfluss von Temperatur und Anreicherungsfaktor 99 5.2. Aerogel-Monolithe 103 5.3. Netzwerkstrukuren aus mikrobiellem Pd 105 5.4. Elektrochemische Oxidation von Methanol 106 5.5. Resümee 111 Zusammenfassung und Ausblick 113 A. Terminologie zu Kolloiden, Aggregaten, Gelen & Co. 115 B. Experimentelle Methoden 117 B.1. Synthesevorschriften 118 B.2. Charakterisierungsmethoden 128 B.3. Elektrochemische Untersuchungen an Aerogel-Elektroden 132 Literaturverzeichnis 135

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In der vorliegenden Arbeit wurden unter Anwendung unterschiedlicher Präparationstechniken vanadiumdotierte Metalloxide bzw. –oxofluoride synthetisiert, umfassend charakterisiert und in katalytischen, selektiven Oxidationsreaktionen (ODH von Propan und Methanoloxidation) getestet. Die Festkörper- und oberflächenchemischen Eigenschaften wurden generell mittels CHN-Analyse, ICP-OES, XRD, Raman-, FTIR-, MAS-NMR- und ESR-Spektroskopie, Py-PAS, TPD und Tieftemperatur-Stickstoffadsorption untersucht. Ergänzend kamen an ausgewählten Proben der temperaturprogrammierte Sauerstoffisotopenaustausch und Adsorptionsuntersuchungen von Methanol zum Einsatz. Als katalytische Testreaktionen dienten die oxidative Dehydrierung von Propan und die selektive Methanoloxidation. Unabhängig von der angewendeten Synthesemethode zeigte sich, dass die Festkörpereigenschaften sowohl durch den Vanadiumgehalt, als auch wesentlich durch die Art des Wirtsgitters beeinflusst werden. Es konnte nachgewiesen werden, dass eine hohe Sauerstoffaustauschaktivität und das Vorhandensein Brønsted-saurer Zentren auf den Katalysatoroberflächen die Aktivierung der Edukte in den hier untersuchten katalytischen Reaktionen begünstigen. In Bezug auf die Selektivität zu den Zielprodukten Propen bzw. Formaldehyd sind diese Eigenschaften allerdings nachteilig, da an derartigen Zentren immer die Produkte der Totaloxidation (CO und CO2) gebildet werden. Besonders bemerkenswert ist das Verhalten der vanadiumdotierten Aluminiumoxofluoride. Diese Phasen wurden mit einer neuen Methode synthetisiert und enthalten fast ausschließlich Lewis-saure Zentren. Die Matrix wird zudem maßgeblich durch die Fluoridionen bestimmt, sodass die Sauerstoffmobilität und –austauschaktivität sehr gering sind. Dadurch reagieren sie, trotz einer relativ hohen katalytischen Aktivität, außerordentlich selektiv in den hier untersuchten selektiven Oxidationsreaktionen. / In this thesis, vanadium containing metal oxides and oxyfluorides were prepared, thoroughly characterised and tested as catalysts in selective oxidation reactions. Bulk and surface properties of all samples were studied by means of CHN-analysis, ICP-OES, XRD, Raman-, FTIR-, MAS-NMR- und ESR-spectroscopy, Py-PAS, TPD and BET-adsorption. Moreover, the oxygen isotope exchange behaviour and the methanol adsorption properties of selected samples were analysed in order to correlate the surface properties with the catalytic behaviour of the materials. Irrespective of the preparation technique applied, the properties of the solids strongly depend on the host lattice as well as on the vanadium content. It has been clearly revealed that a high oxygen exchange activity and the presence of Brønsted acid sites on the catalyst surface promote the activation of the educts in selective oxidation reactions. The enhanced activity, however, is generally accompanied by a low selectivity towards the desired products propylene and formaldehyde, respectively. The low selectivity is caused by the high concentration of catalytically active sites leading to the formation of carbon oxides as total oxidation products of propane and methanol. A very promising catalytic behaviour was observed with vanadium-doped aluminium oxyfluorides. The oxyfluorides were prepared by a new method and contain almost exclusively Lewis-acid sites. The matrix is mainly determined by the fluoride anions resulting in a reduced oxygen mobility and exchange activity. Hence, the vanadium-doped aluminium oxyfluorides exhibit a relatively high catalytic activity accompanied by an excellent selectivity in the oxidation reaction of propane and methanol.

The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. / Polymerelektrolytbränslecellen omvandlar den kemiska energin i ett bränsle, exv. vätgas eller metanol, och syrgas  till elektrisk energi. Den höga verkningsgraden samt möjligheten att använda bränsle från förnyelsebara källor gör dem attraktiva som energiomvandlare i framtida hållbara energisystem. En enorm utveckling har skett under det senaste årtiondet men för att kunna introducera polymerelektrolytbränslecellen på marknaden i en större skala måste livstiden öka och kostnaden minska. Elektroderna har en central del i detta då den platina som används som katalysator står för en stor del av kostnaden för bränslecellen. En stor del av prestandaförsämringen med tiden hos bränslecellen kan också relateras till en degradering av den porösa elektroden och en minskad elektrokemiskt aktiv platinayta. I denna avhandling studeras olika bränslecellsreaktioner samt olika katalysatorer och supportmaterial med målet att undersöka möjligheten att förbättra platinakatalysatorns aktivitet, stabilitet och utnyttjandegrad i bränslecellselektroder. Utbytesströmtätheten, i0, för vätgasoxidationen i bränslecell bestämdes till 770 mA cm-2Pt genom försök med modellelektroderna. Denna var högre än vad som framkommit tidigare i litteratur, vilket visar att de kinetiska förlusterna på anoden är mycket små. Katalysatormängden på anoden borde därför kunna minskas utan några större potentialförluster så länge masstransporten av vätgas är tillräcklig. Den elektrokemiskt aktiva ytan, aktiviteten och stabiliteten hos elektroden visade sig kunna påverkas av supportmaterialet. Platina deponerad på volfram oxid hade en högre aktivitet vid höga potentialer vilket relaterades till den förskjutna oxidbildningen på ytan. Elektroder med platina på volframoxid och iridiumoxid var mer stabila än elektroder med platina på kol. Det var även platina på ett icke grafitiserat kol med låg yta jämfört med platina på grafitiserade kol med en hög yta. Platina på metalloxidskikt av volfram och titan visade en högre elektrokemiskt aktiv yta i de cykliska voltamogrammen än platina på kol, vilket förklarades med att båda metalloxiderna har en bra protonledningsförmåga. CO-stripping gav det säkraste måttet på den elektrokemiskt aktiva ytan i en elektrod i bränslecell. CO-stripping visade sig även vara användbart för karaktärisering av degraderingen av en elektrod. Oxidationen av små organiska föreningar påverkades av borttransporten av intermediärer samt av kloridföroreningar. Pt aoch PtRu påverkades olika vilket gjorde det möjligt att få fram information om reaktionsmekanismer och hastighetsbestämmande steg. / QC 20101014

Synopsis of the thesis entitled “Titanium Nitride-Based Electrode Materials for Oxidation of Small Molecules: Applications in Electrochemical Energy Systems” submitted by Muhammed Musthafa O. T under the supervision of Prof. S. Sampath at the Department of Inorganic and Physical Chemistry of the Indian Institute of Science for the Ph.D degree in the faculty of science. Fuel cells have been the focus of interest for many decades because of the ever increasing demands in energy. Towards this direction, there have been considerable efforts to find efficient electrocatalysts to oxidize small organic molecules (SOMs) such as methanol, ethanol, glycerol, hydrazine and borohydride that are of potential interest in direct fuel cells. Most studies revolve around platinum which is the best electrocatalyst known for the oxidation of many SOMs. However, platinum is extremely susceptible to carbon monoxide (CO) poisoning which is an intermediate in the electrooxidation of aliphatic alcohols. The best known catalyst, platinum-ruthenium alloy (PtRu), suffers from leaching of Ru during cycling resulting in decrease in efficiency in addition to loss of precious metal. Another important aspect of fuel cell catalyst degradation is corrosion of widely-used carbon support, under fuel cell conditions. Corrosion of carbon support weakens the adherence of catalyst particles on the support and in turn results in loss of catalyst and also in its easy oxidation. Carbon corrosion is also reported to decrease the electronic continuity of the catalyst layer. Hence, replacement of carbon support with durable material is required. The present research explores the use of non-carbonaceous, transition metal nitride for anchoring catalytic particles. The favorable physicochemical properties of titanium nitride (TiN) such as extreme hardness, excellent corrosion resistance in aggressive electrolytes, resistance to nearly all chemicals, salt and humidity, very good support for the adherence of fuel cell catalysts and excellent electronic conductivity motivated us to use this material for anchoring fuel cell catalysts such as Pt, PtRu and Pd. In the present studies, TiN coated on stainless steel (SS 304) surface is used as an electrode material. Catalysts such as Pt, Pd and PtRu are anchored on to TiN and used for the oxidation of methanol and ethanol in acidic as well as in alkaline media. Use of bare TiN is explored for the oxidation of sodium borohydride. The efficiency of TiN supported catalysts are compared with carbon supported ones. Preliminary studies on the use of TiN supported catalysts in fuel cells have been conducted as well. Figure 1 shows the topographic atomic force microscopic (AFM) image in combination with scanning Kelvin probe (SKP) image of platinized TiN (Pt-TiN) surface. Since Pt particles are metallic, they are expected to show lower work function values than that of TiN domains which is indeed observed in figure 1B where the location of Pt particles is shown as dip in the work function. Very interestingly, the interface of Pt-TiN possesses very different work function values confirming the existence of metal-support interaction and this is expected to have positive implications in fuel cell catalysis. Figure 1. Contact mode AFM (A) and the corresponding scanning Kelvin probe image (B) of Pt-TiN surface. Figure 2. Cyclic voltammograms of Pt-TiN and Pt-C electrodes in 0.5 M H2SO4 containing 0.5 M methanol at a scan rate of 10 mV/s. Loading of the catalyst used is 1 mg of Pt/cm2. The performance of Pt-TiN and PtRu-TiN are compared with the corresponding carbon supported catalysts (Pt-C, PtRu-C) for the electrooxidation of methanol. Figure 2 shows the voltammograms obtained on Pt-TiN and Pt-C in presence of acidified methanol. TiN supported catalyst performs better than carbon supported catalyst in terms of high currents at low over voltages (based on I-t measurements), long term stability and high exchange current densities (based on Tafel studies). The electrochemical characteristics of methanol oxidation on Pt-TiN and Pt-C catalysts are given in table 1. The current densities observed on TiN supported catalyst are almost three times higher than that of carbon supported catalyst confirming the promoting effect of TiN support towards methanol oxidation reaction. The performance of Pt-TiN electrocatalyst under fuel cell conditions reveals peak power densities close to 396 mW/cm2 at a current density of 375 mA/cm2, at 90C. Table 1. Characteristics of methanol oxidation on TiN and carbon supported catalysts in acidic medium. Material Onset Ep (mV) Ip EAA Ip Ip/Ib E=Ep-Eb potential (mA/mg (cm2/mg)b (mA/cm2 (mV) of Pt)a of Pt)c (mV) Pt-TiN 170 720 56 78.4 0.714 1.24 82 Pt-C 250 700 18 68.6 0.262 0.98 106 a Mass activity; Ip is the forward peak current and Ib is the reverse peak current; Ep and Eb are forward and reverse peak potentials. b Electrochemically active area (EAA) c Current density normalized for EAA Figure 3. In-situ FTIR spectra on bare TiN surface as a function of applied DC bias vs.SCE. The spectra are shown in regions of 1000 to 2000 cm-1 (A) and 2500 to 4000 cm-1 (B). Electrolyte used is 0.5 M methanol in 0.5 M H2SO4. Reference spectrum is obtained at 0 V. In-situ FTIR spectroelectrochemical measurements have been carried out to understand the intermediates and products formed during methanol oxidation. TiN surface is highly reflective and is quite amenable for reflectance IR studies. Figure 3 shows the potential dependant spectral characteristics of TiN in methanolic sulphuric acid. The bands observed at 1600 and 3600 cm-1 correspond to –OH bending and stretching vibrations of adsorbed water molecules. Interestingly, bands corresponding to adsorbed water are observed even at remarkably low over potentials of around 0.1 V vs. SCE where CO poisoning of Pt can be very severe. This experiment confirms the ability of inexpensive TiN to function like expensive Ru in fuel cell catalysis. Similar studies have been carried out for ethanol electrooxidation on TiN supported catalysts such as Pd, Pt and PtRu in acidic as well as alkaline conditions. Adherence of fuel cell catalyst on to TiN and carbon support is followed by cycling the electrode potential continuously as shown in figure 4. The adherence of Pd on TiN surface is very good and the stability tests reveal that Pd adheres and remains on TiN for a long time as compared to carbon support. Figure 4. Cyclic voltammograms of Pd-C (A) and Pd-TiN (B) in 1 M KOH at 100 mV/s. Pd loading used is 83 µg/cm2. In the chapter on borohydride oxidation, bare TiN electrode is used for the electrochemical oxidation of sodium borohydride. In direct borohydride fuel cells (DBFC), H2 evolution that occurs at low over voltages decreases the apparent number of electrons transferred and consequently the fuel cell efficiency. TiN has been shown to be a relatively H2 evolution-free electrocatalyst for borohydride oxidation (figure 5A). As shown in figure 5A, no H2 oxidation is observed (below -0.5 V) on TiN surface with increase in concentration of borohydride. This point to the fact that direct oxidation of borohydride is very favourable on TiN electrode and is confirmed by fuel cell measurements as shown in figure 5B. Non-platinum DBFCs using TiN as the anode (borohydride oxidation) and prussian blue supported carbon (PB-C) as the cathode (oxygen or hydrogen peroxide) electrocatalysts (figure 5B) reveal peak power density of 107 mW/cm2 for a current density 130 mA/cm2, at 80C. Figure 5. Cyclic voltammograms of TiN in 1 M NaOH containing varying concentrations of borohydride at a scan rate of 20 mV/s (A). Polarization studies of DBFC with TiN anode catalyst and PB-C (prussian blue supported on carbon) cathode catalyst (B). Anolyte is 0.79 M borohydride in 5 M NaOH and catholyte is 2.2 M acidified H2O2. The second aspect of the thesis is related to the use of TiN to prepare visible light active, nitrogen doped TiO2 (N-TiO2). This is carried out by electrochemical anodization of TiN in 0.5 M HNO3 at 1.4 V. The X-ray photoelectron spectroscopy (XPS) suggests the formation of oxide phase on anodized TiN surface (figure 6A) and is confirmed by reflectance UV-Visible spectroscopy. The visible light activity is used for the sunlight induced reduction of graphene oxide to reduced graphene oxide. As shown in the Raman spectra (figure 6B), a negative shift of the D and G band positions by about 20 cm-1 and the intensity ratio reversal after reduction confirms the formation of reduced graphene oxide on N-TiO2. Figure 6. (A) Ti (2p) region of XPS of fresh TiN and anodized TiN. Anodization has been carried out at 1.4 V vs. SCE in 0.5 M HNO3. (B) Raman spectra of exfoliated graphene oxide on anodized TiN before and after sunlight induced reduction. In summary, TiN has been shown to be an active support material for fuel cell catalysts in the present studies. The appendix details the basic electrochemical studies on TiN using various redox couples, electroploymerization of aniline and the formation of nanostructures on TiN surface. (For figures pl refer the abstract pdf file)

Alloys, intermetallic compounds and multi-metal oxides are generally made by traditional solid-state methods that often require melting or grinding/pressing powders followed by high temperature annealing (> 1000 degrees C) for days or weeks. The research presented here takes advantage of the fact that nanoparticles have a large fraction of their atoms on the surface making them highly reactive and their small size virtually eliminates the solid-solid diffusion process as the rate limiting step. Materials that normally require high temperatures and long annealing times become more accessible at relatively low-temperatures because of the increased interfacial contact between the nanoparticle reactants. Metal nanoparticles, formed via reduction of metal salts in an aqueous solution and stabilized by PVP (polyvinylpyrrolidone), were mixed into nanoparticle composites in stoichometric proportions. The composite mixtures were then annealed at relatively low temperatures to form alloy and intermetallic compounds at or below 600 degrees C. This method was further extended to synthesizing multi-metal oxide systems by annealing metal oxide nanoparticle composites hundreds of degrees lower than more traditional methods. Nanoparticles of Pt (supported or unsupported) were added to a metal salt solution of tetraethylene glycol and heated to obtain alloy and intermetallic nanoparticles. The supported intermetallic nanoparticles were tested as catalysts and PtPb/Vulcan XC-72 showed enhanced catalytic activity for formic acid oxidation while Pt3Sn/Vulcan XC-72 and Cu3Pt/y-Al2O3 catalyzed CO oxidiation at lower temperatures than supported Pt. Intermetallic nanoparticles of Pd were synthesized by conversion chemistry methods previously mentioned and were supported on carbon and alumina. These nanoparticles were tested for Suzuki cross-coupling reactions. However; the homocoupled product was generally favored. The catalytic activity of Pd3Pb/y-Al2O3 was tested for the Heck reaction and gave results comparable to Pd/y-Al2O3 with a slightly better selectivity. Conversion chemistry techniques were used to convert Pt nanocubes into Ptbased intermetallic nanocrystals in solution. It was discovered that aggregated clusters of Pt nanoparticles were capable of converting to FePt3; however, when Pt nanocubes were used the intermetallic phase did not form. Alternatively, it was possible to form PtSn nanocubes by a conversion reaction with SnCl2.

Abstract The objective of this thesis is to demonstrate multi-dimensional carbon nanotube (CNT) structures in combination with various active materials in order to evaluate their performance in electrode applications such as cold emitters, electric double-layer capacitors (EDLC), and electrochemical sensor/catalyst devices. As the host materials for other active materials, the construction of multi-dimensional CNT nanostructures in this thesis is achieved by two different approaches. In the first, direct growth of 3-dimensional carbon nanostructures by catalytic chemical deposition to produce filamentary carbon as well as vertically aligned forests was applied. The second route that was utilized encompassed the immobilization of CNTs from dispersions to form 2-dimensional surface coatings as well as self-supporting porous buckypapers. Carbonaceous nanocomposites of the active materials are obtained by a number of different methods such as (i) growing nanotubes and filamentous structures on porous Ni catalyst structures, (ii) impregnating CNTs with organic receptor molecules or with Pd nanoparticles, (iii) plating and replacing Cu with Pd on the nanotubes by chemical and galvanic reactions, (iv) annealing W evaporated on CNTs to form CNT-WC composites in solid-solid reactions and (v) reacting S vapor with W coated on CNTs to synthesize CNT-WS2 edge-on lamellar structures of the dichalcogenide in the vertically aligned CNT forests. The 3-dimensional carbon-Raney®Ni composite electrodes show reasonable specific capacitance of ~12 F·g-1 in electric double-layer capacitors as well as a low turn-on field (<1.0 V·µm-1) in field emitter devices. CNT-Nafion®-trifluoroacetylazobenzene coatings on glassy carbon electrodes outperform their Nafion®-trifluoroacetylazobenzene counterparts in electrochemical sensing of different amine compounds (e.g. 10 mM cadaverine, putrescine or ammonia). Cu and CuPd/buckypaper composites display catalytic activity in electrocatalytic oxidation of methanol in alkaline media. On the other hand, nanocomposites of WC and WS2 with aligned CNT forest exhibit a promising performance in hydrogen evolution reactions with an overpotential between -0.5 and -0.7 V at pH~1. In addition, these respective CNT forest aligned nanocomposites also demonstrate a novel method to obtain macroscopic 3-dimensional catalytic electrode assemblies. The results in this thesis elucidate the combination of carbon based nanostructures with organic and inorganic materials as a feasible and versatile approach to produce electrodes for several applications. The following studies of each active carbonaceous composite are expected to boost the technological innovation in relevant fields and initiate further development for commercial exploitation. / Tiivistelmä Työn tavoitteena oli demonstroida moniulotteisia hiilinanoputkirakenteita (CNT), joihin yhdistetään erilaisia aktiivisia materiaaleja sekä arvioida niiden suorituskykyä elektrodisovelluksissa, kuten kenttäemitterissä, sähköisissä kaksoiskerroskondensaattoreissa ja sähkökemiallisissa anturi- ja katalyyttikomponenteissa. Moniulotteisten CNT-nanorakenteiden konstruoiminen muiden aktiivisten materiaalien isäntämateriaaliksi toteutettiin kahdella tavalla. Ensimmäisessä toteutuksessa sovellettiin katalyyttis-kemiallista pinnoitusta, jolla kasvatettiin suoraan kolmiulotteisia hiilinanorakenteita sekä kuitumaisena hiilenä että pystysuuntaan orientoituneina hiilinanoputkimetsinä. Toinen päämenetelmä oli hiilinanoputkien immobilisointi dispersioista kaksiulotteisiksi pinnoitteiksi ja itsetukeutuviksi huokoisiksi hiilinanoputkipapereiksi. Hiiltä sisältäviä aktiivisten materiaalien nanokomposiitteja valmistettiin useilla menetelmillä, kuten (i) kasvattamalla nanoputkia ja kuitumaisia rakenteita huokoisiin Ni-katalyyttirakenteisiin, (ii) kyllästämällä hiilinanoputkia orgaanisilla reseptorimolekyyleillä tai Pd-nanopartikkeleilla, (iii) pinnoittamalla ja korvaamalla nanoputkien päällä olevaa kuparia palladiumilla kemiallisten ja galvaanisten reaktioiden avulla, (iv) hehkuttamalla hiilinanoputkien pinnalle höyrystettyä wolframia (W) muodostamaan CNT-WC-komposiitteja kiinteä–kiinteä-reaktiolla sekä (v) antamalla rikkihöyryn reagoida W-pinnoitettujen hiilinanoputkien kanssa lamellaaristen CNT-WS2-kalkogenidirakenteiden syntetisoimiseksi pystysuuntaan orientoituneisiin CNT-metsiin. Kolmiulotteisilla hiili–Raney®Ni-komposiittielektrodeilla saavutetaan kohtuullinen ominaiskapasitanssi (~12 F·g-1) sähköisissä kaksoiskerroskondensaattoreissa ja pieni kytkeytymiskenttä (<1,0 V·μm-1) kenttäemitterikomponenteissa. CNT-Nafion®-trifluoroasetyyliatsobentseeni-pinnoitteet lasimaisilla hiilielektrodeilla ovat selvästi parempia erilaisten amiiniyhdisteiden (esimerkiksi 10 mM kadaveriini, putreskiini tai ammoniakki) sähkökemiallisessa havaitsemisessa kuin vastaavat Nafion®-trifluoroasetyyliatsobentseeni-pinnoitteet. Cu- ja CuPd-hiilinanoputkipaperikomposiitit osoittavat katalyyttistä aktiivisuutta metanolin sähkökatalyyttisessä hapettumisessa emäksisessä väliaineessa. Toisaalta WC- ja WS2-yhdisteiden ja orientoituneiden CNT-metsien muodostamat nanokomposiitit osoittavat lupaavaa suorituskykyä vedynmuodostamisreaktiossa -0,5…-0,7 V ylipotentiaalilla, ja nämä myös demonstroivat uutta menetelmää makroskooppisten kolmiulotteisten katalyyttisten elektrodirakenteiden toteuttamiseksi. Väitöskirjan tulokset osoittavat, että hiilipohjaisten nanorakenteiden ja orgaanisten/epäorgaanisten materiaalien yhdistäminen on toteuttamiskelpoinen ja monipuolinen lähestymistapa elektrodien valmistamiseksi useisiin sovelluksiin. Kunkin työssä esitetyn aktiivista hiiltä sisältävän komposiitin tutkimuksen odotetaan lisäävän kyseisen alan teknisiä innovaatioita ja synnyttävän lisää kehitystyötä tutkimuksen kaupalliseksi soveltamiseksi.