Palladium Electrocatalysis On Hydrothermal Nanocarbon Supports And Non-conventional Environments

Carbon nanomaterials preparation and their functionalization have currently become a hot topic. Hydrothermal carbonization synthesis based biomass offers a cost-effective method for preparation and functionalization of carbon nanomaterials due to cheap and environmentally friendly precursors. In addition, biomass rich in various functional moieties such as amino, hydroxyl and carboxyl also offers versatile possibility for carbon nanomaterials functionalization. Palladium-based electrocatalyst exhibits high catalytic activity in several electrochemical processes such as oxygen reduction reaction (ORR) and reduction of small organic molecules. In this thesis, the first part is concerned with Pd electrocatalysis in amino-functionalized hydrothermal carbon nanomaterials based chitosan. The second part concerns palladium electrocatalysis in non-conventional environments such as salt matrix and the pore of the polymers of intrinsic microporisity (PIMs). These conclusions are summarized as follows:(1) The preparation of amino-functionalized carbon nanoparticles via partial hydrothermal carbonization from chitosan at180℃(or200℃,230℃) for12h. Raman analysis suggests amorphous carbon core but film electrodes show completely electrically insulating. Anion adsorption capability is exploited in conjuction with a second negatively charged carbon nanoparticles Emperor2000. The useful positive charge is maximized at a hydrothermal carbonization temperature of200℃with a specific anion binding capacity of70Cg-1(2) The preparation of hydrothermal core-shell nanocarbon. Carbon nanoparticles with phenylsulfonate negative surface functionality (Emperor2000, Cabot Corp.) are coated with positive chitosan followed by hydrothermal carbonization to give pH-responsive core shell nanocarbon composites. With optimised core-shell ratio (resulting in an average shell thickness of ca.4nm, estimated from SANS data) modified electrodes exhibit highly pH-sensitive resistance, capacitance and Faradaic electron transfer responses (solution based, covalently bound, or hydrothermally embedded). A shell "double layer exclusion" mechanism is discussed to explain the observed pH switching effects. (3) A nanocomposite of carbon nanoparticles (Emperor2000TM), chitosan, and nano-palladium is synthesized in a one-step hydrothermal process with oxalate used as reducing agent. Nano-palladium composites show selective electrocatalysis toward small molecules as well as strong pH effects on capacitive and Faradaic current responses. Implications of selective electrocatalysis toward small molecules in fuel cell application are discussed.(4) An alternative electrochemical system with the gas phase in closer contact to palladium nanoparticle catalyst is investigated based on a glassy carbon electrode and a solid salt electrolyte. Two relevant redox systems is under investigation:(i) the oxidation of formic acid and (ii) the oxidation of hydrogen. The effects of the type of salt, the partial pressure of formic acid, and the gas flow rate are investigated. A significant salt effect on the palladium catalyzed reaction is observed and potential future applications of "salt cells" in sensing are discussed. It is demonstrated that the reaction zone of salt (here (NH4)2SO4is most effective), palladium nanoparticle catalyst, and gas phase, is where the electrochemical oxidation process occurs. MEA is employed as both a counter electrode and working electrode (with an external SCE reference electrode) for oxidation of hydroquinone in contact with ammonium sulphate under humidified nitrogen gas. A well-defined redox response could be observed.(5) Two intrinsically microporous polymers (PIMs)(i) ethanoanthracene TB-PIM (MW70kDa, BET surface area1027m2) and (ii) dimethyldiphenylmethane TB-PIM (MW100kDa, BET surface area47m2or PIM-L) are investigated as emerging novel membrane and catalyst support materials. Binding sites and binding ability/capacity in aqueous environments are compared in films deposited onto glassy carbon electrodes for (i) indigo carmine dianion immobilisation (weakly binding from water-ethanol) and (ii) PdCl42-immobilisation (strongly binding from acidic media). Electrocatalytic oxidation of formic acid (at pH6) is investigated for PIM-L and PIM-H as a function of film thickness. The more rigid high BET surface area material PIM-H exhibits "open-pore" characteristics with much more promising electrocatalytic activity at Pd within polymer pores.