Synthesis and characterization of controlled metal nanostructures for electrochemical applications

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Nguyet Doan Name of the doctoral dissertation Synthesis and characterization of controlled metal nanostructures for electrochemical applications Publisher School of Chemical Technology Unit Department of Chemistry Series Aalto University publication series DOCTORAL DISSERTATIONS 177/2016 Field of research Physical Chemistry Manuscript submitted 15 June 2016 Date of the defence 23 September 2016 Permission to publish granted (date) 31 August 2016 Language English Monograph Article dissertation Essay dissertation Abstract Metal nanoparticles synthesed by using wet chemical route and nanostructures by electrodeposition has attracted much attention because their properties differ from those of the same material in bulk form and the ease of the electrodeposition method which allows control of the film thickness.These nanostructures have numerous potential applications in various areas such as biomedical sciences, electrodes, optics, magnetism, energy storage and electrochemistry. In the first part of this thesis, synthesis and properties of cobalt and gold nanoparticles were studied. In order to investigate their size distribution and oxidation with different capping ligands, cobalt nanoparticles were synthesized with the decomposition method.Tridodecyl amine stabilized Co nanoparticles with different sizes (8, 22, and 36 nm) were prepared by thermal decomposition of Co2(CO)8 in dodecane, and e.g. particles with an average diameter of 8 nm and a standard deviation of 8 % were obtained. The oxidation of different sized cobalt nanoparticles was studied. The particles capped with carboxylic acid had become hollow and oxidized throughout, while the tridodecyl amine capped ones appeared to have a small core surrounded by oxidized shell. Gold nanoparticles were used as probes to visualize the surface density of functional molecules on silica. The second part of this thesis was focused on preparing nanostructures and mesostructures using an electrodeposition method. Zn/ZnO macroporous films were synthesized via electrodeposition using polystyrene spheres as a template. Subsequent oxidation of the films at elevated temperature yielded structured ZnO films. The results of this work showed that high quality templated Zn and ZnO films can be electrodeposited from ionic liquid onto both semiconductor (ITO) and metallic (Au) substrates. Pt mesoporous films were synthesized via electrodeposition using a liquid crystalline template method. Mesoporous Pt and Pt@CB were electrodeposited using both galvanostatic and potentiostatic methods from liquid crystal templates resulting in Pt structures with pores in the 3-5 nm size range. The Pt@CB electrocatalyst was shown to have a high potential for direct ethanol fuel cells. Pt mesostructures were applied in fuel cells as anodes. Polarization and power curves for both the commercial Pt and the electrodeposited mesoporous Pt at different temperatures (30 ° C, 50 °C and 70 °C) were studied, showing an increase in the performance with the temperature. All the mesoporous samples showed better or similar performance in the direct ethanol fuel cell in comparison with the commercial Pt sample.Metal nanoparticles synthesed by using wet chemical route and nanostructures by electrodeposition has attracted much attention because their properties differ from those of the same material in bulk form and the ease of the electrodeposition method which allows control of the film thickness.These nanostructures have numerous potential applications in various areas such as biomedical sciences, electrodes, optics, magnetism, energy storage and electrochemistry. In the first part of this thesis, synthesis and properties of cobalt and gold nanoparticles were studied. In order to investigate their size distribution and oxidation with different capping ligands, cobalt nanoparticles were synthesized with the decomposition method.Tridodecyl amine stabilized Co nanoparticles with different sizes (8, 22, and 36 nm) were prepared by thermal decomposition of Co2(CO)8 in dodecane, and e.g. particles with an average diameter of 8 nm and a standard deviation of 8 % were obtained. The oxidation of different sized cobalt nanoparticles was studied. The particles capped with carboxylic acid had become hollow and oxidized throughout, while the tridodecyl amine capped ones appeared to have a small core surrounded by oxidized shell. Gold nanoparticles were used as probes to visualize the surface density of functional molecules on silica. The second part of this thesis was focused on preparing nanostructures and mesostructures using an electrodeposition method. Zn/ZnO macroporous films were synthesized via electrodeposition using polystyrene spheres as a template. Subsequent oxidation of the films at elevated temperature yielded structured ZnO films. The results of this work showed that high quality templated Zn and ZnO films can be electrodeposited from ionic liquid onto both semiconductor (ITO) and metallic (Au) substrates. Pt mesoporous films were synthesized via electrodeposition using a liquid crystalline template method. Mesoporous Pt and Pt@CB were electrodeposited using both galvanostatic and potentiostatic methods from liquid crystal templates resulting in Pt structures with pores in the 3-5 nm size range. The Pt@CB electrocatalyst was shown to have a high potential for direct ethanol fuel cells. Pt mesostructures were applied in fuel cells as anodes. Polarization and power curves for both the commercial Pt and the electrodeposited mesoporous Pt at different temperatures (30 ° C, 50 °C and 70 °C) were studied, showing an increase in the performance with the temperature. All the mesoporous samples showed better or similar performance in the direct ethanol fuel cell in comparison with the commercial Pt sample.