• Hiltunen, Arto J.

Abstract

Global warming, caused by the enormous use of fossil fuels to supply our energy demand, is forecast to have a negative net impact on the life on Earth. To fight the excessive heating of the planet, alternative energy technologies to replace the burning of fossil fuels should be explored. In many contexts hydrogen economy stands out as one of the most prominent alternative for the contemporary fossil economy. Hydrogen can be separated from water in the form of hydrogen gas, which reacts back to water when burned to heat or when used in an electrochemical cell to produce electricity. Thus hydrogen can provide a CO2 free source of heat and electricity if the processes for hydrogen gas production are CO2 free. This thesis deals with materials that are able to produce hydrogen gas from water using solar power as the driving force. In this thesis we describe the fabrication of adjustable porous weblike metal oxide nanostructures from cellulose templates. The templated structures were tested in solar water splitting (i.e. hydrogen production) as well as in dye-sensitized solar cells. The fabrication begun by casting a porous cellulose template which then was coated with titanium dioxide using atomic layer deposition (ALD). The ability of the ALD-technique to make nanometer precision coatings enabled us to run optimization on the coating thickness for more efficient solar to hydrogen conversion. Moreover, as a result of varying the coating thickness we were able to reveal the progression of ALD-TiO2 film growth on the cellulose templates. Finally, in order to extend the absorption of the TiO2 photoanodes an additional ALD-Fe2O3 layer was deposited on the surface of TiO2. An increase in photocurrent was observed as a result of extended range of visible light absorption which was attributed to the formation of iron titanium oxides. The results of this thesis clearly show that atomic layer deposition combined with cellulose templating can be used to fabricate materials for sustainable CO2-free energy production that complies with the current climate goals. In light of the results presented here, we expect the ever developing atomic layer deposition techniques of new materials together with the abundance of cellulose templates available in forms of nanofibers and nanocrystals to have the potential to provide new high performance materials for the needs of sustainable energy production.

Topics

• porous
• impedance spectroscopy
• surface
• Hydrogen
• casting
• titanium
• iron
• cellulose
• atomic layer deposition