Preliminary studies on solar water splitting cells and their principle, and preparation of iron(III) oxide photoelectrodes

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Perustieteiden korkeakoulu | Bachelor's thesis
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Teknillinen fysiikka
Degree programme
Teknillinen fysiikka ja matematiikka TFM
In solar water splitting, the abundant and sustainable solar radiation is directly utilized to split water through electrolysis and form hydrogen, which can be used as energy carrier. In the cell, the photo-active semiconductor (usually n-type) absorbs photons which excite electrons from the valence band into the conduction band. At the cathode, the excited electrons reduce water to form hydrogen gas. Semiconductor material has to fulfill several requirements for efficient solar hydrogen production, e.g.: strong light absorption, high chemical stability, and fast charge transport. To date, no single material has been found to fulfill all requirements but iron(III) oxide (hematite, α-Fe2O3) is one of the most promising materials. In the thesis solar water splitting was studied by preparing hematite photoelectrodes (PE) and preliminary cells. Preparation of PEs was found to be challenging because of many parameters: substrate material, hematite source, sintering temperature and time, thickness of the film etc. By developing the preparation methods, smooth and stable hematite PEs could be produced from hematite nanopowder solution via spin-coating. Different cell assemblies and electrolytes were tested. The cells were evaluated by performing current-voltage measurements with a solar simulator. The solar response of the hematite PEs was almost negligible due to fast electron-hole recombination, but consistent with earlier studies. The electrolyte seemed to trap between the electrodes, and with mechanical stirring of the electrolyte higher currents were measured, and also a slight solar response was detected. To obtain higher solar response with hematite PEs, further development or treatment of the material is needed (doping, nanostructures, tandem cells).
Lund, Peter
Thesis advisor
Kemppainen, Erno
solar hydrogen, solar water splitting, photoelectrolysis, hematite, photoelectrode, solar fuel
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