Studies of regular nanostructures for solar water splitting

Abstract

In pursuit of a sustainable energy economy, solar hydrogen generation via direct electrolysis using sunlight is a promising approach towards ecologically friendly fuels. However, photodriven water splitting faces numerous challenges that have to be overcome towards the development of stable and efficient systems, from the designing of new materials, to optimizing of light harvesting and integrating protection schemes for long-term viability. In this pursuit, TiO2 can serve in either of two roles: as a high band-gap absorber or as a protective coating for efficient semiconductors. In this work, the system of highly doped Silicon coated with atomic layer deposited TiO2 was studied with regard to deposition parameters, photoelectrochemical properties and the corrosion process. Amorphous films suffered from significant degradation under illumination in dilute sulphuric acid, which was found to be a two-fold process, chemical etching and a UV-photon induced photocorrosion. Stable and mostly crystalline anatase thin films were coated on precisely and (sub-)micro structured electrodes, based on lithography and plasma etching methods for Silicon, to increase active surface area, increase light absorption and reduce reflective losses. The correlation between structural shape and dimensions was evaluated in regard of beneficial and detrimental factors and an the impact of the conductive substrate became apparent. Optical simulation served to study the influence of electrode surface structuring on light management and is proposed as an invaluable tool for smart design of efficient, structured photoelectrodes.