Electrochemical coating of micro-structured silicon for photoelectrochemical water splitting

The generation and storage of renewable energy is one of the key challenges for the transition to a sustainable society. Hydrogen (H2), the most abundant element on earth, is believed to be an important energy carrier in the near future. It can be either used directly as a fuel, or further converted with CO2 to form hydrocarbons through well-known catalytic processes. Water is the most sustainable resource for production of hydrogen. A highly promising approach to generate hydrogen from water is photoelectrochemistry. Such a device aims to integrate photovoltaics (solar panels) and electrolysis, potentially being an efficient energy conversion system.

The research described in this thesis focuses on the development of photoelectrochemical devices for hydrogen generation from water. In particular, electrochemistry was utilized to coat flat and microwire-structured silicon, one of the main materials in photovoltaic cells, with metals or semiconductors. These layers are necessary, among others, to facilitate oxygen or hydrogen evolution, improve the use of the solar spectrum, and increase photovoltage of devices. Silicon microwire structuring enhances light absorption and increases the active surface area for reaction. The findings of this work provide: i) a way to control the size and density of platinum particles on Si surfaces, ii) a method to deposit materials spatioselectively on top and bottom segments of microwires with axial p/n junctions, iii) a theory for deactivation of tungsten oxide in water oxidation, and iv) evaluation of the functionality of bismuth vanadate, when deposited onto silicon microwires.