Visible-light-induced water splitting on a chip

In this thesis, a photoelectrochemical water splitting cell concept is discussed, based on a combination of semiconductors comprising a Z-scheme. The motivation for the development of the cell is that in the future a transition will take place from a fossil fuel-based economy, to an economy based on renewable energy sources. These renewable energy sources, like solar and wind, fluctuate in yield over time, and require temporary storage of energy till the moment it is needed. An option to store the energy is by decomposition of water, by which H2 is formed, which can be used as an energy carrier. Alternatively to a single photoelectrochemical cell, electricity generated by solar cells can be fed into an electrolysis cell, in which water splitting into H2 and O2 can be achieved. However, H2 produced in this way is much more expensive than H2 made out of fossil fuels. If the goal of a single cell solar-to-H2 efficiency of 10% could be reached, the price per kg H2 could be between the $2.00 - $4.00. The photoelectrochemical water splitting concept we propose and discuss in this thesis, consists out of a Pt divider, on the opposite sides of which WO3 is deposited as photoanode, and Rh:SrTiO3 as photocathode. The concept is based on Z-scheme water splitting, where two semiconductors are combined for full water splitting. Therefore, first a study was done at a powder system of WO3 and Rh:SrTiO3. Here a Fe2+/Fe3+ electron mediator was used to transfer electrons between both photocatalysts. Our measurements showed that the electron mediator did not work as reported in literature, and that short circuiting of the two iron half reactions occurred and this limited full water splitting. Therefore it could be a solution to replace the iron-couple with a conducting Pt film