Although clean energy can be produced economically from aeolian, hydro, solar, etc., only a minor part is stored, since as yet, there is no perfect energy storage technology . Hydrogen offers a viable approach with a large storage capacity of 142 MJ/kg. At present, more than 95% of the hydrogen produced is obtained by steam methane reforming. Although this is the most efficient technology known at present (> 70% efficiency ), this way of producing hydrogen is far from being clean or sustainable, since for every ton of hydrogen produced, 2 to 9 tons of CO2 are emitted depending on the details of the process. Water dissociation into H2 and O2 through electrolysis, offers an alternative for hydrogen production, particularly when using electricity from renewable sources. An important amount of external electrical energy input is mandatory to overcome the water redox potential of 1.23 V (1.6 V if we consider overpotentials at the electrodes). As an example, an industrial electrolyser producing 750 Nm 3 /h consumes an electrical energy of approx. 5 kWh for each Nm 3 of H2 produced . Since 1972, when Fujishima and Honda first proposed the concept of using photosensitive anodes, like TiO2, in dedicated photoelectrochemical (PEC) cells to split water, a major research effort has been devoted to optimizing semiconductor photoelectrodes, to match a list of needed properties regarding: i) light absorption, ii) surface kinetics during electrochemical reactions, iii) charge separation and bulk electrical conduction, iv) chemical composition and stability, etc. .