The most surprising observation is the fact that the NiOx-TiO2 photocathode not only exhibits the highest IPCE values, which can be well conceived in terms of p/n junction formation, but exhibits a significant photoresponse even in the visible range (down to 550 nm). The latter observation is rather puzzling given the fact that both NiOx (bandgap of 3.3 eV) and TiO2