ZnFe 2 O 4 Leaves Grown on TiO 2 Trees Enhance Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) processes offer a direct use of sunlight for a large variety of applications, including hydrogen production for energy storage, as well as hydroxyl radical formation for pollutant degradation. [ 1,2 ] Among the various photocatalysts developed to date, TiO 2 is particularly suited to commercial scale-up because it is abundant, nontoxic, and stable under photochemical conditions. [ 3–6 ] Unfortunately, its large bandgap limits its photoactivity to the ultraviolet (UV) region. As a result, in the best case it can absorb only up to 5% of incident solar photons. This limits its potential to increase further in photoelectrochemical effi ciency. Strategies to expand the TiO 2 optical absorption spectrum into the visible region include the sensitization of TiO 2 with dyes or small-bandgap semiconductors, [ 7–9 ] doping, [ 10–13 ]