3D FTO/FTO‐Nanocrystal/TiO2 Composite Inverse Opal Photoanode for Efficient Photoelectrochemical Water Splitting

A 3D fluorine‐doped SnO₂ (FTO)/FTO‐nanocrystal (NC)/TiO₂ inverse opal (IO) structure is designed and fabricated as a new “host and guest” type of composite photoanode for efficient photoelectrochemical (PEC) water splitting. In this novel photoanode design, the highly conductive and porous FTO/FTO‐NC IO acts as the “host” skeleton, which provides direct pathways for faster electron transport, while the conformally coated TiO₂ layer acts as the “guest” absorber layer. The unique composite IO structure is fabricated through self‐assembly of colloidal spheres template, a hydrothermal method and atomic layer deposition (ALD). Owing to its large surface area and efficient charge collection, the FTO/FTO‐NC/TiO₂ composite IO photoanode shows excellent photocatalytic properties for PEC water splitting. With optimized dimensions of the SnO₂ nanocrystals and the thickness of the ALD TiO₂ absorber layers, the 3D FTO/FTO‐NC/TiO₂ composite IO photoanode yields a photocurrent density of 1.0 mA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5 illumination, which is four times higher than that of the FTO/TiO₂ IO reference photoanode.