Morphology and interfacial energetics controls for hierarchical anatase/rutile TiO₂ nanostructured array for efficient photoelectrochemical water splitting

In this work, a three-dimensional (3D) hierarchical TiO₂ nanostructured array is constructed on the basis of the considerations of morphology and interfacial energetics for photoelectrochemical water splitting. The photoelectrode is composed of a core-shell structure where the core portion is a rutile TiO₂ nanodendrite (ND) array and the shell portion is rutile and anatase TiO₂ nanoparticles (NPs) sequentially located on the surface. The TiO₂ ND array provides a fast electron transport pathway due to its quasi-single-crystalline structure. The 3D configuration with NPs in the shell portion provides a larger surface area for more efficient photocharge separation without significantly sacrificing the electron collection efficiency. Moreover, anatase TiO₂ NPs constructed on the surface of the ND/rutile TiO₂ NP nanostructured array enhance charge separation and suppress charge recombination at the interfacial region due to the higher conduction band edge of anatase TiO₂ compared to that of rutile TiO₂. A photocurrent density and photoconversion efficiency of 2.08 mA cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) and 1.13% at 0.51 V vs RHE are, respectively, attained using the hierarchical TiO ₂ nanostructured array photoelectrochemical cell under illumination of AM 1.5G (100 mW cm^-2).