Enhanced photoelectrochemical water splitting by a 3D hierarchical sea urchin-like structure: ZnO nanorod arrays on TiO2hollow hemisphere.

A hierarchical sea urchin-like hybrid metal oxide nanostructure of ZnO nanorods deposited on TiO2 porous hollow hemisphere with a thin zinc titanate interface layer is specifically designed and synthesized forming a combined type I straddling and type II staggered junctions. The HHSs, synthesized by electrospinning, facilitate light trapping and scattering. The ZnO nanorods offer a large surface area for improved surface oxidation kinetics The interface layer of zinc titanate (ZnTiO3) between the TiO2 HHSs and ZnO nanorods regulates the charge separation in a closely coupled hierarchy structure of ZnO/ZnTiO3/TiO2. The synergistic effects of improved light trapping, charge separation, and fast surface reaction kinetics result in a superior photoconversion efficiency of 1.07% for the photoelectrochemical (PEC) water splitting with an outstanding photocurrent density of 2.8 mA cm-2 at 1.23 V vs. RHE.

Light trapping by porous TiO2 hollow hemispheres for high efficiency photoelectrochemical water splitting.

Photocatalytic water splitting has recently received increasing attention as a green fuel source. The controlled nano-geometry of the photocatalytic material can improve light harvesting. In this study, as a proof of concept, hollow hemisphere (HHS)-based films of TiO2 material were created by a conventional electrospray method and subsequently applied for photoelectrochemical (PEC) water splitting. To preserve the morphology of the HHS structure, a hydrolysis precipitation phase separation method (HPPS) was developed. As a result, the TiO2 HHS-based thin films presented a maximum PEC water splitting efficiency of ca. 0.31%, almost two times that of the photoanode formed by TiO2 nanoparticle-based films (P25). The unique morphology and porous structure of the TiO2 HHSs with reduced charge recombination and improved light absorption are responsible for the enhanced PEC performance. Light scattering by the HHS was demonstrated with total reflection internal fluorescence microscopy (TRIFM), revealing the unique light trapping phenomenon within the HHS cavity. This work paves the way for the rational design of nanostructures for photocatalysis in fields including energy, environment, and organosynthesis.