Exploiting the Bragg Mirror Effect of TiO Nanotube Photonic Crystals for Promoting Photoelectrochemical Water Splitting.

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO nanotube photonic crystal bi-layer structure consisting of a top nanotube layer and a bottom nanotube photonic crystal layer is presented. In this architecture, the photonic bandgap of bottom TiO nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO nanotube photonic crystals overlaps with the electronic bandgap of TiO, the bottom TiO nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO nanotube layer. Benefiting from the promoted UV light absorption, the TiO NT-115-NTPC yields a photocurrent density of 1.4 mA/cm at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO nanotube arrays. Furthermore, incident photon-to-current conversion efficiency is also promoted within ultraviolet light region. This research offers an effective strategy for improving the performance of photoelectrochemical water splitting through intensifying the light-matter interaction.