Exploiting the Bragg Mirror Effect of TiO₂ Nanotube Photonic Crystals for Promoting Photoelectrochemical Water Splitting.

Abstract

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO₂ 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 TiO₂ nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO₂ nanotube photonic crystals overlaps with the electronic bandgap of TiO₂, the bottom TiO₂ nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO₂ nanotube layer. Benefiting from the promoted UV light absorption, the TiO₂ NT-115-NTPC yields a photocurrent density of 1.4 mA/cm² at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO₂ 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.