Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 nanotube arrays and application in visible light driven water splitting

Abstract

We report successful synthesis of low band gap inorganic polyphosphide and TiO₂ heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP₇, SnIP, and (CuI)₃P₁₂) were successfully reacted and deposited into electrochemically fabricated TiO₂ nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO₂ nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP₇. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO₂ hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO₂ emerged to be the most active among the polyphosphide@TiO₂ materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO₂.