Constructing phosphorus-doped TiO2 hierarchical nanotube arrays via a simple route for enhanced photoelectrochemical water oxidation

Abstract

In this paper, we first prepared amorphous TiO₂ hierarchical nanotube arrays (photonic crystal-like top layer/nanotube array bottom layer) through a two-step anodic oxidation process, and then constructed phosphorus-doped crystalline TiO₂ hierarchical nanotube arrays via a simple impregnation/calcination method, using phosphate buffer as a phosphorus precursor. Various characterization techniques were used to confirm the structure and properties of the prepared photoanodes. The influence of different preparation parameters (impregnation time/pH/concentration of the phosphate precursor, anodization voltage and calcination temperature) on the photoelectrochemical water oxidation was systematically investigated. The optimized phosphorus-doped sample achieved a photocurrent density of 0.28 mA cm⁻² at 1.23 V vs. RHE, which far outperformed the unmodified TiO₂ hierarchical nanotube array as well as the boron-doped and phosphate buffer loaded counterparts. We further studied the effect of different reaction parameters such as electrolyte and light source on the photoelectrochemical water oxidation. Through a series of control experiments, the possible mechanism was deeply studied and the results showed that the phosphorus doping could alter the band structure and enhance the separation efficiency of photogenerated carriers. The final stability test also demonstrated the excellent photostability of the prepared sample in photoelectrochemical water oxidation.