Enhanced photoelectrochemical performance of iron and carbon self-doped TiO2 photoanodes modified with nitrogen

The photoelectrochemical performance and the semiconducting properties of iron, carbon and nitrogen modified TiO2 films prepared by a sol-gel method and deposited on 304 stainless steel (304SS) plates by a dip-coating technique were studied. Iron and carbon co-doped films were prepared for comparative purposes. The morphological, structural, optical and photoelectrochemical properties of the as-prepared materials were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and open circuit potential (OCP), linear sweep voltammetry and Mott-Schottky (M-S) analyses. FESEM images of the tri-doped films showed the formation of a homogenous surface with one layer deposited on 304SS, while a cracked surface was observed when the number of layers was increased to three. GIXRD indicated the presence of the anatase phase in the films. XPS showed the doping of the TiO2 with nitrogen, iron and carbon. DRS showed an adsorption edge displacement from 3.00 eV for TiO2 films with one layer to 2.75 eV after nitrogen modification. OCP and M-S measurements obtained in 0.1M HClO4 at pH 1 showed that the flat band potential tends to be more negative after nitrogen modification, therefore increasing the charge carrier density and improving the photoelectrochemical performance. Furthermore, decreasing the number of layers increases the electrochemical efficiency due to the diminution of the grain boundaries. The synergistic effect promoted by iron, carbon and nitrogen introduces the tri-doped TiO2 films as an alternative for photoelectrochemical applications under visible light illumination.